diff --git a/buffered/bufreader.rs b/buffered/bufreader.rs
index 32d194d..b6a810d 100644
--- a/buffered/bufreader.rs
+++ b/buffered/bufreader.rs
@@ -1,8 +1,9 @@
-use crate::cmp;
-use crate::fmt;
+use core::cmp;
+use core::fmt;
 use crate::io::{
     self, BufRead, Initializer, IoSliceMut, Read, Seek, SeekFrom, SizeHint, DEFAULT_BUF_SIZE,
 };
+use crate::io::prelude::*;
 
 /// The `BufReader<R>` struct adds buffering to any reader.
 ///
@@ -44,7 +45,6 @@ use crate::io::{
 ///     Ok(())
 /// }
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct BufReader<R> {
     inner: R,
     buf: Box<[u8]>,
@@ -68,7 +68,6 @@ impl<R: Read> BufReader<R> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new(inner: R) -> BufReader<R> {
         BufReader::with_capacity(DEFAULT_BUF_SIZE, inner)
     }
@@ -89,7 +88,6 @@ impl<R: Read> BufReader<R> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn with_capacity(capacity: usize, inner: R) -> BufReader<R> {
         unsafe {
             let mut buf = Box::new_uninit_slice(capacity).assume_init();
@@ -118,7 +116,6 @@ impl<R> BufReader<R> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_ref(&self) -> &R {
         &self.inner
     }
@@ -141,7 +138,6 @@ impl<R> BufReader<R> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_mut(&mut self) -> &mut R {
         &mut self.inner
     }
@@ -169,7 +165,6 @@ impl<R> BufReader<R> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "bufreader_buffer", since = "1.37.0")]
     pub fn buffer(&self) -> &[u8] {
         &self.buf[self.pos..self.cap]
     }
@@ -192,7 +187,6 @@ impl<R> BufReader<R> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "buffered_io_capacity", since = "1.46.0")]
     pub fn capacity(&self) -> usize {
         self.buf.len()
     }
@@ -216,7 +210,6 @@ impl<R> BufReader<R> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn into_inner(self) -> R {
         self.inner
     }
@@ -234,7 +227,6 @@ impl<R: Seek> BufReader<R> {
     /// the buffer will not be flushed, allowing for more efficient seeks.
     /// This method does not return the location of the underlying reader, so the caller
     /// must track this information themselves if it is required.
-    #[stable(feature = "bufreader_seek_relative", since = "1.53.0")]
     pub fn seek_relative(&mut self, offset: i64) -> io::Result<()> {
         let pos = self.pos as u64;
         if offset < 0 {
@@ -254,7 +246,6 @@ impl<R: Seek> BufReader<R> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<R: Read> Read for BufReader<R> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         // If we don't have any buffered data and we're doing a massive read
@@ -310,7 +301,6 @@ impl<R: Read> Read for BufReader<R> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<R: Read> BufRead for BufReader<R> {
     fn fill_buf(&mut self) -> io::Result<&[u8]> {
         // If we've reached the end of our internal buffer then we need to fetch
@@ -330,7 +320,6 @@ impl<R: Read> BufRead for BufReader<R> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<R> fmt::Debug for BufReader<R>
 where
     R: fmt::Debug,
@@ -343,7 +332,6 @@ where
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<R: Seek> Seek for BufReader<R> {
     /// Seek to an offset, in bytes, in the underlying reader.
     ///
diff --git a/buffered/bufwriter.rs b/buffered/bufwriter.rs
index df60af7..9cd8f47 100644
--- a/buffered/bufwriter.rs
+++ b/buffered/bufwriter.rs
@@ -1,10 +1,10 @@
-use crate::error;
-use crate::fmt;
+use core::fmt;
 use crate::io::{
     self, Error, ErrorKind, IntoInnerError, IoSlice, Seek, SeekFrom, Write, DEFAULT_BUF_SIZE,
 };
-use crate::mem;
-use crate::ptr;
+use core::ptr;
+use core::mem;
+use crate::io::prelude::*;
 
 /// Wraps a writer and buffers its output.
 ///
@@ -66,7 +66,6 @@ use crate::ptr;
 /// [`TcpStream::write`]: super::super::super::net::TcpStream::write
 /// [`TcpStream`]: crate::net::TcpStream
 /// [`flush`]: BufWriter::flush
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct BufWriter<W: Write> {
     inner: W,
     // The buffer. Avoid using this like a normal `Vec` in common code paths.
@@ -92,7 +91,6 @@ impl<W: Write> BufWriter<W> {
     ///
     /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new(inner: W) -> BufWriter<W> {
         BufWriter::with_capacity(DEFAULT_BUF_SIZE, inner)
     }
@@ -110,7 +108,6 @@ impl<W: Write> BufWriter<W> {
     /// let stream = TcpStream::connect("127.0.0.1:34254").unwrap();
     /// let mut buffer = BufWriter::with_capacity(100, stream);
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn with_capacity(capacity: usize, inner: W) -> BufWriter<W> {
         BufWriter { inner, buf: Vec::with_capacity(capacity), panicked: false }
     }
@@ -209,7 +206,6 @@ impl<W: Write> BufWriter<W> {
     /// // we can use reference just like buffer
     /// let reference = buffer.get_ref();
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_ref(&self) -> &W {
         &self.inner
     }
@@ -229,7 +225,6 @@ impl<W: Write> BufWriter<W> {
     /// // we can use reference just like buffer
     /// let reference = buffer.get_mut();
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_mut(&mut self) -> &mut W {
         &mut self.inner
     }
@@ -247,7 +242,6 @@ impl<W: Write> BufWriter<W> {
     /// // See how many bytes are currently buffered
     /// let bytes_buffered = buf_writer.buffer().len();
     /// ```
-    #[stable(feature = "bufreader_buffer", since = "1.37.0")]
     pub fn buffer(&self) -> &[u8] {
         &self.buf
     }
@@ -279,7 +273,6 @@ impl<W: Write> BufWriter<W> {
     /// // Calculate how many bytes can be written without flushing
     /// let without_flush = capacity - buf_writer.buffer().len();
     /// ```
-    #[stable(feature = "buffered_io_capacity", since = "1.46.0")]
     pub fn capacity(&self) -> usize {
         self.buf.capacity()
     }
@@ -303,7 +296,6 @@ impl<W: Write> BufWriter<W> {
     /// // unwrap the TcpStream and flush the buffer
     /// let stream = buffer.into_inner().unwrap();
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn into_inner(mut self) -> Result<W, IntoInnerError<BufWriter<W>>> {
         match self.flush_buf() {
             Err(e) => Err(IntoInnerError::new(self, e)),
@@ -333,7 +325,6 @@ impl<W: Write> BufWriter<W> {
     /// assert_eq!(recovered_writer.len(), 0);
     /// assert_eq!(&buffered_data.unwrap(), b"ata");
     /// ```
-    #[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
     pub fn into_parts(mut self) -> (W, Result<Vec<u8>, WriterPanicked>) {
         let buf = mem::take(&mut self.buf);
         let buf = if !self.panicked { Ok(buf) } else { Err(WriterPanicked { buf }) };
@@ -443,7 +434,6 @@ impl<W: Write> BufWriter<W> {
     }
 }
 
-#[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
 /// Error returned for the buffered data from `BufWriter::into_parts`, when the underlying
 /// writer has previously panicked.  Contains the (possibly partly written) buffered data.
 ///
@@ -476,7 +466,6 @@ pub struct WriterPanicked {
 impl WriterPanicked {
     /// Returns the perhaps-unwritten data.  Some of this data may have been written by the
     /// panicking call(s) to the underlying writer, so simply writing it again is not a good idea.
-    #[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
     pub fn into_inner(self) -> Vec<u8> {
         self.buf
     }
@@ -485,22 +474,12 @@ impl WriterPanicked {
         "BufWriter inner writer panicked, what data remains unwritten is not known";
 }
 
-#[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
-impl error::Error for WriterPanicked {
-    #[allow(deprecated, deprecated_in_future)]
-    fn description(&self) -> &str {
-        Self::DESCRIPTION
-    }
-}
-
-#[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
 impl fmt::Display for WriterPanicked {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "{}", Self::DESCRIPTION)
     }
 }
 
-#[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
 impl fmt::Debug for WriterPanicked {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("WriterPanicked")
@@ -509,7 +488,6 @@ impl fmt::Debug for WriterPanicked {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write> Write for BufWriter<W> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
@@ -638,7 +616,6 @@ impl<W: Write> Write for BufWriter<W> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write> fmt::Debug for BufWriter<W>
 where
     W: fmt::Debug,
@@ -651,7 +628,6 @@ where
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write + Seek> Seek for BufWriter<W> {
     /// Seek to the offset, in bytes, in the underlying writer.
     ///
@@ -662,7 +638,6 @@ impl<W: Write + Seek> Seek for BufWriter<W> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write> Drop for BufWriter<W> {
     fn drop(&mut self) {
         if !self.panicked {
diff --git a/buffered/linewriter.rs b/buffered/linewriter.rs
index d7b620d..1804305 100644
--- a/buffered/linewriter.rs
+++ b/buffered/linewriter.rs
@@ -1,4 +1,4 @@
-use crate::fmt;
+use core::fmt;
 use crate::io::{self, buffered::LineWriterShim, BufWriter, IntoInnerError, IoSlice, Write};
 
 /// Wraps a writer and buffers output to it, flushing whenever a newline
@@ -63,7 +63,6 @@ use crate::io::{self, buffered::LineWriterShim, BufWriter, IntoInnerError, IoSli
 ///     Ok(())
 /// }
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct LineWriter<W: Write> {
     inner: BufWriter<W>,
 }
@@ -83,7 +82,6 @@ impl<W: Write> LineWriter<W> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new(inner: W) -> LineWriter<W> {
         // Lines typically aren't that long, don't use a giant buffer
         LineWriter::with_capacity(1024, inner)
@@ -104,7 +102,6 @@ impl<W: Write> LineWriter<W> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn with_capacity(capacity: usize, inner: W) -> LineWriter<W> {
         LineWriter { inner: BufWriter::with_capacity(capacity, inner) }
     }
@@ -125,7 +122,6 @@ impl<W: Write> LineWriter<W> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_ref(&self) -> &W {
         self.inner.get_ref()
     }
@@ -150,7 +146,6 @@ impl<W: Write> LineWriter<W> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_mut(&mut self) -> &mut W {
         self.inner.get_mut()
     }
@@ -178,13 +173,11 @@ impl<W: Write> LineWriter<W> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn into_inner(self) -> Result<W, IntoInnerError<LineWriter<W>>> {
         self.inner.into_inner().map_err(|err| err.new_wrapped(|inner| LineWriter { inner }))
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write> Write for LineWriter<W> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         LineWriterShim::new(&mut self.inner).write(buf)
@@ -215,7 +208,6 @@ impl<W: Write> Write for LineWriter<W> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write> fmt::Debug for LineWriter<W>
 where
     W: fmt::Debug,
diff --git a/buffered/linewritershim.rs b/buffered/linewritershim.rs
index 0175d26..a052adf 100644
--- a/buffered/linewritershim.rs
+++ b/buffered/linewritershim.rs
@@ -1,5 +1,5 @@
 use crate::io::{self, BufWriter, IoSlice, Write};
-use crate::sys_common::memchr;
+use crate::io::memchr;
 
 /// Private helper struct for implementing the line-buffered writing logic.
 /// This shim temporarily wraps a BufWriter, and uses its internals to
diff --git a/buffered/mod.rs b/buffered/mod.rs
index 179bdf7..1d9083a 100644
--- a/buffered/mod.rs
+++ b/buffered/mod.rs
@@ -8,16 +8,14 @@ mod linewritershim;
 #[cfg(test)]
 mod tests;
 
-use crate::error;
-use crate::fmt;
+use core::fmt;
 use crate::io::Error;
 
-pub use bufreader::BufReader;
-pub use bufwriter::BufWriter;
-#[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
-pub use bufwriter::WriterPanicked;
-pub use linewriter::LineWriter;
-use linewritershim::LineWriterShim;
+pub use self::bufreader::BufReader;
+pub use self::bufwriter::BufWriter;
+pub use self::bufwriter::WriterPanicked;
+pub use self::linewriter::LineWriter;
+use self::linewritershim::LineWriterShim;
 
 /// An error returned by [`BufWriter::into_inner`] which combines an error that
 /// happened while writing out the buffer, and the buffered writer object
@@ -44,7 +42,6 @@ use linewritershim::LineWriterShim;
 /// };
 /// ```
 #[derive(Debug)]
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct IntoInnerError<W>(W, Error);
 
 impl<W> IntoInnerError<W> {
@@ -89,7 +86,6 @@ impl<W> IntoInnerError<W> {
     ///     }
     /// };
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn error(&self) -> &Error {
         &self.1
     }
@@ -124,7 +120,6 @@ impl<W> IntoInnerError<W> {
     ///     }
     /// };
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn into_inner(self) -> W {
         self.0
     }
@@ -144,7 +139,6 @@ impl<W> IntoInnerError<W> {
     /// let err = into_inner_err.into_error();
     /// assert_eq!(err.kind(), ErrorKind::WriteZero);
     /// ```
-    #[stable(feature = "io_into_inner_error_parts", since = "1.55.0")]
     pub fn into_error(self) -> Error {
         self.1
     }
@@ -167,28 +161,17 @@ impl<W> IntoInnerError<W> {
     /// assert_eq!(err.kind(), ErrorKind::WriteZero);
     /// assert_eq!(recovered_writer.buffer(), b"t be actually written");
     /// ```
-    #[stable(feature = "io_into_inner_error_parts", since = "1.55.0")]
     pub fn into_parts(self) -> (Error, W) {
         (self.1, self.0)
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<W> From<IntoInnerError<W>> for Error {
     fn from(iie: IntoInnerError<W>) -> Error {
         iie.1
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<W: Send + fmt::Debug> error::Error for IntoInnerError<W> {
-    #[allow(deprecated, deprecated_in_future)]
-    fn description(&self) -> &str {
-        error::Error::description(self.error())
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<W> fmt::Display for IntoInnerError<W> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         self.error().fmt(f)
diff --git a/copy.rs b/copy.rs
index eb60df2..df99a47 100644
--- a/copy.rs
+++ b/copy.rs
@@ -1,5 +1,6 @@
-use super::{BufWriter, ErrorKind, Read, Result, Write, DEFAULT_BUF_SIZE};
-use crate::mem::MaybeUninit;
+use super::{ErrorKind, Read, Result, Write, DEFAULT_BUF_SIZE};
+#[cfg(feature = "collections")] use super::BufWriter;
+use core::mem::MaybeUninit;
 
 /// Copies the entire contents of a reader into a writer.
 ///
@@ -39,19 +40,12 @@ use crate::mem::MaybeUninit;
 ///     Ok(())
 /// }
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> Result<u64>
 where
     R: Read,
     W: Write,
 {
-    cfg_if::cfg_if! {
-        if #[cfg(any(target_os = "linux", target_os = "android"))] {
-            crate::sys::kernel_copy::copy_spec(reader, writer)
-        } else {
-            generic_copy(reader, writer)
-        }
-    }
+    generic_copy(reader, writer)
 }
 
 /// The userspace read-write-loop implementation of `io::copy` that is used when
@@ -76,6 +70,7 @@ impl<W: Write + ?Sized> BufferedCopySpec for W {
     }
 }
 
+#[cfg(feature = "collections")]
 impl<I: Write> BufferedCopySpec for BufWriter<I> {
     fn copy_to<R: Read + ?Sized>(reader: &mut R, writer: &mut Self) -> Result<u64> {
         if writer.capacity() < DEFAULT_BUF_SIZE {
diff --git a/cursor.rs b/cursor.rs
index ae0cea9..4d60a7d 100644
--- a/cursor.rs
+++ b/cursor.rs
@@ -3,10 +3,10 @@ mod tests;
 
 use crate::io::prelude::*;
 
-use crate::cmp;
+use core::cmp;
 use crate::io::{self, Error, ErrorKind, Initializer, IoSlice, IoSliceMut, SeekFrom};
 
-use core::convert::TryInto;
+#[cfg(feature="collections")] use core::convert::TryInto;
 
 /// A `Cursor` wraps an in-memory buffer and provides it with a
 /// [`Seek`] implementation.
@@ -70,7 +70,6 @@ use core::convert::TryInto;
 ///     assert_eq!(&buff.get_ref()[5..15], &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
 /// }
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 #[derive(Debug, Default, Eq, PartialEq)]
 pub struct Cursor<T> {
     inner: T,
@@ -93,8 +92,6 @@ impl<T> Cursor<T> {
     /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
     /// # force_inference(&buff);
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
     pub const fn new(inner: T) -> Cursor<T> {
         Cursor { pos: 0, inner }
     }
@@ -112,7 +109,6 @@ impl<T> Cursor<T> {
     ///
     /// let vec = buff.into_inner();
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn into_inner(self) -> T {
         self.inner
     }
@@ -130,8 +126,6 @@ impl<T> Cursor<T> {
     ///
     /// let reference = buff.get_ref();
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
     pub const fn get_ref(&self) -> &T {
         &self.inner
     }
@@ -152,7 +146,6 @@ impl<T> Cursor<T> {
     ///
     /// let reference = buff.get_mut();
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_mut(&mut self) -> &mut T {
         &mut self.inner
     }
@@ -176,8 +169,6 @@ impl<T> Cursor<T> {
     /// buff.seek(SeekFrom::Current(-1)).unwrap();
     /// assert_eq!(buff.position(), 1);
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
     pub const fn position(&self) -> u64 {
         self.pos
     }
@@ -199,7 +190,6 @@ impl<T> Cursor<T> {
     /// buff.set_position(4);
     /// assert_eq!(buff.position(), 4);
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn set_position(&mut self, pos: u64) {
         self.pos = pos;
     }
@@ -230,7 +220,6 @@ where
     /// buff.set_position(6);
     /// assert_eq!(buff.remaining_slice(), &[]);
     /// ```
-    #[unstable(feature = "cursor_remaining", issue = "86369")]
     pub fn remaining_slice(&self) -> &[u8] {
         let len = self.pos.min(self.inner.as_ref().len() as u64);
         &self.inner.as_ref()[(len as usize)..]
@@ -255,13 +244,11 @@ where
     /// buff.set_position(10);
     /// assert!(buff.is_empty());
     /// ```
-    #[unstable(feature = "cursor_remaining", issue = "86369")]
     pub fn is_empty(&self) -> bool {
         self.pos >= self.inner.as_ref().len() as u64
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Clone for Cursor<T>
 where
     T: Clone,
@@ -278,7 +265,6 @@ where
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<T> io::Seek for Cursor<T>
 where
     T: AsRef<[u8]>,
@@ -318,7 +304,6 @@ where
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Read for Cursor<T>
 where
     T: AsRef<[u8]>,
@@ -358,7 +343,7 @@ where
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="collections")]
 impl<T> BufRead for Cursor<T>
 where
     T: AsRef<[u8]>,
@@ -398,6 +383,7 @@ fn slice_write_vectored(
 }
 
 // Resizing write implementation
+#[cfg(feature="collections")]
 fn vec_write(pos_mut: &mut u64, vec: &mut Vec<u8>, buf: &[u8]) -> io::Result<usize> {
     let pos: usize = (*pos_mut).try_into().map_err(|_| {
         Error::new_const(
@@ -426,6 +412,7 @@ fn vec_write(pos_mut: &mut u64, vec: &mut Vec<u8>, buf: &[u8]) -> io::Result<usi
     Ok(buf.len())
 }
 
+#[cfg(feature="collections")]
 fn vec_write_vectored(
     pos_mut: &mut u64,
     vec: &mut Vec<u8>,
@@ -438,7 +425,6 @@ fn vec_write_vectored(
     Ok(nwritten)
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl Write for Cursor<&mut [u8]> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
@@ -461,7 +447,7 @@ impl Write for Cursor<&mut [u8]> {
     }
 }
 
-#[stable(feature = "cursor_mut_vec", since = "1.25.0")]
+#[cfg(feature="collections")]
 impl Write for Cursor<&mut Vec<u8>> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         vec_write(&mut self.pos, self.inner, buf)
@@ -482,7 +468,7 @@ impl Write for Cursor<&mut Vec<u8>> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature = "collections")]
 impl Write for Cursor<Vec<u8>> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         vec_write(&mut self.pos, &mut self.inner, buf)
@@ -503,8 +489,8 @@ impl Write for Cursor<Vec<u8>> {
     }
 }
 
-#[stable(feature = "cursor_box_slice", since = "1.5.0")]
-impl Write for Cursor<Box<[u8]>> {
+#[cfg(feature = "alloc")]
+impl Write for Cursor<::alloc::boxed::Box<[u8]>> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         slice_write(&mut self.pos, &mut self.inner, buf)
diff --git a/error.rs b/error.rs
index 51666c0..2ac025b 100644
--- a/error.rs
+++ b/error.rs
@@ -1,11 +1,17 @@
 #[cfg(test)]
 mod tests;
 
-use crate::convert::From;
-use crate::error;
-use crate::fmt;
-use crate::result;
-use crate::sys;
+use core::convert::From;
+use core::fmt;
+use core::result;
+
+use core::convert::Into;
+use core::marker::{Send, Sync};
+use core::option::Option::{self, Some, None};
+#[cfg(feature="alloc")] use alloc::boxed::Box;
+#[cfg(not(feature="alloc"))] use ::FakeBox as Box;
+#[cfg(feature="collections")] use collections::string::String;
+#[cfg(not(feature="collections"))] use ::ErrorString as String;
 
 /// A specialized [`Result`] type for I/O operations.
 ///
@@ -41,7 +47,6 @@ use crate::sys;
 ///     Ok(buffer)
 /// }
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub type Result<T> = result::Result<T, Error>;
 
 /// The error type for I/O operations of the [`Read`], [`Write`], [`Seek`], and
@@ -54,12 +59,10 @@ pub type Result<T> = result::Result<T, Error>;
 /// [`Read`]: crate::io::Read
 /// [`Write`]: crate::io::Write
 /// [`Seek`]: crate::io::Seek
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct Error {
     repr: Repr,
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Debug for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Debug::fmt(&self.repr, f)
@@ -71,13 +74,16 @@ enum Repr {
     Simple(ErrorKind),
     // &str is a fat pointer, but &&str is a thin pointer.
     SimpleMessage(ErrorKind, &'static &'static str),
+    #[cfg(feature="alloc")]
     Custom(Box<Custom>),
+    #[cfg(not(feature="alloc"))]
+    Custom(Custom),
 }
 
 #[derive(Debug)]
 struct Custom {
     kind: ErrorKind,
-    error: Box<dyn error::Error + Send + Sync>,
+    error: String,
 }
 
 /// A list specifying general categories of I/O error.
@@ -89,71 +95,50 @@ struct Custom {
 ///
 /// [`io::Error`]: Error
 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
-#[stable(feature = "rust1", since = "1.0.0")]
 #[allow(deprecated)]
 #[non_exhaustive]
 pub enum ErrorKind {
     /// An entity was not found, often a file.
-    #[stable(feature = "rust1", since = "1.0.0")]
     NotFound,
     /// The operation lacked the necessary privileges to complete.
-    #[stable(feature = "rust1", since = "1.0.0")]
     PermissionDenied,
     /// The connection was refused by the remote server.
-    #[stable(feature = "rust1", since = "1.0.0")]
     ConnectionRefused,
     /// The connection was reset by the remote server.
-    #[stable(feature = "rust1", since = "1.0.0")]
     ConnectionReset,
     /// The remote host is not reachable.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     HostUnreachable,
     /// The network containing the remote host is not reachable.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     NetworkUnreachable,
     /// The connection was aborted (terminated) by the remote server.
-    #[stable(feature = "rust1", since = "1.0.0")]
     ConnectionAborted,
     /// The network operation failed because it was not connected yet.
-    #[stable(feature = "rust1", since = "1.0.0")]
     NotConnected,
     /// A socket address could not be bound because the address is already in
     /// use elsewhere.
-    #[stable(feature = "rust1", since = "1.0.0")]
     AddrInUse,
     /// A nonexistent interface was requested or the requested address was not
     /// local.
-    #[stable(feature = "rust1", since = "1.0.0")]
     AddrNotAvailable,
     /// The system's networking is down.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     NetworkDown,
     /// The operation failed because a pipe was closed.
-    #[stable(feature = "rust1", since = "1.0.0")]
     BrokenPipe,
     /// An entity already exists, often a file.
-    #[stable(feature = "rust1", since = "1.0.0")]
     AlreadyExists,
     /// The operation needs to block to complete, but the blocking operation was
     /// requested to not occur.
-    #[stable(feature = "rust1", since = "1.0.0")]
     WouldBlock,
-    /// A filesystem object is, unexpectedly, not a directory.
-    ///
     /// For example, a filesystem path was specified where one of the intermediate directory
     /// components was, in fact, a plain file.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     NotADirectory,
     /// The filesystem object is, unexpectedly, a directory.
     ///
     /// A directory was specified when a non-directory was expected.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     IsADirectory,
     /// A non-empty directory was specified where an empty directory was expected.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     DirectoryNotEmpty,
     /// The filesystem or storage medium is read-only, but a write operation was attempted.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     ReadOnlyFilesystem,
     /// Loop in the filesystem or IO subsystem; often, too many levels of symbolic links.
     ///
@@ -162,16 +147,13 @@ pub enum ErrorKind {
     ///
     /// On Unix this is usually the result of a symbolic link loop; or, of exceeding the
     /// system-specific limit on the depth of symlink traversal.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     FilesystemLoop,
     /// Stale network file handle.
     ///
     /// With some network filesystems, notably NFS, an open file (or directory) can be invalidated
     /// by problems with the network or server.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     StaleNetworkFileHandle,
     /// A parameter was incorrect.
-    #[stable(feature = "rust1", since = "1.0.0")]
     InvalidInput,
     /// Data not valid for the operation were encountered.
     ///
@@ -183,10 +165,8 @@ pub enum ErrorKind {
     /// `InvalidData` if the file's contents are not valid UTF-8.
     ///
     /// [`InvalidInput`]: ErrorKind::InvalidInput
-    #[stable(feature = "io_invalid_data", since = "1.2.0")]
     InvalidData,
     /// The I/O operation's timeout expired, causing it to be canceled.
-    #[stable(feature = "rust1", since = "1.0.0")]
     TimedOut,
     /// An error returned when an operation could not be completed because a
     /// call to [`write`] returned [`Ok(0)`].
@@ -197,74 +177,59 @@ pub enum ErrorKind {
     ///
     /// [`write`]: crate::io::Write::write
     /// [`Ok(0)`]: Ok
-    #[stable(feature = "rust1", since = "1.0.0")]
     WriteZero,
-    /// The underlying storage (typically, a filesystem) is full.
     ///
     /// This does not include out of quota errors.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     StorageFull,
     /// Seek on unseekable file.
     ///
     /// Seeking was attempted on an open file handle which is not suitable for seeking - for
     /// example, on Unix, a named pipe opened with `File::open`.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     NotSeekable,
     /// Filesystem quota was exceeded.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     FilesystemQuotaExceeded,
     /// File larger than allowed or supported.
     ///
     /// This might arise from a hard limit of the underlying filesystem or file access API, or from
     /// an administratively imposed resource limitation.  Simple disk full, and out of quota, have
     /// their own errors.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     FileTooLarge,
     /// Resource is busy.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     ResourceBusy,
     /// Executable file is busy.
     ///
     /// An attempt was made to write to a file which is also in use as a running program.  (Not all
     /// operating systems detect this situation.)
-    #[unstable(feature = "io_error_more", issue = "86442")]
     ExecutableFileBusy,
     /// Deadlock (avoided).
     ///
     /// A file locking operation would result in deadlock.  This situation is typically detected, if
     /// at all, on a best-effort basis.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     Deadlock,
     /// Cross-device or cross-filesystem (hard) link or rename.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     CrossesDevices,
     /// Too many (hard) links to the same filesystem object.
     ///
     /// The filesystem does not support making so many hardlinks to the same file.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     TooManyLinks,
     /// Filename too long.
     ///
     /// The limit might be from the underlying filesystem or API, or an administratively imposed
     /// resource limit.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     FilenameTooLong,
     /// Program argument list too long.
     ///
     /// When trying to run an external program, a system or process limit on the size of the
     /// arguments would have been exceeded.
-    #[unstable(feature = "io_error_more", issue = "86442")]
     ArgumentListTooLong,
     /// This operation was interrupted.
     ///
     /// Interrupted operations can typically be retried.
-    #[stable(feature = "rust1", since = "1.0.0")]
     Interrupted,
 
     /// This operation is unsupported on this platform.
     ///
     /// This means that the operation can never succeed.
-    #[stable(feature = "unsupported_error", since = "1.53.0")]
     Unsupported,
 
     // ErrorKinds which are primarily categorisations for OS error
@@ -276,12 +241,10 @@ pub enum ErrorKind {
     /// This typically means that an operation could only succeed if it read a
     /// particular number of bytes but only a smaller number of bytes could be
     /// read.
-    #[stable(feature = "read_exact", since = "1.6.0")]
     UnexpectedEof,
 
     /// An operation could not be completed, because it failed
     /// to allocate enough memory.
-    #[stable(feature = "out_of_memory_error", since = "1.54.0")]
     OutOfMemory,
 
     // "Unusual" error kinds which do not correspond simply to (sets
@@ -294,11 +257,6 @@ pub enum ErrorKind {
     /// [`ErrorKind`].
     ///
     /// This [`ErrorKind`] is not used by the standard library.
-    ///
-    /// Errors from the standard library that do not fall under any of the I/O
-    /// error kinds cannot be `match`ed on, and will only match a wildcard (`_`) pattern.
-    /// New [`ErrorKind`]s might be added in the future for some of those.
-    #[stable(feature = "rust1", since = "1.0.0")]
     Other,
 
     /// Any I/O error from the standard library that's not part of this list.
@@ -306,7 +264,6 @@ pub enum ErrorKind {
     /// Errors that are `Uncategorized` now may move to a different or a new
     /// [`ErrorKind`] variant in the future. It is not recommended to match
     /// an error against `Uncategorized`; use a wildcard match (`_`) instead.
-    #[unstable(feature = "io_error_uncategorized", issue = "none")]
     #[doc(hidden)]
     Uncategorized,
 }
@@ -363,7 +320,6 @@ impl ErrorKind {
 
 /// Intended for use for errors not exposed to the user, where allocating onto
 /// the heap (for normal construction via Error::new) is too costly.
-#[stable(feature = "io_error_from_errorkind", since = "1.14.0")]
 impl From<ErrorKind> for Error {
     /// Converts an [`ErrorKind`] into an [`Error`].
     ///
@@ -403,15 +359,14 @@ impl Error {
     /// // errors can also be created from other errors
     /// let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new<E>(kind: ErrorKind, error: E) -> Error
     where
-        E: Into<Box<dyn error::Error + Send + Sync>>,
+        E: Into<String>,
     {
         Self::_new(kind, error.into())
     }
 
-    fn _new(kind: ErrorKind, error: Box<dyn error::Error + Send + Sync>) -> Error {
+    fn _new(kind: ErrorKind, error: String) -> Error {
         Error { repr: Repr::Custom(Box::new(Custom { kind, error })) }
     }
 
@@ -428,25 +383,6 @@ impl Error {
         Self { repr: Repr::SimpleMessage(kind, message) }
     }
 
-    /// Returns an error representing the last OS error which occurred.
-    ///
-    /// This function reads the value of `errno` for the target platform (e.g.
-    /// `GetLastError` on Windows) and will return a corresponding instance of
-    /// [`Error`] for the error code.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::io::Error;
-    ///
-    /// println!("last OS error: {:?}", Error::last_os_error());
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    #[inline]
-    pub fn last_os_error() -> Error {
-        Error::from_raw_os_error(sys::os::errno() as i32)
-    }
-
     /// Creates a new instance of an [`Error`] from a particular OS error code.
     ///
     /// # Examples
@@ -472,7 +408,6 @@ impl Error {
     /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
     /// # }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn from_raw_os_error(code: i32) -> Error {
         Error { repr: Repr::Os(code) }
@@ -507,7 +442,6 @@ impl Error {
     ///     print_os_error(&Error::new(ErrorKind::Other, "oh no!"));
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn raw_os_error(&self) -> Option<i32> {
         match self.repr {
@@ -545,14 +479,13 @@ impl Error {
     ///     print_error(&Error::new(ErrorKind::Other, "oh no!"));
     /// }
     /// ```
-    #[stable(feature = "io_error_inner", since = "1.3.0")]
     #[inline]
-    pub fn get_ref(&self) -> Option<&(dyn error::Error + Send + Sync + 'static)> {
+    pub fn get_ref(&self) -> Option<&String> {
         match self.repr {
             Repr::Os(..) => None,
             Repr::Simple(..) => None,
             Repr::SimpleMessage(..) => None,
-            Repr::Custom(ref c) => Some(&*c.error),
+            Repr::Custom(ref c) => Some(&c.error),
         }
     }
 
@@ -618,14 +551,13 @@ impl Error {
     ///     print_error(&change_error(Error::new(ErrorKind::Other, MyError::new())));
     /// }
     /// ```
-    #[stable(feature = "io_error_inner", since = "1.3.0")]
     #[inline]
-    pub fn get_mut(&mut self) -> Option<&mut (dyn error::Error + Send + Sync + 'static)> {
+    pub fn get_mut(&mut self) -> Option<&mut String> {
         match self.repr {
             Repr::Os(..) => None,
             Repr::Simple(..) => None,
             Repr::SimpleMessage(..) => None,
-            Repr::Custom(ref mut c) => Some(&mut *c.error),
+            Repr::Custom(ref mut c) => Some(&mut c.error),
         }
     }
 
@@ -656,9 +588,8 @@ impl Error {
     ///     print_error(Error::new(ErrorKind::Other, "oh no!"));
     /// }
     /// ```
-    #[stable(feature = "io_error_inner", since = "1.3.0")]
     #[inline]
-    pub fn into_inner(self) -> Option<Box<dyn error::Error + Send + Sync>> {
+    pub fn into_inner(self) -> Option<String> {
         match self.repr {
             Repr::Os(..) => None,
             Repr::Simple(..) => None,
@@ -685,11 +616,10 @@ impl Error {
     ///     print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn kind(&self) -> ErrorKind {
         match self.repr {
-            Repr::Os(code) => sys::decode_error_kind(code),
+            Repr::Os(_code) => ErrorKind::Other,
             Repr::Custom(ref c) => c.kind,
             Repr::Simple(kind) => kind,
             Repr::SimpleMessage(kind, _) => kind,
@@ -703,8 +633,6 @@ impl fmt::Debug for Repr {
             Repr::Os(code) => fmt
                 .debug_struct("Os")
                 .field("code", &code)
-                .field("kind", &sys::decode_error_kind(code))
-                .field("message", &sys::os::error_string(code))
                 .finish(),
             Repr::Custom(ref c) => fmt::Debug::fmt(&c, fmt),
             Repr::Simple(kind) => fmt.debug_tuple("Kind").field(&kind).finish(),
@@ -715,13 +643,11 @@ impl fmt::Debug for Repr {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Display for Error {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self.repr {
             Repr::Os(code) => {
-                let detail = sys::os::error_string(code);
-                write!(fmt, "{} (os error {})", detail, code)
+                write!(fmt, "os error {}", code)
             }
             Repr::Custom(ref c) => c.error.fmt(fmt),
             Repr::Simple(kind) => write!(fmt, "{}", kind.as_str()),
@@ -730,37 +656,6 @@ impl fmt::Display for Error {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
-impl error::Error for Error {
-    #[allow(deprecated, deprecated_in_future)]
-    fn description(&self) -> &str {
-        match self.repr {
-            Repr::Os(..) | Repr::Simple(..) => self.kind().as_str(),
-            Repr::SimpleMessage(_, &msg) => msg,
-            Repr::Custom(ref c) => c.error.description(),
-        }
-    }
-
-    #[allow(deprecated)]
-    fn cause(&self) -> Option<&dyn error::Error> {
-        match self.repr {
-            Repr::Os(..) => None,
-            Repr::Simple(..) => None,
-            Repr::SimpleMessage(..) => None,
-            Repr::Custom(ref c) => c.error.cause(),
-        }
-    }
-
-    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
-        match self.repr {
-            Repr::Os(..) => None,
-            Repr::Simple(..) => None,
-            Repr::SimpleMessage(..) => None,
-            Repr::Custom(ref c) => c.error.source(),
-        }
-    }
-}
-
 fn _assert_error_is_sync_send() {
     fn _is_sync_send<T: Sync + Send>() {}
     _is_sync_send::<Error>();
diff --git a/impls.rs b/impls.rs
index 7a2a49b..5228832 100644
--- a/impls.rs
+++ b/impls.rs
@@ -1,18 +1,22 @@
 #[cfg(test)]
 mod tests;
 
-use crate::alloc::Allocator;
-use crate::cmp;
-use crate::fmt;
+#[cfg(feature="collections")] use core::alloc::Allocator;
+use core::cmp;
+use core::fmt;
 use crate::io::{
-    self, BufRead, Error, ErrorKind, Initializer, IoSlice, IoSliceMut, Read, Seek, SeekFrom, Write,
+    self, Error, ErrorKind, Initializer, IoSlice, IoSliceMut, Read, Seek, SeekFrom, Write,
 };
-use crate::mem;
+#[cfg(feature="collections")] use crate::io::BufRead;
+use core::mem;
+
+#[cfg(feature="alloc")] use alloc::boxed::Box;
+#[cfg(feature="collections")] use collections::string::String;
+#[cfg(feature="collections")] use collections::vec::Vec;
 
 // =============================================================================
 // Forwarding implementations
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<R: Read + ?Sized> Read for &mut R {
     #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
@@ -34,11 +38,13 @@ impl<R: Read + ?Sized> Read for &mut R {
         (**self).initializer()
     }
 
+    #[cfg(feature="collections")]
     #[inline]
     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_to_end(buf)
     }
 
+    #[cfg(feature="collections")]
     #[inline]
     fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_to_string(buf)
@@ -49,7 +55,6 @@ impl<R: Read + ?Sized> Read for &mut R {
         (**self).read_exact(buf)
     }
 }
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write + ?Sized> Write for &mut W {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
@@ -81,7 +86,6 @@ impl<W: Write + ?Sized> Write for &mut W {
         (**self).write_fmt(fmt)
     }
 }
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<S: Seek + ?Sized> Seek for &mut S {
     #[inline]
     fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
@@ -93,7 +97,7 @@ impl<S: Seek + ?Sized> Seek for &mut S {
         (**self).stream_position()
     }
 }
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="collections")]
 impl<B: BufRead + ?Sized> BufRead for &mut B {
     #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> {
@@ -116,7 +120,7 @@ impl<B: BufRead + ?Sized> BufRead for &mut B {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="alloc")]
 impl<R: Read + ?Sized> Read for Box<R> {
     #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
@@ -138,11 +142,13 @@ impl<R: Read + ?Sized> Read for Box<R> {
         (**self).initializer()
     }
 
+    #[cfg(feature="collections")]
     #[inline]
     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_to_end(buf)
     }
 
+    #[cfg(feature="collections")]
     #[inline]
     fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_to_string(buf)
@@ -153,7 +159,7 @@ impl<R: Read + ?Sized> Read for Box<R> {
         (**self).read_exact(buf)
     }
 }
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="alloc")]
 impl<W: Write + ?Sized> Write for Box<W> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
@@ -185,7 +191,7 @@ impl<W: Write + ?Sized> Write for Box<W> {
         (**self).write_fmt(fmt)
     }
 }
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="alloc")]
 impl<S: Seek + ?Sized> Seek for Box<S> {
     #[inline]
     fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
@@ -197,7 +203,7 @@ impl<S: Seek + ?Sized> Seek for Box<S> {
         (**self).stream_position()
     }
 }
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="collections")]
 impl<B: BufRead + ?Sized> BufRead for Box<B> {
     #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> {
@@ -227,7 +233,6 @@ impl<B: BufRead + ?Sized> BufRead for Box<B> {
 ///
 /// Note that reading updates the slice to point to the yet unread part.
 /// The slice will be empty when EOF is reached.
-#[stable(feature = "rust1", since = "1.0.0")]
 impl Read for &[u8] {
     #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
@@ -290,6 +295,7 @@ impl Read for &[u8] {
         Ok(())
     }
 
+    #[cfg(feature="collections")]
     #[inline]
     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
         buf.extend_from_slice(*self);
@@ -299,7 +305,7 @@ impl Read for &[u8] {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="collections")]
 impl BufRead for &[u8] {
     #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> {
@@ -321,7 +327,6 @@ impl BufRead for &[u8] {
 /// If the number of bytes to be written exceeds the size of the slice, write operations will
 /// return short writes: ultimately, `Ok(0)`; in this situation, `write_all` returns an error of
 /// kind `ErrorKind::WriteZero`.
-#[stable(feature = "rust1", since = "1.0.0")]
 impl Write for &mut [u8] {
     #[inline]
     fn write(&mut self, data: &[u8]) -> io::Result<usize> {
@@ -367,7 +372,7 @@ impl Write for &mut [u8] {
 
 /// Write is implemented for `Vec<u8>` by appending to the vector.
 /// The vector will grow as needed.
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="collections")]
 impl<A: Allocator> Write for Vec<u8, A> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
diff --git a/mod.rs b/mod.rs
index e8466fa..7f090d8 100644
--- a/mod.rs
+++ b/mod.rs
@@ -246,68 +246,52 @@
 //! [`Result`]: crate::result::Result
 //! [`.unwrap()`]: crate::result::Result::unwrap
 
-#![stable(feature = "rust1", since = "1.0.0")]
-
 #[cfg(test)]
 mod tests;
 
-use crate::cmp;
-use crate::convert::TryInto;
-use crate::fmt;
-use crate::mem::replace;
-use crate::ops::{Deref, DerefMut};
-use crate::ptr;
-use crate::slice;
-use crate::str;
-use crate::sys;
-use crate::sys_common::memchr;
-
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::buffered::IntoInnerError;
-#[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
-pub use self::buffered::WriterPanicked;
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::buffered::{BufReader, BufWriter, LineWriter};
-#[stable(feature = "rust1", since = "1.0.0")]
+use core::cmp;
+use core::fmt;
+#[cfg(not(core_memchr))]
+mod memchr;
+#[cfg(all(feature="collections",core_memchr))]
+use core::slice::memchr;
+use core::ops::{Deref, DerefMut};
+use core::ptr;
+use core::slice;
+use core::str;
+use core::convert::TryInto;
+use core::mem::replace;
+
+#[cfg(feature="collections")] pub use self::buffered::IntoInnerError;
+#[cfg(feature="collections")] pub use self::buffered::WriterPanicked;
+#[cfg(feature="collections")] pub use self::buffered::{BufReader, BufWriter, LineWriter};
+
 pub use self::copy::copy;
-#[stable(feature = "rust1", since = "1.0.0")]
 pub use self::cursor::Cursor;
-#[stable(feature = "rust1", since = "1.0.0")]
 pub use self::error::{Error, ErrorKind, Result};
-#[unstable(feature = "internal_output_capture", issue = "none")]
-#[doc(no_inline, hidden)]
-pub use self::stdio::set_output_capture;
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::stdio::{stderr, stdin, stdout, Stderr, Stdin, Stdout};
-#[unstable(feature = "stdio_locked", issue = "86845")]
-pub use self::stdio::{stderr_locked, stdin_locked, stdout_locked};
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::stdio::{StderrLock, StdinLock, StdoutLock};
-#[unstable(feature = "print_internals", issue = "none")]
-pub use self::stdio::{_eprint, _print};
-#[stable(feature = "rust1", since = "1.0.0")]
 pub use self::util::{empty, repeat, sink, Empty, Repeat, Sink};
 
-mod buffered;
+#[cfg(feature="collections")] use collections::string::String;
+#[cfg(feature="collections")] use collections::vec::Vec;
+#[cfg(feature="alloc")] use alloc::boxed::Box;
+
+#[cfg(feature="collections")] mod buffered;
 pub(crate) mod copy;
 mod cursor;
 mod error;
 mod impls;
 pub mod prelude;
-mod stdio;
 mod util;
 
-const DEFAULT_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
-
-pub(crate) fn cleanup() {
-    stdio::cleanup()
-}
+const DEFAULT_BUF_SIZE: usize = 8 * 1024;
 
+#[cfg(feature="collections")]
 struct Guard<'a> {
     buf: &'a mut Vec<u8>,
     len: usize,
 }
 
+#[cfg(feature="collections")]
 impl Drop for Guard<'_> {
     fn drop(&mut self) {
         unsafe {
@@ -334,6 +318,7 @@ impl Drop for Guard<'_> {
 // 2. We're passing a raw buffer to the function `f`, and it is expected that
 //    the function only *appends* bytes to the buffer. We'll get undefined
 //    behavior if existing bytes are overwritten to have non-UTF-8 data.
+#[cfg(feature="collections")]
 fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
 where
     F: FnOnce(&mut Vec<u8>) -> Result<usize>,
@@ -361,10 +346,12 @@ where
 //
 // Because we're extending the buffer with uninitialized data for trusted
 // readers, we need to make sure to truncate that if any of this panics.
+#[cfg(feature="collections")]
 fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
     read_to_end_with_reservation(r, buf, |_| 32)
 }
 
+#[cfg(feature="collections")]
 fn read_to_end_with_reservation<R, F>(
     r: &mut R,
     buf: &mut Vec<u8>,
@@ -514,9 +501,7 @@ pub(crate) fn default_read_exact<R: Read + ?Sized>(this: &mut R, mut buf: &mut [
 /// [`&str`]: prim@str
 /// [`std::io`]: self
 /// [`File`]: crate::fs::File
-#[stable(feature = "rust1", since = "1.0.0")]
 #[doc(notable_trait)]
-#[cfg_attr(not(test), rustc_diagnostic_item = "IoRead")]
 pub trait Read {
     /// Pull some bytes from this source into the specified buffer, returning
     /// how many bytes were read.
@@ -597,7 +582,6 @@ pub trait Read {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
 
     /// Like `read`, except that it reads into a slice of buffers.
@@ -609,7 +593,6 @@ pub trait Read {
     ///
     /// The default implementation calls `read` with either the first nonempty
     /// buffer provided, or an empty one if none exists.
-    #[stable(feature = "iovec", since = "1.36.0")]
     fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
         default_read_vectored(|b| self.read(b), bufs)
     }
@@ -622,7 +605,6 @@ pub trait Read {
     /// and coalesce writes into a single buffer for higher performance.
     ///
     /// The default implementation returns `false`.
-    #[unstable(feature = "can_vector", issue = "69941")]
     fn is_read_vectored(&self) -> bool {
         false
     }
@@ -646,7 +628,6 @@ pub trait Read {
     /// This method is unsafe because a `Read`er could otherwise return a
     /// non-zeroing `Initializer` from another `Read` type without an `unsafe`
     /// block.
-    #[unstable(feature = "read_initializer", issue = "42788")]
     #[inline]
     unsafe fn initializer(&self) -> Initializer {
         Initializer::zeroing()
@@ -698,7 +679,7 @@ pub trait Read {
     /// file.)
     ///
     /// [`std::fs::read`]: crate::fs::read
-    #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg(feature="collections")]
     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
         read_to_end(self, buf)
     }
@@ -741,7 +722,7 @@ pub trait Read {
     /// reading from a file.)
     ///
     /// [`std::fs::read_to_string`]: crate::fs::read_to_string
-    #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg(feature="collections")]
     fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
         // Note that we do *not* call `.read_to_end()` here. We are passing
         // `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
@@ -805,7 +786,6 @@ pub trait Read {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "read_exact", since = "1.6.0")]
     fn read_exact(&mut self, buf: &mut [u8]) -> Result<()> {
         default_read_exact(self, buf)
     }
@@ -844,7 +824,6 @@ pub trait Read {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn by_ref(&mut self) -> &mut Self
     where
         Self: Sized,
@@ -881,7 +860,6 @@ pub trait Read {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn bytes(self) -> Bytes<Self>
     where
         Self: Sized,
@@ -919,7 +897,6 @@ pub trait Read {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn chain<R: Read>(self, next: R) -> Chain<Self, R>
     where
         Self: Sized,
@@ -958,7 +935,6 @@ pub trait Read {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn take(self, limit: u64) -> Take<Self>
     where
         Self: Sized,
@@ -1008,29 +984,71 @@ pub trait Read {
 ///     Ok(())
 /// }
 /// ```
-#[unstable(feature = "io_read_to_string", issue = "80218")]
+#[cfg(feature="collections")]
 pub fn read_to_string<R: Read>(reader: &mut R) -> Result<String> {
     let mut buf = String::new();
     reader.read_to_string(&mut buf)?;
     Ok(buf)
 }
 
+#[derive(Copy, Clone)]
+pub struct IoVecBuffer<'a>(&'a [u8]);
+
+impl<'a> IoVecBuffer<'a> {
+    #[inline]
+    pub fn new(buf: &'a [u8]) -> IoVecBuffer<'a> {
+        IoVecBuffer(buf)
+    }
+
+    #[inline]
+    pub fn advance(&mut self, n: usize) {
+        self.0 = &self.0[n..]
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        self.0
+    }
+}
+
+pub struct IoVecMutBuffer<'a>(&'a mut [u8]);
+
+impl<'a> IoVecMutBuffer<'a> {
+    #[inline]
+    pub fn new(buf: &'a mut [u8]) -> IoVecMutBuffer<'a> {
+        IoVecMutBuffer(buf)
+    }
+
+    #[inline]
+    pub fn advance(&mut self, n: usize) {
+        let slice = core::mem::replace(&mut self.0, &mut []);
+        let (_, remaining) = slice.split_at_mut(n);
+        self.0 = remaining;
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        self.0
+    }
+
+    #[inline]
+    pub fn as_mut_slice(&mut self) -> &mut [u8] {
+        self.0
+    }
+}
+
 /// A buffer type used with `Read::read_vectored`.
 ///
 /// It is semantically a wrapper around an `&mut [u8]`, but is guaranteed to be
 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
 /// Windows.
-#[stable(feature = "iovec", since = "1.36.0")]
 #[repr(transparent)]
-pub struct IoSliceMut<'a>(sys::io::IoSliceMut<'a>);
+pub struct IoSliceMut<'a>(IoVecMutBuffer<'a>);
 
-#[stable(feature = "iovec-send-sync", since = "1.44.0")]
 unsafe impl<'a> Send for IoSliceMut<'a> {}
 
-#[stable(feature = "iovec-send-sync", since = "1.44.0")]
 unsafe impl<'a> Sync for IoSliceMut<'a> {}
 
-#[stable(feature = "iovec", since = "1.36.0")]
 impl<'a> fmt::Debug for IoSliceMut<'a> {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Debug::fmt(self.0.as_slice(), fmt)
@@ -1043,10 +1061,9 @@ impl<'a> IoSliceMut<'a> {
     /// # Panics
     ///
     /// Panics on Windows if the slice is larger than 4GB.
-    #[stable(feature = "iovec", since = "1.36.0")]
     #[inline]
     pub fn new(buf: &'a mut [u8]) -> IoSliceMut<'a> {
-        IoSliceMut(sys::io::IoSliceMut::new(buf))
+        IoSliceMut(IoVecMutBuffer::new(buf))
     }
 
     /// Advance the internal cursor of the slice.
@@ -1069,7 +1086,6 @@ impl<'a> IoSliceMut<'a> {
     /// buf.advance(3);
     /// assert_eq!(buf.deref(), [1; 5].as_ref());
     /// ```
-    #[unstable(feature = "io_slice_advance", issue = "62726")]
     #[inline]
     pub fn advance(&mut self, n: usize) {
         self.0.advance(n)
@@ -1107,7 +1123,6 @@ impl<'a> IoSliceMut<'a> {
     /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
     /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
     /// ```
-    #[unstable(feature = "io_slice_advance", issue = "62726")]
     #[inline]
     pub fn advance_slices(bufs: &mut &mut [IoSliceMut<'a>], n: usize) {
         // Number of buffers to remove.
@@ -1130,7 +1145,6 @@ impl<'a> IoSliceMut<'a> {
     }
 }
 
-#[stable(feature = "iovec", since = "1.36.0")]
 impl<'a> Deref for IoSliceMut<'a> {
     type Target = [u8];
 
@@ -1140,7 +1154,6 @@ impl<'a> Deref for IoSliceMut<'a> {
     }
 }
 
-#[stable(feature = "iovec", since = "1.36.0")]
 impl<'a> DerefMut for IoSliceMut<'a> {
     #[inline]
     fn deref_mut(&mut self) -> &mut [u8] {
@@ -1153,18 +1166,14 @@ impl<'a> DerefMut for IoSliceMut<'a> {
 /// It is semantically a wrapper around a `&[u8]`, but is guaranteed to be
 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
 /// Windows.
-#[stable(feature = "iovec", since = "1.36.0")]
 #[derive(Copy, Clone)]
 #[repr(transparent)]
-pub struct IoSlice<'a>(sys::io::IoSlice<'a>);
+pub struct IoSlice<'a>(IoVecBuffer<'a>);
 
-#[stable(feature = "iovec-send-sync", since = "1.44.0")]
 unsafe impl<'a> Send for IoSlice<'a> {}
 
-#[stable(feature = "iovec-send-sync", since = "1.44.0")]
 unsafe impl<'a> Sync for IoSlice<'a> {}
 
-#[stable(feature = "iovec", since = "1.36.0")]
 impl<'a> fmt::Debug for IoSlice<'a> {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Debug::fmt(self.0.as_slice(), fmt)
@@ -1177,10 +1186,9 @@ impl<'a> IoSlice<'a> {
     /// # Panics
     ///
     /// Panics on Windows if the slice is larger than 4GB.
-    #[stable(feature = "iovec", since = "1.36.0")]
     #[inline]
     pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
-        IoSlice(sys::io::IoSlice::new(buf))
+        IoSlice(IoVecBuffer::new(buf))
     }
 
     /// Advance the internal cursor of the slice.
@@ -1203,7 +1211,6 @@ impl<'a> IoSlice<'a> {
     /// buf.advance(3);
     /// assert_eq!(buf.deref(), [1; 5].as_ref());
     /// ```
-    #[unstable(feature = "io_slice_advance", issue = "62726")]
     #[inline]
     pub fn advance(&mut self, n: usize) {
         self.0.advance(n)
@@ -1240,7 +1247,6 @@ impl<'a> IoSlice<'a> {
     /// IoSlice::advance_slices(&mut bufs, 10);
     /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
     /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
-    #[unstable(feature = "io_slice_advance", issue = "62726")]
     #[inline]
     pub fn advance_slices(bufs: &mut &mut [IoSlice<'a>], n: usize) {
         // Number of buffers to remove.
@@ -1263,7 +1269,6 @@ impl<'a> IoSlice<'a> {
     }
 }
 
-#[stable(feature = "iovec", since = "1.36.0")]
 impl<'a> Deref for IoSlice<'a> {
     type Target = [u8];
 
@@ -1274,13 +1279,11 @@ impl<'a> Deref for IoSlice<'a> {
 }
 
 /// A type used to conditionally initialize buffers passed to `Read` methods.
-#[unstable(feature = "read_initializer", issue = "42788")]
 #[derive(Debug)]
 pub struct Initializer(bool);
 
 impl Initializer {
     /// Returns a new `Initializer` which will zero out buffers.
-    #[unstable(feature = "read_initializer", issue = "42788")]
     #[inline]
     pub fn zeroing() -> Initializer {
         Initializer(true)
@@ -1294,21 +1297,18 @@ impl Initializer {
     /// read from buffers passed to `Read` methods, and that the return value of
     /// the method accurately reflects the number of bytes that have been
     /// written to the head of the buffer.
-    #[unstable(feature = "read_initializer", issue = "42788")]
     #[inline]
     pub unsafe fn nop() -> Initializer {
         Initializer(false)
     }
 
     /// Indicates if a buffer should be initialized.
-    #[unstable(feature = "read_initializer", issue = "42788")]
     #[inline]
     pub fn should_initialize(&self) -> bool {
         self.0
     }
 
     /// Initializes a buffer if necessary.
-    #[unstable(feature = "read_initializer", issue = "42788")]
     #[inline]
     pub fn initialize(&self, buf: &mut [u8]) {
         if self.should_initialize() {
@@ -1362,9 +1362,7 @@ impl Initializer {
 /// `write` in a loop until its entire input has been written.
 ///
 /// [`write_all`]: Write::write_all
-#[stable(feature = "rust1", since = "1.0.0")]
 #[doc(notable_trait)]
-#[cfg_attr(not(test), rustc_diagnostic_item = "IoWrite")]
 pub trait Write {
     /// Write a buffer into this writer, returning how many bytes were written.
     ///
@@ -1410,7 +1408,6 @@ pub trait Write {
     /// ```
     ///
     /// [`Ok(n)`]: Ok
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn write(&mut self, buf: &[u8]) -> Result<usize>;
 
     /// Like [`write`], except that it writes from a slice of buffers.
@@ -1444,7 +1441,6 @@ pub trait Write {
     /// ```
     ///
     /// [`write`]: Write::write
-    #[stable(feature = "iovec", since = "1.36.0")]
     fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize> {
         default_write_vectored(|b| self.write(b), bufs)
     }
@@ -1459,7 +1455,6 @@ pub trait Write {
     /// The default implementation returns `false`.
     ///
     /// [`write_vectored`]: Write::write_vectored
-    #[unstable(feature = "can_vector", issue = "69941")]
     fn is_write_vectored(&self) -> bool {
         false
     }
@@ -1487,7 +1482,6 @@ pub trait Write {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn flush(&mut self) -> Result<()>;
 
     /// Attempts to write an entire buffer into this writer.
@@ -1521,7 +1515,6 @@ pub trait Write {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
         while !buf.is_empty() {
             match self.write(buf) {
@@ -1586,7 +1579,6 @@ pub trait Write {
     /// assert_eq!(writer, &[1, 2, 3, 4, 5, 6]);
     /// # Ok(()) }
     /// ```
-    #[unstable(feature = "write_all_vectored", issue = "70436")]
     fn write_all_vectored(&mut self, mut bufs: &mut [IoSlice<'_>]) -> Result<()> {
         // Guarantee that bufs is empty if it contains no data,
         // to avoid calling write_vectored if there is no data to be written.
@@ -1642,7 +1634,6 @@ pub trait Write {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> Result<()> {
         // Create a shim which translates a Write to a fmt::Write and saves
         // off I/O errors. instead of discarding them
@@ -1698,7 +1689,6 @@ pub trait Write {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn by_ref(&mut self) -> &mut Self
     where
         Self: Sized,
@@ -1733,7 +1723,6 @@ pub trait Write {
 ///     Ok(())
 /// }
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub trait Seek {
     /// Seek to an offset, in bytes, in a stream.
     ///
@@ -1749,7 +1738,6 @@ pub trait Seek {
     /// Seeking can fail, for example because it might involve flushing a buffer.
     ///
     /// Seeking to a negative offset is considered an error.
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
 
     /// Rewind to the beginning of a stream.
@@ -1780,7 +1768,6 @@ pub trait Seek {
     /// f.read_to_string(&mut buf).unwrap();
     /// assert_eq!(&buf, hello);
     /// ```
-    #[stable(feature = "seek_rewind", since = "1.55.0")]
     fn rewind(&mut self) -> Result<()> {
         self.seek(SeekFrom::Start(0))?;
         Ok(())
@@ -1820,7 +1807,6 @@ pub trait Seek {
     ///     Ok(())
     /// }
     /// ```
-    #[unstable(feature = "seek_stream_len", issue = "59359")]
     fn stream_len(&mut self) -> Result<u64> {
         let old_pos = self.stream_position()?;
         let len = self.seek(SeekFrom::End(0))?;
@@ -1857,7 +1843,6 @@ pub trait Seek {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "seek_convenience", since = "1.51.0")]
     fn stream_position(&mut self) -> Result<u64> {
         self.seek(SeekFrom::Current(0))
     }
@@ -1867,29 +1852,26 @@ pub trait Seek {
 ///
 /// It is used by the [`Seek`] trait.
 #[derive(Copy, PartialEq, Eq, Clone, Debug)]
-#[stable(feature = "rust1", since = "1.0.0")]
 pub enum SeekFrom {
     /// Sets the offset to the provided number of bytes.
-    #[stable(feature = "rust1", since = "1.0.0")]
-    Start(#[stable(feature = "rust1", since = "1.0.0")] u64),
+    Start(u64),
 
     /// Sets the offset to the size of this object plus the specified number of
     /// bytes.
     ///
     /// It is possible to seek beyond the end of an object, but it's an error to
     /// seek before byte 0.
-    #[stable(feature = "rust1", since = "1.0.0")]
-    End(#[stable(feature = "rust1", since = "1.0.0")] i64),
+    End(i64),
 
     /// Sets the offset to the current position plus the specified number of
     /// bytes.
     ///
     /// It is possible to seek beyond the end of an object, but it's an error to
     /// seek before byte 0.
-    #[stable(feature = "rust1", since = "1.0.0")]
-    Current(#[stable(feature = "rust1", since = "1.0.0")] i64),
+    Current(i64),
 }
 
+#[cfg(feature="collections")]
 fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>) -> Result<usize> {
     let mut read = 0;
     loop {
@@ -1965,7 +1947,7 @@ fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>) -> R
 ///     Ok(())
 /// }
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="collections")]
 pub trait BufRead: Read {
     /// Returns the contents of the internal buffer, filling it with more data
     /// from the inner reader if it is empty.
@@ -2006,7 +1988,6 @@ pub trait BufRead: Read {
     /// let length = buffer.len();
     /// stdin.consume(length);
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn fill_buf(&mut self) -> Result<&[u8]>;
 
     /// Tells this buffer that `amt` bytes have been consumed from the buffer,
@@ -2028,7 +2009,6 @@ pub trait BufRead: Read {
     /// that method's example includes an example of `consume()`.
     ///
     /// [`fill_buf`]: BufRead::fill_buf
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn consume(&mut self, amt: usize);
 
     /// Check if the underlying `Read` has any data left to be read.
@@ -2057,7 +2037,6 @@ pub trait BufRead: Read {
     ///     println!("{:?}", line);
     /// }
     /// ```
-    #[unstable(feature = "buf_read_has_data_left", reason = "recently added", issue = "86423")]
     fn has_data_left(&mut self) -> Result<bool> {
         self.fill_buf().map(|b| !b.is_empty())
     }
@@ -2116,7 +2095,6 @@ pub trait BufRead: Read {
     /// assert_eq!(num_bytes, 0);
     /// assert_eq!(buf, b"");
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
         read_until(self, byte, buf)
     }
@@ -2179,7 +2157,6 @@ pub trait BufRead: Read {
     /// assert_eq!(num_bytes, 0);
     /// assert_eq!(buf, "");
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn read_line(&mut self, buf: &mut String) -> Result<usize> {
         // Note that we are not calling the `.read_until` method here, but
         // rather our hardcoded implementation. For more details as to why, see
@@ -2217,7 +2194,6 @@ pub trait BufRead: Read {
     /// assert_eq!(split_iter.next(), Some(b"dolor".to_vec()));
     /// assert_eq!(split_iter.next(), None);
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn split(self, byte: u8) -> Split<Self>
     where
         Self: Sized,
@@ -2254,7 +2230,6 @@ pub trait BufRead: Read {
     /// # Errors
     ///
     /// Each line of the iterator has the same error semantics as [`BufRead::read_line`].
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn lines(self) -> Lines<Self>
     where
         Self: Sized,
@@ -2269,7 +2244,6 @@ pub trait BufRead: Read {
 /// Please see the documentation of [`chain`] for more details.
 ///
 /// [`chain`]: Read::chain
-#[stable(feature = "rust1", since = "1.0.0")]
 #[derive(Debug)]
 pub struct Chain<T, U> {
     first: T,
@@ -2296,7 +2270,6 @@ impl<T, U> Chain<T, U> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
     pub fn into_inner(self) -> (T, U) {
         (self.first, self.second)
     }
@@ -2319,7 +2292,6 @@ impl<T, U> Chain<T, U> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
     pub fn get_ref(&self) -> (&T, &U) {
         (&self.first, &self.second)
     }
@@ -2346,13 +2318,11 @@ impl<T, U> Chain<T, U> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
     pub fn get_mut(&mut self) -> (&mut T, &mut U) {
         (&mut self.first, &mut self.second)
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Read, U: Read> Read for Chain<T, U> {
     fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
         if !self.done_first {
@@ -2380,7 +2350,7 @@ impl<T: Read, U: Read> Read for Chain<T, U> {
     }
 }
 
-#[stable(feature = "chain_bufread", since = "1.9.0")]
+#[cfg(feature="collections")]
 impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
     fn fill_buf(&mut self) -> Result<&[u8]> {
         if !self.done_first {
@@ -2420,7 +2390,6 @@ impl<T, U> SizeHint for Chain<T, U> {
 /// Please see the documentation of [`take`] for more details.
 ///
 /// [`take`]: Read::take
-#[stable(feature = "rust1", since = "1.0.0")]
 #[derive(Debug)]
 pub struct Take<T> {
     inner: T,
@@ -2453,7 +2422,6 @@ impl<T> Take<T> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn limit(&self) -> u64 {
         self.limit
     }
@@ -2481,7 +2449,6 @@ impl<T> Take<T> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "take_set_limit", since = "1.27.0")]
     pub fn set_limit(&mut self, limit: u64) {
         self.limit = limit;
     }
@@ -2506,7 +2473,6 @@ impl<T> Take<T> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "io_take_into_inner", since = "1.15.0")]
     pub fn into_inner(self) -> T {
         self.inner
     }
@@ -2531,7 +2497,6 @@ impl<T> Take<T> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
     pub fn get_ref(&self) -> &T {
         &self.inner
     }
@@ -2560,13 +2525,11 @@ impl<T> Take<T> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
     pub fn get_mut(&mut self) -> &mut T {
         &mut self.inner
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Read> Read for Take<T> {
     fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
         // Don't call into inner reader at all at EOF because it may still block
@@ -2584,6 +2547,7 @@ impl<T: Read> Read for Take<T> {
         self.inner.initializer()
     }
 
+    #[cfg(feature="collections")]
     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
         // Pass in a reservation_size closure that respects the current value
         // of limit for each read. If we hit the read limit, this prevents the
@@ -2592,7 +2556,7 @@ impl<T: Read> Read for Take<T> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="collections")]
 impl<T: BufRead> BufRead for Take<T> {
     fn fill_buf(&mut self) -> Result<&[u8]> {
         // Don't call into inner reader at all at EOF because it may still block
@@ -2634,13 +2598,11 @@ impl<T> SizeHint for Take<T> {
 /// Please see the documentation of [`bytes`] for more details.
 ///
 /// [`bytes`]: Read::bytes
-#[stable(feature = "rust1", since = "1.0.0")]
 #[derive(Debug)]
 pub struct Bytes<R> {
     inner: R,
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<R: Read> Iterator for Bytes<R> {
     type Item = Result<u8>;
 
@@ -2695,6 +2657,7 @@ impl<T> SizeHint for &mut T {
     }
 }
 
+#[cfg(feature="alloc")]
 impl<T> SizeHint for Box<T> {
     #[inline]
     fn lower_bound(&self) -> usize {
@@ -2726,14 +2689,14 @@ impl SizeHint for &[u8] {
 /// Please see the documentation of [`split`] for more details.
 ///
 /// [`split`]: BufRead::split
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="collections")]
 #[derive(Debug)]
 pub struct Split<B> {
     buf: B,
     delim: u8,
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="collections")]
 impl<B: BufRead> Iterator for Split<B> {
     type Item = Result<Vec<u8>>;
 
@@ -2758,13 +2721,13 @@ impl<B: BufRead> Iterator for Split<B> {
 /// Please see the documentation of [`lines`] for more details.
 ///
 /// [`lines`]: BufRead::lines
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="collections")]
 #[derive(Debug)]
 pub struct Lines<B> {
     buf: B,
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(feature="collections")]
 impl<B: BufRead> Iterator for Lines<B> {
     type Item = Result<String>;
 
diff --git a/prelude.rs b/prelude.rs
index d806431..6b9791a 100644
--- a/prelude.rs
+++ b/prelude.rs
@@ -8,7 +8,8 @@
 //! use std::io::prelude::*;
 //! ```
 
-#![stable(feature = "rust1", since = "1.0.0")]
+pub use super::{Read, Seek, Write};
+#[cfg(feature="collections")] pub use super::BufRead;
 
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use super::{BufRead, Read, Seek, Write};
+#[cfg(feature="collections")] pub use alloc::boxed::Box;
+#[cfg(feature="collections")] pub use collections::vec::Vec;
diff --git a/util.rs b/util.rs
index a8812f1..56c6aaa 100644
--- a/util.rs
+++ b/util.rs
@@ -3,16 +3,16 @@
 #[cfg(test)]
 mod tests;
 
-use crate::fmt;
+use core::fmt;
 use crate::io::{
-    self, BufRead, Initializer, IoSlice, IoSliceMut, Read, Seek, SeekFrom, SizeHint, Write,
+    self, Initializer, IoSlice, IoSliceMut, Read, Seek, SeekFrom, SizeHint, Write,
 };
+#[cfg(feature="collections")] use crate::io::BufRead;
 
 /// A reader which is always at EOF.
 ///
 /// This struct is generally created by calling [`empty()`]. Please see
 /// the documentation of [`empty()`] for more details.
-#[stable(feature = "rust1", since = "1.0.0")]
 #[non_exhaustive]
 #[derive(Copy, Clone, Default)]
 pub struct Empty;
@@ -32,13 +32,10 @@ pub struct Empty;
 /// io::empty().read_to_string(&mut buffer).unwrap();
 /// assert!(buffer.is_empty());
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
 pub const fn empty() -> Empty {
     Empty
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl Read for Empty {
     #[inline]
     fn read(&mut self, _buf: &mut [u8]) -> io::Result<usize> {
@@ -50,7 +47,8 @@ impl Read for Empty {
         Initializer::nop()
     }
 }
-#[stable(feature = "rust1", since = "1.0.0")]
+
+#[cfg(feature="collections")]
 impl BufRead for Empty {
     #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> {
@@ -60,7 +58,6 @@ impl BufRead for Empty {
     fn consume(&mut self, _n: usize) {}
 }
 
-#[stable(feature = "empty_seek", since = "1.51.0")]
 impl Seek for Empty {
     fn seek(&mut self, _pos: SeekFrom) -> io::Result<u64> {
         Ok(0)
@@ -75,7 +72,6 @@ impl Seek for Empty {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Empty {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("Empty").finish_non_exhaustive()
@@ -93,7 +89,6 @@ impl SizeHint for Empty {
 ///
 /// This struct is generally created by calling [`repeat()`]. Please
 /// see the documentation of [`repeat()`] for more details.
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct Repeat {
     byte: u8,
 }
@@ -112,13 +107,10 @@ pub struct Repeat {
 /// io::repeat(0b101).read_exact(&mut buffer).unwrap();
 /// assert_eq!(buffer, [0b101, 0b101, 0b101]);
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
 pub const fn repeat(byte: u8) -> Repeat {
     Repeat { byte }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl Read for Repeat {
     #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
@@ -160,7 +152,6 @@ impl SizeHint for Repeat {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Repeat {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("Repeat").finish_non_exhaustive()
@@ -171,7 +162,6 @@ impl fmt::Debug for Repeat {
 ///
 /// This struct is generally created by calling [`sink`]. Please
 /// see the documentation of [`sink()`] for more details.
-#[stable(feature = "rust1", since = "1.0.0")]
 #[non_exhaustive]
 #[derive(Copy, Clone, Default)]
 pub struct Sink;
@@ -192,13 +182,10 @@ pub struct Sink;
 /// let num_bytes = io::sink().write(&buffer).unwrap();
 /// assert_eq!(num_bytes, 5);
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
 pub const fn sink() -> Sink {
     Sink
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl Write for Sink {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
@@ -222,7 +209,6 @@ impl Write for Sink {
     }
 }
 
-#[stable(feature = "write_mt", since = "1.48.0")]
 impl Write for &Sink {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
@@ -246,7 +232,6 @@ impl Write for &Sink {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Sink {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("Sink").finish_non_exhaustive()