diff --git a/buffered.rs b/buffered.rs
index aaf628e..259eba3 100644
--- a/buffered.rs
+++ b/buffered.rs
@@ -1,13 +1,13 @@
 //! Buffering wrappers for I/O traits
 
+use core::prelude::v1::*;
 use crate::io::prelude::*;
 
-use crate::cmp;
-use crate::error;
-use crate::fmt;
+use core::cmp;
+use core::fmt;
 use crate::io::{self, Initializer, DEFAULT_BUF_SIZE, Error, ErrorKind, SeekFrom, IoSlice,
         IoSliceMut};
-use crate::memchr;
+use crate::io::memchr;
 
 /// The `BufReader` struct adds buffering to any reader.
 ///
@@ -47,7 +47,6 @@ use crate::memchr;
 ///     Ok(())
 /// }
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct BufReader<R> {
     inner: R,
     buf: Box<[u8]>,
@@ -71,7 +70,6 @@ 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)
     }
@@ -92,7 +90,6 @@ 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 buffer = Vec::with_capacity(capacity);
@@ -127,7 +124,6 @@ impl<R> BufReader<R> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_ref(&self) -> &R { &self.inner }
 
     /// Gets a mutable reference to the underlying reader.
@@ -148,7 +144,6 @@ impl<R> BufReader<R> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_mut(&mut self) -> &mut R { &mut self.inner }
 
     /// Returns a reference to the internally buffered data.
@@ -172,7 +167,6 @@ impl<R> BufReader<R> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "bufreader_buffer", since = "1.37.0")]
     pub fn buffer(&self) -> &[u8] {
         &self.buf[self.pos..self.cap]
     }
@@ -195,7 +189,6 @@ impl<R> BufReader<R> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn into_inner(self) -> R { self.inner }
 
     /// Invalidates all data in the internal buffer.
@@ -211,7 +204,6 @@ 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.
-    #[unstable(feature = "bufreader_seek_relative", issue = "31100")]
     pub fn seek_relative(&mut self, offset: i64) -> io::Result<()> {
         let pos = self.pos as u64;
         if offset < 0 {
@@ -231,7 +223,6 @@ 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
@@ -269,7 +260,6 @@ 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
@@ -289,7 +279,6 @@ 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 {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt.debug_struct("BufReader")
@@ -299,7 +288,6 @@ impl<R> fmt::Debug for BufReader<R> where R: fmt::Debug {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<R: Seek> Seek for BufReader<R> {
     /// Seek to an offset, in bytes, in the underlying reader.
     ///
@@ -408,7 +396,6 @@ impl<R: Seek> Seek for BufReader<R> {
 /// [`TcpStream::write`]: ../../std/net/struct.TcpStream.html#method.write
 /// [`TcpStream`]: ../../std/net/struct.TcpStream.html
 /// [`flush`]: #method.flush
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct BufWriter<W: Write> {
     inner: Option<W>,
     buf: Vec<u8>,
@@ -443,7 +430,6 @@ pub struct BufWriter<W: Write> {
 /// };
 /// ```
 #[derive(Debug)]
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct IntoInnerError<W>(W, Error);
 
 impl<W: Write> BufWriter<W> {
@@ -458,7 +444,6 @@ 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)
     }
@@ -476,7 +461,6 @@ 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: Some(inner),
@@ -525,7 +509,6 @@ 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.as_ref().unwrap() }
 
     /// Gets a mutable reference to the underlying writer.
@@ -543,7 +526,6 @@ 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 { self.inner.as_mut().unwrap() }
 
     /// Returns a reference to the internally buffered data.
@@ -559,7 +541,6 @@ 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
     }
@@ -583,7 +564,6 @@ 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(self, e)),
@@ -592,7 +572,6 @@ impl<W: Write> BufWriter<W> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write> Write for BufWriter<W> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         if self.buf.len() + buf.len() > self.buf.capacity() {
@@ -628,7 +607,6 @@ 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 {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt.debug_struct("BufWriter")
@@ -638,7 +616,6 @@ impl<W: Write> fmt::Debug for BufWriter<W> where W: fmt::Debug {
     }
 }
 
-#[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.
     ///
@@ -648,7 +625,6 @@ 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.inner.is_some() && !self.panicked {
@@ -687,7 +663,6 @@ impl<W> IntoInnerError<W> {
     ///     }
     /// };
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn error(&self) -> &Error { &self.1 }
 
     /// Returns the buffered writer instance which generated the error.
@@ -720,23 +695,13 @@ impl<W> IntoInnerError<W> {
     ///     }
     /// };
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn into_inner(self) -> W { 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> {
-    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)
@@ -807,7 +772,6 @@ impl<W> fmt::Display for IntoInnerError<W> {
 ///     Ok(())
 /// }
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct LineWriter<W: Write> {
     inner: BufWriter<W>,
     need_flush: bool,
@@ -828,7 +792,6 @@ 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)
@@ -849,7 +812,6 @@ 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),
@@ -873,7 +835,6 @@ impl<W: Write> LineWriter<W> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_ref(&self) -> &W { self.inner.get_ref() }
 
     /// Gets a mutable reference to the underlying writer.
@@ -896,7 +857,6 @@ 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() }
 
     /// Unwraps this `LineWriter`, returning the underlying writer.
@@ -922,7 +882,6 @@ 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(|IntoInnerError(buf, e)| {
             IntoInnerError(LineWriter {
@@ -933,7 +892,6 @@ impl<W: Write> LineWriter<W> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write> Write for LineWriter<W> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         if self.need_flush {
@@ -978,7 +936,6 @@ 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 {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt.debug_struct("LineWriter")
diff --git a/cursor.rs b/cursor.rs
index a94176e..7768d39 100644
--- a/cursor.rs
+++ b/cursor.rs
@@ -1,9 +1,9 @@
 use crate::io::prelude::*;
 
-use crate::cmp;
+use core::cmp;
 use crate::io::{self, Initializer, SeekFrom, Error, ErrorKind, IoSlice, IoSliceMut};
 
-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.
@@ -71,7 +71,6 @@ 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(Clone, Debug, Default)]
 pub struct Cursor<T> {
     inner: T,
@@ -94,7 +93,6 @@ impl<T> Cursor<T> {
     /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
     /// # force_inference(&buff);
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new(inner: T) -> Cursor<T> {
         Cursor { pos: 0, inner: inner }
     }
@@ -112,7 +110,6 @@ impl<T> Cursor<T> {
     ///
     /// let vec = buff.into_inner();
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn into_inner(self) -> T { self.inner }
 
     /// Gets a reference to the underlying value in this cursor.
@@ -128,7 +125,6 @@ impl<T> Cursor<T> {
     ///
     /// let reference = buff.get_ref();
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_ref(&self) -> &T { &self.inner }
 
     /// Gets a mutable reference to the underlying value in this cursor.
@@ -147,7 +143,6 @@ 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 }
 
     /// Returns the current position of this cursor.
@@ -169,7 +164,6 @@ impl<T> Cursor<T> {
     /// buff.seek(SeekFrom::Current(-1)).unwrap();
     /// assert_eq!(buff.position(), 1);
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn position(&self) -> u64 { self.pos }
 
     /// Sets the position of this cursor.
@@ -189,11 +183,9 @@ 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; }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<T> io::Seek for Cursor<T> where T: AsRef<[u8]> {
     fn seek(&mut self, style: SeekFrom) -> io::Result<u64> {
         let (base_pos, offset) = match style {
@@ -222,10 +214,9 @@ impl<T> io::Seek for Cursor<T> where T: AsRef<[u8]> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Read for Cursor<T> where T: AsRef<[u8]> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
-        let n = Read::read(&mut self.fill_buf()?, buf)?;
+        let n = Read::read(&mut self.get_buf()?, buf)?;
         self.pos += n as u64;
         Ok(n)
     }
@@ -244,7 +235,7 @@ impl<T> Read for Cursor<T> where T: AsRef<[u8]> {
 
     fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
         let n = buf.len();
-        Read::read_exact(&mut self.fill_buf()?, buf)?;
+        Read::read_exact(&mut self.get_buf()?, buf)?;
         self.pos += n as u64;
         Ok(())
     }
@@ -255,12 +246,16 @@ impl<T> Read for Cursor<T> where T: AsRef<[u8]> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> BufRead for Cursor<T> where T: AsRef<[u8]> {
-    fn fill_buf(&mut self) -> io::Result<&[u8]> {
+impl<T> Cursor<T> where T: AsRef<[u8]> {
+    fn get_buf(&mut self) -> io::Result<&[u8]> {
         let amt = cmp::min(self.pos, self.inner.as_ref().len() as u64);
         Ok(&self.inner.as_ref()[(amt as usize)..])
     }
+}
+
+#[cfg(feature="collections")]
+impl<T> BufRead for Cursor<T> where T: AsRef<[u8]> {
+    fn fill_buf(&mut self) -> io::Result<&[u8]> { self.get_buf() }
     fn consume(&mut self, amt: usize) { self.pos += amt as u64; }
 }
 
@@ -292,6 +287,7 @@ 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(ErrorKind::InvalidInput,
@@ -318,6 +314,7 @@ 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>,
@@ -331,7 +328,6 @@ 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> {
@@ -347,7 +343,7 @@ impl Write for Cursor<&mut [u8]> {
     fn flush(&mut self) -> io::Result<()> { Ok(()) }
 }
 
-#[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)
@@ -361,7 +357,7 @@ impl Write for Cursor<&mut Vec<u8>> {
     fn flush(&mut self) -> io::Result<()> { Ok(()) }
 }
 
-#[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)
@@ -375,8 +371,8 @@ impl Write for Cursor<Vec<u8>> {
     fn flush(&mut self) -> io::Result<()> { Ok(()) }
 }
 
-#[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 c29a68e..c94d8c5 100644
--- a/error.rs
+++ b/error.rs
@@ -1,8 +1,13 @@
-use crate::error;
-use crate::fmt;
-use crate::result;
-use crate::sys;
-use crate::convert::From;
+#[cfg(feature="alloc")] use alloc::boxed::Box;
+#[cfg(not(feature="alloc"))] use ::FakeBox as Box;
+use core::convert::Into;
+use core::fmt;
+use core::marker::{Send, Sync};
+use core::option::Option::{self, Some, None};
+use core::result;
+#[cfg(feature="collections")] use collections::string::String;
+#[cfg(not(feature="collections"))] use ::ErrorString as String;
+use core::convert::From;
 
 /// A specialized [`Result`](../result/enum.Result.html) type for I/O
 /// operations.
@@ -38,7 +43,6 @@ use crate::convert::From;
 ///     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
@@ -52,12 +56,10 @@ pub type Result<T> = result::Result<T, Error>;
 /// [`Write`]: ../io/trait.Write.html
 /// [`Seek`]: ../io/trait.Seek.html
 /// [`ErrorKind`]: enum.ErrorKind.html
-#[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)
@@ -67,13 +69,16 @@ impl fmt::Debug for Error {
 enum Repr {
     Os(i32),
     Simple(ErrorKind),
+    #[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.
@@ -85,48 +90,35 @@ struct Custom {
 ///
 /// [`io::Error`]: struct.Error.html
 #[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 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 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 parameter was incorrect.
-    #[stable(feature = "rust1", since = "1.0.0")]
     InvalidInput,
     /// Data not valid for the operation were encountered.
     ///
@@ -138,10 +130,8 @@ pub enum ErrorKind {
     /// `InvalidData` if the file's contents are not valid UTF-8.
     ///
     /// [`InvalidInput`]: #variant.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)`].
@@ -152,15 +142,12 @@ pub enum ErrorKind {
     ///
     /// [`write`]: ../../std/io/trait.Write.html#tymethod.write
     /// [`Ok(0)`]: ../../std/io/type.Result.html
-    #[stable(feature = "rust1", since = "1.0.0")]
     WriteZero,
     /// This operation was interrupted.
     ///
     /// Interrupted operations can typically be retried.
-    #[stable(feature = "rust1", since = "1.0.0")]
     Interrupted,
     /// Any I/O error not part of this list.
-    #[stable(feature = "rust1", since = "1.0.0")]
     Other,
 
     /// An error returned when an operation could not be completed because an
@@ -169,7 +156,6 @@ 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,
 }
 
@@ -200,7 +186,6 @@ 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`].
     ///
@@ -245,14 +230,13 @@ 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>>
+        where 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,
@@ -261,24 +245,6 @@ impl Error {
         }
     }
 
-    /// 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")]
-    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
@@ -304,7 +270,6 @@ impl Error {
     /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
     /// # }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn from_raw_os_error(code: i32) -> Error {
         Error { repr: Repr::Os(code) }
     }
@@ -335,7 +300,6 @@ impl Error {
     ///     print_os_error(&Error::new(ErrorKind::Other, "oh no!"));
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn raw_os_error(&self) -> Option<i32> {
         match self.repr {
             Repr::Os(i) => Some(i),
@@ -369,12 +333,11 @@ impl Error {
     ///     print_error(&Error::new(ErrorKind::Other, "oh no!"));
     /// }
     /// ```
-    #[stable(feature = "io_error_inner", since = "1.3.0")]
-    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::Custom(ref c) => Some(&*c.error),
+            Repr::Custom(ref c) => Some(&c.error),
         }
     }
 
@@ -440,12 +403,11 @@ impl Error {
     ///     print_error(&change_error(Error::new(ErrorKind::Other, MyError::new())));
     /// }
     /// ```
-    #[stable(feature = "io_error_inner", since = "1.3.0")]
-    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::Custom(ref mut c) => Some(&mut *c.error),
+            Repr::Custom(ref mut c) => Some(&mut c.error),
         }
     }
 
@@ -474,8 +436,7 @@ impl Error {
     ///     print_error(Error::new(ErrorKind::Other, "oh no!"));
     /// }
     /// ```
-    #[stable(feature = "io_error_inner", since = "1.3.0")]
-    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,
@@ -501,10 +462,9 @@ impl Error {
     ///     print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     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,
         }
@@ -516,22 +476,18 @@ impl fmt::Debug for Repr {
         match *self {
             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(),
+                    .field("code", &code).finish(),
             Repr::Custom(ref c) => fmt::Debug::fmt(&c, fmt),
             Repr::Simple(kind) => fmt.debug_tuple("Kind").field(&kind).finish(),
         }
     }
 }
 
-#[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()),
@@ -539,33 +495,6 @@ impl fmt::Display for Error {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
-impl error::Error for Error {
-    fn description(&self) -> &str {
-        match self.repr {
-            Repr::Os(..) | Repr::Simple(..) => self.kind().as_str(),
-            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::Custom(ref c) => c.error.cause(),
-        }
-    }
-
-    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
-        match self.repr {
-            Repr::Os(..) => None,
-            Repr::Simple(..) => 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 c959f2d..b645bc8 100644
--- a/impls.rs
+++ b/impls.rs
@@ -1,13 +1,15 @@
-use crate::cmp;
-use crate::io::{self, SeekFrom, Read, Initializer, Write, Seek, BufRead, Error, ErrorKind,
-        IoSliceMut, IoSlice};
-use crate::fmt;
-use crate::mem;
+#[cfg(feature="alloc")] use alloc::boxed::Box;
+use core::cmp;
+use crate::io::{self, SeekFrom, Read, Initializer, Write, Seek, Error, ErrorKind, IoSliceMut, IoSlice};
+#[cfg(feature="collections")] use crate::io::BufRead;
+use core::fmt;
+use core::mem;
+#[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> {
@@ -24,11 +26,13 @@ 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)
@@ -39,7 +43,6 @@ 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> { (**self).write(buf) }
@@ -62,12 +65,11 @@ 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> { (**self).seek(pos) }
 }
-#[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]> { (**self).fill_buf() }
@@ -86,7 +88,7 @@ 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> {
@@ -103,11 +105,13 @@ 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)
@@ -118,7 +122,7 @@ 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> { (**self).write(buf) }
@@ -141,12 +145,12 @@ 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> { (**self).seek(pos) }
 }
-#[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]> { (**self).fill_buf() }
@@ -186,7 +190,6 @@ impl Write for Box<dyn (::realstd::io::Write) + Send> {
 ///
 /// 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> {
@@ -245,6 +248,7 @@ 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);
@@ -254,7 +258,7 @@ 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]> { Ok(*self) }
@@ -268,7 +272,6 @@ impl BufRead for &[u8] {
 ///
 /// Note that writing updates the slice to point to the yet unwritten part.
 /// The slice will be empty when it has been completely overwritten.
-#[stable(feature = "rust1", since = "1.0.0")]
 impl Write for &mut [u8] {
     #[inline]
     fn write(&mut self, data: &[u8]) -> io::Result<usize> {
@@ -307,7 +310,7 @@ 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 Write for Vec<u8> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
diff --git a/mod.rs b/mod.rs
index 09b6b69..fdcc2de 100644
--- a/mod.rs
+++ b/mod.rs
@@ -257,50 +257,38 @@
 //! [`Result`]: ../result/enum.Result.html
 //! [`.unwrap()`]: ../result/enum.Result.html#method.unwrap
 
-#![stable(feature = "rust1", since = "1.0.0")]
-
-use crate::cmp;
-use crate::fmt;
-use crate::slice;
-use crate::str;
-use crate::memchr;
-use crate::ops::{Deref, DerefMut};
-use crate::ptr;
-use crate::sys;
-
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::buffered::{BufReader, BufWriter, LineWriter};
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::buffered::IntoInnerError;
-#[stable(feature = "rust1", since = "1.0.0")]
+use core::cmp;
+use core::fmt;
+#[cfg(feature="collections")] use collections::string::String;
+use core::str;
+#[cfg(feature="collections")] use collections::vec::Vec;
+#[cfg(not(core_memchr))]
+mod memchr;
+#[cfg(all(feature="collections",core_memchr))]
+use core::slice::memchr;
+use core::slice;
+use core::ops::{Deref, DerefMut};
+use core::ptr;
+
+#[cfg(feature="collections")] pub use self::buffered::{BufReader, BufWriter, LineWriter};
+#[cfg(feature="collections")] pub use self::buffered::IntoInnerError;
 pub use self::cursor::Cursor;
-#[stable(feature = "rust1", since = "1.0.0")]
 pub use self::error::{Result, Error, ErrorKind};
-#[stable(feature = "rust1", since = "1.0.0")]
 pub use self::util::{copy, sink, Sink, empty, Empty, repeat, Repeat};
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::stdio::{stdin, stdout, stderr, Stdin, Stdout, Stderr};
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::stdio::{StdoutLock, StderrLock, StdinLock};
-#[unstable(feature = "print_internals", issue = "0")]
-pub use self::stdio::{_print, _eprint};
-#[unstable(feature = "libstd_io_internals", issue = "42788")]
-#[doc(no_inline, hidden)]
-pub use self::stdio::{set_panic, set_print};
 
 pub mod prelude;
-mod buffered;
+#[cfg(feature="collections")] mod buffered;
 mod cursor;
 mod error;
 mod impls;
-mod lazy;
 mod util;
-mod stdio;
 
-const DEFAULT_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
+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 { self.buf.set_len(self.len); }
@@ -325,6 +313,7 @@ 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>
 {
@@ -352,10 +341,12 @@ fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
 //
 // 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: Read + ?Sized>(r: &mut R,
                                                   buf: &mut Vec<u8>,
                                                   reservation_size: usize) -> Result<usize>
@@ -484,7 +475,6 @@ where
 /// [`BufReader`]: struct.BufReader.html
 /// [`&str`]: ../../std/primitive.str.html
 /// [slice]: ../../std/primitive.slice.html
-#[stable(feature = "rust1", since = "1.0.0")]
 #[doc(spotlight)]
 pub trait Read {
     /// Pull some bytes from this source into the specified buffer, returning
@@ -552,7 +542,6 @@ 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.
@@ -563,7 +552,6 @@ 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)
     }
@@ -590,7 +578,6 @@ pub trait Read {
     ///
     /// [`Initializer::nop()`]: ../../std/io/struct.Initializer.html#method.nop
     /// [`Initializer`]: ../../std/io/struct.Initializer.html
-    #[unstable(feature = "read_initializer", issue = "42788")]
     #[inline]
     unsafe fn initializer(&self) -> Initializer {
         Initializer::zeroing()
@@ -643,7 +630,7 @@ pub trait Read {
     /// file.)
     ///
     /// [`std::fs::read`]: ../fs/fn.read.html
-    #[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)
     }
@@ -686,7 +673,7 @@ pub trait Read {
     /// reading from a file.)
     ///
     /// [`std::fs::read_to_string`]: ../fs/fn.read_to_string.html
-    #[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`
@@ -749,7 +736,6 @@ pub trait Read {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "read_exact", since = "1.6.0")]
     fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
         while !buf.is_empty() {
             match self.read(buf) {
@@ -801,7 +787,6 @@ pub trait Read {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
 
     /// Transforms this `Read` instance to an [`Iterator`] over its bytes.
@@ -838,7 +823,6 @@ pub trait Read {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn bytes(self) -> Bytes<Self> where Self: Sized {
         Bytes { inner: self }
     }
@@ -873,7 +857,6 @@ pub trait Read {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn chain<R: Read>(self, next: R) -> Chain<Self, R> where Self: Sized {
         Chain { first: self, second: next, done_first: false }
     }
@@ -909,22 +892,52 @@ pub trait Read {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn take(self, limit: u64) -> Take<Self> where Self: Sized {
         Take { inner: self, limit: limit }
     }
 }
 
+pub struct IoVecBuffer<'a>(&'a [u8]);
+
+impl<'a> IoVecBuffer<'a> {
+    #[inline]
+    pub fn new(buf: &'a [u8]) -> IoVecBuffer<'a> {
+        IoVecBuffer(buf)
+    }
+
+    #[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 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", 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)
@@ -937,14 +950,12 @@ 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))
     }
 }
 
-#[stable(feature = "iovec", since = "1.36.0")]
 impl<'a> Deref for IoSliceMut<'a> {
     type Target = [u8];
 
@@ -954,7 +965,6 @@ 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] {
@@ -967,11 +977,9 @@ impl<'a> DerefMut for IoSliceMut<'a> {
 /// It is semantically a wrapper around an `&[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 IoSlice<'a>(sys::io::IoSlice<'a>);
+pub struct IoSlice<'a>(IoVecBuffer<'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)
@@ -984,14 +992,12 @@ 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))
     }
 }
 
-#[stable(feature = "iovec", since = "1.36.0")]
 impl<'a> Deref for IoSlice<'a> {
     type Target = [u8];
 
@@ -1002,13 +1008,11 @@ 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)
@@ -1022,21 +1026,18 @@ 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() {
@@ -1090,7 +1091,6 @@ impl Initializer {
 /// `write` in a loop until its entire input has been written.
 ///
 /// [`write_all`]: #method.write_all
-#[stable(feature = "rust1", since = "1.0.0")]
 #[doc(spotlight)]
 pub trait Write {
     /// Write a buffer into this writer, returning how many bytes were written.
@@ -1139,7 +1139,6 @@ pub trait Write {
     ///     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.
@@ -1150,7 +1149,6 @@ pub trait Write {
     ///
     /// The default implementation calls `write` with either the first nonempty
     /// buffer provided, or an empty one if none exists.
-    #[stable(feature = "iovec", since = "1.36.0")]
     fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize> {
         default_write_vectored(|b| self.write(b), bufs)
     }
@@ -1178,7 +1176,6 @@ 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.
@@ -1211,7 +1208,6 @@ 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) {
@@ -1263,7 +1259,6 @@ 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
@@ -1319,7 +1314,6 @@ pub trait Write {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
 }
 
@@ -1349,7 +1343,6 @@ pub trait Write {
 ///     Ok(())
 /// }
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub trait Seek {
     /// Seek to an offset, in bytes, in a stream.
     ///
@@ -1365,7 +1358,6 @@ pub trait Seek {
     /// Seeking to a negative offset is considered an error.
     ///
     /// [`SeekFrom::Start`]: enum.SeekFrom.html#variant.Start
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
 
     /// Returns the length of this stream (in bytes).
@@ -1403,7 +1395,6 @@ pub trait Seek {
     ///     Ok(())
     /// }
     /// ```
-    #[unstable(feature = "seek_convenience", issue = "59359")]
     fn stream_len(&mut self) -> Result<u64> {
         let old_pos = self.stream_position()?;
         let len = self.seek(SeekFrom::End(0))?;
@@ -1442,7 +1433,6 @@ pub trait Seek {
     ///     Ok(())
     /// }
     /// ```
-    #[unstable(feature = "seek_convenience", issue = "59359")]
     fn stream_position(&mut self) -> Result<u64> {
         self.seek(SeekFrom::Current(0))
     }
@@ -1454,29 +1444,26 @@ pub trait Seek {
 ///
 /// [`Seek`]: trait.Seek.html
 #[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;
@@ -1556,7 +1543,7 @@ fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>)
 /// }
 /// ```
 ///
-#[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.
@@ -1597,7 +1584,6 @@ 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,
@@ -1619,7 +1605,6 @@ pub trait BufRead: Read {
     /// that method's example includes an example of `consume()`.
     ///
     /// [`fill_buf`]: #tymethod.fill_buf
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn consume(&mut self, amt: usize);
 
     /// Read all bytes into `buf` until the delimiter `byte` or EOF is reached.
@@ -1675,7 +1660,6 @@ 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)
     }
@@ -1734,7 +1718,6 @@ 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
@@ -1775,7 +1758,6 @@ 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 {
         Split { buf: self, delim: byte }
     }
@@ -1814,7 +1796,6 @@ pub trait BufRead: Read {
     /// Each line of the iterator has the same error semantics as [`BufRead::read_line`].
     ///
     /// [`BufRead::read_line`]: trait.BufRead.html#method.read_line
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn lines(self) -> Lines<Self> where Self: Sized {
         Lines { buf: self }
     }
@@ -1826,7 +1807,6 @@ pub trait BufRead: Read {
 /// Please see the documentation of [`chain`] for more details.
 ///
 /// [`chain`]: trait.Read.html#method.chain
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct Chain<T, U> {
     first: T,
     second: U,
@@ -1852,7 +1832,6 @@ 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)
     }
@@ -1875,7 +1854,6 @@ 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)
     }
@@ -1902,13 +1880,11 @@ 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 = "std_debug", since = "1.16.0")]
 impl<T: fmt::Debug, U: fmt::Debug> fmt::Debug for Chain<T, U> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("Chain")
@@ -1918,7 +1894,6 @@ impl<T: fmt::Debug, U: fmt::Debug> fmt::Debug for Chain<T, U> {
     }
 }
 
-#[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 {
@@ -1950,7 +1925,7 @@ 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 {
@@ -1977,7 +1952,6 @@ impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
 /// Please see the documentation of [`take`] for more details.
 ///
 /// [`take`]: trait.Read.html#method.take
-#[stable(feature = "rust1", since = "1.0.0")]
 #[derive(Debug)]
 pub struct Take<T> {
     inner: T,
@@ -2012,7 +1986,6 @@ impl<T> Take<T> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn limit(&self) -> u64 { self.limit }
 
     /// Sets the number of bytes that can be read before this instance will
@@ -2038,7 +2011,6 @@ 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;
     }
@@ -2063,7 +2035,6 @@ impl<T> Take<T> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "io_take_into_inner", since = "1.15.0")]
     pub fn into_inner(self) -> T {
         self.inner
     }
@@ -2088,7 +2059,6 @@ impl<T> Take<T> {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
     pub fn get_ref(&self) -> &T {
         &self.inner
     }
@@ -2117,13 +2087,11 @@ 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
@@ -2141,6 +2109,7 @@ 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> {
         let reservation_size = cmp::min(self.limit, 32) as usize;
 
@@ -2148,7 +2117,7 @@ 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
@@ -2175,13 +2144,11 @@ impl<T: BufRead> BufRead for Take<T> {
 /// Please see the documentation of [`bytes`] for more details.
 ///
 /// [`bytes`]: trait.Read.html#method.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>;
 
@@ -2205,14 +2172,14 @@ impl<R: Read> Iterator for Bytes<R> {
 /// `BufRead`. Please see the documentation of `split()` for more details.
 ///
 /// [split]: trait.BufRead.html#method.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>>;
 
@@ -2237,13 +2204,13 @@ impl<B: BufRead> Iterator for Split<B> {
 /// `BufRead`. Please see the documentation of `lines()` for more details.
 ///
 /// [lines]: trait.BufRead.html#method.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 2e19edf..66294a3 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, Write, Seek};
+#[cfg(feature="collections")] pub use super::BufRead;
 
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use super::{Read, Write, BufRead, Seek};
+#[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 33cc87e..75b8032 100644
--- a/util.rs
+++ b/util.rs
@@ -1,8 +1,9 @@
 #![allow(missing_copy_implementations)]
 
-use crate::fmt;
-use crate::io::{self, Read, Initializer, Write, ErrorKind, BufRead, IoSlice, IoSliceMut};
-use crate::mem::MaybeUninit;
+use core::fmt;
+use crate::io::{self, Read, Initializer, Write, ErrorKind, IoSlice, IoSliceMut};
+#[cfg(feature="collections")] use crate::io::BufRead;
+use core::mem::MaybeUninit;
 
 /// Copies the entire contents of a reader into a writer.
 ///
@@ -39,7 +40,6 @@ 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) -> io::Result<u64>
     where R: Read, W: Write
 {
@@ -70,7 +70,6 @@ pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> io::Result<
 /// the documentation of [`empty()`][`empty`] for more details.
 ///
 /// [`empty`]: fn.empty.html
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct Empty { _priv: () }
 
 /// Constructs a new handle to an empty reader.
@@ -90,10 +89,8 @@ pub struct Empty { _priv: () }
 /// io::empty().read_to_string(&mut buffer).unwrap();
 /// assert!(buffer.is_empty());
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub fn empty() -> Empty { Empty { _priv: () } }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl Read for Empty {
     #[inline]
     fn read(&mut self, _buf: &mut [u8]) -> io::Result<usize> { Ok(0) }
@@ -103,7 +100,8 @@ 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]> { Ok(&[]) }
@@ -111,7 +109,6 @@ impl BufRead for Empty {
     fn consume(&mut self, _n: usize) {}
 }
 
-#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Empty {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.pad("Empty { .. }")
@@ -124,7 +121,6 @@ impl fmt::Debug for Empty {
 /// see the documentation of `repeat()` for more details.
 ///
 /// [repeat]: fn.repeat.html
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct Repeat { byte: u8 }
 
 /// Creates an instance of a reader that infinitely repeats one byte.
@@ -141,10 +137,8 @@ pub struct Repeat { byte: u8 }
 /// io::repeat(0b101).read_exact(&mut buffer).unwrap();
 /// assert_eq!(buffer, [0b101, 0b101, 0b101]);
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub 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> {
@@ -169,7 +163,6 @@ impl Read 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.pad("Repeat { .. }")
@@ -182,7 +175,6 @@ impl fmt::Debug for Repeat {
 /// see the documentation of `sink()` for more details.
 ///
 /// [sink]: fn.sink.html
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct Sink { _priv: () }
 
 /// Creates an instance of a writer which will successfully consume all data.
@@ -199,10 +191,8 @@ pub struct Sink { _priv: () }
 /// let num_bytes = io::sink().write(&buffer).unwrap();
 /// assert_eq!(num_bytes, 5);
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub fn sink() -> Sink { Sink { _priv: () } }
 
-#[stable(feature = "rust1", since = "1.0.0")]
 impl Write for Sink {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> { Ok(buf.len()) }
@@ -217,7 +207,6 @@ impl Write for Sink {
     fn flush(&mut self) -> io::Result<()> { Ok(()) }
 }
 
-#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Sink {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.pad("Sink { .. }")