Second change to Architecture Manual

[Ken Smith]

This is a second change I was thinking might make a good addition
to the Architecture Manual.  Virtually every book that talks about
UNIX devices describes character and block devices.  Developers new
to FreeBSD sometimes wonder what happened to block devices.  And a
lot of places in lots of manual pages, books, etc. still at least
slightly suggest there could be more than just Character devices.

Is this worth adding?  Thanks...

--- chapter.sgml_orig	Fri Oct 10 09:37:18 2003
+++ chapter.sgml	Tue Oct 14 21:21:07 2003
@@ -527,6 +527,22 @@
     </para>
   </sect1>
 
+  <sect1 id="driverbasics-block">
+    <title>Block Devices (Are Gone)</title>
+
+    <para>Developers familiar with other UNIX systems expect there to
+      be a second type of device known as block devices.  On those other
+      UNIX systems block devices are associated with the buffer cache.
+      Data blocks from block devices are buffered inside the kernel 
+      and filesystems get mounted on block devices.  This improves
+      I/O efficiency.  &os; has shifted the management of the buffer
+      cache away from block devices.  It is associated it with the virtual
+      memory system and vnode system used to keep track of open files inside
+      the kernel.  As a result &os; no longer needs block devices and they
+      have been removed from the system.  Only character devices remain.
+    </para>
+  </sect1>
+
   <sect1 id="driverbasics-net">
     <title>Network Drivers</title>
 


-- 
						Ken Smith
- From there to here, from here to      |       kensmith at cse.buffalo.edu
  there, funny things are everywhere.   |
                      - Theodore Geisel |