20 Sep
2004
20 Sep
'04
4:56 p.m.
It was thus said that the Great Vintage Computer Festival once stated:
On Mon, 20 Sep 2004, Teo Zenios wrote:
Raymond Chen's blog The Old New Thing
(http://weblogs.asp.net/oldnewthing/) recently covered virtual memory
handling under Windows. In fact, his blog explains a lot of wierdness in
Windows and makes for some pretty interesting reading. The series starts
with
http://weblogs.asp.net/oldnewthing/archive/2004/08/05/208908.aspx
-spc (No one should ever need more than 4G ... )
CAUSE
The Windows 32-bit protected-mode cache driver (Vcache) determines the
maximum cache size based on the amount of RAM that is present when Windows
starts. Vcache then reserves enough memory addresses to permit it to access
a cache of the maximum size so that it can increase the cache to that size
if needed. These addresses are allocated in a range of virtual addresses
from 0xC0000000 through 0xFFFFFFFF (3 to 4 gigabytes) known as the system
arena.
On computers with large amounts of RAM, the maximum cache size can be
large enough that Vcache consumes all of the addresses in the system arena,
leaving no virtual memory addresses available for other functions such as
opening an MS-DOS prompt (creating a new virtual machine).
Bill Gates must've thought that, surely, no one will ever need more than
640MB of memory!