22 Apr
2007
22 Apr
'07
8:54 a.m.
Thanks fred, it's been quite a while since I've had to worry about the
memory location of a video card so I'm obviously rusty :)
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
On Behalf Of Fred Cisin
Sent: Saturday, April 21, 2007 7:31 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: RE: The 640k "barrier" (was: Re: cctalk Digest, Vol 44, Issue 54)
On Sat, 21 Apr 2007, Geoff Reed wrote:
The 640K barrier was due to the location of the memory
map for CGA
graphics
IIRC. If you were running monochrome you could
squeeze a little more ram
out of the system IIRC.
CGA was at segment B800.
MDA was at segment B000
640K was at segment A000
A000 - B000 was "reserved for future expansion (EGA, VGA, etc.)
384K seems like a lot of space to set aside. But, at the time, 640K was
10 times what was otherwise available (64K), and surely nobody would need
more than THAT!