Old MS-DOS & WIN Software

[Gil Carrick]

According to Peter Norton, the BIOS code in a PC scans memory starting at
C000 and looking at every 2K block for the signature 0x55AA. (I am
paraphrasing.) This marks a ROM extension, probably in a software cartridge
or on a controller. What follows is supposedly a 1 byte length and a 3 byte
jump instruction. The BIOS initialization will then branch to this code and
execute it. The code can do anything, even take control of the system as is
done with some software cartridges. This ROM block can be at any even 2K
address. The IBM EGA adapter went at C000, so graphics cards tend to end up
there. Comments in this block might be really informative or might simply
try to look very much like some IBM module so as to facilitate
interoperability. 

HTH,

Gil

> -----Original Message-----
> From: cctalk-bounces at classiccmp.org 
> [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Jim Battle
> Sent: Saturday, December 03, 2005 11:03 PM
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: Re: Old MS-DOS & WIN Software
> 
> Jim Leonard wrote:
> ...
> > Yep, I get funny looks from others when I use debug to 
> determine what 
> > video chipset is in unknown machines so I know what updated 
> drivers to 
> > download. (Seriously -- in XP, do start->run->cmd then type 
> debug then 
> > type "d c000:0000" enter then enter again.)
> 
> OK, I'll bite:
> 
> C:\Documents and Settings\Owner>debug
> -d c000:0000
> C000:0000  55 AA 7A EB 4B 37 34 30-30 E9 4C 19 77 CC 56 49   
> U.z.K7400.L.w.VI
> C000:0010  44 45 4F 20 0D 00 00 00-84 02 9B 0E 00 00 49 42   
> DEO ..........IB
> C000:0020  4D 20 56 47 41 20 43 6F-6D 70 61 74 69 62 6C 65   
> M VGA Compatible
> C000:0030  01 00 00 00 B0 10 B2 EF-30 38 2F 30 37 2F 30 33   
> ........08/07/03
> C000:0040  00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00   
> ................
> C000:0050  E9 E7 E4 00 B0 10 21 04-03 D0 30 7E 3C 21 C0 80   
> ......!...0~<!..
> C000:0060  00 00 00 00 10 00 00 80-22 00 A5 8B E9 D0 0D E9   
> ........".......
> C000:0070  D7 0D 50 4D 49 44 6C 00-6F 00 00 00 00 A0 00 B0   
> ..PMIDl.o.......
> -
> -
> 
> You are a genius if, from that, you can tell what card I 
> have.  (answer below if you scroll down far enough)
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> Nvidia Gforce FX5200
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>