Need Docs for XT RAM Board...

Chuck Guzis cclist at
Wed Nov 8 20:12:23 CST 2006

On 8 Nov 2006 at 17:01, Fred Cisin wrote:

> The PC (5150) had TWO sets of switches, one for RAM, and one for other
> configuration (drives, FPU, etc.)

It's one of those endearing things about the 5150 that I like.  The 
5150 actually needed NO DIP switches--the hardware designers must 
have had a very low opinion of the software people.

Consider:  the first bank, memory size, describes available memory 
only up to 64K (on the original 5150).    The number of available 
diskette drives can be determined easily by software (note that there 
was no "drive type" setting, as all drives were assumed to be 5.25" 
320/360/160/180K types).  NDP presence is again easy to determine 
with software.   Presence of a CGA or MDA is easy enough--and if a 
CGA was detected, it's easy enough to start things in 40x25 mode--a 
switch to 80x25 can be made in the autoexec.bat file easily enough 
(or the SCREEN command in ROM BASIC).


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