[comp.sys.ibm.pc] 640K limit & soft pointers to I/O memory.

john@wsl.UUCP (John Allen on wsl) (01/23/90)

In article <6680@tekgvs.LABS.TEK.COM> toma@tekgvs.LABS.TEK.COM (Tom Almy) writes:
>In article <729@jethro.Corp.Sun.COM> acm@sun.UUCP (Andrew MacRae) writes:
>>Simple.  IBM/MicroSoft *should* have used soft pointers to the I/O memory
>>areas.  They made the same mistake that was made with CP/M, hardcoding

The PC (iAPX processors) have a wonderful low memory area where 255 interrupt
vectors are stored. These all point to various functions in the BIOS. IBM
purposely designed it this way. (one up for IBM).  This theorectically allows 
IBM/Microsoft to move the BIOS anywhere.

PROBLEM: Too many hot shit software houses bypasss this mechanism and now
IBM has basically promised not to move the locations of various things,
eg. Colour/Mono screen memory addresses. As a result even if the BIOS would
fit in the top 20k we still could not use more than 709k, and that only with
a MONO display card.

Of couse we are still stuck with the 1 meg limit of the processor (8088/6)


-- 
People that don't know want to know from the people that do know and if the 
poeple that do know don't tell the people that don't know then the people
that don't know still won't know.
				   "Don't quote me on any issue whatsoever."