identifying PC Simms
cclist at sydex.com
Fri Sep 30 16:57:51 CDT 2005
On 9/30/2005 at 3:24 PM Jules Richardson wrote:
>> I beliee that most PCs could make use of the added parity bit, while
> > Macs didn't care if it was present.
>(ignoring attributions here I know)
>Isn't that the other way around? Nearly all PCs I've come across don't
>care about parity, but the rest of the world always seemed to make use
Nope, PC's right up through the PS/2 used NMI (int 2) to diagnose memory parity and bus errors, as well as 80x87 exceptions. PS/2's also had a watchdog timer that could be activated (int 15h, ah=C3) to trip if the timer interrupt went un-serviced. The NMI could be selectively masked, of course (port 61h).
There were a fiew BIOSes out there ("were" is operative, isn't it? No one actulaly makes new PC's using 30-pin SIMMs.) that would note the lack of the parity bit and simply mask it at POST time.
I can recall that 30 pin non-parity SIMMs were specifically called out by some retailers as being for "Macintosh only).
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