A 1256 -15 chip was a 256K chip that was rated at 150 nanoseconds. The chip
"package" was called a DIP. A -12 ("dash twelve") was faster, and a -10 even
faster.
Before the technology of memory chips changed to SIMMs, SIPPs and thence to
DIMMs, etc., I recall seeing RAM DIPs that went as fast as -50 (yeah, the
meaning printed on the chips changed over time, and a -50 really meant "dash
fifty" for 50 nanoseconds, while a -15 had meant "dash one-fifty"). Even more
confusing was SRAM DIPs, which would be marked as -15, and they really *were*
15ns (SRAMs were *much* more expensive) ...although I don't recall SRAMs being
used in Mac's. (SRAMs were *expensive*, and were used for cache memory in early
PC board designs, which was in an era prior to the design of CPUs with built-in
caches.)
A 4164 -12 chip (which obviously took 4 chips to equal the same capacity as a
single 256K chip) would be a 64K chip rated at 120 nanoseconds.
When we were a small shop building clone PC's for local sale in the mid-
late-1980's, we purchased a DIP tester ...it more then paid for itself, as the
quality of batch sets of RAM could be very uneven; the failure rate was often
as
high as 15-17%. I've hand-tested countless *thousands* of the bloody things.
(We also found that matching the chip speeds was sometimes more effective at
getting a stable box then having a mix of faster chips. Timing issues could be
a
real problem for mis-matched chips.)
Btw, a "faster" chip rating didn't mean that putting in "faster" machine memory
was going to make your system benchmark faster (i.e., your computer wasn't
going
to be faster), because clock speed is set by oscillator chip frequency, and is
"designed in" by the logicboard designers (as a best-mix for market cost and
availability). And the older Macs were designed by Apple engineers to run just
fine with 180 and 150 nanosecond rated chips (yes, I've seen oodles of -18
chips).
Also, there was another chip issue often bruited about, because back in the day
when SIMMs came along, there could be 8 or 9 of the memory DIPs on a SIMM
board.
The 9th chip was a parity-chip; early PC logicboards were often designed to use
it (actually, most of them *required* it). Macs weren't designed to use parity.
So it doesn't matter to a Mac whether the chip is parity or not ...so you can
safely use 9 chip SIMMs in Macs. I probably would try to avoid mixing parity &
non-parity though (as much for aesthetics - and potential timing issues - as
anything else). More important is to match the chip ratings (if you have a
choice), then manufacturers, then batches.
--- brandon davis ---
-- sacramento, ca --
----- Original Message -----
Compact Macs Digest #2287
----------------------------------------------------------------------
Date: Sun, 20 Mar 2005 13:02:16 -0800
Subject: Re: Fat Mac Won't POST
From: <[EMAIL PROTECTED]>
>>Also, what is the difference between the 1256-15 and -12, -10, 64-12 chips?
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