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From: debra@alice.UUCP (Paul De Bra)
Newsgroups: comp.unix.questions,comp.sys.ibm.pc
Subject: Re: 100ns .vs. 120ns
Message-ID: <8687@alice.UUCP>
Date: 6 Jan 89 16:48:41 GMT
References: <377@fantasci.UUCP>
Reply-To: debra@alice.UUCP ()
Distribution: na
Organization: AT&T, Bell Labs
Lines: 28

In article <377@fantasci.UUCP> jep@fantasci.UUCP (Joseph E Poplawski) writes:
>How bad of a speed difference would my UNIX V.3 for the 80386 system incur if
>I added 120ns chips instead of the 100ns chips it already has 2 meg of?  The
>system is a personal system with no more than 3-5 users on at the extreme most.
>
>The reason I am considering the slower chip is mainly the price.
>

There is no magic in the PC and AT compatibles (including 80386's) to detect
what speed the memory can handle. There are 2 possibilities: either your
system doesn't really need 100ns chips and will run just as fast with 120ns
chips, or else the system will not run at all with 120ns chips (it will give
parity errors at least). Considering the price of memory chips it is very
unlikely that you got the machine with 100ns chips when it only needs 120ns.

The only way to make your system work with slower chips is to lower the
clock-frequency (like from 20Mhz to 16Mhz).

What ram-chips your system needs is very motherboard-dependent. Some boards
use very fast rams (60ns) and no cache memory, others use slow ram (up to
120ns) and compensate with cache memory. In any case the hardware expects
a minimal speed of ram which is really necessary at the highest clock rate.

Paul.
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