From: zevans@nyx.cs.du.edu (Zack Evans) Subject: Re: 70ns or 60ns RAM with a 486/66: does it matter? Date: Fri, 9 Jul 1993 18:39:37 GMT
In article <mr2C9rpJC.1rv@netcom.com> mr2@netcom.com (Jongyoon Lee) writes:
>Chris Metcalf (metcalf@CATFISH.LCS.MIT.EDU) wrote:
>: I'm about to buy a 486/66 with 16M of RAM, 256K 20ns cache. Is it worth $50
>: or so to get 60ns RAM instead of 70ns RAM? I'll summarize in a day or two.
>
>It depends on the motherboard. If the motherboard can be configured
>for different speed of SIMMs, you might benefit from faster memory.
>However, a lot of motherboards require only 70ns or 80ns SIMMs. I use
>a 486DX-66 and it requires 80ns SIMMs. So I can use my 4x9@70ns SIMMs
>safely.
Hold on...if the motherboard is running at 33Mhz, then each tick is
reciprocal 33Mhz seconds long, right? That's 30.030303... ns as far as
I can see, which means there will always be an advantage to faster RAM
until you start comparing 30ns with 29ns SIMMs. (I know that there
aren't many instances where a CISC chip will want to read from memory
on two sucessive ticks, but the principal is the same, I think).
I've never worked that out before - I can see how DX2 chips are justified now.
Anyway, the answer is get 60ns RAM, but only if you can tell the motherboard
that you've got it. Presumably if you have 60ns rather than 70 you are only
going to get 85% of the wait states after a cache miss, wich will mean you end
up running faster. Probaly more so under Linux than DOS even as Linux uses
memory more heavily.
Zack