From: tooraj@daneel.rdt.monash.edu.au (Tooraj Enayati)
Subject: Re: DRAM refresh rates
Organization: Monash University, Melb., Australia.
Date: Wed, 30 Dec 1992 10:13:14 GMT

tooraj@daneel.rdt.monash.edu.au (Tooraj Enayati) writes:

>chuckst@microsoft.com (Chuck Strouss) writes:

>>In article <1gske7INNgje@coli-gate.coli.uni-sb.de> chbl@sbustd.rz.uni-sb.de (Christian Blum) writes:
>>>
>>>No way this will work. The refresh rate is set to 18.2 per second; since
>>>there are 512 rows to refresh, this means every bit in your computer's
>>>DRAM is refreshed every 20 seconds! There are DRAMS that survive 15ms
>>>without being refreshed, but a 70ns DRAM can't take it. Try about 10ms
>>>......

>>It is surprising how long some DRAMs can go without refresh.  For
>>production systems, you must believe the manufacturers worst-case
>>specs, but DRAMs rarely need to be refreshed that often.

>>A while back, I was working on the software for a computer system that
>>did its DRAM refresh with a software interrupt -- it only took about
>>5% of the CPU time.  At first, we had a bug in our refresh code, but
>>the system was still working remarkably well.  Tracing down another bug
>>revealed that we weren't refreshing at all, except for the natural
>>refreshing that came from the execution of code.

>>Once we got the refresh working, we decided to determine exactly
>>how slow we could refresh and still have the system work.  We made
>>sure that the CPU was executing in a tight loop the rest of the time,
>>so that normal execution wasn't refreshing.

>>Turns out the particular DRAMs we were using, at the temperatures
>>we were running, held their contents just fine with a 1-2 second
>>refresh rate.  They started failing a bit at 5 sec, and were
>>still 80% correct after 15 sec.

>>We expanded our experiments a bit, and tried DRAMs from different
>>manufacturers, and also tried different temperatures.  There
>>were remarkable differences with both parameters.  We ended up
>>taking the full 5% CPU hit requirred to meet the manufacturers'
>>specs, which I think is a good decision for anybody who is tempted
>>to play around with refresh rates.

>Ther are couple of files at simtel-20 (or its mirrors) under sysutl
>called qram.zip and fastram.zip (or maybe .arc) that let you play
        ^^^^^^^\     ^^^^^^^^^^^^\_ dramfast.acr
                |_ qram.acr

Sorry guys for the mistake.

>with the DRAM refresh rate and results in 5% to 10% CUP speed increase.

>I managed to increse my CPU speed from 16.2Mhz to 17.33Mhz (checked it
>out using Landmark SPEED200). Interesting enough the video speeds up to
>and i can see inprovement when Windows is redrawing the screen.

>-- 
>==============================================================================
>Tooraj Enayati     Melbourne     Australia     tooraj@daneel.rdt.monash.edu.au
>Monash University       Robotic and Digital Technology       (Graduate/Alumni)
>==============================================================================
-- 
==============================================================================
Tooraj Enayati     Melbourne     Australia     tooraj@daneel.rdt.monash.edu.au
Monash University       Robotic and Digital Technology       (Graduate/Alumni)
==============================================================================
Newsgroups: alt.lang.asm