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From: rbono@necis.UUCP ( NM1D)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Refreshing RAM slooows down diskette operation? Huh?
Summary: Because . . .
Message-ID: <1404@necis.UUCP>
Date: 4 Jan 91 19:04:59 GMT
References: <1041@accucx.cc.ruu.nl>
Organization: NEC Technologies, Inc., Boxborough, MA
Lines: 80

In article <1041@accucx.cc.ruu.nl>, jaapv@accucx.cc.ruu.nl (Jaap Verhage) writes:
> A while ago, in article <995@accucx.cc.ruu.nl> I wrote:
> >I've got a strange little problem - to me, that is. A while ago, I
> >ftp'ed some of the RAM refresh rate-twiddling programs from Simtel.
> >The idea is that by refreshing your RAM chips less often than the
> >standard rate for your PC, you cut down on CPU overhead, thus
> >increasing the speed at which the thing operates - seemingly, at
> >least. Don't expect anything gorgeous - if speed increases by
> >anything like 5 % or a bit more, that's it. Still, every little bit
> >helps, and I like fooling around, so I tried. The Landmark test for
> >CPU speed showed my work-based Olivetti M28, a 8-MHz AT, to start
> >running at 8.5 MHz; my home-based Laser AT went from 11.6 to 12.5
> >MHz. Wow! You can imagine I noticed this *instantly* in running
> >applications :-). But. The Laser's 5.25" HD diskettedrive came up
> >with horrendously long seek times on disks! The Olivetti had no
> >problems at all. Seek times on the Laser's diskettes grew as I
> >cranked up the speed of the CPU by lowering the RAM refresh rates.
> >Now what *is* this?
> >May be stuff for a nice little discussion. If you don't think so,
> >but do have suggestions, email me and I'll summarize. Thanks for
> >your time and trouble.
> 
> Reactions to this were as follows:
> 

 Sorry that I missed the original post.... No one seemed to have the correct
answer, so I thought that I would give you my few cents worth.  From the
answers, many of you with various BIOSs have seen this (Award, etc.)

First, I will state that it is my belief that messing around with system
timing is a dangerous thing to do at best.  Ram refresh timing is one of
those areas where you could be asking for reliablility problems, not to
mention other side effects (as many of you have noticed).   Yes, I am aware
that many of you have done this, and have not seen (or noticed) any problems
as of yet (this is not to say that you will have problems).  Suffice to say
that if you want a reliable system, don't mess with your refresh timing, if
speed is more important to you than reliability, then go ahead and have fun!

Now, with that 'dislaimer' here is your answer:

  This discussion is not relative to any particular type or brand of BIOS,
but to the functions any BIOS must perform.

  There are many times that the BIOS needs to generate accurate timing delays,
especially when communicating with periphials (like floppy and hard disks).
Of course, this is what the BIOS is designed to do!  Timing delays must be
generated independantly of CPU speed, as many of todays systems have CPU's
that can be switched between multiple speeds (6/8/16/33 MHz, etc).  To do
this, these BIOSs make use of known hardware that has a particular rate.
In general the BIOS can't make use of the hardware timer chip, because that
is used by many applications.  One thing that is *always* running is the RAM
refresh (if it is not running, then the system would not function, DRAM
requires refreshing to hold it's data).   The refresh rate is known by the BIOS
and there is a way for the BIOS to detect when a refresh has occured (I/O port
61h, bit 4).  Therefore the BIOS could generate accurate delays by monitoring
the refresh rate.

  By changing the refresh rate you have changed the BIOSs timebase!  This
can lead to all kinds of problems (could even cause disks to be 'trashed' as
improper delays are generated when trying to write to disks). 

  By the symtoms many of you have discussed, my opinion is that many of you
have BIOSs that make use of the refresh timing to generate delays.

  Of course, your BIOS may not use the refresh timing for delays, and then
you will probably not see this 'problem'.

  Keep in mind that other software may also try to use the refresh rate for
non CPU dependant timing delays... changing the refresh rate may affect these
programs also.

  My advice?  Don't mess with the refresh rate if you wan't a reliable system!

Disclaimer:  These are my own opinions

-- 
 /**************************************************************************\
 * Rich Bono (NM1D)      Note NEW email address:     rbono@necis.ma.nec.com * 
 * (508) 635-6300          NEC Technologies Inc.                NM1D@WB1DSW * 
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