Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!sam!douglass
From: douglass@davidsys.com (JEFF (PC) DOUGLASS)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: ACTUAL DATA THROUGHPUT FROM A HARD DRIVE???
Message-ID: <13225@davidsys.com>
Date: 23 Apr 91 19:35:20 GMT
References: <1991Apr12.043027.2695@techbook.com>
Distribution: comp
Organization: DAVID Systems Inc, Sunnyvale CA
Lines: 69

In article <1991Apr12.043027.2695@techbook.com>, garys@techbook.com (Gary Scott) writes:
> 
>   I intend to purchase a new hard drive and controller for use on a 486/33
>[ ... ] 
> solution. My computer has a standard AT bus, so at some point the bus speed
> becomes the limiting factor along with the controller card. High transfer
> rate specs for drives only covers the exchange between the drive and
> controller and is not the (w)hole picture as the bus and processor cannot
> run at drive transfer speed.

A 33.3 MHz 80386 with an 8.33 MHz AT bus can handle about 3 MB/s.
(At least that's what I get.  On an 8 MHz 80286 I get 2+ MB/s.)
This is flat out, assuming that the device on the bus supports 0 ws.
Faster on certain machines under certain conditions.

Most hard drives spin at 3600 RPM.  That's 60 RPS(revs per second).
All current (PC) hard drives only read one head at a time.  (Too bad)
Many hard drives have 36 or fewer 512 byte sectors per track.
Taking all these together, I get:

60*36*512 = 1,105,920 or about 1 MB/sec. drive transfer rate.

Yes, there are some drives with >36 sectors/track.
I have heard rumors about future drives that will spin faster than 3600 RPM,
and have 64+ sectors per track.  Sector size would probably still be 512 bytes.
Consider 5400 RPM, 64 sectors at 512 bytes is close to 3 MB/s.  Not bad,
but the bus can still probably keep up with it.
Best would be a hard drive that reads/caches all heads.  In that case,
60*36*(15 heads)*512 = about 15 MegaBytes per second!

> Ideally, I would want to purchase a controller and drive combo that would
> exceed the bus throughput rate by say 10%.

You shouldn't want a controller that exceeds the speed of the bus by anything.

> My current research says that I should go with an EDSI drive with about a
> 20MB transfer rate and the cheap Ultrastore controler that has a 32K cache.
> I can't find any reason to use the multi-meg cache controllers as the system
> will be running single user DOS/Windows.

Some ESDI-buses are 15 Mb/s (that's 15 Mega-bit/second) = under 2 MB/s
 if you can find a drive to keep up.
Any 20 MB/s (read MegaByte/sec) drive of ANY kind I WANT to know about!
No, I'm not interested in a floor-mount model :-)

> Any thoughts/experiences/help would be greatly appreciated. Thanks.
> Gary Scott
> -- 
> Gary L. Scott,  Decision Technology, Beaverton, OR (503) 642-4196
> "Strategic Business Applications"    garys@techbook.com (subscription unix)
> Any opinion expressed are mine and do not reflect the opinion of anyone
> including myself!!!

[personal opinion mode on]
ST-506  I've had these up to 500+ KB/s, 1:1 interleave 17 sector drive.
SCSI    I've gotten over 1 MB/s with a small drive of _only_ 300 MB (36 sec).
        The larger drives (1 GB) ARE quicker.
ESDI    I've tried the older 10 Mb/s ESDI-bus. Drive had ?? sec, I saw 1 MB/s.
IDE     Actually a variant of ST-506 with embedded controller on the drive.
        My current drive has 32 sectors/track.  I get 880+ KB/s uncached.

Of course this doesn't even consider that there could be a cache on the
drive itself.  Since the bus is slower than main RAM by a factor of up to
(fill in this blank), I kinda prefer local write-through cacheing
(in CPU space) using any/all 'unneeded' ram (up to 15 MB?).
[personal opinion mode off]
-- 
-{JD}-  Jeff (Douglass@DavidSys.Com) David Systems, Sunnyvale CA,(408)720-8000
    "Never count on the inevitable until it happens. . ."