Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!crdgw1!sixhub!davidsen
From: davidsen@sixhub.UUCP (Wm E. Davidsen Jr)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: MFM vs RLL vs IDE vs ESDI vs SCSI
Keywords: data transfer rates comparisons
Message-ID: <1950@sixhub.UUCP>
Date: 22 Sep 90 21:59:24 GMT
References: <2132@bnlux0.bnl.gov>
Reply-To: davidsen@sixhub.UUCP (bill davidsen)
Organization: *IX Public Access UNIX, Schenectady NY
Lines: 34


  Sanity check here!

  The vendors can claim anything they want for these disks, but in truth
this is how you get the transfer rate: multiply the physical sectors per
track by the rpm of the disk, times 68.2666 and that's how fast it's
coming off (or going on) the disk.

Before you ask:
    RPM/60 = rps * 512 = bytes/sec * 8 = bps
    512 * 8 / 60 = 68.2666

So your big bucks ESDI drive with 15mbit interface has 34 sectors and
turns at 3600, or ~8mbit. Hummmm. The only drive I know which really has
transfer rate is a 60 spt 2 in drive running 5400 rpm (50% faster) which
goes ~21mbit. And the only place you see those is in trade shows right
now.

  What makes a fast disk is (a) seek time, (b) interleave (the
controller can help). Correct setup helps, too. If you can adjust skew
for head to head and track to track you can save almost a full
revolution when you change.

  An RLL system 1:1 is about as fast as an ESDI 1:1 in actual practice.
SCSI depends on the controller and software, and MFM is slower however
hacked. There is a *lot* more diference between controllers (and BIOS if
you run DOS) then the interface typically makes.

  Hope this blew a little light into the fog.
-- 
bill davidsen - davidsen@sixhub.uucp (uunet!crdgw1!sixhub!davidsen)
    sysop *IX BBS and Public Access UNIX
    moderator of comp.binaries.ibm.pc and 80386 mailing list
"Stupidity, like virtue, is its own reward" -me