Path: utzoo!utgpu!water!watmath!clyde!rutgers!ucla-cs!cit-vax!mangler
From: mangler@cit-vax.Caltech.Edu (Don Speck)
Newsgroups: comp.periphs
Subject: Re: disk recomendation for sun-3/50
Message-ID: <5175@cit-vax.Caltech.Edu>
Date: 15 Jan 88 06:47:18 GMT
References: <2604@aramis.rutgers.edu> <3091@phri.UUCP>
Organization: California Institute of Technology
Lines: 30

In article <3091@phri.UUCP>, roy@phri.UUCP (Roy Smith) writes:
>			      I think small disks have dropped in price
> faster than big ones over the past couple years, making the cost per Mbyte
> much more even accross the spectrum of disk capacities.

What has mostly happened is that small disks have grown in capacity
without getting much more expensive, and the big disks have mostly
stood still.  These days, anything over 9 inches doesn't make sense,
because larger-diameter disks don't offer any higher capacity or
better price ratio.  The 8-inch disks are rapidly catching up (I know
of at least six 8-inch drives with at least SuperEagle capacity).

The reason, I think, is that the larger disks are pushing against the
limits of SMD controllers, not the limits of the media.  The CDC 9771
14-inch drive is a good example; it's built with 1064 cylinders, but
on typical controllers you can only use 1024, and they had to grossly
slow down the rotation rate in order not to exceed the bit-rate limit
of many controllers.  And that's an old drive.	Perhaps IPI offers
some hope (nobody is going to take SCSI seriously for big drives),
but it may be too late.

8-inch drives are pushing the controllers just as hard.  CDC's latest
has 1635 cylinders and transfers at 24 MHz.  In a couple of years,
we'll be seeing 5.25 inch drives with the same specs.  What are we
going to hook them up to?  Not ESDI, it has an even lower bit rate
than SMD.  The only option left will be native SCSI, and it will
need lots of buffering, because even the Sun-3/60 SCSI bus appears
to be limited to 0.8 MB/s.

Don Speck   speck@vlsi.caltech.edu  {amdahl,ames!elroy}!cit-vax!speck