Path: utzoo!attcan!uunet!husc6!bloom-beacon!tut.cis.ohio-state.edu!mailrus!bcm!svedberg!rick
From: rick@svedberg.bcm.tmc.edu (Richard H. Miller)
Newsgroups: comp.arch
Subject: Re: Why no disks with two HDAs ?
Summary: Multiple (large) HDA's
Keywords: diskdrives, headdiskassemblies
Message-ID: <1141@gazette.bcm.tmc.edu>
Date: 24 Jun 88 16:40:30 GMT
References: <2351@uklirb.UUCP> <2440@winchester.mips.COM>
Sender: usenet@bcm.tmc.edu
Lines: 28

In article <2440@winchester.mips.COM>, cprice@mips.COM (Charlie Price) writes:
> 
> 
> The current technology really favors building the same sort
> of system out of a larger number of smaller HDAs.  It isn't
> clear to me that IBM's choice made technological sense.
> STC built the HDA with two actuators because at the time you
> couldn't sell a plug-compatible product to an IBM customer
> if it wasn't very similar to the IBM offering.

Well, one reason could be floor space and environmental conditions. In large
mainframe shops, as you pointed out, the job is data intensive and many shops
require many gigbytes of storage. It is more economical of floor space, power
and air conditioning to have a smaller number of very large HDA's than a large
number of smaller HDA's since in many cases the drive external to the HDA would
require about the same amount of material. Another reason is architectual
limitations of the O/S (number of addresable drives on a channel, number of
channels, etc.) It is easier to modify the I/O routines to support higher
density drives, multiple arms and the like than to redesign the entire IO
complex to add additional addressing.




Richard H. Miller                 Email: rick@svedberg.bcm.tmc.edu
Head, System Support              Voice: (713)799-4511
Baylor College of Medicine        US Mail: One Baylor Plaza, 302H
                                           Houston, Texas 77030