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