Path: utzoo!attcan!uunet!husc6!encore!pinocchio
From: terryk@pinocchio (Terence Kelleher)
Newsgroups: comp.periphs
Subject: Re: Hard drive speeds
Message-ID: <9864@multimax.Encore.COM>
Date: 3 Sep 89 22:00:14 GMT
References: <17640@ut-emx.UUCP> <3170009@hprnd.HP.COM> <19.filbo@gorn.santa-cruz.ca.us>
Sender: news@Encore.COM
Reply-To: terryk@pinocchio (Terence Kelleher)
Organization: Encore Computer Corp
Lines: 33
In-reply-to: filbo@gorn.santa-cruz.ca.us (Bela Lubkin)

In article <19.filbo@gorn.santa-cruz.ca.us>, filbo@gorn (Bela Lubkin) writes:
>>up to 4800 and 5400 RPM, respectively!
>
>Why not build a second set of heads radially opposite the first?  This halves
>latency instantly (doubles RPM, if you wish); alternatively, it lets you play
>adaptive seeking games where the two sets of heads are stationed over different
>cylinders, etc.  This can be extended to N sets of heads, N probably < 8 (you
>start running out of room...)  

The head arm assemblies are built with the idea in mind that, so long
as the heads remain in relativly in the same position as compared to
the servor head, the tolerance to build up each head are is not that
important.  If the head on one arm assembly is required to read data
that may have been writen on the other assembly, then the position of
the head must be correct when compared to either of the 2 servor
heads.  This is eliminated if embedded servos are used, but other
problems arise, like limitations on the number of bytes per sector.
Lots of systems use funny sizes here and would not be able to use a
drive with restrictions on sector size.

>Another idea is to put multiple heads on a
>single arm on each platter, so that while head 5A is over track 50, 5B is over
>track 600 (e.g.).  This can halve your maximum seek distance (which doesn't
>halve your maximum seek >time<, but does lower it).
>
If I'm not mistaken, the NEC 9 in drive does use 2 head assemblies on
each arm.  I'm not sure why, but its seek time does not look any
better than other 9 in drives.
-- 
Terry Kelleher, Encore Computer
Phone: 508-460-0500
UUCP: {bu-cs,decvax,necntc,talcott}!encore!terryk
Internet: terryk%pinocchio@multimax.ARPA