Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!xanth!mcnc!thorin!clocs!davis
From: davis@clocs.cs.unc.edu (Mark Davis)
Newsgroups: comp.periphs
Subject: Re: ST296 - How does Seagate Do it?
Summary: 5.25 HH SCSI 80MEG - RLL 34 sectors
Keywords: hard disk capacity encoding techniques
Message-ID: <5875@thorin.cs.unc.edu>
Date: 14 Dec 88 02:48:04 GMT
References: <5754@thorin.cs.unc.edu>
Sender: news@thorin.cs.unc.edu
Reply-To: davis@clocs.UUCP (Mark Davis)
Organization: University Of North Carolina, Chapel Hill
Lines: 27


In article <5754@thorin.cs.unc.edu> davis@clocs.cs.unc.edu (Mark Davis) writes:
>The Seagate advertisement on page 36 of the December 5 Info world
>claims that the ST296 ...
> ...  However, for the 296,
>they would have to be using some exotic encoding technique (like ARLL)
>to get the almost 200% capacity increase.

>So, how do they do it[?]

From the Seagate Product description, the drive is in fact part of the
ST 251 family except they only make the 28ms average seek (higher speed) 
version.  They get the 80 Megabyte capacity by 
	(1) using RLL (regular 2,7 RLL).
	(2) using 34 sectors per track (instead of 26 for normal RLL
		and 17 for MFM).  I have heard of a couple of 34
		sector/track controllers, but they are not common.

Apparently having your own controller on the drive has its advantages.
Incidently, Seagate also has a 3.5 inch 80meg SCSI drive (ST1096) but
there they added a platter to the ST151 to get the extra capacity and
stuck with 26 sectors per track.

SCSI is neat in that it lets the drive manufacturer better match the
drive and the analog part of the controller.  Of course ESDI is neat,
too.

Thanks for listening - Mark (davis@cs.unc.edu or uunet!mcnc!davis)