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From: wyatt@cfa.harvard.EDU (Bill Wyatt)
Newsgroups: comp.unix.questions,comp.unix.wizards,comp.bugs.4bsd,comp.periphs
Subject: Re: /etc/disktab and RA8x drives
Message-ID: <847@cfa.cfa.harvard.EDU>
Date: 27 Dec 87 18:51:52 GMT
References: <80@sickkids.UUCP>
Organization: Harvard-Smithsonian Ctr. for Astrophysics
Lines: 23

> A few questions regarding the information in /etc/disktab (4.3bsd):  Where
> did the RA80/RA81 entries originally come from, and are they even correct?
> 	:ty=winchester:ns#51:nt#14:nc#1248:so:\
[...] 
> The DEC RA81 Disk Drive User Guide (document EK-ORA81-UG-001) contains the
> following information:
> 
> 	Number of heads		14 data, 1 servo
> 	Cylinders per head	1258
> 	Sectors per track	52
[...]

The extra sector is held back for on-cylinder bad-block forwarding, which
has far better performance. Remember that /etc/disktab is mainly for the
newfs(8) program to lay out filesystems, so the information there is the
`visible' disk, as opposed to what the controller may really be using.
-- 

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