Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!hplabs!otter.hpl.hp.com!hpltoad!hpopd!hpcpbla!prn
From: prn@hpcpbla.HP.COM (Peter Nicholls)
Newsgroups: comp.periphs.scsi
Subject: Re: Info on 600 MB HP 97548 drive
Message-ID: <9850019@hpcpbla.HP.COM>
Date: 8 Apr 91 14:09:34 GMT
References: <542@rc6.urc.tue.nl>
Organization: HP Computer Peripherals Bristol, UK
Lines: 25

>According to an ad by a local distributor the HP should be a 20Mb/s drive
>with an average access of 16ms. According to SCSICNTL the drive has 1457
>cylinders with 16 heads and 57 sectors per track. This seems to indicate a
>data transfer of slighly above 15 Mb/s. So is 20 Mb/s the real transfer rate
>and if so why are there so little sectors per track.

There are two factors to take into account. The HP drive spins at 4002 rpm,
and has an embedded servo. The burst transfer rate is the rate seen 
transfering one sector of data. The bit density of the data in the sector
is equivalent to a 657 byte sector on a non-embedded servo. (58 bytes are
used for the embedded servo).

So...  657*57*8*4002/60 = 19,982,786    Close enough.

The track transfer rate is quoted at 15.57 Mbits/s - which matches the
figure above. The reduced transfer rate is one of the penalities of the
superior reliability of embedded servo.

Peter Nicholls
--------------
European Disk Integration Engineering
Hewlett-Packard Ltd.,
Bristol,
ENGLAND.
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