From: Chuck Simmons
Organization: You jest.
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Subject: Re: Q. why 5400 and 7200 rpm disk drives?
Date: Thu, 10 Oct 2002 02:09:25 GMT
NNTP-Posting-Date: Wed, 09 Oct 2002 19:09:25 PDT
Winfield Hill wrote:
> Hmm, why did disk drive manufacturers settle on rotation speeds
> like 5400 and 7200 rpm? These correspond to 90 and 120 rps, or
> 1.5 and 2.0 rotations per ac cycle for 60Hz ac power. Early disk
> drives ran at 3600rpm = 60Hz, and perhaps some ran from ac motors,
> and such numbers would make sense for a synchronous ac motor.
> But modern disk drives run from dc power, and therefore should
> not be beholden to any ac-power parameters. While it's true that
> the bleeding-edge of new disk-drive performance is in 10000 and
> 15000 rpm drives, etc., we still see impressive new 5400 and 7200
> rpm drives. So, hey, what's the deal? How come no spec. creep?
> E.g., no 6000 rpm versions to out-compete the 5400 rpm models?
> Is there in fact some engineering magic in 5400 and 7200 rpm?
Actually, the first drive I worked on was 2850 RPM. That was in 1980 and
I was analog chief cook and bottle washer on a controller project. I
also did the digital control code for the head servo. Why 2850 RPM? I
don't know. I scounged a prototype from a drive engineering group and
that's what it was. Belt driven from a 3600 RPM motor. 3600, 5400 and
7200 have long been target speeds but they seem to come from tradition.
The real issue for the designer is linear velocity at the OD and linear
density target. The faster the disk spins, the faster the read channel
and the hotter (quite literally) the read channel. Capacities are
arbitrary too. When I went to WD, I worked on the AC31000 which was 1.08
gig. Before the project was over, we had reached 1.2 gig in that drive
but marketing said they wanted a 1 gig and that was the end of it.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons email@example.com