Re: [gentoo-user] Normal disk speed?

[Peter Humphrey <peter@humphrey.ukfsn.org>]

On Thursday 30 September 2010 17:50:41 Florian Philipp wrote:
> Am 30.09.2010 18:00, schrieb Peter Humphrey:
> > On Thursday 30 September 2010 14:10:42 Florian Philipp wrote:
> >> An HDD gets slower when you read the inner tracks.  The angular
> >> velocity is constant (5400 RPM) while the tangential velocity gets
> >> lower with the radius.
> > 
> > Are you telling us that the length of a stored bit is constant? I'd
> > have thought it was the time needed to read or write a bit that
> > was constant; otherwise the electronics would get extremely
> > complex. In that case it's the angular velocity that counts, not
> > the linear velocity, and it matters not which track your data are
> > on. (If a block goes past the head twice as fast, it also occupies
> > twice the space, so you're back where you were.)
> 
> Yes, the length of a block is constant. If the innermost "ring"
> (track) contains 4 blocks, the next ring contains maybe 5 blocks.[1]
> 
> Put another way: If you could pack your bits more densely on
> innermost tracks, why wouldn't you pack them that densely on the
> whole disk and thereby increase the overall capacity?
> 
> > That's the way it was with our imposing new 2MB disks in 1974,
> > anyway. They occupied boxes four feet tall and six feet long, and
> > had external air systems; I was one of those responsible for the
> > maintenance; we were sent on a training course specifically for
> > the disks. I can't remember who made them, but they were part of a
> > Ferranti Argus 500 system at the then national grid control
> > centre.
> > 
> > Maybe technology has changed since then.
> 
> Well, we are talking about devices employing the GMR effect while
> also doing error correction and remapping of defect sectors
> on-the-fly. I guess a little lookup table from track number to
> time-per-block doesn't add too much complexity.
> 
> You can easily test this if you have various partitions on your HDD.
> Just compare dd throughput for your first partition versus your last
> one.

Seems like technology has moved on. Well, it has had 35 years or more.

-- 
Rgds
Peter.          Linux Counter 5290, 1994-04-23.