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.
