Which disk to buy?

[Dave Platt]

In article <1990Aug9.144555.18566 at sun.soe.clarkson.edu> abstine at image.soe.clarkson.edu (Arthur Stine) writes:

> If you are looking for some fast disks in the 300MB range, look into the
> CDC (now Seagate) Wren-Runners. They have a faster seek time (since they spin
> faster than 3600 rpm) and their transfer rates are also higher I believe. 
> The other Wren's are good too, just not quite as speedy as the WrenRunner.

According to a conversation I had with an Imprimis/CDC/Seagate rep at
Systems/USA earlier this year, Wren Runner drives spin at the same speed
as normal Wrens.

A 300-meg Wren Runner is built using the same mechanism as a 600-meg
Wren... but the Runner firmware is set up to use only the outer half of
the disk.  A 600-meg Wren (or a 300-meg Wren Runner) has its cylinders
packed roughly twice as closely as a normal 300-meg Wren.  Hence, when a
300-meg Wren Runner must move its heads to a new cylinder, it must move
them (on average) only about half as far as a normal Wren would have to
move.  This cuts the seek-time by roughtly one third, on average (e.g.
10 msec typical rather than 16).

It's true that Seagate/Imprimis is working on drives which spin faster
than the usual 3600 RPM.  This increases the drive's transfer rate...
the speed with which it can read or write data _after_ the seek has been
completed and the drive is on-sector.  It doesn't directly affect seek
speed by very much (except for latency within the track being sought).