19 Jul
2010
19 Jul
'10
9:10 p.m.
On 7/19/10, Chuck Guzis <cclist at sydex.com> wrote:
On 19 Jul 2010 at 8:00, Steven Hirsch wrote:
That's one issue I recall with the transition from RK05 to RL01 as
"inexpensive" cartridge media in the DEC world. The RK05 has a
manually-aligned external positioner, and the RL01 (and RL02) uses
embedded servo data. One advantage to the RK05 technique is that you
can format packs that have been bulk-erased (since the platters only
contain data, not positioning info) One advantage to the RL01 is that
you don't have to be quite as precise with head alignment (you have to
be close enough for the embedded servo data to be legible, then, IIRC,
the positioner circuit can lock on the rest of the way).
There was another method that was acceptable for multi-surface packs -
a servo surface. It's not worth dedicating an entire surface to
positioner data if you only have two surfaces - you get a poor
space-to-cost ratio. If you have 4-8 surfaces, it's more practical to
give up a surface (vs a loss of some space for embedded servo info).
An advantage of a servo-surface pack is that you can easily format the
data surfaces as long as you leave the servo surface untouched.
I've heard of a field service device for writing servo data on a wiped
RL pack, but I've never seen one in person.
-ethan
Reminds me of
the DEC Rainbow (wasn't that system deliberately crippled to prevent
it from being able to format blank media?).
If the Amlyn disks use an embedded servo, formatting one is a
mechanical issue--you need to periodically offset from the central
track axis a bit one way or the other to write a servo burst. Not
easy to do wth a conventional read/write drive.