DSQD Drives (Was: RE: Diags/Boot image for Altos 580)

From: Joe <rigdonj_at_cfl.rr.com>
Date: Mon Mar 18 09:11:48 2002

At 06:01 AM 3/18/02 -0800, you wrote:
>--- Doc <doc_at_mdrconsult.com> wrote:
>> I must admit I got no clue what an "Oerstedt" is. Or why I need to
>> know....

    Oerstedt is a measure of how easy or difficult it is to magnetize
something. In this case, the magnetic media on the disk. It's **roughly**
the same thing that ohms are to current flow in an electrical conductor.
Drives are designed to create a certain strength magnetic field and you
need to match the magnetic media to that strength. It's important because
too strong a field can cause a disk can become so magnetized that a drive
can't erase or write new data to it and it has to be bulk erased. OTOH too
week field can leave a disk that has unreliable reads. Fortunately it's
usually real easy to right the right media since disk specifications are
pretty standardized. Just use the disk that's designed to operate with the
drive that you're using. Generally thre are only three types (in the 5
1/4" size); DSDD, DSQD and DSHD. The DSDD and DSQD disks both use 300
Oerstedt media but have 40 and 80 tracks (actually cylinders if you're
fussy about the correct terminology) respectively; DSHD (1.2M) also uses 80
tracks but uses 600 Oerstedt media.
   I recommended that you try and find a QD drive but several people have
correctly (and vigorously!) pointed out that a 1.2Mb drive does use 80
tracks and that you COULD use one of them. (once you over come the possible
double stepping and write-strength pin select problems!) The problem is
that they use a different magnetic field strength and I've had that led to
trouble, partricularly in long term storage. For me it's easier to get the
CORRECT drive and media than it is to cobble something up that may or may
not work or be reliable!


Received on Mon Mar 18 2002 - 09:11:48 GMT

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