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

At 06:01 AM 3/18/02 -0800, you wrote: 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! Joe Joe