[I am using the popular names (such as "360K", rather than more
technically correct designations.]
The most important parameter is the magnetic coercivity.
"360K" is 300 Oerstedt.
"1.2M" is 600 Oerstedt. Therefore, the two will not interchange
satisfactorily. Unlabeled disks can sometimes be differentiated by
color. If a disk has a reinforcer around the center hub, then it is
probably a 360K, although it COULD be an after-market reinforcer (jigs
used to be available.) If there is NOT a reinforcer, then it is either a
1.2M, or a very early "360K"
"720K" is 600 Oerstedt.
"1.4M" is about 750 Oerstedt. Therefore, although there is SOME loss of
reliability, the probability of "getting away with" the wrong media is
actually pretty good. IF the drive has a media sensor, then you would
need to punch the additional hole, or cover the hole, depending on which
WRONG combination you are attempting.
<RANT> There ain't no sech thing as a 1.44M disk. The IBM style of HD 3.5
has 2 sides, 80 tracks per side, 18 sectors per track, and 512 bytes per
sector. If you multiply that out, you get 1.406 HONEST Megabytes
(1048576). The only way to get 1.44 out of that is to creatively redefine
a Megabyte to be 1024000 bytes. That leaves IBM in the position of
claiming that a megabyte of memory is 1048576 bytes, but that a megabyte
of disk space is 1024000 bytes! If IBM ran a donut shop, how many donuts
would there be in a dozen??? </RANT>
DS v SS (5.25"): The disks are manufactured the same, but the difference
is whether BOTH sides are tested and/or "certified". Using DS for SS is
acceptable. Using SS for DS is taking a chance on using untested media.
There used to be rumors that SS disks were repackaged DS ones that had
FAILED testing on one side; but the realities of volume production make that
seem unlikely.
"Flippy": The second side can often be used in a single sided drive by
flipping the disk over. In the case of Apple ][ and Commodore, it
requires punching a write enable notch. (Which does NOT need to be square.)
On TRS-80, IBM, etc, it is necessary to also punch an additional
(symmetric) access hole for the index hole. (jigs for marking and
punching used to be available.)
DS V SS (8"): The index hole opening is in a different location.
Punching a new hole through the jacket normally works OK.
720K 5.25" v 360K 5.25": again, an issue of testing/certification,
similar to SS v DS. At least for a while, they were manufactured the same,
but were tested/certified for 48tpi or 96 tpi.
Hard-sectored v soft-sectored: In a system that does not use the index
hole (Commodore, Apple ][), it doesn't matter. In all others, the only
way to use the wrong diskette would be to modify the drive to index off
of the spindle instead of using the sensor.
3", 3.25": Many newbies will get sloppy in reference to 3.5" diskettes,
without realizing that there actually were 3" and 3.25" diskettes. 3"
were used by Amstradt, some non-US Canon?, and Amdek add-on drives for Coco
and Apple ][. 3.25" was used only by Chameleon 325 (that I know of).
Dysan bet the company on 3.25"; but that's another story. Anyone have
any extra 2.5" or 3.9" that you'd like to trade for 3" or 3.25"?
--
Fred Cisin cisin_at_xenosoft.com
XenoSoft http://www.xenosoft.com
2210 Sixth St. (510) 644-9366
Berkeley, CA 94710-2219
Received on Thu Jan 21 1999 - 14:30:40 GMT