"Higher density" indeed. One of the first hard drives I used was 128 kB (DEC
RC11/RS64).
Well, I said that it CAN have higher density, not quaranteeing that it
would :-)
The original 23FD was 80K
TLDR: long (too long) ramble about disk capacities:
8" SSSD (77 tracks * 26 SPT * 128 bytes poer sector) was 250K.
8" DSDD (77 tracks * 26 SPT * 256? bytes per sector) was about 1000 K
5.25" 500K data transfrer rate ("high density") was 2 sided 80 tracks per
side 15 secors per track of 512 bytes each),was 1200K, or 1.17M, NOT
1.2M unless you define meg as 2**10 * 10**3. instead of an honest 2**20
(1048576)
The earliest 5.25" (35 track SA400) had a capacity of 87.5K when formatted
with FM, ten sectors of 256 bytes each. (TRS80 and early Osborn).
other choices of size of sectors and number of sectors will vary that a
little.
But VERY soon they lengthened the slot for 40 tracks (100K)
GCR (Apple) gave an slmost 50% increase
But, FM double sided, then double density (MFM), and 96tpi for 80
cylinders (80 tracks per side)
MFM doubled the capacity (Higher density / more bits per track)
Going to 96tpi gave twice the total capacity, at 80 tracks per side, but
each track was the same as a 48tpi track.
Doubling the data transfer speed, was still MFM ("double density), but the
changed speed enabled almost twice as many bits per track
Yes, I know that later, there were barrium ferrite disks (E[xtended] D[ensity])
even some 192 track per inch, andsome bizarre ways to get a lot of data
onto a disk.
Changing a single sided format to double sided doubled the capacity, but
changing capacity is not the same as changing density.
One company (Intertec superbrain) insisted on calling the 340K double
sided version of its 170K single sided, "Double Density"!
Then when they went to 340K double sided, double density, they called that
"quad density"; everybody else in the world called it double sided double
density, and used "quad density" to refer to 640K - 800k 96tpi double
sided double density.
But then, when Superbrain went to 780K (which almost everybody else was
calling "quad density", Superbrain had already used up that name! So,
they called their 780K format, "SUPER Density"!
Then 3.5"
The Epson PF10 had 40 cylinders with 67.5 traxks per inch, but
everybody else immediately went to 135 tpi, giving it essentially the same
geometry visible to the computer as 5.25" double sided 96tpi.
One peculiar aspect of the RAMAC is that it only had one head, or one pair, so
track switching was a lot slower than cylinder switching: it had to retract all
the way, then move the head vertically to the correct track, then seek in again
to the right cylinder.
As opposed to ST225, with 4 heads for one platter. :-)
. . . or the Lisa Twiggy. :-) They claimed that the second thumb slot was
for the other heads, not just to make sure that all media would have
plenty of thumbprints.
Yes, switching to "side B" of a double sided disk was obviously much
quicker than stepping to another track.
--
Grumpy Ol' Fred [email protected]
