On 2017-11-15 1:44 PM, Fred Cisin via cctalk wrote:
No, the 9122C model has two 1.44M drives. HP made several earlier 3.5"
On Wed, 15 Nov 2017, Christian Corti via cctalk wrote:
No, the 9122C has two high-density, two-sided 80 cylinder drives. A
drive has no capacity, this is the function of the on-disk format.
;-)
"high-density" is even more meaningless than referring to them by
their capacity in a given format. It is a BOGUS marketing term!
Referring to a drive by the capacity of most commonly used format for
that configuration is indeed inaccurate, but less ambiguous than
adopting the marketing terminology. MOST people will successfully
understand what is meant by "360K", "720K", "400K", "800K', "1.2M",
"1.44M" (which is just plain wrong, and SHOULD be "1.4M"), "2.88M",
even though such names are not technically accurate. Although there
can be, AND ARE, some different configurations that result in the same
final capacities, it is generally accepted as to WHICH kind of
drive/controller configuration is meant by each of those names.
"400K" generally means Macintosh single sided, not DEC Rainbow, etc.
Unformatted capacity would be a more correct nomenclature, although
not always precise, and relatively meaningless to the majority of
users, who didn't CARE except for how much space was available to
them. Formatted capacity is generally between 40 and 60 percent of
unformatted capacity.
The early drives in the current branch of evolution (ignoring NRZI,
phase-modulated, etc.) were "FM" (Frequency-Modulated).
The next innovation was to leave out clock pulses that could be
interpolated instead of explicitly included, resulting in a "less
crowded" signal, which could handle being done at twice the data
transfer rate. The engineers called that "MFM" (Modified Frequency
Modulation), which was not an optimum choice, since other modulations
were possible, including the later MMFM (Modified Modified Frequency
Modulation). The MARKETING people called the current recording system
"DOUBLE DENSITY". Intertec/Superbrain called their "DOUBLE
DENSITY"/double-sided, "QUAD DENSITY"; although twice the CAPACITY,
the density was unchanged. When drives became available that had
twice the number of tracks (96tpi 5.25"), marketing called that "QUAD
DENSITY". Although twice the CAPACITY, the density was unchanged.
Intertec/Superbarin had already used the name "QUAD DENSITY" for their
DSDD disks, so THEY, and ONLY Intertec/Superbrain called the 96tpi
DSDD, "SUPER DENSITY", which they abbreviated "SD", in order to be
confused with "SINGLE DENSITY".
AFTER "DOUBLE DENSITY" came into being, the previous system becaame
known as "SINGLE DENSITY". I say that it is analogous to the way the
"Great War" became known as "World War One" AFTER discussion of "World
War Two" began. Note that archival searches show that "World War Two"
as a search term has earlier hits in archives than does "World War One".
Fortunately, Kennedy's obsession over Cuba, and Nikita's
disappointment over being denied admission to Disneyland did not
result in World War Three. Yet.
When improvement in media and drives permitted doubling the data
transfer rate, with the same recording method, MARKETING called that
"HIGH DENSITY". Note that "HIGH DENSITY" IS "DOUBLE DENSITY", merely
with twice the data transfer rate.
When Barrium-Ferrite disks, and perpendicular recording were
developed, they were capable of twice the bit density on the disk, so
the data transfer rate was doubled again. MARKETING called that
"EXTENDED DENSITY".
(cf. sizes of olives: "giant", "enormous", "huge", etc. There was a
comedic few minute documtary about that 45? years ago)
Some specifications:
8" FM "Single Density" was 360 RPM at 250,000 bits per second. (about
500K unformatted per side)
8" MFM "Double Density" was 360 RPM at 500,000 bits per second. (about
1M unformatted per side)
5.25" FM "Single Density" was 300 RPM at 125,000 bits per second.
(about 125K unformatted per side)
5.25" MFM "Double Density" was 300 RPM at 250,000 bits per second.
(about 250K unformatted per side with 48 tpi, about 500K unformatted
with 96tpi)
5.25" MFM "High Density" was 360 RPM at 500,000 bits per second.
(about 1M unformatted per side)
In 5.25" 360 RPM drives that were not capable of switching to 300 RPM,
5.25" MFM "Double Density" in a 360 RPM drive was 300,000 bits per
second.
The 3" MFM disks that I have seen were 300 RPM at 250,000 bits per
second.
(500K unformatted per side)
3.25" MFM disks were 300 RPM at 250,000 bits per second.
(500K unformatted per side)
3.5" MFM "Double Density" (sometimes called "720K" due to the most
common format, or "400K"/"800K" at Apple) were 300 RPM at 250,000 bits
per second. (500K unformatted per side)
3.5" MFM "High Density" (sometimes called "1.44M", due to the most
common formsat being 1.41 Mebibytes, or 1.44 of a unit of 1000*1024
bytes), were 300 RPM at 500,000 bits per second. (1M unformatted per
side)
3.5" MFM "ED" (vertical recording?/barrium ferrite) were 300 RPM at
1,000,000 bits per second. (2M unformatted per side) NeXT referred
to theirs by the unformatted capacity: 4M, further confusing their users.
Note that there were always some exceptions.
Weltec made a 5.25" drive at 180 RPM, to do "HIGH DENSITY"/"1.2M" at
250,000 bits per second on PC/XT.
Sony made some 3.5" drives that were 600 RPM, to use 500,000 bits per
second.
NEC used 360 RPM 3.5" drives, to have the same format structure on
their 8" "DOUBLE DENSITY", 5.25" "HIGH DENSITY", and 3.5" "HIGH
DENSITY". Sometimes called "Type 3"
Epson (Geneva PX-8) used a 3.5" with 67.5 tpi, instead of the common
135tpi
Can you name another 20 exceptions? (Chuck and Tony probably can)
--
Grumpy Ol' Fred ci...@xenosoft.com
HP used 3.5" drives made by Sony that rotated at 600 RPM twice the data
rate but same density.
Paul
