Drive capacity names (Was: WTB: HP-85 16k RAM Module and HPIB Floppy Drive
phb.hfx at gmail.com
Wed Nov 15 11:53:04 CST 2017
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
> The 3" MFM disks that I have seen were 300 RPM at 250,000 bits per
> (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
> 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
> 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
> Can you name another 20 exceptions? (Chuck and Tony probably can)
> Grumpy Ol' Fred cisin at xenosoft.com
HP used 3.5" drives made by Sony that rotated at 600 RPM twice the data
rate but same density.
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