Drive capacity names (Was: WTB: HP-85 16k RAM Module and HPIB Floppy Drive

[Fred Cisin]

>> 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     		cisin at xenosoft.com