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

[Chuck Guzis via cctalk]

On 11/17/2017 09:17 AM, allison via cctech wrote:

> Also the Syquest 270mb IDE/parallel port cartridge disk.  I have one
> that works
> and over a dozen carts.  Its still in use in a ITX box using the IDE
> interface.  After
> two decades of use it seems solid.

I've left out the non-floppy technologies.   I have a Squest Sparq,
unused still in its packaging, for example.  After being sent one for
evaluation, I rejected it because it was offered only in the
printer-port version, which necessarily limits transfer bandwidth.

But there were plenty of "floppy" technologies, such as the UHD144, or
LS120 or Drivetec stuff.   I treat Bernoulli and Zip as a floppy-sort-of
technology, because they are incapable of reading standard floppies, so
I don't include them either, even though they employed flexible media.

--Chuck

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

[allison via cctalk]

On 11/16/2017 03:30 PM, Geoffrey Reed via cctech wrote:
>
> On 11/15/17, 9:44 AM, "cctalk on behalf of Fred Cisin via cctalk"
>  wrote:
>> Can you name another 20 exceptions?   (Chuck and Tony probably can)
>>
>>
>> --
>> Grumpy Ol' Fred  ci...@xenosoft.com
>
>  ³Floptical² disks 720 rpm 1.6 Mb/s transfer 1250 TPI and 25MB unformatted
> capacity
>
>  LS-120 and LS-240 (which sadly I can¹t remember the specs of :(
>
>
>

Also the Syquest 270mb IDE/parallel port cartridge disk.  I have one
that works
and over a dozen carts.  Its still in use in a ITX box using the IDE
interface.  After
two decades of use it seems solid.

Allison

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

[Fred Cisin via cctalk]

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!


On Thu, 16 Nov 2017, Christian Corti via cctalk wrote:
Fred, you should know by now that you don't need to tell *me* the correct 
definitions and terms.


I know that, but I was addressing the entire group with my rant, and not 
everybody is as closely familiar with these details as you are.


And with "high-density", I didn't mean the media capacity but the analog 
recording aspects like coercivity, write current, frequency and so on.


Actually, when speaking about the MEDIA, it is much easier to create a 
name that is both accurate and unambiguous.
For example, with 5.25" disks, we have "5.25 inch with 300 Oersted" and 
"5.25 inch with 600 Oersted".
Of course, if somebody wants to be difficult, there are still variant 
forms, including both 10 and 16 sector hard-sectored, Amlyn 600 Oersted 
with special cutouts for the disk changer, Twiggy, no-notch disks for some 
minor tamper resistance in software distribution, etc.



Unformatted capacity would be a more correct nomenclature, although ...
Unformatted capacity doesn't tell you much without reference to the recording 
layout, i.e. no. of tracks, modulation, frequency and so on.


True.


Some specifications:
5.25" MFM "High Density" was 360 RPM at 500,000 bits per second. (about 1M 
unformatted per side)


What about 5¼" FM "High Density" at 360 RPM?


By "Some specifications", I meant specifications of SOME examples of the 
most common form of each size.  I was absolutely not intending it to be 
an exhaustive, comprehensive list of all possibilities.



The Amiga (more exactly, the "HD" Chinon FZ-357A drives used in Amigas) 
switched to 150 RPM to keep the raw bit rate at 250kbits/s.


THAT is exactly what I was including as examples in my later "exceptions" 
list.  Although a different disk size, that is the same engineering kludge 
as the Weltec 5.25" 180RPM drive.


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.

What about FM?


Again, just listing examples of most common, NOT intending it as a list of 
all possibilities that were theoretically possible.  I have never seen an 
ED disk recorded FM, and do not believe that there was ever a commercial 
system that used that.  If you know of one, please give us the details!




Can you name another 20 exceptions?   (Chuck and Tony probably can)


Do you want me to start with things like 100tpi drives, GCR, M²FM, 
hard-sectored and other crazy formats?


It can be a very long list.  I was trying to stick with ones that were 
very close to the main branch of our "current" evolutionary tree, but 
there isn't a clear boundary.  I estimate that there were approximately 
2500 different microcomputer floppy disk formats, with a large portion of 
those being variant forms, not just different choices of number and size 
of sectors, directory location and structure, etc. 
I implemented just over 400 formats in XenoCopy that were straight-forward 
to handle with IBM PC hardware.  Those are not all that could have been 
implemented, nor does it deny the existence of many variants, or 
completely different ones that are not feasable with PC.



Just accept that I am not as dumb as you may think.


I have NEVER thought that you were dumb.  Everything that I have seen 
of your posts has been competent and well-informed.  But, I don't think 
that you follow what I was attempting to convey.


I wanted to:
1) rant about marketing creating terminology, including "double density" 
and "high density".  And creating a new definition of Megabyte (1,024,000) 
for the "1.44M" format (1,474,560 bytes/1.40625Mebibytes)


2) state my opinion that using the specific one that comprises at least 
75%? of the use of a given configuration as the name for that 
configuration creates a name that is admittedly inaccurate, and fraught 
with exceptions, nevertheless relatively unambiguous, at least to the 
extent that purchases will usually be usable.


If I buy "360K diskette", it will usually be the 300 Oersted 5.25 inch, 
and be the closest of what is available to buy for 87.5K TRS80, 
Apple2, PET, Osborne, PC 160K/180K/320K/360K, DEC Rainbow, Canon AS100, 
Elcompco, Eagle, Otrona, etc. 
Yes, there were people who used 41 or 42 tracks of a 40 track drive, but I 
consider those to be "corner cases", to be considered as alterations, not 
as the main form.
Admittedly, there were differences in testing between SSSD, DSSD, DSSD, 
DSDD, and 48tpi v 96tpi marketing of disks with the same chmical 
formulation.  Purchasing diskettes now for something such as a DEC 
Rainbow, I would settle for the 360K 

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

[Liam Proven via cctalk]

On 16 November 2017 at 21:30, Geoffrey Reed via cctalk
 wrote:
>
>  ³Floptical² disks 720 rpm 1.6 Mb/s transfer 1250 TPI and 25MB unformatted
> capacity

Just FYI, your quote marks render on Linux as superscript 2s.

Using an Apple device? You might want to turn off smart quotes...

https://www.jordanmerrick.com/posts/ios-11-smart-punctuation/

http://appleinsider.com/articles/17/09/26/tips-turn-off-ios-11-smart-punctuation-to-avoid-data-entry-problems

-- 
Liam Proven • Profile: https://about.me/liamproven
Email: lpro...@cix.co.uk • Google Mail/Talk/Plus: lpro...@gmail.com
Twitter/Facebook/Flickr: lproven • Skype/LinkedIn/AIM/Yahoo: liamproven
UK: +44 7939-087884 • ČR/WhatsApp/Telegram/Signal: +420 702 829 053

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

[Chuck Guzis via cctalk]

On 11/16/2017 12:30 PM, Geoffrey Reed via cctalk wrote:

>  ³Floptical² disks 720 rpm 1.6 Mb/s transfer 1250 TPI and 25MB unformatted
> capacity
> 
>  LS-120 and LS-240 (which sadly I can¹t remember the specs of :(

How about the Caleb "it" drive (UHD144):

http://www.obsoletemedia.org/caleb-uhd144/

I've still got a stack of those drives and media.

Or the DTC "TakeTen" drive (got the drive but no media), or the Qume
Hyperflex drive or the Kodak/Drivetec floppy drives or the DTC TeamMate
for Apple...

The list is very long indeed.

--Chuck

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

[Geoffrey Reed via cctalk]

On 11/15/17, 9:44 AM, "cctalk on behalf of Fred Cisin via cctalk"
 wrote:
>
>Can you name another 20 exceptions?   (Chuck and Tony probably can)
>
>
>--
>Grumpy Ol' Fredci...@xenosoft.com


 ³Floptical² disks 720 rpm 1.6 Mb/s transfer 1250 TPI and 25MB unformatted
capacity

 LS-120 and LS-240 (which sadly I can¹t remember the specs of :(

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

[Peter Corlett via cctalk]

On Wed, Nov 15, 2017 at 09:44:24AM -0800, Fred Cisin via cctalk wrote:
[...]
> 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)

Another oddity for your collection: because the Amiga's floppy controller had a
500kHz maximum clock, they needed custom drives which slowed down to 150RPM
when they detected a "HD" disk.

Given the Amiga did read-modify-write of whole tracks rather than overwriting
individual sectors, the performance of those things was particularly bad.
Mercifully, nobody attemted to bodge a quarter-speed ED drive onto the Amiga.

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

[Christian Corti via cctalk]

On Wed, 15 Nov 2017, Fred Cisin wrote:

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!

[...]

Fred, you should know by now that you don't need to tell *me* the 
correct definitions and terms.
And with "high-density", I didn't mean the media capacity but the analog 
recording aspects like coercivity, write current, frequency and so on.


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.


I disagree, that is not generally accepted, at least not any more, and 
this is good!


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.


Unformatted capacity doesn't tell you much without reference to the 
recording layout, i.e. no. of tracks, modulation, frequency and so on.



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)


I beg to differ. The raw bit rate is about the same. With FM, you have a
500kbits/s raw bit rate but half of the bits are clock bits. It is 
effectively the same density.


5.25" MFM "High Density" was 360 RPM at 500,000 bits per second. (about 1M 
unformatted per side)


What about 5¼" FM "High Density" at 360 RPM?

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)


The Amiga (more exactly, the "HD" Chinon FZ-357A drives used in Amigas) 
switched to 150 RPM to keep the raw bit rate at 250kbits/s.


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.


What about FM?

Your list just mixes two aspects that are not strictly correlated, 
raw recording density (bit rate) and data modulation (e.g. FM, MFM).



Can you name another 20 exceptions?   (Chuck and Tony probably can)


Do you want me to start with things like 100tpi drives, GCR, M²FM, 
hard-sectored and other crazy formats?


Just accept that I am not as dumb as you may think.

Christian

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

[Tapley, Mark via cctalk]

On Nov 15, 2017, at 11:44 AM, Fred Cisin via cctalk  
wrote:

>  "400K" generally means Macintosh single sided, not DEC Rainbow, etc

For once, the physical format disambiguates those two! 
The Rainbow disks are in flexible envelopes (and ~1.75” greater diameter).
(Got many of each, couldn’t keep them straight otherwise ;-) )

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

[Fred Cisin via cctalk]

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!




On Wed, 15 Nov 2017, Mark J. Blair via cctalk wrote:

Bogus as it may be, compatible media for those drives commonly has "HD" printed 
on the box and molded into the diskette's plastic jacket. It's a useful term for 
identifying the compatible media.


Yes.

Sadly, the least ambiguous ways that we can describe what we mean require 
that we use BOGUS marketing deceptive names.

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

[Fred Cisin via cctalk]

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

On Wed, 15 Nov 2017, Paul Berger via cctalk wrote:
HP used 3.5" drives made by Sony that rotated at 600 RPM twice the data rate 
but same density.


One of my favorite examples; mentioned about a dozen lines up!

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

[Mark J. Blair via cctalk]

> On Nov 15, 2017, at 09:44, 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!


Bogus as it may be, compatible media for those drives commonly has "HD" printed 
on the box and molded into the diskette's plastic jacket. It's a useful term 
for identifying the compatible media.

-- 
Mark J. Blair, NF6X 
http://www.nf6x.net/

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

[Paul Berger via cctalk]

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 

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

[Fred Cisin via cctalk]

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)