Re: The Name of the disk (Was: Disk imaging with IMD - question

[Al Kossow via cctalk]

http://www.retrotechnology.com/herbs_stuff/drive.html
is more detailed than the 

On 8/10/17 1:32 PM, Tom Gardner via cctalk wrote:
> Me too - great rant.

RE: The Name of the disk (Was: Disk imaging with IMD - question

[Tom Gardner via cctalk]

Me too - great rant.
Thanks
Tom

-Original Message-
From: Mark J. Blair [mailto:n...@nf6x.net] 
Sent: Thursday, August 10, 2017 9:56 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: The Name of the disk (Was: Disk imaging with IMD - question


> On Aug 9, 2017, at 12:08, Fred Cisin via cctalk 
wrote:
> 
> 
[...]
> 


I'm keeping your rant as reference material. Thanks!

The Tandy Portable Disk Drive (TPDD) for the Model 100 series is one of the
odd-ball "rare" configurations: 3.5", 40 track (later, 80 track on the
TPDD2), single sided, two (!) sectors of 1280 bytes each per track. Disk
capacities are nominally called "100k" or "200k". I have not yet tried
examining a TPDD disk on some sort of imaging setup to get insight into its
low-level format, but that's on my growing "one of these days" list. The
drives had internal controllers and brains, and connected to the computer
over an RS-232 interface.

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

Re: The Name of the disk (Was: Disk imaging with IMD - question

[Ali via cctalk]

> On Aug 9, 2017, at 12:08, Fred Cisin via cctalk  
> wrote:> 
> 
[...]
> 


>I'm keeping your rant as reference >material. Thanks!
I second that! Fred ranting is a good thing ;). Generally there are a number of 
good posts here that go into my archive folder for future reference. I just 
wish I had more time to make use of material. :(

Re: The Name of the disk (Was: Disk imaging with IMD - question

[Mark J. Blair via cctalk]

> On Aug 9, 2017, at 12:08, Fred Cisin via cctalk  wrote:
> 
> 
[...]
> 


I'm keeping your rant as reference material. Thanks!

The Tandy Portable Disk Drive (TPDD) for the Model 100 series is one of the 
odd-ball "rare" configurations: 3.5", 40 track (later, 80 track on the TPDD2), 
single sided, two (!) sectors of 1280 bytes each per track. Disk capacities are 
nominally called "100k" or "200k". I have not yet tried examining a TPDD disk 
on some sort of imaging setup to get insight into its low-level format, but 
that's on my growing "one of these days" list. The drives had internal 
controllers and brains, and connected to the computer over an RS-232 interface.

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

The Name of the disk (Was: Disk imaging with IMD - question

[Fred Cisin via cctalk]

The structure used on most diskette tracks is based on an IBM design 
(3740, etc.), and was referred to as "IBM format".  BUT, the general 
public think that "IBM" means the machines that followed the 5150, so "IBM 
format" is oft misconstrued to mean PC.  To avoid ambiguity, I sometimes 
call it "IBM/Western Digital style format".


It includes substantial structures, including sector headers, gaps, 
write splice areas, etc., which require a substantial overhead  (about a 
quarter? of the disk capacity), so decisions about how many sectors of 
what size can have an effect on the final usable capacity.  In spite of 
that, in the interest of "uniformity", it is commonplcae to refer to 
different types of diskettes by one of their commonly used formatted 
capacities  ("360K", "1.2M", "720K", "1.4M")  THAT certainly doesn't 
remove all confusion - for example Apple "400K" and "800K" are the same 
diskettes as IBM "720K"


8" disks used a different jacket for double sided disks than single sided, 
with the index hole aperture in a different location.  That let the 
computer recognize which type of diskette was inserted, and therefore to 
refuse to cooperate if the user asked for a different format than that 
diskette had been intended for.


5.25" dropped that, and also reversed the write-protect notch to a write 
enable notch.
Single sided and double sided 5.25" diskettes are interchangeable, and 
single sided ones can be flipped over to use the other side (single sided, 
of course) by punching additional holes in the jackets (cf. Berkeley 
Microcomputer "Flip Jig")

5.25" diskettes were once known as "mini-floppy".

Besides GCR (Commodore, Apple][, Macintosh 400K and 800K, etc.), there are 
a variety of obscure alternate possibilities, such as Amiga MFM but 
without the IBM/WD structures, hard sector, NRZ, FSK?, etc.)


 the drive and disks are double-sided double density. Are you 
saying that's quad density?


AARRGGHH!
Would it work to kill off people that say "quad density"?

Originally, 5.25" disks were single sided 35 track, soon changed to 40 
track.   Diskette was 300 Oersted.

Capacity depended on formatting choices, typically between 80K and 100K.
These disks were an FM ("Frequency Modulation") recording. 
There was NO mention of "density", although some engineers might call it 
"half density", since there is one bit of data for every two pulses/flux 
transitions.


Apple chose to use GCR for their 35 track single sided disks, resulting in 
about 140K.


Then there was MFM ("Modified Frequency Modulation").  The premise was 
that clock pulses/flux transitions weren't reaally needed between adjacent 
data pulses/flux transitions.  That put more space between the 
pulses/transitions, which meant that the data transfer rate could be 
increased (they doubled it), getting about twice as much data per track.

About 1.5? pulses/transitions per data bit.
Depending on format choices, typically between 150K to 200K capacity.
Instead of just calling it "MFM", the marketing people called it "DOUBLE 
DENSITY".


AFTER that, they renamed "FM" to "SINGLE DENSITY".  That means that if you 
look back, historically, you'll find earlier mentions of the phrase 
"double density" then the earliest mentions of "single density".
(The same historical principle applies to the phrases "World War TWO" V 
"World War One" (which had previously just been "the great war"))


But, there was also single sided and then double sided.
hence, SSSD, SSDD, DSSD, DSDD.
Depending on format choices, between 240K and 400K for DSDD.

BUT, the marketing people at Intertec (Superbrain) chose to call DSDD: 
"QUAD density".

They were the only ones who did that.

Soon thereafter, 5.25" disks came out with 96tpi, instead of 48tpi, 
resulting in 80 tracks instead of 40 tracks.  The "density" on each track 
was not affected.

Depending on format choices, between 640K and 800K.

The marketing people of many/most? computer companies called THAT "QUAD 
DENSITY".  (DSDD, with 80 tracks, instead of 40 tracks)

I think that that was a very stupid naming choice.

So, is "quad density": 40 track DSDD (Superbrain)?
or 80 track DSDD (MANY CP/M computers)?
or 1.2M (DSDD with twice the linear density/data transfer rate, where they 
really did get 4 times as much data per track)?



BUT, it gets WORSE!!
Intertec (Superbrain) started making 80 track DSDD (800K?) available. 
But, they had already used "QUAD DENSITY" to refer to 40 track DSDD!  So, 
they called the 80 track DSDD, "SUPER DENSITY"!   If that wasn't bad 
enough, they abbreviated "Super Density" as "SD".

OK, is "SD" FM/single density,
or is "SD" "SUPER DENSITY"?
Thankfully, NOBODY else was THAT stupid.

I have a special fond spot in my heart for Intertec.  At NCC (National 
Computer Conference) in 1983, I stopped by their booth to ask some minor 
questions about their formats for XenoCopy.  (They had multiple formats, 
with their own unique names, inverted the data bits, short-changed 
some of the