[comp.sys.atari.st] Atari Disk formats

csrobe@ICASE.ARPA (Charles S. Roberson) (03/21/88)

I would like some help sorting out the available disk formats.  I've used
Twister and given the explanation in the STart article, I have a lot of
confidence in it.  Recently, I tried using DCformat (especially for its
intelligent copy (I only have one disk drive while my HD is being repaired,
again :-( )).   The most significant thing about DCformat is that it allows
you to format 82 tracks per disk.  I also remember some people saying that
certain drives won't let the r/w head go that far -- I think mine is one.

Would some kind soul take the time to explain DCformat (especially when
are the options (sectors per track, tracks, side, etc) active).  If I
am doing a disk copy, do these options have any effect?

Also, I know have disks that have total storage of:

	815,600
	805,179
	695,891

and I'm think I have seen 82x,xxx or something like that.  Is there
a utility that I can use to determine how a disk is formated.

Thanks,
-chip
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woodside@ttidca.TTI.COM (George Woodside) (03/23/88)

In article <8803210013.AA22627@icase.arpa> csrobe@ICASE.ARPA (Charles S. Roberson) writes:

[edited a bit...]

> I would like some help sorting out the available disk formats. 

OK, here goes, from the ground up. It gets deeper as it goes along:

A disk is a series of concentric circles, called tracks. The standard for the
ST is to have 80 tracks on a disk. The first track (usually called track zero)
is at the outer edge, and the last track is toward the center. If your disk 
drive has two heads (SF 314), it can read and write on both sides of the disk. 
If it has only one head (SF 354), it can write only on one side. Each track is 
divided into sections called sectors, sort of like cutting a pie into equal 
pieces, straight out from the center. The standard for the ST is to have nine 
sectors per track.

> The most significant thing about DCformat is that it allows
> you to format 82 tracks per disk.  I also remember some people saying that
> certain drives won't let the r/w head go that far -- I think mine is one.

That's true. The manufacturer of a disk drive specifies the amount the
read/write head can move. The ST uses the industry standard of 135 tracks
per inch, so the head must be able to move (step) in 79/135ths of an inch to
reach the innermost track. If there is another 1/135th of an inch left
before the head stop, you can reach track 81, 82, or further, depending
on exactly how much extra room there is. That will vary from manufacturer
to manufacturer, model to model, and possibly even drive to drive in the
same model. Atari has used different manufacturers, so there are variances
in the drives in the world today.

> Would some kind soul take the time to explain DCformat (especially when
> are the options (sectors per track, tracks, side, etc) active). 

I didn't write DCFORMAT, but I've used it. The version I have is 2.03,
which is the last one I saw come across the net. Nice job to Paul Lee,
Keith Gerdes, and Michael Vederman, the authors. I'm not sure I like
the darkening of the options as the mouse passes over them, though.
Generally, the options active are the ones that are dark when the mouse
is away from them. The upper box selects the disk format characteristics
(SIDES, TRACKS, SECTORS, FAST/NORMAL), and the lower ones are functions 
you can execute after a disk is formatted.

You should understand the "tracks" and "sides" options from above. On to 
sectors, those pie shaped wedges. As you move in on the disk, the circles
get smaller, so the wedges get smaller. The amount of data you can write is
dependant, therefore, on the amount that fits on the innermost track. Now,
you can read or write data on the disk only in whole sectors, which are
512 bytes on the ST. When you write a sector, the disk drive has to be certain
not to start writing too soon, or write too late, or it will mess up the
data in the preceeding or following sector. To help with that, there is some
space between each sector on a disk, called a gap. There are standards for
gap sizes. There is also some leftover space after the last sector on a track.
If you use the leftover space at the end of the track, and maybe make the gaps
smaller, you can crowd one or even two extra sectors onto each track. However,
you get a non-standard disk, which can cause problems.

When writing 10 sectors per track, DCFORMAT uses gaps slightly smaller than
the Desktop's built in formatter, but well within the specs for the Western
Digital 1770 (the disk controller inside the ST). There are other formatters
around which attempt to put eleven sectors on a track. This, in my opinion,
is past the limits, and will eventually lead to disk errors.

There is information in the first sector of a disk which explains to the
operating system the format of a disk. When you change disks, TOS/GEMDOS
reads this information to determine how to read the data on the disk you
just inserted. It will correctly read data from the disk if the information
in the first sector (boot sector) is correct, within GEMDOS's limits, and
within the capabilities of the disk drive. 

One very important option you didn't ask about is "FAST". The way the ST
is built, the disk controller doesn't usually get to tell the ST when it 
is done with a task unless an error occurrs. The DMA chip is in the way.
Consequently, things run a little slower than they should. Dave Small
came up with a way around this with TWISTER. He staggered the sequence of
the sectors on the tracks, so the extra time lost by the controller, 
moving the disk heads, and waiting for things to settle down would amount
to the time taken by the staggered sectors to pass under the disk head.
That way, just as the head is ready to read or write, there's the right
sector. Another way to do this is by writing what looks like a bad sector
on the disk, but making sure it is a sector that the disk will never use
(like sector number 10 on a 9 sector disk). That causes an error, ends
the disk controller task, and gets things moving sooner. The error is on
a sector you didn't want anyway, so no harm done. This trick, however,
may bite back in later versions of the ROMs due to better error reporting.
DCFORAT 2.03 uses the bad sector mark trick on 9 sector disks, and the stagger
the sectors trick on 10 sector disks. Note that it appears to use these
tricks whether you select "FAST" or "NORMAL".  No matter which one you
select, you get the same result (couldn't be a bug, could it?).

> If I am doing a disk copy, do these options have any effect?

This is where the risks of using non-standard formats rear their ugly heads.

It depends on how you do the copy. If you copy files one at a time, from
one disk to another, GEMDOS will read and write the files correctly. If you
use the desktop's disk-to-disk copy, by dragging one disk icon onto another,
you must be sure the disks are the same format. The desktop will detect an
error if one disk is single sided and the other is double sided. It will not
detect an error if one disk has nine sectors per track, and the other has
ten (or anything else). You will wind up with a useless disk. If you are 
using some copy utility program, you'll have to try it and see for yourself.
If you are referring specifically to DCFORMAT's copy function, the same rules
as the desktop apply. You must be certain that the disks are the same, but
the options on the format dialog (TRACKS, SECTORS, SIDES) do not matter.
DCFORMAT reads the boot sector to decide what to do. It just doesn't check
all the information available to it to be sure the disks are the same.
A side note about the desktop: If you open the destination drive icon, then 
drag the source disk into the open window, GEMDOS copies all files and folders 
to the destination correctly, regardless of formatting differences. It does it
a file at a time, though, so it's not fast.

> Also, I know have disks that have total storage of:
>
>	815,600
>	805,179
>	695,891
>
>and I'm think I have seen 82x,xxx or something like that.  

You've got some funny numbers there.

There is some amount of overhead in the use of a disk. The boot sector,
the disk directory, and a map of how files are laid out on the disk (called
the File Allocation Table) all take up space. The rest of the disk should
be available for your data. I say should, because a glitch in GEMDOS causes
it to lose a little space, normally four sectors per disk. To determine the
amount of space a disk offers, multiply the number of tracks by the number
of sides (or heads), then by the number of sectors per track, and finally
by the number of bytes per sector (512). Deduct the overhead mentioned,
and you have the number of bytes available to you. The more common values:

                Single Sided                     Double Sided
            9 Sectors    10 Sectors          9 Sectors   10 Sectors
80 Tracks     357,376       398,336            726,016      807,936
81 Tracks     361,984       403,456            735,232      818,176
82 Tracks     366,592       408,576            744,448      828,416

> Is there a utility that I can use to determine how a disk is formated.

Not really. There are quite a few things that vary, as you can see. You can
determine the more important things (tracks, sides, sectors, and sequence)
with the program I'm attaching to this note. It will also tell you what the
serial number on a disk is, and if it contains self-booting code. It
attempts to determine these things by reading full track images, and scanning
the image for the sector and data marking values. It my be fooled by some
unusual formatting programs, or copy protection schemes.

> Thanks,
> -chip

You're welcome. Please pass the information and the program along, so that
others can learn, too.

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end


-- 
*George R. Woodside - Citicorp/TTI - Santa Monica, CA 
*Path: ..!{trwrb|philabs|csun|psivax}!ttidca!woodside

uace0@uhnix2.UUCP (Michael B. Vederman) (03/27/88)

In article <8803210013.AA22627@icase.arpa> csrobe@ICASE.ARPA (Charles S. Roberson) writes:
>I would like some help sorting out the available disk formats.  I've used
>intelligent copy (I only have one disk drive while my HD is being repaired,
>again :-( )).   The most significant thing about DCformat is that it allows
>you to format 82 tracks per disk.  I also remember some people saying that
>certain drives won't let the r/w head go that far -- I think mine is one.
>Would some kind soul take the time to explain DCformat (especially when
>are the options (sectors per track, tracks, side, etc) active).  If I
>am doing a disk copy, do these options have any effect?
etc....
>+-------------------------------------------------------------------------+
>|Chip Roberson                ARPANET:  csrobe@icase.arpa                 |

In fact, none of the disk options (except MAGIC) have any effect during
the disk copy portion of DC Formatter.

You can usually hear your disk head go 'CLUNK' when you reach the last track
of a disk drive that does not allow 82 tracks.

line eater
line eater
.
.
.
-- 
for (;;)                              : Use ATARINET, send an interactive
        do_it(c_programmers);         : message such as:
                                      : Tell UH-INFO at UHUPVM1 ATARINET HELP
University Atari Computer Enthusiasts : University of Houston UACE

unpowell@csvax.liv.ac.uk (04/18/88)

In article <517@uhnix2.UUCP>, uace0@uhnix2.UUCP (Michael B. Vederman) writes:
> In article <8803210013.AA22627@icase.arpa> csrobe@ICASE.ARPA (Charles S. Roberson) writes:
>>I would like some help sorting out the available disk formats.  I've used
>>intelligent copy (I only have one disk drive while my HD is being repaired,
>>again :-( )).   The most significant thing about DCformat is that it allows
>>you to format 82 tracks per disk.  I also remember some people saying that
>>certain drives won't let the r/w head go that far -- I think mine is one.
>>Would some kind soul take the time to explain DCformat (especially when
>>are the options (sectors per track, tracks, side, etc) active).  If I
>>am doing a disk copy, do these options have any effect?
> etc....
>>+-------------------------------------------------------------------------+
>>|Chip Roberson                ARPANET:  csrobe@icase.arpa                 |

Atari external drives can cope with 83 tracks.
Early Atari internal drives can cope with 82 tracks.
More recent internal models can only cope with 81 tracks.

I don't know about the States, but in England, if you purchase a non-Atari
external drive, such as Cumana or A,S&T it will generally be able to cope
with 86 tracks (yes 86!).
I definately know that A,S&T drives can cope with 86 tracks, as I own one.

As to sectors per tracks. Any drive (any?) should be able to read and write
10 sectors per track. The number of drives that can handle 11 sectors per
track is limited. My Atari external drive can read/write 11 sectors quite
unhappily (it slows down file reading and writing). My A,S&T external drive,
on the other hand, cannot handle 11 sectors per track.

I've tried without little success to vary the sectors per cluster. I think
this is always taken to be 2 by the ST.

I've tried to vary the number of FAT tables without much success. I think
the ST has to have 2 FAT tables per disk. (This is a good idea anyway. If
you lose your, only, FAT table, you can forget your data).

Sectors per FAT can be altered quite readily. You must calculate how many
clusters you have on your disk, before setting the sectors/FAT. The Desktop
formatter uses 5 sectors/FAT which is too many for any floppy. To calulate
the number of sectors/FAT your format needs, perform the following calulation.

RES=number of reserved sectors i.e 1 for the boot sector
FAT=number of FAT tables
DIR=number of directory entries. Usually $70, but is variable
SEC=number of sectors on disk
SPF=sectors per FAT

SPF=INT(INT((SEC-INT((DIR+15)/16)-FAT*SPF)/2)+2*3/2)/512

Simple really.

		Mark Powell.

********************************************************************************

 "...there's no success   JANET unpowell@uk.ac.lis.csvax
  like failure and        UUCP  {backbone}!mcvax!ukc!mupsy!lis-cs!unpowell
  failure's no success    ARPA  unpowell%csvax.lis.ac.uk@nss.cs.ucl.ac.uk
  at all..." B.Dylan

********************************************************************************