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The Floppy Mystery
Data transfer between Atari ST and PC/Windows

I will try here to give first really correct and complete explanation about troubles in data transfer between 16-bit Ataris and PC. And of course how to do it, without data loss, corruption. There are guides, explanations around, with incorrect and shallow statements, which just increase already big confusion in all this. It is last time, in few years floppies will be out of use, new PCs will have no drives for.
  1. Simplest, and safe way is this (well known): format floppy on PC and use it for data transfer. In Win XP type this in command prompt: format a: /t:80 /n:9 . It will produce 720KB floppy, usable on all Ataris. If have High density floppy drive in Atari, may use 1440KB standard PC floppies. It will not help in transferring existing floppies, so go to point 2:

  2. For correct reading and writing on PC floppies formatted on Atari (from desktop, with diverse format programs) - collections, archives you need floppy imaging program. This is only secure way. It's not true that TOS 1.4 and above can format PC compatible floppy. It will be explained later in deep.

  3. Use some good formatting program on Atari, which can produce real PC compatible floppies. Examples: my new Floppy Formatter for Atari  or  Kobold 2.

  4. Extract files directly from floppies or images. I know only one program which can extract reliable from diverse ST format floppies in Win XP : Floppy Image NEW
    Gemulator Explorer is outdated and probably discontinued.

Why Windows/DOS can not work reliable with Atari floppies?
   Because of very badly made floppy support, drivers. Hardware is not real limit. Non-protected floppies can read/write without errors, only problem is hyperformat, but it was unreliable on Atari too. Part of guiltiness goes to Atari - they messed up 720K floppy format, and used incorrect FAT length.
Atari ST's (TOS) floppy driver is very flexible, and works with lot of different formats, while DOS/Win on PC with only few predefined.

Looking deeper in problem:
So looks info about floppy formatted with TOS 1.4 , in Win XP:  scane711.png

At bottom you may see that we have 711 allocation units, instead of 713 by standard PC 720K floppy. Yes, it is where Atari made mistake. They set FAT length to 5 sectors instead 3, what is stupid waste of space. But real problem is unreliable work of Windows, DOS with such floppies. Depending on version of OS, you may expect incorrect read of datas, FAT corruption by write and similar.

Just try to write some file on such floppy under Win XP: slow1.png - it is very slow (normally we get about 15 KB/sec). It indicates that something is wrong

Windows simple can not work well with floppy what is not strictly DOS standard formatted. Worst in all is that despite of it, it opens and works with non-standard (for him) floppies. Check of disk format is very superficial - if there is 0xE9 or 0xEB at start and more-less standard BPB, such floppy will be opened.... and messed up.
Strictly PC standard 720KB floppy is: 9 sec/tr, 2 sides, 80 cylinders, FAT size: 3 sectors (2 FAT copies), Root DIR size: 7 sectors. Total 713 allocation units (clusters) on disk.

Hurra! My PC works with 800K floppies! :

DIR:
cp800k.png  Total Commander: tc800k.png 
Explorer, properties: expl800k.png 

Here starts real mess. Short said: don't trust to Microsoft! Don't read anything from such floppies in Windows explorer,  Total Commander. You will get corrupted files with missing parts.
It sounds pretty unbelievable, and I spent lot of time examining it: Windows will simple skip every tenth sector of such floppies, and instead it will read following one. It results in reading different areas of disk than needed. But, for instance first short file of 3KB will be read without error - nice to encourage people!
Notes: above floppy has 0xE9 at start. If formatted with another format program (Superaccessory for instance) it will not be opened on PC.
According to my memory, Windows 95 could read such floppies correct, at least I was able to do it in Gemulator. But it is now history.
Opening 800K floppy in  Gemulator Explorer promises, Root DIR is OK :gemexp1.png
Not for long, opening SubDir will show garbage instead content : gemexp1.png
After it, we may be happy that image creation of such floppy not works at all - better nothing than corrupted image. It was under Win XP, in Win 98 it opened correct directories, but very slowly. (Imaging of floppies failed in both OS). Gemulator is one of rare Atari emulators which can work with floppies, not only floppy images. But it will fail with 800KB floppies. Reason is miserable Windows floppy driver, which skips every tenth sector on such floppies in XP, W2K. (it stays for Gem. Explorer too, of course).  On the other side, Gemulator will work well with standard Atari 720K floppies (those with 5 sec/FAT) - because file access goes true Atari's TOS and not Windows, and physical format is same.

Utilities for 'making floppies DOS compatible' as ST2DOS.EXE are almost worthless - they can not correct FAT len, or transfer 800K floppy to 720K one (what an idea!  ;-)  ).
Here I must to add that me, and most of Atari users in my area used very much 800K format in golden era of Atari (1987-1991). It showed as reliable, there was couple program for creating such floppies, and Atari worked flawless with them. It means, that there is probably still lot of such floppies.

Conclusion: use one of above mentioned 4 methods for data transfer (and preservation) of Atari floppies, files,  or for writing files to floppies to use them on Atari.
For playing games downloaded from Internet in floppy image formats (ST, MSA, STT) on real Atari use FloImg   - designed for Win XP (with special floppy driver), simple to use.
Use same program for transfer/image/preserve your existing diverse format Atari, non-protected floppies, files from. It is last time for saving, they gradually loose informations on them.
Note: there are some other Windows programs for imaging Atari ST floppies, but they usually use Win floppy driver, and therefore will fail with 800K floppies - for instance Wdfcopy.


Some sites with incorrect informations (list will grove):
Makedisk FAQ there says that plain 720KB floppies are compatible. What is plain 720K disk is not detailed.
Gemulator's instructions - it says that can work with 800K floppies, but it stays only for Win 95. Not aware about problems with FAT size.
Here is image of floppy from which I took screenshots with Gem. Explorer: 800KB image. It will work well in emulators, but if you write it to floppy, and then try with Gemulator... Here to mention that STE Emulator (German shareware) will even not open it, and in manual is said why.
SOS Software Quoting: "...Luckily, provided that the floppy is formatted properly, the PC can read and write to a DD disk. You will have to format the disk on your ST, as Windows XP no longer provides options to format DD disks." - Well, they obviously don't know about command prompt. What is properly formatted DD disk remains unclear on SOS.
Steem, beginners guide says: "most disks on the ST were nonstandardly formatted in order to squeeze more onto them. Unfortunately most PC disk controllers can't read these extended formats." - Again incorrect blaming of hardware. Nobody remember good old 800.COM for DOS?

Was it good idea, to 'blame' such sites? Maybe not. I spent lot of time in testing, experimenting , while I have impression that other did not so. If they can prove that I'm wrong in something, I will correct things here. But, unfortunatelly, based on my experiences, most of sites will remain as it is, with all mistakes and outdated/limited SW :-(

Some people said: why suddenly now, 21 years after launch of ST? Because I had still some not imaged floppies, because there was need for imaging program under Windows, which works reliable. Because I want to see all my floppies and files on CD. Because some software simply became outdated - incompatible with new Windows versions (it is nothing unusual). While finished Floppy Formatter for Atari I performed lot of tests about PC compability. Results were frustrating, unexpected. Another frustrating factor is communication with authors of software, actually, there is no communication at all in many cases.
10 sector/track issue is general Windows problem, and not only by Atari ST floppies. Some people (Simon Owen for instance) discovered it years ago, but Atari community is after things as usual :( . It's not easy for PC beginner to even start DOS today. And in this case, seemingly trivial operation as floppy imaging/reading appeared as pretty insecure and frustrating.


Pera Putnik, August 2006