OK, welcome to the *bain* of my life - converting PC disk images back to a format your Atari machine can understand, and converting your Atari disks to images.
In order to transfer files between ST and PC and vice versa, you will need to have some 3.5" disks formatted to 720KB capacity. If you cannot get hold of 3.5" 720KB Double-sided Double Density diskettes, you can use 3.5" 1.4MB High Density diskettes (as used with PCs) by sticking tape over the hole in the top left corner (NOT the write protect/enable hole - this should be left alone) This method is supposedly less reliable, but I haven't encountered any problems yet - touch wood!
It is better to format disks on your PC than your ST, as I found that I sometimes experienced problems reading ST-formatted disks on my PC. Right-click on the floppy disk icon in Windows Explorer (usually the A:\ drive) and select "Format...". Set "Capacity" to 3.5", 720KB, 512bytes/sector. The rest of the options can be left as they are. Click "Start" and the formatting process should begin. If Windows displays an alert box mentioning that it can't get access to the disk drive, try closing the Windows Explorer window, opening up a new Explorer window and trying the process again. However, if you find that this does not work, try formatting on the ST anyway - it still works for me. I use Loud Format ('cus I love the talking voice!) but there are numerous ST formatting programs which will do the job, and let you specify what format type you would like (sectors etc).
Now you have a disk which can be used on both your PC and ST! Its capacity is approximately 720KB (although Windows Explorer indicates 713KB!) which will be sufficient in most cases. However, some ST disk images are larger than 720KB because they are images of disks which have been formatted with greater capacity (i.e. more than 80 tracks, 10 or more sectors per track) Many cracked game compilation disks available on the internet use these "extended" formats. Windows disk formatting mechanism only supports 80 tracks, 9 sectors per track (as far as I'm aware) but there are ways around this little problem which will be covered later.
MSA files are images of Atari ST disks. They can be downloaded from many websites. ST Emulators use these files instead of "real" floppy disks. MSA files cannot be copied onto a floppy disk and used directly on your ST, because your ST just sees a floppy disk containing an MSA file, rather than the disk image contained within the MSA file.
There are 2 ways to convert them into a form which can be used on ST hardware. One way is to use a program called "Makedisk" (click to download) which runs on a PC and creates an ST disk from an MSA file. "Makedisk" only runs under "true" DOS mode (i.e. it won't work from a DOS command prompt within Windows) This can be a problem if your version of Windows does not enable you to boot up in "true" DOS mode.
The second method of converting MSA files into "real" ST disks uses a program which runs on your ST. Copy your MSA file onto a floppy disk and copy "MSA.prg" (click to download) onto another floppy disk. You will also need a 3rd blank floppy disk to be the "target" ST disk. "MSA.prg" is an ST program which converts MSA files into ST disks. Run "MSA.prg" on your ST. The main screen allows you to set up the source of the MSA file and the destination drive. These must be logically different drives but on a single drive system this just means swapping the disk in drive A when prompted to during the conversion process. There are 2 other options to set up:
"Format disk" - this should be selected, as the MSA image might be of a disk which is of a different format to your intended target disk (or your target disk may not have been formatted yet)
"Protect disk" - this should NOT be selected. This option enables the program to write a virus checker to the boot-sector of the disk. The MSA image may contain data in its boot-sector which must not be over-written.
Once the options have been set up, select "File -> Disk". The program will read the contents of the MSA file off the source disk. Then it will prompt you to insert the target disk into drive A. Finally you will see the formatting/writing process as the MSA image is written to the target disk. Once the process is complete, re-boot your ST with the target disk in drive A and it should be accessed as an ST disk... et Voila! You can now use MSA images on your ST!
The process described above involves copying MSA files onto a floppy disk to transfer them onto your ST. Unfortunately, many MSA files are larger than 720KB and thus will not fit onto a single floppy disk. It is possible to split them into 2 smaller MSA files which can be copied onto 2 floppy disks and then reassembled onto 1 target disk on your ST.
First of all, convert your large MSA file into an ST file (ST files are another form of ST disk image used by ST emulators) To do this, run "MSATOST.exe" (click to downloa) from a DOS prompt within windows. You need to specify the name of the source (MSA) file and the name of the new target (ST) file eg:
> MSATOST large.msa large.st
This will create an ST file. Now run "STTOMSA.exe" to convert the ST file back into an MSA file. To create 2 smaller MSA files, simply specify 2 output file names eg:
> STTOMSA large.st smaller1.msa smaller2.msa
This will create 2 MSA files, each of which will be about half the size of the original large MSA file. One MSA file contains the data for tracks 0-40(approx) of the target disk, the other contains data for tracks 41-80(approx).
Now copy these 2 MSA files onto 2 floppy disks and transfer them onto your ST with "MSA.prg" using the process described earlier - REMEMBER TO USE THE SAME TARGET DISK FOR BOTH OF THE SMALLER MSA FILES... YOU SHOULD HAVE ONLY CREATED ONE ST DISK AT THE END OF THE PROCESS!
I have encountered one problem with "MSA.prg". If the MSA file you want to convert into an ST disk has a format of more than 10 sectors per track, "MSA.prg" is unable to format the target disk. However, this problem can be overcome by formatting your target disk to the required format in advance (using any popular ST disk copying/formatting tool - I use ACopy 1.2 or FastCopy) Then just unselect the "Format disk" option in "MSA.prg" so that it does not attempt to format the target disk.
Good luck! Let me know if you have any other ideas you'd like to see on this page.