Transfer Atari ST images from PC to Atari ST using floppy disks

There are many very good options to transfer Atari ST images to an actual Atari ST using devices like a HXC Floppy Disk Emulator or an Ultrasatan.

However I wanted to transfer a few games to floppy disk using items I had on hand. This post explains how I achieved this.

I don’t have a PC with an internal floppy drive. I do have a USB floppy disk drive. One of these, which is a TEAC brand. My understanding is that not all USB floppy drives can format a disk to 720KB. Luckily this one can.




Generally .ST game images come in 720KB size and 820KB size. For 720KB images it is possible to image the floppy disk in the USB floppy connected to the PC. However for 820KB images these can not be written using the floppy drive. So first up we can deal with the 720KB images.

Start out by formatting the floppy disk. If you do not have DD floppies, you can use HD floppies but will need to use tape to cover the notch on the top left hand corner. Otherwise the floppy drive will not be able to format the disk at 720KB. Note that when used in the Atari ST the hole does not need to be covered for the drive to recognise the disk.



To format the floppy disk, open a command window and type format a: / T:80  /N:9


Note that you may need to substitute a: for b: depending on what the drive letter assigned to the USB floppy is.

To write the 720KB .ST file to the floppy disk, use a program called OmniFlop

Download and run the software.



Click Next



Click OK if you get this warning


Select Write disk



Select the relevant drive. In my case it was B:




Select the appropriate image format 3.5″ Atari ST DSDD


Browse to your 720KB .ST image file




The image writing process will begin.



Once completed, you will see the success message.

Now for 800KB – 820KB .ST images it is a bit trickier. The external USB floppy cannot handle this format. So what needs to happen is to split the file into 2 pieces on the PC, copy the files onto 2 separate 720KB floppy disks and then write them back together on an actual Atari ST. It is a bit clumsy, but it works, doesn’t cost anything and is worth it if there is a game you really want to play!

The splitting of the file into 2 pieces will also convert the files to .MSA format. For this a program is required named STTOMSA. Extract and place the program into the same folder as your .ST files. Be aware that this program will not work with 64 bit Windows. I used it on an old Windows XP 32 bit laptop.

Open up a command window and change to the directory containing the .ST files and STTOMSA. There is documentation available at 

Use the following syntax to split the files:

STTOMSA <ST filename> <filename1.msa> <filename2.msa>

For example:



After the process is complete, 2 new files named as specified will appear in the folder. These files will not be exactly 50% in size each, but represent a sort of half split. Now copy those 2 files to separate floppy disks.

Now to piece them back together on the Atari ST you can use software named MSA_2_32

Extract the PRG file and place on a disk that can be used in an Atari ST.

Load up the software on the Atari ST, and get another floppy that will be used to extract the image to. This does not need to be formatted in advance.




Refer to the picture above. Up the top, select Diskdrive B. This represents that the output will by made to drive B, you will be asked to put the target disk in when ready to drive A. The reference to drive B: is sort of like a virtual allocation.

Click the MSA file path to specify the source MSA file.

Ensure Format Disk is checked. Do not check Protect Disk.

Click File – Disk when ready. Firstly the contents of the first file will be read, then you will be asked to insert the target disk.

Once you have completed the first part of the disk image, place the disk with the second part of the msa file in the drive, and click on the MSA file path to select the latter MSA file.

Click File – Disk, and the second part of the disk will be read, then formatted and applied to the target disk.

Finally you have the complete image file on the floppy, ready to be used to play on the real ST. Yes it is some effort, but it works.




  1. Hello,
    Juist a question from a noob 🙂
    I tried to fix the msa files wit MSA_2_33 prg.
    When I run my 1040stf the first file goes without problem to disk. When write/format stops I insert second disk with last Msa file.
    And that’s were it ends, program shuts off or Atari goes bonkers!
    What could go wrong? Because first part goes wel.


    1. Hi There,

      Hmm I am not sure. Have you tried splitting a different file in case there is a problem with the source file you have split?

      What file are you trying to do this with?

  2. Hello, thank you very much for this guide! I got an Atari ST at a thrift store recently and this has enabled me to give many games a shot!

    I have followed your guide (I found the same USB floppy drive you have on Ebay and it works great!) and it works for small games, but I am a bit confused as to how to get the 800kb+ games working using the instructions you’ve provided.

    I got the STTOMSA program working in Dosbox, and it split the ST file into two MSA files just fine, but I’m confused about a few things:

    1. How can I get the MSA files onto the floppy disks? (I am using 1.44MB disks with tape on the corner)

    The OmniFlop program will let me burn the .ST files, but it won’t let me burn the MSA files. Furthermore, Windows 10 does not recognize the ST-formatted disk and won’t let me just copy the file over. How did you get the MSA files onto disks? Do I need to use some other program to do this?

    2. How do I get the MSA_2_32.PRG file onto the ST?

    The download link contains the .PRG executable file, but just like my problem with the MSA files above, I don’t know how to burn these to the floppy when Windows does not understand the disk format.

    3. Once I can copy the MSA_2_32.PRG onto the ST, how can I save it if my ST has no hard drive?

    I have a 1040STE, and it does not have a hard drive. Is is possible to just copy it off the disk and just sit in the ST’s RAM, and run it from there? I’d need to do that so I can put the disks containing the MSA files into the drive.

    Thanks so much for this guide. I do hope you still remember some of this stuff even though it’s been four years since you wrote this article.

    1. Hello Richard, glad this guide has helped you out!

      1) I copied the MSA files to the floppy disks like a normal file transfer using a Windows 10 Pro Desktop PC. I’m not sure why you can’t just copy the files over. You might have more luck trying on an old PC with an older version of Windows.

      2) Same thing for the PRG file, I just copy over on my Windows 10 PC like a normal file drag and drop to the A: drive, and it works. I tried it again on my setup, and it worked fine. Maybe try using command line to try and copy over to the floppy rather than drag & drop?

      3) Yes that’s right. The file is just copied into the ST RAM and it can be run from there.

      I hope this helps!

      1. That worked like a charm, thanks!

        I do have two further, separate questions though:

        Have you ever had an issue with games loading forever? I have tried multiple games (both actual retail ones and ones I’ve burned) get stuck at the “Loading” screen for well over an hour. Could this be a problem with my STe?

        Also, sometimes after I burn a .ST file to a disk with OmniFlop, I pop it into the Atari and is says the disk is blank. Have you run into this issue before?


        1. I can’t be exactly sure about the games loading forever and blank disks after burning, whether it is a problem with the floppy disk, disk image or the STe. In my experience there are a few reasons this could happen
          – The disk image file has problems running on a real floppy disk. Some images online will work fine in an emulator, but not on real hardware.
          – The floppy disk has an issue and won’t work fully on the ST. I have seen these many times with old disks. But if stored well, I find more work than don’t work.
          – The ST floppy drive is fussy and random loading issues may occur.
          – The STe does have some compatibility issues with some games, as the TOS & chipset are different. to the earlier STFM models.

          I recommend doing the following:
          – Trying a different disk rom image
          – Trying a different floppy disk

          If that doesn’t work, you may need to research to see if there is an issue with the particular game running on an STe. Sometimes crackers have made STE compatible hacks for games.

          Fortunately for me I have the best of both worlds, with multiple Atari STe/ STFM computers with the choice of using real disks or a Gotek USB floppy emulator.

  3. I installed omniflop on my windows 10 machine.. if I go straight to write it pulls many formats, but not Atari ST like yours does… HELP!

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