Even if you are not deep into emulation, sooner or later you will stumble upon disk images in .MSA or .ST format. Basically those files are similar to ZIP archives or ISO images. they do not only hold files and there directory structure, but the exact layout of tracks on the original floppy disk is preserved.
JayMSA by Jaysoft  is free to download and use. The utility runs on all Atari STs and compatibles and fully utilizes the GEM desktop and is multitasking friendly.
With JayMSA one cannot only read disk images and save their contents as .MSA or .ST disk images ready for use with known ST emulators, but it also can write those images back onto disk. It also allows to extract files from a disk image. This feature is particular handy for hard drive users who do not want to run software from a floppy. Basically this saves the need to fully write the disk image onto a floppy disk.
Imaging a disk is simple with JayMSA. Just put the floppy you want to image into your drive, use the “Disk” menu to select the destination drive and click “Compress”. In the next dialogue select the options you want to employ for imaging
. If you are using TOS, the CRC feature seems to be buggy. It crashed for me in the past. But if you disable it, everything will work nicely.
You can select different target formats with MSA and ST being the most reasonable. Disk images in .ST format are not packed by default so I don’t recommend using them. After selecting where you want the fresh disk image to be stored, the program asks for confirmation and begins the imaging process.
When the imaging process has finished, JayMSA will list the contents of the new disk image in its main window. This will work as long as there is a FAT filesystem on the image. Software that loads from raw tracks will most likely only display some garbage here.
In this dialogue files can be selected, viewed with a configured text viewer from within the active disk image and ofcourse, extracted on their own to disk. Handy if you want to copy a single file from an entire disk image to your hard disk. Just click “Extract” in the “File” menu.
To write a disk image back to disk, select “Open” in the “File” menu to display the contents of your file. Now go to the “Disk” menu and select “Extract” to write the disk image back to a floppy. The process is similar to imaging a disk and ofcourse, JayMSA can write the same disk images back to disk that it created, e.q. you can write .ST files to disk with this.
- compatible with all previous MSA disk imagers
- handles multiple disk image formats including .ST
- has its own MSA file format with LZH compression
- can clean bootsectors if desired (handy for those Ghost virus infested disk boxes)
- shows contents of a disk image and allows to extract individual files
- nice GUI
- as a clean application, it works on all Ataris
- as most other disk imagers, JayMSA cannot image floppy disks with copy protection
- uses “clean” disk access only so may not image everything no retry upon disk errors
- the LZH compressed image formats can only be read and written by JayMSA itself
- CRC option seems not to be compatible with TOS
- window font display is buggy in ST-LOW and ST-MEDIUM if no NVDI is installed
All in all, I like JayMSA a lot and I use it regularly to write .MSA and .ST files to disk – and for the odd disk I need to image. Definitly a valuable tool for your Atari ST!
- JaySoft website