Ghost disks were also introduced before in this forum section.
Some original games saved scores on the disk. Some games saved the progress. Ghost disks allow you to keep changed sectors of a normally read-only disk image (STX, IPF...) in an apart file, thereby leaving the "original" intact.
A new option has been added in Steem to that effect.
When it's checked, and a pasti or caps disk image is trying to write a sector, a new file with the same name and extension, ending with ".STG" will be created to store this sector in an efficient way (compact file).
Notice that the extension is "STG", not "STW". STW is something else.
When later you open the same disk image, this new file will be opened as well, and when the same sectors are read by the game, the sectors of the ghost disk will be used instead of those of the STX or IPF/CTR image.
My motorcycle exploits saved forever.
One day I'm gonna beat this dude!
You can say who's playing by the score.
The table is still there one day later. Notice that to use the pasti version, you need the manual, or the Steem patch (provided with v3.7).
Platoon (US, TOS100US) is a more intricate case. The game first formats the track then uses the "write multiple sectors" command where the sectors are 1024 bytes, and the DMA sector counter is too high.
It turns out however that we don't need to emulate all this to be able just to save the score. Only the multiple version of read/write sector (WD1772 commands $90, $B0) really must be handled. We do as if the sectors were regular (512 bytes), and it's fine for the game.
Maybe when Steem v3.7 is released we'll get more reports of difficulties.
The system we use is a hack anyway (intercepting commands). Ideally writing to disks should be managed by plugins in charge of the images.
In the case of Caps, maybe it will come one day. In the case of Pasti, the probability is smaller, as the author hasn't come here for a long time now. The advantage of STG files is that they work with both Pasti and Caps without duplication.
edit 1, 2: updated