For one, to put retro systems to great use. For another, to keep as much cruft/unnecessary bells & whistles from being present as possible. Just because the space is there doesn't mean it has to be used.
A "1.44 MB floppy" has that capacity for files when formatted with the FAT file system from MS-DOS. The unformatted capacity is actually closer to 2 MB but a proper file system has disk-space overhead for metadata and check sums.
You could have a file system with much less disk-space overhead than FAT, and there are many out there. A demo disk would typically be read-only, and in particular there are some read-only file-systems that are really space-optimised,
Another option would be to treat the disk sectors as a single compressed file which the bootloader decompresses into a RAM-disk image which the OS then boots from, but that would require a bit more than 2 MB of RAM.
It's not 2 mb in particular; honestly, I'd say 4 mb is the practical starting limit once you're into 16/32 bit CPUs — a Mac Plus / Classic would go to 4, for instance, and every speck of memory free under that made a difference in performance. 2 is a nice limit for total system size, as it allows for (as can be seen in QNX) a very capable, flexible OS, while leaving headroom for programs to run.
I restricted myself, I wanted to say 1MB.
I can't help but to find the min-max of everything. Well at least fantasize about what could be.
For one, to put retro systems to great use. For another, to keep as much cruft/unnecessary bells & whistles from being present as possible. Just because the space is there doesn't mean it has to be used.
What specific retro systems have a 2MB limit?
A "1.44 MB floppy" has that capacity for files when formatted with the FAT file system from MS-DOS. The unformatted capacity is actually closer to 2 MB but a proper file system has disk-space overhead for metadata and check sums.
You could have a file system with much less disk-space overhead than FAT, and there are many out there. A demo disk would typically be read-only, and in particular there are some read-only file-systems that are really space-optimised,
Another option would be to treat the disk sectors as a single compressed file which the bootloader decompresses into a RAM-disk image which the OS then boots from, but that would require a bit more than 2 MB of RAM.
2.88 for Extra High Density - pretty rare outside of Japan iirc.
http://209.68.14.80/ref/fdd/formatKB2880-c.html
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It's not 2 mb in particular; honestly, I'd say 4 mb is the practical starting limit once you're into 16/32 bit CPUs — a Mac Plus / Classic would go to 4, for instance, and every speck of memory free under that made a difference in performance. 2 is a nice limit for total system size, as it allows for (as can be seen in QNX) a very capable, flexible OS, while leaving headroom for programs to run.