IS-DOS

iS-DOS is a disk operating system (DOS) for Russian ZX Spectrum clones. iS-DOS was developed in 1990 or 1991, by Iskra Soft, in Leningrad, Soviet Union, now Saint Petersburg, Russia.
It handles floppy disks (double sided, double density), hard disk drivess, and CD-ROMs. Maximum iS-DOS partition size on a hard disk is 16 MiB.
Unlike TR-DOS, iS-DOS is random-access memory (RAM) based. Such operating systems reduce the amount of memory available for user programs.
Versions.
"iS-DOS Chic" is a version developed for Nemo KAY. It provides more memory for user programs.
"TASiS", based on iS-DOS Chic, is a modern version developed by NedoPC for ATM Turbo 2+ in 2006. It supports text mode and high memory of that machine.