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Electronika MS-1502 (transliterated name), 'mc1502' driver.

Not quite a PC XT, not quite a PCjr -- designed to be cheap like the latter, but has none of its extensions (no fancy sound or 16-color mode).

What's it like:

- Has single 16 MHz crystal, thus the CPU and timer clocks are higher (5.33 and 1.33 MHz).
- No DMA.
- No keyboard controller, key matrix is connected to second i8255.
- Base system has 128K memory on board (96K available to the user); with the expansion installed, user memory is 608K, not 640K.
- CGA implementation has more video memory (32K), which is shared with system memory; there is space for 4 fonts in the chargen ROM, but only one is present (at 0).
- Has two cartridge slots for expansion. There are at least three (extra 512 KB of memory, a BASIC ROM and a FDC).

These are incompatible on the low level, but have compatible BIOS interfaces:
- FDC -- uses a FD1793.
- Serial port -- uses a i8251.
- Parallel port.
- Cassette interface.

Software: SF-DOS ('Sigma Four', a MS-DOS clone); OTS ('One Track System', an OS for 128KB systems). Base system shipped software on cassettes.

Pictures and manuals: http://comp.disneyjazz.net/index.html?action=w_podrazdela&id_soderjanie=74

MESS screenshot (with my fixes; will send them to Micko):