MSX

What is MSX?

MSX was a standardized home computer platform co-conceived by Kazuhiko Nishi of ASCII Corporation and Microsoft Japan, announced in June 1983. The goal was ambitious: create an open standard that any manufacturer could license, ensuring software and hardware compatibility across all MSX machines—a vision that predated the IBM PC clone era and deeply influenced how the industry thought about interoperability.

Unlike proprietary systems such as the Commodore 64 or ZX Spectrum, MSX defined a minimum hardware specification. A program written for one MSX machine would run on any other, regardless of the manufacturer. This led to over 5 million units sold globally and adoption by more than 50 manufacturers across Japan, Europe, Latin America, and the Middle East.

System Architecture

The MSX standard defined a precise hardware architecture that every compliant machine had to implement. This was not a suggestion—it was a contract between manufacturers and the software ecosystem.

Memory Map & Slot System

The most distinctive architectural feature of MSX is its slot system. The Z80's 64 KB address space is divided into four 16 KB pages (Page 0–3), each of which can be mapped to one of up to four primary slots. Each primary slot can optionally be expanded into four sub-slots, giving a theoretical maximum of 16 addressable memory regions.

I/O Port Map

Minimum MSX 1 Specifications

CPU — Zilog Z80

Every MSX generation through MSX 2+ used the Zilog Z80A running at 3.579545 MHz (derived from the NTSC color subcarrier frequency). This was a deliberate choice: a well-documented, widely supported 8-bit processor with a rich instruction set and large developer community.

MSX turbo R — R800 CPU

The turbo R introduced ASCII Corporation's R800 processor—a 16-bit internal architecture CPU maintaining full Z80 instruction-set compatibility, but executing code 2–7× faster depending on memory access patterns. It featured a hardware multiplier and ran at 7.16 MHz effective throughput.

The turbo R could switch between R800 and Z80 modes under software control, allowing compatibility with games that relied on Z80 timing for sound or gameplay.

Video — VDP Chips

TMS9918A — MSX 1

Texas Instruments' TMS9918A (or compatible clone) powered MSX 1 machines. It operated independently of the main Z80, handling all display generation autonomously. Communication was done via two I/O ports: one for data, one for register/address control.

Sprites on the TMS9918A are 8×8 or 16×16 pixels, with magnification. A limit of 32 sprites total and 4 sprites per scanline applied.

V9938 — MSX 2

Yamaha's V9938 was a quantum leap forward. It added 128 KB VRAM (expandable to 192 KB), hardware scroll, bitmap modes, and line-based interrupts.

The V9938 also introduced hardware commands: LMMC, LMMM, HMMM, LINE, PSET, SRCH—allowing fast block copies, line drawing, and search operations offloaded from the Z80.

V9958 — MSX 2+ & turbo R

The V9958 extended the V9938 with two critical additions: YJK color encoding (enabling up to 19,268 simultaneous colors on screen) and a hardware horizontal scroll register. Screen modes 10, 11, and 12 were added.

Sound — Audio Evolution

AY-3-8910 PSG — All MSX Generations

The General Instrument AY-3-8910 (or compatible: YM2149, T7766A) provided the baseline audio for every MSX machine. Beyond sound, it doubled as a peripheral controller, hosting two 8-bit I/O ports used for joystick reading.

Y8950 MSX-AUDIO

The Yamaha Y8950 (MSX-AUDIO) brought FM synthesis to MSX via the OPL (FM Operator Type-L) core, plus a built-in ADPCM sample playback channel with 32 KB sample RAM. Found in the Panasonic FS-CA1 and MSX Music Modules.

YM2413 MSX-MUSIC (OPLL)

The simplified YM2413 OPLL was included on MSX 2+ machines (built-in) and available as an expansion for MSX 2. It offered 9 FM channels using 15 preset instrument patches plus one user-definable patch, or alternatively 6 FM channels + 5 rhythm channels.

YMF278B — OPL4 (MSX turbo R era)

The premium Moonsound expansion card brought the YMF278B (OPL4), combining 24 FM channels with a wave table synthesizer capable of 24 simultaneous PCM samples from a 512 KB (expandable to 4 MB) ROM/RAM bank. It became the pinnacle of MSX audio.

Konami SCC — Wave Table Cartridge

Konami's proprietary SCC (Sound Creative Chip) and later SCC+ chips were embedded in game cartridges. Each channel had a 32-byte user-defined waveform table, enabling realistic instrument sounds far beyond the PSG. Used in titles like Gradius 2, Snatcher, and Space Manbow.

MSX Generations

Notable MSX Computers

Peripherals & Expansions

Storage

Display Output

Joystick & Input

MSX defined a standard DB-9 joystick port (two ports on every machine, via the AY-3-8910's I/O ports). Up to 8 directions + 2 fire buttons. Compatible with Atari-style joysticks. Some machines included a trackball, mouse, or touchpad. The MSX mouse used quadrature encoding on the joystick port.

Memory Expansion

Memory expansion cartridges allowed MSX 1 machines to reach 64–512 KB RAM through the slot system. MSX 2 machines commonly had memory mappers allowing up to 4 MB of addressable memory through bank switching via port FCh–FFh.

Printers

A Centronics-compatible parallel printer port was available on most MSX machines. MSX BASIC supported LPRINT and LLIST for printer output. Epson-compatible dot matrix printers were most commonly used.

Network & Communications

MSX-Engine ICs

Later MSX designs integrated multiple chips into single ICs. Yamaha's S1985 (MSX-Engine) combined the PPI (8255), clock generator, and I/O management into one chip, reducing PCB complexity and cost. The T7775 further consolidated audio support.

MSX BASIC

MSX BASIC was developed by Microsoft (hence the Microsoft branding on early boot screens) and stored in 16–32 KB ROM. It was one of the most capable BASICs available on any 8-bit home computer, with direct access to all hardware features through reserved keywords and commands.

BASIC Versions

Core Commands Reference

Screen & Graphics

10 REM MSX BASIC Graphics Demo
20 SCREEN 2           ' 256x192, 16 colors
30 COLOR 15,1,1      ' FG=white, BG=black, BORDER=black
40 LINE (0,0)-(255,191),9,BF  ' filled box
50 CIRCLE (128,96),60,12    ' circle at center
60 PAINT (128,96),4,12     ' flood fill
70 PSET (100,80),15       ' plot single pixel

Sound & Music

10 BEEP                    ' system beep
20 PLAY "CDE FGA BC"        ' music macro language (MML)
30 PLAY "T120 L8 CDEFGAB>C" ' T=tempo, L=note length
40 ' Three-voice simultaneous play:
50 PLAY "CEG","EGC","GCE"  ' voices A, B, C

Sprites

10 SCREEN 2
20 SPRITE$(0)=CHR$(&HFF)&CHR$(&HFF)&CHR$(&H00)&CHR$(&H00)  ' 8-byte pattern
30 PUT SPRITE 0,(100,80),15,0   ' sprite#, (x,y), color, pattern
40 ON SPRITE GOSUB 1000        ' collision interrupt handler
50 SPRITE ON

File I/O (Disk BASIC)

10 OPEN "DATA.TXT" FOR OUTPUT AS #1
20 PRINT #1, "Hello MSX!"
30 CLOSE #1
40 OPEN "DATA.TXT" FOR INPUT AS #2
50 INPUT #2, A$
60 PRINT A$
70 CLOSE #2

Hardware Register Access

10 ' Read/write VDP registers directly
20 VDP(1) = &HE0            ' VDP register 1: sprites on, 16KB VRAM
30 PRINT VDP(0)            ' Read VDP status register

40 ' Direct I/O port access
50 OUT &HA0, 7            ' Select PSG register 7
60 OUT &HA1, &HB8         ' All tones on, noise off
70 X = INP(&HA2)          ' Read PSG register value

MSX BASIC — Key Statements

MSX-DOS

MSX-DOS was an MSX-specific operating system closely modeled on CP/M-80 and partially compatible with MS-DOS (FAT12 disk format). MSX-DOS 2 (for MSX 2+) added subdirectories, environment variables, and extended memory management. Accessed via the CALL SYSTEM BASIC command or by booting with a disk containing MSXDOS.SYS and COMMAND.COM.

Legacy & Modern MSX

MSX left a profound mark on the gaming and computing industries. Hideo Kojima created Metal Gear on MSX2, and the platform was home to groundbreaking titles from Konami, ASCII, and HAL Laboratory. The MSX sound chip conventions influenced composers who later worked on Super Nintendo and PlayStation titles.

Today, MSX remains remarkably alive: