The Sega Master System (first-generation “Model 1”, product code MK-2000) is an 8-bit home console released by Sega to compete directly with Nintendo’s Famicom/NES. Re-branded from the Japan-only Sega Mark III, the Master System introduced the distinctive black-and-red industrial design, a combo cartridge + “Sega Card” slot, and an edge expansion port supporting FM audio, 3-D glasses and future accessories. Although outsold by Nintendo in Japan & North America, it enjoyed major success across Europe, Brazil and Australasia, shipping an estimated ≈ 13 million units worldwide.
Sega Master System (Model 1)
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| First-generation «Master System» console (MK-2000, 1986) with cartridge & Sega Card slots |
| Specifications |
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| Manufacturer | Sega Enterprises, Ltd. |
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| Type | Home video-game console |
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| Released |
- JP (as Sega Mark III) – 20 Oct 1985
- NA – Jun 1986
- EU / Oceania – Sep 1987
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| Discontinued |
- JP – 1989 (replaced by Master System [JP])
- NA – 1991
- EU – 1996 (budget rerelease by Majesco)
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| Intro price | US$199 (NA launch bundle, 1986) |
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| CPU | Zilog Z80A @ 3 579 545 Hz (NTSC) / 3 546 895 Hz (PAL) |
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| Memory | 8 KB work-RAM • 16 KB video-RAM |
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| Storage | ROM cartridges (max 4 Mbit) • Sega Card (256 Kbit) • optional FM sound BIOS (Japan) |
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| Display | VDP 315-5124/5246 → 256 × 192 (nom.) / 32-colour on-screen from 64-colour palette |
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| Sound | SN76489-compatible PSG (3 square + 1 noise) • optional YM2413 FM add-on (JP) |
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| Dimensions | 365 mm W × 170 mm D × 66 mm H |
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| Weight | ≈ 2.1 kg |
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| OS / Firmware | None (8 KB BIOS v1.3 – menu + hidden Snail Maze) |
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| Predecessor | Sega SG-1000 II |
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| Successor | Sega Master System II |
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| Codename | Mark III |
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| Model no. | MK-2000 / MK-3000 |
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| Sub-system |
Specification (Master System Model 1)
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| CPU |
Z80A 8-bit @ 3.58 MHz (NTSC) / 3.55 MHz (PAL) • 16-bit address – 64 KB space
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| VDP |
Sega 315-5124 (NTSC) / 315-5246 (PAL)
TMS9918-derived: 2× pattern tables, 32 sprites (8 per scan-line)
VRAM 16 KB (dual 8 KB SRAM, 5 ns page registers)
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| Palette |
64 colours (6-bit RGB) – 32 on-screen (background & sprite)
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| Audio |
TI SN76489 PSG (integrated into VDP) – 3 square + 1 noise
Expansion pin-out for YM2413 FM (used in JP “FM Unit” & Mark III)
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| Main RAM |
2 × 8 KB HM6264 (work-RAM) @ ~150 ns
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| Cartridge ROM |
Up to 4 Mbit/512 KB (LoROM/HiROM mapper chips: Sega 315-5235, 315-5208, etc.)
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| BIOS |
8 KB mask ROM ver 1.3 (NA/EU) — intro menu + hidden Snail Maze (hold ↑+1+2)
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| I/O |
2× DE-9 game-pad, RF-UHF & 8-pin AV, Card slot (36-pin), 50-pin cart, 35-pin EXT
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Exact 64 KB CPU Memory-Map (Model 1)
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Z80 Address Space
| Range |
Size |
Purpose / Notes
|
| $0000 – $3FFF |
16 KB |
ROM–0 (Cartridge / Card / BIOS)
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| $4000 – $7FFF |
16 KB |
ROM–1 (bank-selectable via mapper)
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| $8000 – $BFFF |
16 KB |
ROM–2 (bank-selectable)
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| $C000 – $DFFF |
8 KB |
Work-RAM (on-board)
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| $E000 – $FFFF |
8 KB |
Mirror of $C000 – $DFFF
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Mapper registers are written through bogus addresses $FFFC–$FFFF (upper bits decoded by on-cart ASICs such as 315-5196).
BIOS Entry Points (v1.3)
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| Address |
Routine
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| $0000 |
Soft reset → Sega splash & checksum
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| $00A8 |
PSG mute / init
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| $0150 |
Card detect loop
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| $0200 |
Hidden game “Snail Maze” (activate ↑+1+2 at logo)
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| Parameter |
NTSC |
PAL
|
| Master clock |
10.738635 MHz |
10.644606 MHz
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| Pixel clock |
5.369 MHz |
5.322 MHz
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| Lines/frame |
262 |
313
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| Refresh |
59.92 Hz |
49.70 Hz
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Edge-Connector Pin-out
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50-pin Cartridge Bus (looking into console)
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| Pin |
Signal |
Description |
Pin |
Signal |
Description
|
| 1 |
GND |
Ground |
26 |
A11 |
Address 11
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| 2 |
+5 V |
+5 V DC |
27 |
A9 |
Address 9
|
| 3 |
CLOCK |
M-clock (5.37 MHz) |
28 |
A8
|
| 4 |
A15 |
Address 15 |
29 |
A13
|
| 5 |
A14 |
Address 14 |
30 |
A7
|
| 6 |
A12 |
Address 12 |
31 |
A6
|
| 7 |
/MREQ |
Z80 Memory Request |
32 |
A5
|
| 8 |
/IORQ |
I/O Request |
33 |
A4
|
| 9 |
/RD |
Read strobe |
34 |
A3
|
| 10 |
/WR |
Write strobe |
35 |
A2
|
| 11 |
D7 |
Data 7 |
36 |
A1
|
| 12 |
D6 |
Data 6 |
37 |
A0
|
| 13 |
D5 |
Data 5 |
38 |
CE (low)
|
| 14 |
D4 |
Data 4 |
39 |
+5 V
|
| 15 |
D3 |
Data 3 |
40 |
/BUSREQ (rarely used)
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| 16 |
D2 |
Data 2 |
41 |
PAUSE (pulled-up: cartridge can assert)
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| 17 |
D1 |
Data 1 |
42 |
/RESET
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| 18 |
D0 |
Data 0 |
43 |
AUDIO IN (FM/stereo mods)
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| 19 |
M1 |
Op-code fetch |
44 |
/NMI (3-D glasses)
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| 20 |
RFSH |
Refresh |
45 |
GND
|
| 21 |
/HALT |
CPU halt |
46 |
GND
|
| 22 |
A10 |
Address 10 |
47 |
+5 V
|
| 23 |
- |
(n/c) |
48 |
+5 V (cart power)
|
| 24 |
- |
(n/c) |
49 |
-
|
| 25 |
A16 |
Address 16 (mapper) |
50 |
-
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Historical Context & Sales
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- 1985 – Sega launches the Mark III in Japan; hardware overhaul of the SG-1000 line.
- 1986 – Re-packaged for North America as the “Sega System”, quickly re-branded Master System under Tonka; bundled with Hang-On/Safari Hunt combo cartridge.
- 1987–1992 – Becomes the dominant 8-bit console across Europe, distributed by Virgin Mastertronic; library balloons to 300+ PAL titles.
- Brazil – Tec Toy begins local production (1989) and continues updated revisions into the 2020s; > 8 million units sold in Brazil alone.
Global lifetime sales are estimated at ≈ 13 million (vs ~62 M NES).
Maintenance & Common Faults
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Board Revisions & Known Errata
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| Rev |
Region (year) |
Notes / quirks
|
| VA0 |
JP (1985) |
Mark III PCB – discrete VDP/PSG, no BIOS, external FM Unit
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| VA2 |
NA/EU (1986) |
First “Master System” – large RF can, 8 KB BIOS v1.3, 5 × 5 V regulators; early units prone to jail-bar video (unscreened VRAM lines)
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| VA3 |
EU (1987) |
Card slot EMI shield deleted, improved RF modulator
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| VA5 |
EU (1989) |
315-5246 PAL VDP, YM2413 traces removed; RGB DIN 8 output added
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| VA6 |
BR (1991) |
Tec Toy – onboard TMSS lockout stub, composite only (no RF)
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- ROM Cartridges up to 512 KB; larger titles employ paging ASICS (315-5208, 315-5235).
- Sega Card thin 35 g card, limited to 32 KB/256 Kbit – discontinued 1989.
- FM soundtrack detected via mapper bit 6; Western carts often contain unused FM data later unlocked by community patches.
Trivia & Pop-Culture
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- Hidden “Snail Maze” game embedded in BIOS v1.3 – launch by holding ↑ + 1 + 2 at the Sega logo.
- Original Japanese unit’s 3-D glasses used active shutter synced via the /NMI pin; later re-used on Mega Drive add-ons.
- The console appears in Charlie Brooker’s _Black Mirror_ episode “Bandersnatch” (retro game-dev setting).
- Tec Toy released Brazilian-exclusive ports: Street Fighter II, Mônica no Castelo do Dragão (Wonder Boy II reskin), sustaining the platform into the late 1990s.
- Sega Master System Service Manual (1986) – Part #420-5718-01
- Chris Covell, “SMS VDP documentation & palette research” (covell.ski)
- Charles MacDonald, “Master System Hardware Notes” (github.com/CharlesMacDonald)
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