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Sega NAOMI

Sega arcade platform (1998), Dreamcast architecture with more memory. It runs in a candy cab via JVS (modern serial I/O), and comes in cartridge, GD-ROM (via DIMM board) and netboot forms. An often-misunderstood point: the DIMM board battery — not a "suicide" as brutal as the CPS-2's.

NAOMI PowerVR2 GPU
PowerVR2 (315-6201) GPU of the Sega NAOMI. Photo: Yaca2671, Wikimedia Commons, CC BY-SA 3.0.

Identification

Field Value
Manufacturer Sega
Year 1998 (NAOMI 2: 2000)
Base Dreamcast + more RAM (32/16/8 MB main/graphics/sound)
Media ROM cartridge, GD-ROM (via DIMM), netboot (NetDIMM)
I/O JVS (JAMMA Video Standard, serial)
Multiboard 3-4 boards per game

Architecture

Block Chip Clock Role
CPU Hitachi SH-4 ~200 MHz + FPU/vector unit
GPU NEC/VideoLogic PowerVR2 (CLX2) ~100 MHz Tile-Based Deferred Rendering
Sound ARM7 + Yamaha AICA 64 voices
RAM 32 MB main + 16 MB VRAM + 8 MB sound 2× the Dreamcast (hence "superior" ports)

NAOMI = New Arcade Operation Machine Idea. Architecture identical to the Dreamcast but with more RAM — hence near-perfect arcade↔home conversions (often superior on the arcade side). Region/language set at the BIOS.

Media & loading

  • ROM cartridge: the simplest, no critical battery.
  • GD-ROM: GD drive + DIMM board (RAM). At boot, the game is copied from the GD to the DIMM.
  • Netboot (NetDIMM): loads the game from a PC over the network → no GD or cartridge.

The DIMM board battery

The DIMM board has a battery that keeps the loaded game (+ its key) in RAM between power cycles — to avoid recopying the GD at every boot (several minutes).

  • Dead battery ≠ dead board: at the next boot, the game reloads from the GD (slow), or you switch to netboot.
  • It's therefore far less serious than a CPS-2/CPS-3 suicide (as long as you have the GD or netboot).

Netboot (NetDIMM) — step by step

Netboot is the NAOMI preservation route: you send the game image from a PC into the DIMM board's RAM over Ethernet — no GD or cartridge. Principle and steps:

  1. Required hardware: a network DIMM board (NetDIMM) (not all are — check for the Ethernet port), the NAOMI, a JVS I/O, and the appropriate security PIC (per-game key; community setups bypass this point).
  2. DIMM firmware: the DIMM must have a netboot-capable firmware (flash it once if needed).
  3. Network: connect PC ↔ NetDIMM over Ethernet (crossover cable or switch). Set the IPs in the NAOMI system menu (the DIMM shows "Network booting…" / waits for the transfer).
  4. Transfer: on the PC, a send tool (community scripts like triforcetools.py / naomi.py, or sending via emulators that talk to the NetDIMM) pushes the game image into the DIMM's RAM.
  5. Launch: once the transfer finishes, the NAOMI boots the game from RAM. Thanks to the DIMM battery, the game stays loaded between power cycles — no need to re-send each time.

Why it's the best route

Netboot removes the GD drive (the wear point) and doesn't depend on a rare cartridge. Combined with a fresh DIMM battery, it's a reliable, silent setup. → See also ODE (GDEMU/MODE, netboot). (We describe the method; no ROM hosting.)

JVS (I/O)

The NAOMI uses JVS: serial I/O that replaces the parallel JAMMA wiring (sticks, buttons, coins via a JVS I/O board). It's the standard for modern Sega cabinets; it can be driven/emulated (see JVS-adapter type projects).

Cabinets

  • Naomi Universal Cabinet (dedicated cabinet).
  • In a candy cab (Astro City & co.) via a JVS I/O board + suitable power.

NAOMI 2 (2000)

A high-end evolution of the NAOMI for heavy 3D: it adds a second SH-4 dedicated to geometry and two PowerVR2 graphics engines (+ an ELAN for transform/lighting), i.e. far more polygon power — while staying compatible with the NAOMI's cartridge/GD-ROM format and JVS I/O.

  • Games: Virtua Fighter 4 (+ Evolution/Final Tuned), Club Kart, Wild Riders, Virtua Striker 3, Beach Spikers, Soul Surfer…
  • Preservation: the same routes as the NAOMI (imaged GD-ROM, netboot, DIMM battery), handled by Flycast/Demul for emulation.
  • Not to be confused with the Hikaru (another contemporary high-end 3D, different hardware).

Common faults

Symptom Likely cause Lead
Game reloads at every boot / load time DIMM battery flat Replace the DIMM battery, or netboot
GD read errors Worn GD-ROM drive Repair/replace, or netboot (removes the GD)
No image / crash Power, caps, contacts Base diagnosis
I/O not responding JVS I/O board / wiring Check JVS, I/O power

Mods & preservation

  • Netboot (NetDIMM): the modern solution — no GD or critical battery; loads from a PC. → ODE (GDEMU/MODE, netboot)
  • GD-ROM emulation / SD storage (depending on solutions).
  • Replace the DIMM battery with a holder.
  • Emulation: Flycast / Demul (Dreamcast lineage) + MAME. No FPGA/MiSTer core (SH-4 + PowerVR2 out of budget).

Manual (archived)

Modernisation & mods

The common ground for every JAMMA board

Video, power, control panel and upscalers depend on the cabinet rather than the board: everything is centralised in Modernising a cabinet. To run the board outside a cabinet (at home, on a display): supergun.

  • Battery 🟢: a save battery is fitted (settings/counters/RTC). ⚠️ On this platform, a dead battery does NOT kill the game — it is a leaking battery that corrodes traces. Check and replace it before it leaks → save batteries.
  • Optical storage 🟡: the drive is the number-one wear part. Modern routes: an ODE, netboot, or replacement by flash storage depending on the platform → PCB preservation hub.
  • Scan rate 📺: ~32.83 kHz / 61.7 Hz — high resolution (VGA class), ⚠️ you need a 31 kHz / tri-sync monitor; a 15 kHz chassis is incompatible → tri-sync and upscalers. (Computed from the MAME sources — sega/naomi.cpp — pixel clock ÷ htotal.)
  • FPGA / emulation: see the Emulation & FPGA section below.

Repair (technician)

  • DIMM board (GD-ROM / NetDIMM): the game loaded into RAM is held by a battery → flat battery = full reload at every start-up (slow). Some cartridges carry a key/RTC battery → watch for suicide on encrypted games (backup batteries).
  • Per-game encryption (key on cartridge/DIMM): an unreadable game = the key, not the motherboard.
  • GD-ROM: drive/laser = a weak point → ODE mods (GDEMU).
  • Sound: ARM7 + AICA — diagnose the sound stage. Capacitors: recap.

→ Methods: PCB fault-finding · Recap · Backup batteries · Traces & vias

DIP settings ✅

2 games on this platform, settings extracted from the MAME sources (INPUT_PORTS_START blocks). The Position column gives the switch's physical reference on the board (SW2:!3,!4 = bank SW2, levers 3 and 4) — which is what lets you set it up without the paper manual. Games are sorted by MAME set name.

DIP settings — MAME set alpilota
Setting Position Options (default in bold)
Monitor SW1:1 31 kHz · 15 kHz
DIP settings — MAME set naomi_mie
Setting Position Options (default in bold)
Monitor SW1:1 31 kHz · 15 kHz

Check against your own board

These settings apply to the game and revision described by MAME. One title may have several DIP sets depending on region or revision, and some systems use soft-dips (settings in memory, via the test menu) rather than physical switches. In case of a discrepancy, the board's silkscreen and the test menu are authoritative.

See also: DIP reference · game manuals

Photos / assets

(To add: NAOMI board, DIMM board + battery, ROM cartridge, GD drive, JVS I/O.)

Sources & attribution

Image:

Review & corrections

How this space is used

Spotted a wrong value, an outdated procedure, a chip reference that does not match your board? Say so here, with what you observed (model, board revision, serial number, measurement). Every report is cross-checked against a source before anything changes — an unverifiable correction is published as “reported by …, not cross-checked” rather than silently applied.

Reading is open to everyone; posting requires signing in with Discord. Reports from the wiki's declared reviewers are handled first; anyone else's are read too, but go through a human before anything is changed.