This F.A.Q. covers some of the most commonly asked questions regarding the emulation of Neogeo systems.

If you have further questions please make use of our forums.

What is the Neo Geo?

The Neo Geo is a cartridge based video game computer designed and marketed by SNK and it’s successors from ca. 1989 until the present time.

What are MVS and AES?

MVS stands for Multiple Video game System. It is the version of Neo Geo hardware intended for use in arcades, and there are models that can hold 1, 2, 4, or 6 game cartridges at the same time, allowing arcades to use upto 6 games at a time in one cabinet.

AES stands for Advanced Entertainment system, and it refers to the Neo Geo console intended for home use. Although the cartridge format is different, it has the exact same video and sound hardware, and only lacks details such as the backup RAM and clock/calender.

Lastly, a version of Neo Geo hardware that can run games stored on CD was produced. This one does differ from the above in that the amount of memory (including video and sound memory) it has is smaller, but it still shares the same video and sound hardware otherwise. Neo Geo CD games have CD quality soundtrack stored on the CD as well.

What are the hardware specifications?

The basic specifications of all Neo Geo models are as follows:
Main CPU: MC68000 at 12MHz
Sound CPU: Z80 at 4MHz
Sound hardware: YM2610 at 8MHz, stereo sounds upto 56KHz
4 channels FM (4 operators + LFO) + 3 PSG + 1 noise + 7 4-bit ADPCM
Video hardware: resolution 320×224, 2 palette banks with 4096 (15-bit) colours each
Simple (4-bit) tile layer + 384 zoomable, linkable sprite-strips
sprite-strips consist of upto 32 16×16 (4-bit) tiles each

MVS and AES only:
Work RAM (main): 64KB
Work RAM (sound): 2KB
Video RAM: 128KB (only 68KB is used)
Main ROM: 128KB on-board (BIOS) + upto 8MB on cartridges
Sound ROM 128KB on-board (only less then 32KB used) + upto 512KB on cartridges
Sprite ROM: upto 64MB
Tile ROM: 128KB on-board + 128KB on cartridges
recent cartridges use a portion of sprite ROM that can be larger
Sound ROM: upto 16MB

MVS only:
Backup RAM: 64KB
Clock/calender: NEC uPD4990a

Neo Geo CD only:
Work RAM (main): 2MB
work RAM (sound): 64KB
Video RAM: 128KB (only 68KB is used)
Sprite RAM: 4MB
Tile RAM: 128KB
Sound RAM: 2MB
Main ROM: 512KB (BIOS)
CD-ROM drive: single-speed or (almost) double-speed, also used for game music

What controllers are used with Neo Geo games?

Most Neo Geo games work with joysticks, AES and CD systems have 2 controller ports and most MVS cabinets have 2 joysticks. Neo Geo joysticks have 4 buttons each. Some games can use alternative controllers:

- Mahjong games can use a special mahjong controller. It was cancelled early
on, although a number of them have been produced as an add-on for AES systems.
- The MVS version of Irritating Maze uses a trackball, and requires a special
BIOS to work. A dedicated cabinet that shot compressed air at you when you lost
a life was also produced.
- The MVS version of Pop’n Bounce can use either joysticks or paddles (you can
select which by setting the soft dips). I don’t know if a dedicated cabinet
or a conversion set with paddles was ever produced.
- There is a version of Kizuna Encounter that can use 4 joysticks. I don’t know
if it was ever released or if it never got past the prototype stage.

Some emulators supprt all of the above, some only support 2 joysticks, some are in between.

What is the memory card?

The memory card is a little device that has some battery-backed RAM, which Neo Geo games can store things such as settings, highscores, and save-games on. Even the most recent games can use it, and it can be used with MVS, AES, and CD units, although not all Neo Geo units have a card slot. You can simply insert the card into the slot when needed, it will be automatically formatted for you if needed.

The physical cards are actually a standard type, following the JEIDA v3.0 specification, the precursor of PCMCIA/PC-Cards (PCMCIA cards are reported to work as well).

Emulators can’t use real memory cards, and some emulators don’t emulate them at all.

What are raster effects?

As you probably know, a CRT draws the image on the screen scanline by scanline. Some graphics hardware will check the settings and video memory each scanline. With such hardware, the program can quickly change some settings while the CRT moves the electron beam into position to draw the next scanline. That’s what’s generally referred to with the term raster effects.

Where are raster effects used in Neo Geo games?

Some places to see how raster effects are used are:
- Art of Fighting (the AOF logo in attract mode)
- Eight Man (the 8 logo in attract mode)
- Galaxy Fight (the floor and other elements during gameplay)
- Karnov’s Revenge (the floor during gameplay)
- Neo Geo Cup ‘98 (the pitch during gameplay)
- Neo Turf masters (the perspective views during gameplay)
- Samurai Shodown 3 (the floor in all levels, when characters jump)
- Sengoku 2 (the Sengoku logo at the start of the attract mode sequence)
- Syougi no Tatsujin: Master of Syougi (the logo again)
- Super Sidekicks 2 (the pitch during gameplay)
- Super Sidekicks 3 (the pitch during gameplay)
- Riding Hero (the road during gameplay)
- Super Dodgeball (the fire during attract mode)
- The Ultimate Eleven (the pitch during gameplay)
- Viewpoint (the Sammy logo in attract mode)
- World Heroes (the floor in most levels during gameplay)
- World Heroes 2 (the floor in most levels during gameplay)
- World Heroes 2 Jet (the floor in most levels during gameplay)
- Zed Blade (the parallax scrolling during gameplay)

There are some other, sometimes less obvious places where they are used as well, e.g. Neo Driftout, Thrash Rally, and Top Players Golf use raster effects to align their zooming backgrounds.

No emulator can emulate raster effects on the Neo Geo perfectly, some emulators don’t emulate them at all.

What is the BIOS?

Because the Neo Geo is a cartridge based system, it is useful to have a program that works even when no cartridge is inserted (e.g. to test the hardware), to provide services needed by many cartridges (e.g. memory card access), and in an arcade environment, to handle tasks such as book-keeping. The Neo Geo BIOS is the program that does this.

Why so many files?

SNK used 3 different regional options, and each had it’s own BIOS program. Because MVS and AES hardware are different, they have seperate BIOS programs as well. Lastly, there are different revisions of each of those 6 different BIOS programs. In addition to the BIOS program, there is some graphics data, a sound test program that runs on the Z80, and a table used for sprite zooming.

There are also some special-purpose BIOS prgrams, such as the one used by The Irritating Maze, the Universe BIOS, and the debug-BIOS.

Why didn’t we need all those files before?

It turns out that most BIOS programs have most of the functionality for other versions built-in as well. Older emulators patched the BIOS program to be able to use it. Newer emulators simply use the correct BIOS programs for different setups. Some Older emulators also ignore the sound test program completely, and build their own table for sprite zooming.