Video RAM
In one sentence
Video RAM is 8 kilobytes inside the Game Boy, from address 8000 to 9FFF. It holds the tile pictures and the two background maps. It does not hold your ROM, and it does not hold a save.
The detail
The picture unit reads those 8 KB while it draws the screen. The CPU can write them safely in the border between frames, and it fights the picture unit if it writes in the middle of a line. Torn tiles are usually that fight, not a bad art file.
Eight kilobytes is small on purpose. Tile patterns take most of it, and two maps take the rest. A game cannot upload a 160 by 144 photograph every frame. It uploads tiles, then changes the map. Retroable backgrounds are built that way even when the prompt described a painting.
Sprite tiles share this same memory. Fill it with background tiles and the characters have nowhere to live. The ROM can be many banks larger than 8 KB. Only this slice is the picture.
Worth keeping
- Video RAM is 8 KB at 8000–9FFF
- It stores tile pictures and two background maps, not the program
- Writing it mid-frame tears the picture. The safe window is the border between frames
Questions
Is VRAM the cartridge?
No. The cartridge holds the ROM and maybe SRAM. VRAM is inside the handheld.
Why can't the game show a new photo every frame?
Because 8 KB cannot hold a fresh full-screen image, and the CPU would not finish copying it in one border.
What are the two maps?
Two background layouts. Games use them for a HUD, a status window, or a second scene.
Related
Game Boy is a trademark of Nintendo. Retroable is independent and is not affiliated with Nintendo.