View source for PPU nametables

== Nametables ==
<div style="float:right; margin-left: 1em">
      (0,0)     (256,0)     (511,0)
        +-----------+-----------+
        |           |           |
        |           |           |
        |   $2000   |   $2400   |
        |           |           |
        |           |           |
 (0,240)+-----------+-----------+(511,240)
        |           |           |
        |           |           |
        |   $2800   |   $2C00   |
        |           |           |
        |           |           |
        +-----------+-----------+
      (0,479)   (256,479)   (511,479)
</div>
The NES has four nametables, arranged in a 2x2 pattern. Each occupies a 1 KiB chunk of PPU address space, starting at $2000 at the top left, $2400 at the top right, $2800 at the bottom left, and $2C00 at the bottom right.
Each byte in the nametable controls one 8x8 pixel character cell, and each nametable has 30 rows of 32 tiles each, for 960 ($3C0) bytes; the rest is used by each nametable's attribute table.
With each tile being 8x8 pixels, this makes a total of 256x240 pixels in one map, the same size as one full screen.

But the NES system board itself has only 2 KiB of VRAM (called CIRAM), enough for two nametables; hardware on the cartridge controls address bit 10 of CIRAM to map one nametable on top of another.
* Vertical mirroring: $2000 equals $2800 and $2400 equals $2C00 (e.g. ''Super Mario Bros.'')
* Horizontal mirroring: $2000 equals $2400 and $2800 equals $2C00 (e.g. ''Kid Icarus'')
* One-screen mirroring: All nametables refer to the same memory at any given time, and the mapper directly manipulates CIRAM address bit 10 (e.g. many Rare games using [[AxROM]])
* Four-screen mirroring: CIRAM is disabled, and the cartridge contains additional VRAM used for all nametables (e.g. ''Gauntlet'', ''Rad Racer 2'')