see Bank Switching
8K ROM
64 bytes RAM
The 2600's 4K cartridge address space is broken into four 1K segments. The desired arrangement of 1K banks is selected by accessing $30 - $3F of TIA address space. The banks are mapped into all 4 segments at once as follows:
$0030, $0038: 0,0,1,3
$0031, $0039: 0,1,2,3
$0032, $003A: 4,5,6,7
$0033, $003B: 7,4,2,3
$0034, $003C: 0,0,6,7
$0035, $003D: 0,1,7,6
$0036, $003E: 2,3,4,5
$0037, $003F: 6,0,5,1
The 64 bytes of RAM are accessible at $1000 - $103F (read port) and $1040 - $107F (write port). Because the RAM takes 128 bytes of address space, the range $1000 - $107F of segment 0 ROM will never be available.
Examples
"Wickstead Design" prototype cart.