From Sega Retro
The CD BackUp RAM Cart is a memory card designed for the Mega CD that plugs into the Mega Drive cartridge port. For the North American version, the cart resembles a regular Genesis cartridge, aside from a blue edging saying "Sega CD", as opposed to the usual red edging found on standard Genesis cartridges. The unit contains 2045 blocks (1 Mbit) of memory for game saves. Some RPGs - most notably Shining Force CD - used this for memory, as there was often not enough space for the save files in the internal backup RAM. In the case of Shining Force CD, this cartridge allows the player to unlock the last story segment of the game, inaccessible without the backup cart due to the Sega CD's internal memory limitations.
Maximum Capacity
While the only officially-released RAM cartridge for the Sega CD has a capacity of 1 Mbit (128 KB; 2045 blocks), the system actually supports up to 4 Mbit (512 KB; 8189 blocks). The memory size is specified by a 3-bit value mapped to Main 68000 address $400001. This value indicates the memory size as a power of two, multiplied by the base memory size of 8 KB.
Memory Size
3-bit Value
@ $400001
|
Size (Kbit)
|
Size (KB)
|
| 000
|
64 Kbit
|
8 KB
|
| 001
|
128 Kbit
|
16 KB
|
| 010
|
256 Kbit
|
32 KB
|
| 011
|
512 Kbit
|
64 KB
|
| 100
|
1024 Kbit
|
128 KB
|
| 101
|
2048 Kbit
|
256 KB
|
| 110
|
4096 Kbit
|
512 KB
|
| 111
|
not present
|
Manuals
Physical Scans
| Mega CD, US
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Cover
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