8k 2600?

[OldAtarian]

Has anyone tried this yet? I know the 6507 can address 8k of RAM, but has anyone actually tried upgrading a 2600 with that much memory? You could probably write some pretty decent games in 8k.

[eshu]

Has anyone tried this yet? I know the 6507 can address 8k of RAM, but has anyone actually tried upgrading a 2600 with that much memory? You could probably write some pretty decent games in 8k.

 

The 2600 can address an 8k address space - 4k of which is taken by the cartridge, and the rest is mostly mapped to the TIA and RIOT chips etc, there is a lot of mirroring going on. If a some of the mirros were removed it might be possible to map some of the space made to extra RAM, but then lot's of existing games wouldn't work.

[A.J. Franzman]

I know the 6507 can address 8k of RAM, but has anyone actually tried upgrading a 2600 with that much memory? You could probably write some pretty decent games in 8k.

You seem to be confused about RAM and ROM. The 6507 can directly address 8K (full stop). The CPU doesn't know what's RAM or what's ROM when reading it. By design, 4K of the VCS's addressable volume is in the cartridge space. However, in order to write to RAM, a write signal line is usually needed, which the VCS only provides to its internal IC's. So, originally cartridges only contained 2K or 4K of ROM. Later, different companies came up with several methods by which to include RAM in the cartridge space (and be able to write to it). Also, several variations of a technique known as "bankswitching" were developed, which allowed expansion of the cartridge space by several times the original limit. Single-game cartridges released during the original run of the 2600 were up to 32K in size (Fatal Run), and a rare mini clone unit called the Megaboy had an educational cartridge that was 64K. I think there is at least one modern bankswitching method which allows for up to 512K, but I believe the only thing written in that size has been a "Dancing Babies" demo by Andrew Davie.

 

For a more detailed description of bankswitching, consult 'the Bible', sizes.txt written by Kevin Horton, which also includes a list of the sizes of the cartridge space for many games.

Edited October 6, 2010 by A.J. Franzman