- Selectable RAM upgrade, to to 32K
- Selectable Read only for RAM blocks 3 and 5
- Selectable ROM image, one of 8 - 8K ROM images only
- Externally accessible configuration and reset switches
- Selectable ROM image, one of 32 up to 16K ROM images
- Integrated IEEE-488 adapter
- Integrated IEEE-488 SD card disk drive (a version of PET microSD)
There is now a V2 board, with the additional option of 3K + 8K + 8K + 8K + 8K to give 35K which only seems to be used by the VIC20 port of DOOM. The V2 boards can also support up to 32 x 16K cartridges, see the article on the VIC20 Penultimate Cartridge V2 for more info.
On a slightly related note, the issues in GadgetUK164's video with Rockwell chips, I can't say I've had any problems. I've tested this on a VIC20 with a Rockwell R6522P, and they are fine, as expected. Also tested with the original CPU (a standard MOS 6502) and a Rockwell R6502P. I've used this to load Dig Dug from an SD2IEC into my Penultimate Cartridge, and that seems to run fine with no need for the diode mod. Maybe he had a duff chip, or a fault elsewhere on that particular VIC20.
Update: As requested, I've also checked the Rockwell R6522AP, which is just their version of the MOS 6522A, which is a faster speed graded version of the MOS 6522.