The CPU in the VMU (dubbed, "the potato") is a customized Sanyo microcontroller which is code compatible with the LC86000 series.
The VMU flash memory contains 128 kilobytes of storage. These are divided into 256 blocks of 512 bytes each. Of these blocks, 200 are available for user files.
The rest of the blocks contain filesystem information, or are simply not used at all.
As i experiment with the device's firmware, CPU, and LCD frame buffer i am slowly progressing towards writing "snake" for the device.
Many thanks to Marcus Comstedt