Not only the BASIC programs you wrote (which do indeed live in VDP RAM). The BASIC interpreter itself was stored in GROM, which was read-only but had a similar

Not only the BASIC programs you wrote (which do indeed live in VDP RAM). The BASIC interpreter itself was stored in GROM, which was read-only but had a similar slow 8-bit interface with an address port and a data port on it, and written in GPL bytecode which was then interpreted by a GPL interpreter which lived in real ROM. If they'd written the BASIC interpreter in actual machine code and put it in ROM then your BASIC programs (and the interpreter's own volatile data) could still have lived in VDP RAM, but everything would have been rather faster... http://www.unige.ch/medecine/nouspikel/ti99/gpl.htm http://www.unige.ch/medecine/nouspikel/ti99/gpl.htm is a detailed description of what GPL looks like.