If I expand my VIC's memory, will I be able to run programs written for the 64?
Only programs written in straightforward BASIC with few or no PEEKS, POKES, machine language routines, sound effects, or graphics can be used on the VIC (which eliminates about 95 percent of Commodore 64 programs). There are numerous differences between the VIC and 64 that go far beyond memory size. The 64 has a 40-column by 25-line screen format (versus the VIC's 22-column by 23line screen), the SID synthesizer chip (versus the VIC's tone generator), multicolor sprite graphics (not found on the VIC), and a different memory layout. The operating systems of the two computers also are not the same.
The same principles hold true for the new Commodore Plus/4 and 16. Neither of these computers is compatible with VIC and 64 software, except for very simple programs written in generic BASIC. However, the Plus/4 and 16 are generally compatible with each other, assuming the program is written to fit in the 16K RAM found in the Commodore 16.