I think he meant 2 instead of 1, Schumi. ;p On some system, opcodes have parameters trailing behind their identifier, thus... length can vary depending on the opcode. The program counter needs to be incremented accordingly or otherwise, you'd start fetching weird stuffs.
Not that I know anything about Space Invaders at all... but I do know that that's almost the case with MIDI and Gameboy. Amen.
On another side note, Chip-8 opcodes have a fixed length of 2 bytes regardless... making it almost "too" easy to emulate...
(why so conveniently 2 bytes? lol)
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cChip interpreter WIP - current status: Release Candidate
LRx Filter RC - current performance rating: 9/10