Ah, I see. I use ZXSP too, and it has lots of good features including ZX81 support (obviously), but I don't think it actually saves ZX81 snapshots. It wouldn't reload your .z80 file, anyway. I'm afraid I'm not sure what ZX81 emulators on the Mac do support outputting .p and .tzx files; most of them only seem to support loading, not saving. At a guess, ZEsarUX probably does; it supports just about everything… it's just rather complex to use.