The ps2 memory card was 8MB by default, with some bigger third party ones. ps1 was ~120KB (reported in "blocks") Never thought buying a psp memory stick was worth it, since micro SD adapters existed and were orders of magnitude cheaper.

Sadly, when the vita came around, the only way to use an SD was to hack it and use an adapter in the game port. Since the vita card format was smaller than a micro SD.