<I said 'ROM' because on a number of machines, it was just a few TTL chips <that gated C3, lobyte, hibyte onto the data bus on the first 3 fetches <after reset. Most used a mux and jumpers to fake a 3byte rom with the first byte hardwired as C3h (jmp in 8080/8085/z80) and it was jammed on the bus for boot and only then. another approach was to on power up map rom to loc 000 and also F800h and then disable the mapping after the code was running up high. Plenty of tricks to fake that. Allison