[rasz]

Apparently IBM XT also had a way of being bootstrapped with no drives attached

https://hackaday.com/2011/10/03/resurrecting-an-xt/

    ;————————————————————————
    ; LOAD A BLOCK OF TEST CODE THROUGH THE KEYBOARD PORT :
    ; FOR MANUFACTURING TEST. :
    ; THIS ROUTINE WILL LOAD A TEST (MAX LENGTH=FAFFH) THROUGH :
    ; THE KEYBOARD PORT. CODE WILL BE LOADED AT LOCATION :
    ; 0000:0500. AFTER LOADING, CONTROL WILL BE TRANSFERRED :
    ; TO LOCATION 0000:0500. STACK WILL BE LOCATED JUST BELOW :
    ; THE TEST CODE. THIS ROUTINE ASSUMES THAT THE FIRST 2 :
    ; BYTES TRANSFERRED CONTAIN THE COUNT OF BYTES TO BE LOADED :
    ; (BYTE 1=COUNT LOW, BYTE 2=COUNT HI.) :
    ;————————————————————————

[the_only_law]

Interesting. I had a 5155 (XT luggable) with drives but no disks. I debated writing a machine code bootstrapping program (POKE’d in through the ROM basic) to boot over the serial port.

I sold it before I got the chance. It’s a neat machine, but not my particular niche in the retro realm.

[rvalles]

I had never heard about this one. Neat.

re: Amiga, it is sad that, with 256KB of ROM, they couldn't fit a key combination to call exec's Debug() in the strap module.

I understand that, somehow, nobody thought about it.