Well, if I remember, AppleII never booted from floppy. The whole OS was there on chip. But it used the floppy for other, non-boot, process.
The first “real” pc virus was Brain, an advertising stunt from a Pakistani.
I don’t know, every Apple II that I ever used booted from floppy and had no hard disk unless you connected an external one.
Apple II ProDos was loaded from a “system disk.” The actual boot loader was burned into ROM but all it did was direct the primary disk drive head to Track 0 Sector 0 and start a load there, then JMP to the load-point address.
If I remember my Apple II internals ...