 Only one second processor could be connected at a time.The terminology of "second" processor was slightly misleading, since connected and switched on, the system worked on a "host-parasite" model, with the processor in the external unit taking control while the 6502 in the "main" computer simply took on responsibility for I/O.The 6502 Second Processor (using a 65C02) was clocked at 3 MHz, a full 50% faster than the 6502 inside a BBC Model B, and also had 64 KB of RAM, of which typically 30–44 KB was free for application data (compared to as little as 8½ KB on an unexpanded Model B in graphics mode, or even less with the disc interface).