Permanent Memory Systems produced a 6502 second processor, the B2P 6502, employing a 2 MHz 65C02 processor - as opposed to the faster 6502 device used by the Acorn 6502 Second Processor unit - together with 64 KB of RAM. Connecting to the Tube and 1 MHz bus connectors, the expansion did not use Acorn's Tube ULA and thus risked incompatibility with some software written for the Acorn unit, but the benefit of this approach was the B2P's more competitive price of around £100.