The standard Master 128 was a 65C102, compared to the BBC B's 6502A.
It also had 64K of "sideways" RAM into which you could install sideways ROM "images" as well as plug ROMs into both the mainboard on the inside or via the two catridge slots.
It also had 20K of "shadow" RAM which alleviated a lot of the issues the BBC B had with the higher resolution modes leaving very little user RAM. The remaining 12K of "extra" RAM was used as private workspace for the MOS (Machine Operating System) and the sideways ROMS.
It had an internal TUBE slot for internal co-processors (mine here at home is the Master 512 which is a Master 128 with internal 80C186 co-processor running DOS+) as well as a (little used) modem connector.
Built in floppy disc interface (using the WD1770/1772) complete with DFS and ADFS. All of those were extras on the BBC B, which also ate up precious user RAM, and the "standard" disc interface used the Intel 8271 which couldn't do ADFS.
Finally it had a CMOS RAM for maintaining the various configuration settings. Oh it also had various bits of software built into the system ROM (as sideways ROMS) including the View word processor and ViewSheet speadsheet.
So all in all a VERY "suped up" Beeb.