Superficially it looked quite different to the BBC Model B/B+, featuring a Numeric Keypad in an attempt to look more professional like it’s PC compatible opposition.
The BBC Master 128 as the name suggests supported twice the RAM of the BBC Model B+, a grand total of 128k. It still ran BBC Basic, and the vast majority of applications found for the Master grew out of it’s Model B Heritage. It also featured a ROM Cartridge Slot just above the Numeric Keypad, which made it easier to fit and remove ROM Modules which were generally internal on the older machines.
The one exception I know of is the SCSI additions provided to support the BBC Doomsday Project