One of the key differences from the GE 635 was the addition of "appending unit" (APU) which was used to implement a hybrid "Paged Segmentation" model of virtual memory. The APU was also used to implement a single-level store which is one of the fundamental abstraction that Multics is built around. The instruction format was also extended with the previously unused bit 29 controlling whether the operand address of an instruction used an 18-bit format (bit 29 = 0) or one that was made up of a 3-bit Base Register address with a 15-bit offset (bit 29 = 1).
One of the key differences from the GE 635 was the addition of "appending unit" (APU) which was used to implement a hybrid "Paged Segmentation" model of virtual memory. The APU was also used to implement a single-level store which is one of the fundamental abstraction that Multics is built around The instruction format was also extended with the previously unused bit 29 controlling whether the operand address of an instruction used an 18-bit format (bit 29 = 0) or one that was made up of a 3-bit Base Register address with a 15-bit offset (bit 29 = 1).