IBM Personal Computer XT/370

In October, 1983, IBM announced the IBM Personal Computer XT/370. This was an XT with three custom 8-bit cards. The processor card (370PC-P), contained two modified Motorola 68000 chips,and an 8087 modified to emulate the S/370 floating point instructions. The second card (370PC-M), which connected to the first with a unique card back connector contained 512Kib of memory. The third card (PC3277-EM), was a 3270 terminal emulator required to download system software from the host mainframe. The XT/370 computer booted into DOS, then ran the VM/PC Control Program. The card's memory space added additional system memory, so the first 256Kib (motherboard) memory could be used to move data to the 512kb expansion card. The expansion memory was dual ported, and provided an additional 384Kb to the XT Machine bringing the total ram on the XT side to 640 kb. The memory arbitrator could bank switch the second 128 kb bank on the card to other banks, allowing the XT 8088 processor to address all the RAM on the 370PC-M card.