IBM PALM processor

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The IBM PALM processor (Put All Logic in Microcode) was a board-level 16-bit processor used in the IBM 5100 Portable Computer, a predecessor of the IBM PC. PALM was also used in the IBM 5110 and IBM 5120 followon machines. PALM was likely used in other IBM products as an embedded controller.

IBM referred to PALM as a microprocessor, though they used that term to mean a processor that executes microcode to implement a higher-level instruction set, rather than its conventional definition of a complete processor on a single silicon integrated circuit. The PALM processor was an entire circuit board containing 13 square metal-can bipolar gate arrays, 3 conventional DIP transistor-transistor logic (TTL) parts and 1 round metal can part.

PALM has a 16-bit data bus, with an additional two bits used for parity. PALM can directly address 64 Kbytes of memory. The IBM 5100 could be configured with up to 32 Kbytes of Executable ROS (ROM) and up to 64 Kbytes of RAM, so a simple bank switching scheme was used to extend the address space.