IBM PALM processor
The IBM PALM processor (Put All Logic in Microcode) is a board-level 16-bit central processing unit used in the IBM 5100 Portable Computer, a predecessor of the IBM PC. PALM was also used in the IBM 5110 and IBM 5120 follow-on 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 two additional bits used for parity. PALM can directly address 64 kB (64 KiB) of memory. The IBM 5100 could be configured with up to 64+ kB (APL + BASIC ROMs make 64+ kB) of Executable ROS (ROM) and up to 64 kB of RAM. A simple bank switching scheme was used to extend the address space.
In 1973 the IBM Los Gatos Scientific Center developed a portable computer prototype called SCAMP (Special Computer APL Machine Portable) based on the IBM PALM processor with a Philips compact cassette drive, small CRT and full function keyboard.
- TOSEC: IBM PC Compatibles (2012-04-23) Internet Archive
- Daves Old Computers, This page has a link with a picture of the IBM PALM circuit board as well as many photos of the IBM 5100. The Maintenance Information Manual linked at the bottom of the page includes an appendix describing the microcode.