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IBM PALM processor

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Title: IBM PALM processor  
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Subject: Timeline of portable computers, IBM Personal Computer, Personal computer, History of personal computers
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IBM PALM processor

The IBM PALM processor (Program 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.

External links

Pictures
  • 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.
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