IBM PALM processor

{{Short description|Heart component of IBM 51x0 early day luggable/portable}}

{{use mdy dates|date=July 2021}}

{{use American English|date=July 2021}}

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The PALM (Program All Logic in MicrocodeA Microprocessor-based portable computer: The IBM 5100, Proceedings of the IEEE ( Volume: 64, Issue: 6, June 1976)) is a 16-bit central processing unit (CPU) developed by IBM. It was used in the IBM 5100 Portable Computer, a predecessor of the IBM PC, and the IBM 5110 and IBM 5120 follow-on machines. It is likely PALM was also 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 CPU on an integrated circuit. The PALM processor was a circuit boardsalvaging a huge IBM 1130 APL program {{cite magazine |magazine=PC Magazine

|url=https://books.google.com/books?id=q8fwTt09_MEC&pg=RA5-PA9-IA1

|title=What is a Personal Computer?

|quote=not a chip but a single board .. an IBM 1130 emulator in PALM microcode

|date=November 1983}} containing 13 bipolar gate arrays packaged in square metal cans, 3 conventional transistor–transistor logic (TTL) ICs in dual in-line packages, and 1 round metal can part.

The PALM was used to implement an emulator, which in turn could run machine instructions originally written for other machines; this is how IBM System/360 APL ran on the 5100.{{cite web

|url=https://alt.folklore.computers.narkive.com/b3MlCvVT/john-titor-was-right-ibm-5100

|title=John Titor was right? IBM 5100

|quote=an emulator, used only for APL, not for BASIC}}

PALM has a 16-bit data bus, with two additional bits used for parity. PALM can directly address 64{{nbsp}}KB (64{{nbsp}}KiB) of memory. The IBM 5100 could be configured with up to 64+{{nbsp}}KB (APL + BASIC ROMs make 64+{{nbsp}}KB) of Executable ROS (ROM) and up to 64{{nbsp}}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 PALM processor with a Philips compact cassette drive, small CRT display, and full-function keyboard.[https://archive.org/details/IBM_PC_Compatibles_TOSEC_2012_04_23 TOSEC: IBM PC Compatibles (2012-04-23)] Internet Archive