Editing 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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| name           = IBM PALM processor
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The '''PALM''' ('''Program All Logic in Microcode'''<ref>A Microprocessor-based portable computer: The IBM 5100, Proceedings of the IEEE ( Volume: 64, Issue: 6, June 1976)</ref>) is a 16-bit [[central processing unit]] (CPU) developed by IBM. It was used in the [[IBM 5100|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 board<ref name=PALM.APL1130Board>salvaging 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}}</ref> containing 13 [[Bipolar junction transistor|bipolar]] [[gate array]]s [[Semiconductor package|packaged]] in square metal cans, 3 conventional [[transistor–transistor logic]] (TTL) ICs in [[dual in-line package]]s, 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 (programming language)|APL]] ran on the ''5100''.<ref>{{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}}</ref>

PALM has a 16-[[bit]] data bus, with two additional bits used for [[parity bit|parity]].  PALM can directly address 64{{nbsp}}KB (64{{nbsp}}[[kibibyte|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'' ([[read-only memory|ROM]]) and up to 64{{nbsp}}KB of [[random-access memory|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 [[Portable_computer#SCAMP|SCAMP]] (Special Computer APL Machine Portable) based on the PALM processor with a Philips compact cassette drive, small CRT display, and full-function keyboard.<ref>[https://archive.org/details/IBM_PC_Compatibles_TOSEC_2012_04_23 TOSEC: IBM PC Compatibles (2012-04-23)] Internet Archive</ref>

==References==
{{reflist}}

==External links==
* [https://news.ycombinator.com/item?id=14483823 about various Microcode implementations]


;Pictures
*[https://web.archive.org/web/20191129005737/http://www.classiccmp.org/dunfield/ibm5100/index.htm 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.

[[Category:IBM personal computers|PALM]]
[[Category:IBM microprocessors]]