Xerox Alto - Revision history

Jnc: /* External links */ trim URL

2025-04-22T17:48:40Z

‎External links: trim URL

Jnc: /* External links */ +one from Paul Allen's collection at the LCM

2025-04-22T11:50:28Z

‎External links: +one from Paul Allen's collection at the LCM

Jnc: /* External links */ Add a few

2024-11-18T00:48:53Z

‎External links: Add a few

Jnc: Explain how a micro-PC per priority level allowed zero-overhead switching between execution of different micro-tasks

2024-11-17T13:02:21Z

Explain how a micro-PC per priority level allowed zero-overhead switching between execution of different micro-tasks

Jnc: /* External links */ + Xerox PARC Alto filesystem archive links

2023-10-03T20:39:52Z

‎External links: + Xerox PARC Alto filesystem archive links

Jnc: /* External links */ + Two IEEE articles; one excellent

2023-10-03T19:41:58Z

‎External links: + Two IEEE articles; one excellent

Jnc: /* External links */ +A couple of columns about debugging a classic Alto

2023-06-01T14:51:57Z

‎External links: +A couple of columns about debugging a classic Alto

Larsbrinkhoff: Category: Xerox

2022-05-04T13:46:31Z

Category: Xerox

Jnc: link to later copy of Alto paper online, fix links

2021-12-09T13:33:32Z

link to later copy of Alto paper online, fix links

Jnc: /* External links */ +tfs.tty

2021-11-14T19:35:08Z

‎External links: +tfs.tty

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 * [https://spectrum.ieee.org/xerox-alto 50 Years Later, We're Still Living in the Xerox Alto's World] - an excellent history from the [[IEEE]]
 * [https://spectrum.ieee.org/the-xerox-alto-struts-its-stuff-on-its-40th-birthday The Xerox Alto Struts Its Stuff on Its 40th Birthday]
-* [https://www.christies.com/en/lot/lot-6495042?ldp_breadcrumb=back Xerox Alto II XM] - an Alto from [[Paul Allen]]'s collection at the [[Living Computer Museum|LCM]], includes several images
+* [https://www.christies.com/en/lot/lot-6495042 Xerox Alto II XM] - an Alto from [[Paul Allen]]'s collection at the [[Living Computer Museum|LCM]], includes several images
 * [https://www.newyorker.com/magazine/2011/05/16/creation-myth Creation Myth] - [[Steve Jobs]] meets the Alto

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-The '''Alto''', built by [[Xerox]]' [[Xerox PARC]] laboratory, was a ground-breaking and extremely influential [[personal computer]] - in fact, all contemporary personal computers are effectively descendants of the Alto.
+The '''Alto''', built by [[Xerox]]' [[Xerox PARC]] laboratory, was a ground-breaking and extremely influential [[personal computer]] - in fact, ''all'' contemporary personal computers are effectively descendants of the Alto.
 The Alto was novel, for its time, in that each machine had a [[bit-mapped display]], allowing the creation of a [[graphical user interface]], and was also attached to a high-speed [[local area network|LAN]], the then-new [[Ethernet]], also invented at PARC. In addition to the [[keyboard]], users could use a [[mouse]] to interact with applications.
@@ Line 43: / Line 43: @@
 * [https://spectrum.ieee.org/xerox-alto 50 Years Later, We're Still Living in the Xerox Alto's World] - an excellent history from the [[IEEE]]
 * [https://spectrum.ieee.org/the-xerox-alto-struts-its-stuff-on-its-40th-birthday The Xerox Alto Struts Its Stuff on Its 40th Birthday]
 * [https://www.newyorker.com/magazine/2011/05/16/creation-myth Creation Myth] - [[Steve Jobs]] meets the Alto

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 * [http://www.bitsavers.org/pdf/xerox/alto/ Hardware documentation] - also contains some high-level software documentation
 ** Charles P. Thacker, Edward M. McCreight, [http://www.bitsavers.org/pdf/xerox/alto/memos_1974/Alto_A_Personal_Computer_Dec74.pdf Alto - A Personal Computer System] December, 1974 - a [http://gordonbell.azurewebsites.net/Computer_Structures_Principles_and_Examples/csp0565.htm later version] was re-printed in ''Computer Structures: Principles and Examples'', second edition, editors Daniel P. Siewiorek, C. Gordon Bell and Allen Newell, McGraw-Hill, 1981, pp. 549-572
 ** [http://www.bitsavers.org/pdf/xerox/alto/memos_1979/A_Field_Guide_to_Alto-Land_Apr79.pdf A Field Guide to Alto-Land]
-** [http://www.bitsavers.org/pdf/xerox/alto/memos_1979/Alto_Hardware_Manual_May79.pdf Alto: A Personal Computer System Hardware Manual] May, 1979
+** [http://www.bitsavers.org/pdf/xerox/alto/Alto_Hardware_Manual_Aug76.pdf ALTO: A Personal Computer System Hardware Manual] August 1976
 ** [http://www.bitsavers.org/pdf/xerox/alto/ifs_trident/ IFS and the Trident disk controller]
 *** [http://www.bitsavers.org/pdf/xerox/alto/ifs_trident/TriconDoc.pdf Trident disk for the Alto]

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 The Alto was novel, for its time, in that each machine had a [[bit-mapped display]], allowing the creation of a [[graphical user interface]], and was also attached to a high-speed [[local area network|LAN]], the then-new [[Ethernet]], also invented at PARC. In addition to the [[keyboard]], users could use a [[mouse]] to interact with applications.
-Xerox attempted to commercialize the lessons of the Alto, in the [[Xerox Star]], but it was not a commercial success. Other companies, including [[International Business Machines|IBM]] ([[hardware]]), [[Microsoft]] ([[software]]) and [[Apple]] (both) did manage to produce succesful products along the lines pioneered by the Alto.
+Xerox attempted to commercialize the lessons of the Alto, in the [[Xerox Star]], but it was not a commercial success. Other companies, including [[International Business Machines|IBM]] ([[hardware]]), [[Microsoft]] ([[software]]) and [[Apple]] (both) did manage to produce successful products along the lines pioneered by the Alto.
 ==Details==
-The Alto's 16-bit-wide [[Central Processing Unit|CPU]] was [[microcode]]d (which resulted in it being called the machine's '[[microprocessor]]', although that term did not at the time have the meaning that it does now). As a result; it could emulate several different CPUs. It was built out of [[Transistor-transistor logic|TTL]], and the microprocessor's clock rate was 170 nsec. The CPU was implemented as 5 [[printed circuit board|PCBs]] which plugged into a common [[backplane]], along with four PCBs for [[main memory]] (in a 64KW [[address space]] of 16-bit [[word]]s), and those for [[device controller]]s such as the [[disk]], display, and Ethernet.
+The Alto's 16-bit-wide [[Central Processing Unit|CPU]] was [[microcode]]d (which resulted in it being called the machine's '[[microprocessor]]', although that term did not at the time have the meaning that it does now). As a result, it could emulate several different CPUs. It was built out of [[Transistor-transistor logic|TTL]], and the microprocessor's [[clock]] rate was 170 nsec. The CPU was implemented as 5 [[printed circuit board|PCBs]] which plugged into a common [[backplane]], along with four PCBs for [[main memory]] (in a 64KW [[address space]] of 16-bit [[word]]s), and those for [[device controller]]s such as the [[disk]], display, and Ethernet.
-There were two different versions, the Alto I and Alto II, which were almost identical; the latter was a re-engineered version of the former. The biggest difference was that the Alto II could have a maximum of 256 KW of memory, using [[bank switching]], compared to the 64KW of the Alto I (although in actuality, limited use was made of the extended memory). Data in the memory of an Alto I is protected with [[parity]]; the Alto II uses [[error-correcting code|ECC]], with 6 bits plus a parity bit per double-word. Also, all Altos had 1KW of [[Read-only memory|ROM]] microcode (microcode words were 32 bits wide), and eventually also 1KW of writeable [[Random Access Memory|RAM]] microcode memory. (The basic ROM microcode more or less emulated a [[Data General]] [[Nova]].) Some Alto IIs supported a second 1KW of PROM microcode; others had three 1KW banks of microcode RAM.
+The Alto provided several paths for [[input/output]]. For the highest speeds [[peripheral]]s, the CPU did not support [[Direct Memory Access|DMA]]; rather, such devices ([[disk]], display, LAN) connected to the CPU's main [[bus]]. The processor then had provision for up to 16 prioritized microcode [[task]]s, some of which were dedicated to particular devices, and did bulk I/O; a timer task handled others, such as the mouse. A [[Program Counter|PC]] per priority level allowed zero-overhead switching between [[execute|execution]] of [[microcode|microinstructions]] at different priority levels when the hardware called for another one to be active. ([[Emulator|Emulation]] of the Alto's native [[instruction set]] was assigned to the lowest priority level.)
-The Alto provided several paths for [[input/output]]. For the highest speeds [[peripheral]]s, the CPU did not support [[Direct Memory Access|DMA]]; rather, such devices ([[disk]], display, LAN) connected to the CPU's main [[bus]]. The processor had provision for up to 16 prioritized microcode [[task]]s, some of which were dedicated to particular devices, and did bulk I/O; a timer task handled others, such as the mouse. Slower devices (keyboard, etc) could be attached to the machine's memory bus, allowing their [[register]]s to appear in the memory address space, for access by [[programmed I/O]]; the last two 'pages' (nothing to do with [[virtual memory]], which the Alto did not support) of memory address space, 512 words, were dedicated to this. Finally, a [[parallel interface|parallel port]], connected to the CPU's memory control board, allowed miscellaneous slow devices (e.g. slow [[printer]]s) to be connected.
+Slower devices (keyboard, etc) could be attached to the machine's memory bus, allowing their [[register]]s to appear in the memory address space, for access by [[programmed I/O]]; the last two 'pages' (nothing to do with [[virtual memory]], which the Alto did not support) of memory address space, 512 words, were dedicated to this. Finally, a [[parallel interface|parallel port]], connected to the CPU's memory control board, allowed miscellaneous slow devices (e.g. slow [[printer]]s) to be connected.
 Altos all had a 1.25Mbyte cartridge [[disk]] [[drive]] from [[Diablo Systems]] (the same drive as in the [[RK02/03 disk drive|RK02 disk drive]]); the Alto-based Interim File System (IFS) [[file server]]s used [[Trident]] disk drives.
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 ==External links==
-* [https://xeroxalto.computerhistory.org/ Xerox PARC Alto filesystem archive]
+* [http://bwl-website.s3-website.us-east-2.amazonaws.com/38a-WhyAlto/Abstract.html Why Alto] - the famous Xerox internal memorandum by [[Butler Lampson]] that started the Alto ball rolling
 * [http://www.bitsavers.org/pdf/xerox/alto/ Hardware documentation] - also contains some high-level software documentation
 ** Charles P. Thacker, Edward M. McCreight, [http://www.bitsavers.org/pdf/xerox/alto/memos_1974/Alto_A_Personal_Computer_Dec74.pdf Alto - A Personal Computer System] December, 1974 - a [http://gordonbell.azurewebsites.net/Computer_Structures_Principles_and_Examples/csp0565.htm later version] was re-printed in ''Computer Structures: Principles and Examples'', second edition, editors Daniel P. Siewiorek, C. Gordon Bell and Allen Newell, McGraw-Hill, 1981, pp. 549-572
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 *** [http://www.bitsavers.org/pdf/xerox/alto/ifs_trident/TriconDoc.pdf Trident disk for the Alto]
 **** [https://xeroxalto.computerhistory.org/_cd8_/altodocs/tfs.tty!2 Software and Utilities for Trident Disks]
 * [https://spectrum.ieee.org/xerox-alto 50 Years Later, We're Still Living in the Xerox Alto's World] - an excellent history from the [[IEEE]]
 * [https://spectrum.ieee.org/the-xerox-alto-struts-its-stuff-on-its-40th-birthday The Xerox Alto Struts Its Stuff on Its 40th Birthday]
-* [http://www.righto.com/2016/06/y-combinators-xerox-alto-restoring.html Y Combinator's Xerox Alto: restoring the legendary 1970s GUI computer] - contains a good overview of the hardware
+* [https://www.newyorker.com/magazine/2011/05/16/creation-myth Creation Myth] - [[Steve Jobs]] meets the Alto
 **[http://www.righto.com/2018/03/a-1970s-disk-drive-that-wouldnt-seek.html A 1970s disk drive that wouldn't seek: getting our Xerox Alto running again]
 [[Category: Workstations]]
 [[Category: Xerox]]

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 ==External links==
-* [https://xeroxalto.computerhistory.org/xerox_alto_file_system_archive.html Xerox Alto file system archive]
+* [https://xeroxalto.computerhistory.org/ Xerox PARC Alto filesystem archive]
 * [http://www.bitsavers.org/pdf/xerox/alto/ Hardware documentation] - also contains some high-level software documentation
 ** Charles P. Thacker, Edward M. McCreight, [http://www.bitsavers.org/pdf/xerox/alto/memos_1974/Alto_A_Personal_Computer_Dec74.pdf Alto - A Personal Computer System] December, 1974 - a [http://gordonbell.azurewebsites.net/Computer_Structures_Principles_and_Examples/csp0565.htm later version] was re-printed in ''Computer Structures: Principles and Examples'', second edition, editors Daniel P. Siewiorek, C. Gordon Bell and Allen Newell, McGraw-Hill, 1981, pp. 549-572

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	[[Category: Workstations]]		[[Category: Workstations]]
		+	[[Category: Xerox]]