Manchester Baby - Revision history

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	The Baby had 32-bit [[word]]s, with a main memory of only 32 words. Two more Williams tubes held the [[accumulator]] ('A') in one, and the [[Program Counter\|program counter]] ('CI') and the [[Instruction Register\|instruction register]] ('PI') in the other. Its [[arithmetic logic unit\|ALU]] was [[serial]], and used [[two's complement]].		The Baby had 32-bit [[word]]s, with a main memory of only 32 words. Two more Williams tubes held the [[accumulator]] ('A') in one, and the [[Program Counter\|program counter]] ('CI') and the [[Instruction Register\|instruction register]] ('PI') in the other. Its [[arithmetic logic unit\|ALU]] was [[serial]], and used [[two's complement]].

	[[Instruction]]s included a 3-bit [[operation code]], and a 13-bit memory [[address]] (the other 16 bits were unused. It had only 7 instructions:		[[Instruction]]s included a 3-bit [[operation code]], and a 13-bit memory [[address]] (the other 16 bits were unused). It had only 7 instructions:

	{\| class="wikitable"		{\| class="wikitable"

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Further reading: +Lavington, ''Early Computing in Britain"

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	The '''Manchester Baby''' (formal name '''Small-Scale Experimental Machine''', sometimes abbreviated to '''SSEM''') was a very early experimental computer, built at the University of Manchester. Exactly like the [[Memory Test Computer]], it was not really intended for computational use; rather, its primary intended purpose was to test out a new form of [[main memory]], the [[Williams tube]].		The '''Manchester Baby''' (formal name '''Small-Scale Experimental Machine''', sometimes abbreviated to '''SSEM''') was a very early experimental computer, built at the University of Manchester. Exactly like the [[Memory Test Computer]], it was not really intended for computational use; rather, its primary intended purpose was to test out a new form of [[main memory]], in this case the [[Williams tube]].

	It was constructed out of [[vacuum tube]]s, starting early in 1948; starting later that year, it was re-built into the [[Manchester Mark I]].		It was constructed out of [[vacuum tube]]s, starting early in 1948; starting later that year, it was re-built into the [[Manchester Mark I]].
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	==Further reading==		==Further reading==

			* Simon H. Lavington, ''Early Computing in Britain: Ferranti Ltd. and Government Funding, 1948-1958'', Springer Nature, Cham, 2019 - the background to the creation of the Baby is covered in appendix A
	* Simon H. Lavington, ''A History of Manchester Computers'', National Computer Centre, Manchester, 1976		* Simon H. Lavington, ''A History of Manchester Computers'', National Computer Centre, Manchester, 1976
	* Simon H. Lavington, ''Early British Computers'', Manchester University, Manchester, 1980		* Simon H. Lavington, ''Early British Computers'', Manchester University, Manchester, 1980
	* Raúl Rojas, Ulf Hashagen (editors), ''The First Computers ~~—~~ History and Architectures'', MIT Press, Cambridge, 2000 - the Baby is covered in Part IV-2, pp. 365-377; the re-build is covered in Part IV-3, pp. 379-386		* Raúl Rojas, Ulf Hashagen (editors), ''The First Computers - History and Architectures'', MIT Press, Cambridge, 2000 - the Baby is covered in Part IV-2, pp. 365-377; the re-build is covered in Part IV-3, pp. 379-386

	==External links==		==External links==

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External links: +From Cathode Ray Tube to Ferranti Mark I

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	* [https://curation.cs.manchester.ac.uk/computer50/www.computer50.org/kgill/mark1/mark1book.html Mark 1 Documents] - includes documents about the SSEM		* [https://curation.cs.manchester.ac.uk/computer50/www.computer50.org/kgill/mark1/mark1book.html Mark 1 Documents] - includes documents about the SSEM
	* [https://curation.cs.manchester.ac.uk/computer50/www.computer50.org/mark1/prog98/ssemref.html The Manchester University Small-Scale Experimental Machine Programmer's Reference Manual]		* [https://curation.cs.manchester.ac.uk/computer50/www.computer50.org/mark1/prog98/ssemref.html The Manchester University Small-Scale Experimental Machine Programmer's Reference Manual]
			* [http://www.cs.man.ac.uk/CCS/res/res02.htm#e From Cathode Ray Tube to Ferranti Mark I] - personal memories from Tom Kilburn
	* [https://curation.cs.manchester.ac.uk/digital60/www.digital60.org/rebuild/ Rebuilding the Baby]		* [https://curation.cs.manchester.ac.uk/digital60/www.digital60.org/rebuild/ Rebuilding the Baby]
	* [https://computerconservationsociety.org/ssemvolunteers/volunteers/ SSEM (Baby) Documentation]		* [https://computerconservationsociety.org/ssemvolunteers/volunteers/ SSEM (Baby) Documentation]

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A good start

New page

The '''Manchester Baby''' (formal name '''Small-Scale Experimental Machine''', sometimes abbreviated to '''SSEM''') was a very early experimental computer, built at the University of Manchester. Exactly like the [[Memory Test Computer]], it was not really intended for computational use; rather, its primary intended purpose was to test out a new form of [[main memory]], the [[Williams tube]].

It was constructed out of [[vacuum tube]]s, starting early in 1948; starting later that year, it was re-built into the [[Manchester Mark I]].
__NOTOC__
==Architecture==

The Baby had 32-bit [[word]]s, with a main memory of only 32 words. Two more Williams tubes held the [[accumulator]] ('A') in one, and the [[Program Counter|program counter]] ('CI') and the [[Instruction Register|instruction register]] ('PI') in the other. Its [[arithmetic logic unit|ALU]] was [[serial]], and used [[two's complement]].

[[Instruction]]s included a 3-bit [[operation code]], and a 13-bit memory [[address]] (the other 16 bits were unused. It had only 7 instructions:

{| class="wikitable"
! Opcode !! Instruction !! Description
|-
| 0 || s,C || Copy content of memory to CI
|-
| 1 || c+s,C || Add content of memory to CI
|-
| 2 || -s,A || Load negated memory content to accumulator
|-
| 3 || a,S || Copy content of accumulator to memory
|-
| 4 || a-s, A || Subtract content of memory from accumulator
|-
| 6 || Test || Skip next instruction if accumulator is negative
|-
| 7 || Stop || Light "Stop" light and halt
|}

==First computer==

It was thought for many years that the Baby had been the first stored-[[program]] [[computer]] to ever run (on a problem of finding the largest factor of a given integer); on 21st June, 1948. It has recently been brought to wider attention that, on a suggestion from [[John von Neumann]], the [[ENIAC]] was re-configured fairly early in its life into a stored-program computer - albeit one of very limited capability. It used the machine's 'function table' (an array of switches) to hold the program, thereby acting as a form of [[EPROM]] for ENIAC.

It can be argued that this does not make the ENIAC, so configured, a [[Turing machine]], as it cannot modify its own program. However, contemporary [[embedded system]]s often have a [[microprocessor]] with all their [[object code|code]] contained in [[read-only memory|ROM]], but no-one argues that those machines are not Turing machines.

Planning for that conversion started in the Fall of 1947; several different [[instruction set]]s were proposed. The re-configuration actually started at the end of March, 1948; the first run (on a problem related to atomic bomb work) happened at the end of April, 1948, finishing in May - effectively contemporaneous with the first run of the Baby.

==Re-creation==

The original Baby was not saved, but a replica was produced for the 50th anniversary with the assistance of the [[Computer Conservation Society]].

{{semi-stub}}

==Further reading==

* Simon H. Lavington, ''A History of Manchester Computers'', National Computer Centre, Manchester, 1976
* Simon H. Lavington, ''Early British Computers'', Manchester University, Manchester, 1980
* Raúl Rojas, Ulf Hashagen (editors), ''The First Computers — History and Architectures'', MIT Press, Cambridge, 2000 - the Baby is covered in Part IV-2, pp. 365-377; the re-build is covered in Part IV-3, pp. 379-386

==External links==

* [https://curation.cs.manchester.ac.uk/computer50/www.computer50.org/kgill/mark1/ssem.html Universal High-Speed Digital Computers: A Small-Scale Experimental Machine] - the original paper about it
* [https://curation.cs.manchester.ac.uk/computer50/www.computer50.org/mark1/new.baby.html The Manchester Small Scale Experimental Machine -- "The Baby"]
* [https://curation.cs.manchester.ac.uk/computer50/www.computer50.org/kgill/mark1/mark1book.html Mark 1 Documents] - includes documents about the SSEM
* [https://curation.cs.manchester.ac.uk/computer50/www.computer50.org/mark1/prog98/ssemref.html The Manchester University Small-Scale Experimental Machine Programmer's Reference Manual]
* [https://curation.cs.manchester.ac.uk/digital60/www.digital60.org/rebuild/ Rebuilding the Baby]
* [https://computerconservationsociety.org/ssemvolunteers/volunteers/ SSEM (Baby) Documentation]

[[Category: Early Computers]]
[[Category: Unique Computers]]

← Older revision		Revision as of 17:31, 20 September 2026
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	* Simon H. Lavington, ''Early Computing in Britain: Ferranti Ltd. and Government Funding, 1948-1958'', Springer Nature, Cham, 2019 - the background to the creation of the Baby is covered in appendix A		* Simon H. Lavington, ''Early Computing in Britain: Ferranti Ltd. and Government Funding, 1948-1958'', Springer Nature, Cham, 2019 - the background to the creation of the Baby is covered in appendix A
	* Simon H. Lavington, ''A History of Manchester Computers'', National Computer Centre, Manchester, 1976		* Simon H. Lavington, ''A History of Manchester Computers'', National Computer Centre, Manchester, 1976
	* Simon H. Lavington, ''Early British Computers'', Manchester University, Manchester, 1980		* Simon H. Lavington, ''Early British Computers: The Story of Vintage Computers and the People Who Built Them'', Manchester University, Manchester, Digital Press, Bedford, 1980
	* Raúl Rojas, Ulf Hashagen (editors), ''The First Computers - History and Architectures'', MIT Press, Cambridge, 2000 - the Baby is covered in Part IV-2, pp. 365-377; the re-build is covered in Part IV-3, pp. 379-386		* Raúl Rojas, Ulf Hashagen (editors), ''The First Computers - History and Architectures'', MIT Press, Cambridge, 2000 - the Baby is covered in Part IV-2, pp. 365-377; the re-build is covered in Part IV-3, pp. 379-386