Memory Test Computer - Revision history

Jnc: Second computer built at MIT

2024-06-04T19:21:03Z

Second computer built at MIT

Jnc: /* External links */ +MTC memos

2024-03-01T20:10:09Z

‎External links: +MTC memos

Jnc: An important machine which is poorly covered on the Web

2024-02-27T18:45:56Z

An important machine which is poorly covered on the Web

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The '''Memory Test Computer''' was an early [[vacuum tube]] computer which was a spin-off of the pioneering [[Whirlwind]] effort; it was built by [[Ken Olsen]] and others to test the first [[core memory]], devised for Whirlwind. It was a [[parallel]] computer, with a 16-bit [[word]] length (since the memory it was to test was for Whirlwind, which was that size); it was similar in many other ways to Whirlwind, also.

It first ran in March, 1953; the prototype core memory was installed and operational by the end of May. Later, the MTC was used to test various system components to be used in the [[Semi-Automatic Ground Environment|SAGE]] system. It was shut down permanently on March 21, 1958; but unlike Whirlwind and the later [[TX-0]], it unfortunately was apparently not preserved. It was a considerable influence on the TX-0, through people who had worked on the MTC.

==Technical details==

The MTC had had 26 [[instruction]]s; for [[main memory]] it had 4KW of core memory (after the main core memory unit had been moved to Whirlwind), a [[drum]] (originally only 4KW in size), and 64W of [[read-only memory|ROM]], implemented in a toggle [[switch]] array and a [[plug-board]]. (NB: memory locations are referred to as "registers" in the documentation.) [[Address]]es consisted of a 4-bit 'field number' and an 11-bit 'address' within that field; field 0 was the ROM, 1 and 2 were the core, and 3 and 4 were the drum. The pair of a field number and an address were termed an 'extended address'.

Most [[register]]s and [[data path]]s had an additional bit, for [[parity]] error checking. Bits were numbered using [[big-endian]] notation; the MTC used [[one's complement]] arithmetic ([[overflow]]s cause an 'overflow alarm', which halts the MTC). For [[input/output|I/O]] it had two [[paper tape]] readers and a punch, [[printer]]s, and several [[display]]s (one with a camera controlled by the MTC).

===Registers===

There were 11 visible registers (built out of [[flip-flop]]s) in the final design:

{| class="wikitable"
! Function !! Name || Size (bits) || Use !! Comment
|-
| PC ||   || 11 || [[Program Counter]]
|-
| Partial Sum ||   || 16? || General purpose || rowspan="2" | Together termed the 'Accumulator (AC)', but that name was often informally applied to the Partial Sum Register
|-
| Carry ||   || 1? || Momentarily store carries generated in addition operations
|-
| A || AR || 16 || Buffer register between all the data sources and sinks in the system; connected to 'A-Register-In' and 'A-Register-Out' [[bus]]es
|-
| B || BR || 16 || Effectively an extension of the PSR during multiplications
|-
| Live Register 1 || LR1 || 16 || Can be substituted for any ROM location || rowspan="5" | Addressed as main memory in field 0
|-
| Live Register 2 || LR2 || 16|| rowspan="2" | Can be substituted for any plug-board location
|-
| Live Register 5 || LR5 || 16
|-
| Live Register 3 || LR3? || 16
|-
| Live Register 4 || LR4? || 16
|-
| Operation Field Register ||   || 4? || rowspan="2" | Can only be written, not read
|-
| Program Field Register ||   || 4? || Loading does not take immediate effect
|}

===Instructions===

Instruction words contained a 5-bit [[operation code]], and 11 bits of address - although in some instructions the 'address' field is used for other purposes. Since the address portion was not long enough to hold an extended address, the MTC used [[bank switching]] to gain access to all of main memory.

{| class="wikitable"
! Opcode !! Abbreviation || Function !! Comment
|-
| 0 || ha || Halt machine
|-
| 1 || mh || Multiply AC by memory, leave result in BR,AC
|-
| 2 || ds || Display memory contents
|-
| 3 || ic || 'Identity check'; compares AC with memory contents
|-
| 4 || st || Store AC in memory
|-
| 6 || ra || 'Replace address'; stores bits 5-15 of AC in memory
|-
| 7 || rf || 'Return from'; stores bits 5-15 of LR2 in memory
|-
| 8 || ca || 'Clear and add'; load AC from memory
|-
| 9 || ad || Add memory to AC
|-
| 10 || cs || 'Clear and subtract'; load AC with negative of memory
|-
| 11 || su || Subtract memory from AC
|-
| 12 || et || 'Extract'; AND memory into AC
|-
| 14 || ch || 'Charactron display' || Refer to Programming Manual
|-
| 15 || sm || 'Subtract Magnitudes'; copy AC to BR, subtract memory from AC
|-
| 16 || tr || 'Transfer'; load memory address into PC || rowspan="2" | Consult Programming Manual for side-effects on LR2
|-
| 17 || tro || 'Transfer Out'; load memory address into PC, update field of PC from Program Field Register
|-
| 18 || tn || 'Transfer on negative'; if AC is negative, as 'tr' above
|-
| 19 || tno || 'Transfer on negative out'; if AC is negative, as 'tro' above
|-
| 20 || md || 'Memory address display' || Refer to Programming Manual
|-
| 21 || sof || 'Select operation field'; load Operation Field Register
|-
| 22 || to || 'Transfer on overflow'; if an overflow condition exists, as 'tr' above
|-
| 24 || cr || 'Cycle right' || rowspan="5" | Refer to Programming Manual
|-
| 25 || sr || 'Shift right'
|-
| 28 || pr || 'Print/punch'
|-
| 30 || ri || 'Read in'
|-
| 31 || op || 'Operate'
|}

==External links==

* [http://www.bitsavers.org/pdf/mit/lincolnLaboratory/mtc/ MTC] - documents at [[Bitsavers]]
** [http://www.bitsavers.org/pdf/mit/lincolnLaboratory/mtc/M2527-1_MTC_ProgrammingManual_Apr54.pdf Memory Test Computer: Programming Manual]
* [https://archivesspace.mit.edu/repositories/2/archival_objects/276913 Memory Test Computer Memoranda, 1952-1958]
* C. Gordon Bell, Gerald Butler, Robert Gray, John E. Mcnamara, Donald Vonada, and Ronald Wilson, [http://gordonbell.azurewebsites.net/Computer_Engineering/00000146.htm The PDP-1 and Other 18-Bit Computers], in C. Gordon Bell, J. Craig Mudge, John. E. McNamara, ''Computer Engineering: A DEC View of Hardware Systems Design'', Digital Press, Bedford, 1978 - contains some detail about the MTC
* [https://www.computerhistory.org/collections/catalog/102633143 Dick Best and Wally Wheaton with Memory Test Computer at MIT]

[[Category: Early Computers]]
[[Category: 16-bit Computers]]
[[Category: Unique Computers]]

@@ Line 1: / Line 1: @@
-The '''Memory Test Computer''' was an early [[vacuum tube]] computer which was a spin-off of the pioneering [[Whirlwind]] effort; it was built by [[Ken Olsen]] and others to test the first [[core memory]], devised for Whirlwind. It was a [[parallel]] computer, with a 16-bit [[word]] length (since the memory it was to test was for Whirlwind, which was that size); it was similar in many other ways to Whirlwind, also.
+The '''Memory Test Computer''' was an early [[vacuum tube]] computer which was a spin-off of the pioneering [[Whirlwind]] effort; it was built by [[Ken Olsen]] and others to test the first [[core memory]], devised for Whirlwind.  It was apparently the second computer built at [[Massachusetts Institute of Technology|MIT]].
 It first ran in March, 1953; the prototype core memory was installed and operational by the end of May. Later, the MTC was used to test various system components to be used in the [[Semi-Automatic Ground Environment|SAGE]] system. It was shut down permanently on March 21, 1958; but unlike Whirlwind and the later [[TX-0]], it unfortunately was apparently not preserved. It was a considerable influence on the TX-0, through people who had worked on the MTC.
@@ Line 5: / Line 7: @@
 ==Technical details==
-The MTC had had 26 [[instruction]]s; for [[main memory]] it had 4KW of core memory (after the main core memory unit had been moved to Whirlwind), a [[drum]] (originally only 4KW in size), and 64W of [[read-only memory|ROM]], implemented in a toggle [[switch]] array and a [[plug-board]]. (NB: memory locations are referred to as "registers" in the documentation.) [[Address]]es consisted of a 4-bit 'field number' and an 11-bit 'address' within that field; field 0 was the ROM, 1 and 2 were the core, and 3 and 4 were the drum. The pair of a field number and an address were termed an 'extended address'.
+The MTC had 26 [[instruction]]s; for [[main memory]] it had 4KW of core memory (after the main core memory unit had been moved to Whirlwind), a [[drum]] (originally only 4KW in size), and 64W of [[read-only memory|ROM]], implemented in a toggle [[switch]] array and a [[plug-board]]. (NB: memory locations were referred to as "registers" in the documentation.) [[Address]]es consisted of a 4-bit 'field number' and an 11-bit 'address' within that field; field 0 was the ROM, 1 and 2 were the core, and 3 and 4 were the drum. The pair of a field number and an address were termed an 'extended address'.
-Most [[register]]s and [[data path]]s had an additional bit, for [[parity]] error checking. Bits were numbered using [[big-endian]] notation; the MTC used [[one's complement]] arithmetic ([[overflow]]s cause an 'overflow alarm', which halts the MTC). For [[input/output|I/O]] it had two [[paper tape]] readers and a punch, [[printer]]s, and several [[display]]s (one with a camera controlled by the MTC).
+Most [[register]]s and [[data path]]s had an additional bit, for [[parity]] error checking. Bits were numbered using [[big-endian]] notation; the MTC used [[one's complement]] arithmetic ([[overflow]]s caused an 'overflow alarm', which halted the MTC). For [[input/output|I/O]] it had two [[paper tape]] readers and a punch, [[printer]]s, and several [[display]]s (one with a camera controlled by the MTC).
 ===Registers===

@@ Line 117: / Line 117: @@
 * [http://www.bitsavers.org/pdf/mit/lincolnLaboratory/mtc/ MTC] - documents at [[Bitsavers]]
 ** [http://www.bitsavers.org/pdf/mit/lincolnLaboratory/mtc/M2527-1_MTC_ProgrammingManual_Apr54.pdf Memory Test Computer: Programming Manual]
 * [https://archivesspace.mit.edu/repositories/2/archival_objects/276913 Memory Test Computer Memoranda, 1952-1958]
 * C. Gordon Bell, Gerald Butler, Robert Gray, John E. Mcnamara, Donald Vonada, and Ronald Wilson, [http://gordonbell.azurewebsites.net/Computer_Engineering/00000146.htm The PDP-1 and Other 18-Bit Computers], in C. Gordon Bell, J. Craig Mudge, John. E. McNamara, ''Computer Engineering: A DEC View of Hardware Systems Design'', Digital Press, Bedford, 1978 - contains some detail about the MTC