Editing IBM 701 (section)

==Description==
===Hardware configuration===
[[File:IBM 701 frame.jpg|thumb|IBM 701 processor frame, showing 1071 of the vacuum tubes]]
[[File:IBM 700 logic module.jpg|thumb|[[Vacuum tube]] logic module from a 700 series IBM computer.]]
The IBM 701 system<ref>{{cite journal|title=IBM Type 701 Electronic Data Processing Machine|journal=Digital Computer Newsletter|date=October 1953|volume=5|issue=4|pages=7–8|url=http://www.bitsavers.org/pdf/onr/Digital_Computer_Newsletter/Digital_Computer_Newsletter_V05N04_Oct53.pdf|language=en}}</ref> was composed of the following units:
*IBM 701 - Analytical Control Unit ([[Central processing unit|CPU]])
*IBM 706 - Electrostatic Storage Unit (2048 words of [[Williams tube]] Memory)
*[[IBM 711]] - [[Punched card|Punched Card]] Reader (150 Cards/min.)
*[[IBM 716]] - Printer (150 Lines/min.)
*IBM 721 - Punched Card Recorder (100 Cards/min.)
*[[IBM 726]] - [[Magnetic Tape]] Reader/Recorder (100 Bits/inch)
*[[IBM 727]] - Magnetic Tape Reader/Recorder (200 Bits/inch)
*IBM 731 - [[Drum memory|Magnetic Drum]] Reader/Recorder
*IBM 736 - Power Frame #1
*IBM 737 - Magnetic Core Storage Unit (4096 words of 12 μs Core Memory)  
*[[IBM 740]] - Cathode Ray Tube Output Recorder
*IBM 741 - Power Frame #2
*IBM 746 - Power Distribution Unit
*IBM 753 - Magnetic Tape Control Unit (controlled up to ten IBM 727s)

The total weight (depending on configuration) was about {{Convert|20516|lb|ST MT|1}}.<ref>
*{{Cite web|url=http://www.ed-thelen.org/comp-hist/BRL61-ibm07.html#IBM-701|title=IBM 701|last=Weik|first=Martin H.|date=March 1961|website=www.ed-thelen.org|series=A Third Survey of Domestic Electronic Digital Computing Systems|access-date=2018-05-25}}<br/><br/>What's included in total weight:
*{{Cite web|url=http://ed-thelen.org/comp-hist/BRL-i.html#IBM-701|title=IBM-701|last=Weik|first=Martin H.|date=December 1955|website=www.ed-thelen.org|series=A Survey of Domestic Electronic Digital Computing Systems|access-date=2018-05-25}}</ref>

===Memory===
[[Image:Williams tube.agr.jpg|thumb|upright|Williams tube from an IBM 701 at the [[Computer History Museum]]]]
The system used [[vacuum tube]] logic circuitry and electrostatic storage, consisting of 72 [[Williams tube]]s with a capacity of 1024 [[bit]]s each, giving a total memory of 2048 [[Word (data type)|words]] of 36 bits each. Each of the 72 Williams tubes was 3 inches in diameter. Memory could be expanded to a maximum of 4096 words of 36 bits by the addition of a second set of 72 Williams tubes or (later) by replacing the entire memory with magnetic-[[core memory]]. The Williams tube memory and later core memory each had a memory cycle time of 12 microseconds. The Williams tube memory required periodic refreshing, mandating the insertion of [[Memory refresh|refresh cycles]] into the 701's timing. An addition operation required five 12-microsecond cycles, two of which were refresh cycles, while a multiplication or division operation required 38 cycles (456 microseconds). In addition, magnetic drum and magnetic tape were utilized for secondary storage.<ref name="comp-arch-n-org">{{cite book |title=Computer Architecture and Organization |last1=Hayes |first1=John P. |isbn=0-07-027363-4 |date=1978 |page=22}}</ref>

===Instruction set===
[[Instruction set|Instructions]] were 18 [[bit]]s long, single address.
*Sign (1 bit) - Whole word (-) or Half word (+) operand address
*Opcode (5 bits) - 32 instructions
*Address (12 bits) - 4096 Half word addresses

Numbers were either 36 bits or 18 bits long, [[Signed number representations|signed magnitude]], [[Fixed-point arithmetic|fixed point]]. The full word has a precision of about ten decimal digits. A decimal digit corresponds to <math>log_2 10</math> or 3.322 bits.

The IBM 701 had only two programmer accessible registers:
#The [[Accumulator (computing)|accumulator]] was 38 bits long (adding two overflow bits).
#The multiplier/quotient was 36 bits long.

===Peripherals===
The Magnetic Drum Reader/Recorder was added on the recommendation of [[John von Neumann]], who said it would reduce the need for high speed I/O.<ref>{{cite book |title=John von Neumann: Selected Letters, Letter to R.S. Burlington |page=73 |publisher=American Mathematical Society and London Mathematical Society |year=2005}}</ref>

The first magnetic tape drives were used on the Tape Processing Machine (TPM) and then adapted to the 701.<ref>{{cite web|last=da Cruz|first=Frank|date=July 2003|title=IBM 701 Tape Drive - The First Magnetic Tape Drive for Computer Data Storage|url=http://www.columbia.edu/cu/computinghistory/701-tape.html|access-date=19 December 2020|website=Columbia University Computing History}}</ref>