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USA 1947


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stored program


The EDVAC is the successor of the ENIAC. Made by the same designers: Mauchly and Eckert.

design by Mauchly and Eckert

This computer was called by acronym EDVAC (Electronic Discrete Variable Automatic Computer) and its public presentation was carried through in 1947

This machine should be abel to hold any programme in memory that was fed to it. This would be possible because EDVAC was going to have more internal memory than any other computing device to date. In other words a multipurpose computer.

The idea being that given a tube of mercury, an electronic pulse could be bounced back and forth to be retrieved at will--another two state device for storing 0s and 1s. This on/off switchability for the memory was required because EDVAC was to use binary rather than decimal numbers, thus simplifying the construction of the arithmetic units.



Internal number system                 Binary
Binary digits per word                   44
Binary digits per instruction        4 bits/command
  10 bits each address
Instruction per word                     1
Instructions decoded                     16
Instruction used                         12
Arithmetic system               Floating and Fixed point
Instruction type                   Four-address code
                    EDVAC Floating Point (U.S. Army Photo)
Number range


-(1-2^-43) less than or equal to n less than or equal to (1-2^-43)


-(1-2^-33)2^511 less than or equal to n less than or equal to (1-2^-33)2^511

The fractional part of floating point number has 33 bits plus sign, and the exponent of 2 may range from -512 to +511.

Instruction word format
Alpha-Add      Beta-Add      Gamma-Add      Delta-Add      Order
  1-10          11-20          21-30          31-40        41-44
Add time (includ. stor. access)             864
  (min 192 max 1,536)
Mult time (includ. stor. access)          2,880
  (min 2,208 max 3,552)
Div time (includ. stor. access)           2,930
  (min 2,256 max 3,600)

Construction                           Vacuum-tubes and Diode-gates
Number of rapid access word registers  4
Basic pulse repetition rate            1.0 megacycle/sec

Arithmetic mode     Serial
Timing              Synchronous
Operation           Sequential
                          Number of          Number of
   Media                    Words             Digits        Access Microsec
Mercury A.D.L.              1,024             48-384             48-384
Magnetic Drum               4,608             48/Word            17,000
  Includes relay hunting and closure.
  The rate of information transfer to and from the drum is at one megacycle
per second.  The block length is optional from 1 to 384 words per transfer
Magnetic tape               48/Word
  Maximum number of units that can be connected to the system   7 Units
  Maximum number of characters per linear inch of tape        112 Char/inch
  Channels or tracks on the tape                                8 Track/tape
  Blank tape separating each record                           1.5 Inches
  Tape speed                                                   75 Inches/sec
  Start time                                                    3 Milliseconds
  Stop time                                                     3 Milliseconds
  Average time for experienced operator to change reel of tape 30 Seconds
  Physical properties of tape
    Width                                                     5/8 Inches
    Length of reel                                    1,250/2,500 Feet
    Composition                                               Red Oxide

The magnetic tape system has the following features: Variable block length from 2 to 1,024 words. The search order releases the machine for computation during search. Information which has been taken from a block and operated upon, can be automatically re-recorded in the same block.

         Media                                      Speed
Photoelectric Tape Reader                    942 sexadec char/sec
                                              78 words/sec
Card Reader (IBM)                            146 cards/min
                                               8 words/card
         Media                                      Speed
Paper Tape Perf.                               6 sexadec char/sec
                                              30 words/min
Teletypewriter                                 6 sexadec char/sec
                                              30 words/min
Card Punch                                   125 cards/min
                                           1,000 words/min
Type                Quantity             Type              Quantity
Tubes, total                    5,937
6Y6                   1,000              6AN5                 275
6J6                   1,500              2D21                 160
6AG7                  1,127              6SN7                 150
6V6                     900              6AS6                  50
6L6                     275              Misc                 500
Diodes, total                  12,000
1N297                 6,000              Misc               1,200
1N 34                 4,800
Transistors, total                328
2N398                   256              2N123                  4
2N1008B                  60              2N167                  4
2N 43                     4



1947 first issue



Go Back Last Updated on October 11, 2002 For suggestions please mail the editors 

Footnotes & References

1 History of Computing EDVAC.htm
2 www.upenn.edu\Penn Special Collections-Mauchly Exhibition 9.htm
3 Electronic Computers Within The Ordnance Corps, Appendix II -- EDVAC.htm