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~VIbyy~f:&uilMd it ii LfIL 4 N Cqa:~s wno~nvlpuiters T'he extreme complexity of modern scientific and engineering problems has developed a great need for this new type of m athematical tool.'............................................ Many problems, whose solutions have previously been considered too laborious andl expensive, can now be (ealt with quickly and economically. With the advent of these new digital machines, it is no longer necessary to construct actual scientific or engineering systems for initial design studies. Scientists may now set up a "mathemati. cal model" of an intricate system, follow such a system's behavior through the patterns of opera-. tion, and predict and evaluate its performance. Elfectronic computers can provide models of complex physical structures ranging in size and behavior from the innermost structure of the atomic nucleus to an air traffic control system.. The University of Michigan Digital Automatic Computer, or MIJ)AC, as it was nameed, now takes its place as one of six large-scale digital computers planned for operation in the nation's universities and technical institutions and one of about twenty throughout the country.'l'he first such computer in the Midwest, it is I' located at Willow Run in the i)etroit industrial area.'

In the field of system simrulation, electronic digital computers can simulate the dynamics of such complicated devices as guided missiles, supersonic aircraft, torpeloes, and the multiple array of new devices that have appeared during the past few years. Because MIDAC is all-electronic, it performs at very high speed as compared to mechanical or hand methods of computation. Because it is a digital computer, it can calculate and produce answers to whatever accuracy is desired. In the general scientific and engineering fields, MIDAC will be especially useful in obtaining solutions to the following types of mathematical problems, for which numerical solutions were previously thought to be impractical: i Solution of large sets of linear simultaneous equations and the inversion of high-order matrices. 0 IDetermination of real or complex roots of algebraic or transcendental equations. Q Solution of high-order differential equations (linear or non-linear). I)etermination of the eigenvalues and eigenvectors of real or complex matrices and ordinary differential and partial differential operators. *:: Solution of partial differential equations (linear or nonlinear). c Computation of various correlation functions and other statistics of large volumes of data. Q Solution of "minimization problems" of the calculus of variations. 1;| Solutions of boundary-value problems of classical and quanttum physics. In the field of process control, MIDAC will be able to provide hard-to-get answers to problems of oil-well production, refinery controls, automatic solution of machine tool operation, and control of chemical 1 ray tracing, reactions. In sutch varied fields as molecular strucs, electronic ture research, design of chemical solvolysis proces-,as and steam ses, control of large-scale power systems, nuclear o cite only a spectroscopy, and compilation of oil exploration ted on high- tables, high-speed computers similar to MIDAC have already proved their worth. MIDAC will be valuable in the design problems in such fields as optica dynamical systems, servomechanism! networks, internal combustion engines, P turbines, and nuclear reactor design, t few of the problems already investiga speed computing machinery.

MIDAC is a general purpose, high-speed, electronic digital computer. It operates in a serial mode, using the binary (base two) number system. The binary system uses only two (ligits, "0" and "1," which correspond in the machine to the absence or presence of an electronic pulse. The MIDAC uses a group of 45 binary digits (44 digits:............. plus a sign) as a fundamental unit of information, or "word." This "word" may convey operational instructions or numerical i.?.... information to the machine. Its storage elements contain 512!!?! ~i i: words of high-speed memory, plus 6,144 words of slower-speed memory, with provision for expansion.. /). O::~,~:~ "The same memory equipment is used to store both instrucS,'..... tions and numbers, and the relative apportionment of me.mory... ~l'~""i —~,: isp a:.d....:';.-....,:: i:': f space to each is arbitrary. Because the comuter stores and uses these two types of words in identical form, instructions may....... easily be modified by the computer by the same logical and.........., / arithmetic operations performed on numbers and vice versa. -;.... -" - This ability allows MID)AC to program some of its own comn-': ~!:i',,~i;":,i",ii i:?::::':.' putation on the basis of results of calculation within the ma" chine, and this, with its ability to make numerical comparisons,. i gives th he machine its important decision property...... Instructions are of the "three-address" type, involving two operaind locations and result location. ()f^: 0.. NNumbers may be given to the computer in the decimal nums' ber system; these may be converted toti cally ato ill n input 0*P 1|,i"' tjetranslation program to the binary number system in which the 2 t): ^ ^^: j computer works. Numbers may be represented in MII)AC to!'i,.i ea precision of 44 bin ary ligits, which is approximately equiva0a*) 0*..'" | 3? lent to 13 decimal digits. The computer has a fixed binary point 4 f A o: located such that the absolute value of all numbers as operated 4 >: ton by the computer is less than one. However, MIi)AC may 0*^ (CO ) 0 |:~ S i: b e programmed1 automatically to operate with a floating deci0 0 0.... I6i mal Ipoint or automatic scale factor, using special instructions i. ^!ii! incorporated in the computer design to facilitate this operation. Q*l * * | 7 EU. /y Four main units, or blocks, make up MII)AC. These are (1) *: 1 () (';i:l: the input and output units, (2) the memory, or storage units,..... 8........... (3) the control units, and (4) the arithmetic units. A control -9: 0 0 0(I 9 l'':l'::;:,. console allows the operator to insert problems and monitor the?,:-: performance of the machine.

Nineteen basicn machine operations will be available on I MIDAC: Six of these will be the standard arithmetic operations in the m achine code:........................... Add (ad) Subtract (su): lMultiply, Unrounded (mu) "" Multiply, Low Order (ml) Multiply, Rounded (mr) )Division (dv) Two operations will shift digits in a word to the right, or to the left, and locate the significant digits in a word: l Shift Number (sn). Power Extract (px) A particularly useful operation will allow individual digits in a word to be replaced without erasing the rest of the word. This operation will be used in modifying instructions within the machine and in withdrawing significant parts of a number for special consideration or printing: is: Extract (ex) Three "change-of-control" operations allow the machine to make decisions based on the result of arithmetic operations, and to transfer control to autoitmatic sutibrotinets:.. [.... Compare Number (cn) ['.... Compare Magnitude (cm) File (fi) A special sequencing operation allows the computer to decide, on the basis of the relative positions of two address locations, whether to repeat a sequence of instructions just executed using new data, or to contilnue on into a new sequence of instructions. This operation is useful for experimental data reduction and evaluation of formulas for a large nutiber of artgett.....s: (.* B; ase (ba) Two number conversion operations allow the machine to convert numbers from outside form into the machine's own word structure and back again:'......Decimal-to-Binary Conversion (db).s Binary-to-Decimal Conversion (bd) Two input-output instructions allow the machine to communicate to and from primary storage with secondary storage and the outside world: 1 iReatd In (ri) Read Out (ro) Finally, two tape control instructions will allow the machine to manipulhate external magnetic tape units: M..... Move rape Forward (mf).. Move Tape Back (tlb) By use of combinations of these instructions, Once such a program is written and plerfected, MIDAC will perform automatically any sequence of MIDAC will perform such computations autosteps, and thus any required computation, no mat- matically and rapidly. What is more important, ter how complicated. However, MIDAC is not the ) MII)AC will repeat these computations as often as "Giant Brain" of the science-fiction writers. It can- desired with different sets of numerical data, as not "think" in the terms of human creativeness, It furnished from outside. can make decisions only if told upon what basis to MII)AC is a powerful tool, ready for use in I.. (decide, and what to do in each case. Much work - solving the important problems of today, but a tool..) mtust be done by mathematicians and programmers whose value will be only inl proportion to the skill |T for the machine in breaking (lown a problem into and imagination of those who use it. B; the simple operations of which MIDAC is capable.:. ii ii r~;-a ~~~~~~~~~~~~~::;~ -:-lt~~~~~~~{

.....~~~~~~~~~~~~~~~~~~~~~~- -...............~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~i...l,...I Il......I.......... J; A.......... Control UJnit'The Control Unit of the MIDAC is the central switchboard for the machine. In this clement, an instruction is called in froml the High-Speed (Acoustic) Memory, broken down into its component parts, and "micro-instructions" are sent out in sequence to each unit in the machine so that tle overall operation may b)e performed. Here the machine also makes "decisions" on( the basis of results obtained b)y the Arithmetic Unit. Magahnetic D)nrum MeI4cmor) The low-speed mtemory in thle machine, presently containing over 6,000 "words" of storage, but with provision to expand to almost 25,000 "words," is a Magnetic Drum IIi Unit. Information here is stored as magnetized regions on the surface of the cylindrical drum, and is transferred in and ou t by "read" and "write" magnetic heads. D)ata can be read out of the High-Speed Memory and stored on tlhe Drum or read off the Drum and returned to the High-Speed Memory, when the Control Unit receives tlhe proper instruction. Pretested subroutites and input programs can be kept permanently in this storage element. W [! Comp Ur lter Cowsiole At the Console of the MIDAC, the machine operator starts andt stops the machine and monitors the intermediate calculations. lie has at his ingertips the main power switches, start-stop switches, and control switches for inserting information into the machine. Light patterns on the Console aid him in telling whether or not a problem is running satisfactorily. lighiSbpeed (Acou stic) Both tile instructions which control the Control Unit and the numbers onl which the Arithmetic Unit otperates are stored in the High-Speed (Acoustic) Memory. Here information is stored in the form of sound pulses in a litquid (mercury) medium, to be called in when the appropriate number or intstruction is required. \hen more information than the 512 "wotrds" available here is needed, the Control Unit can be instructed to call in more information from the MNagnetic Drum Memory to replace any portion of the 512 words.

IIts.(flq.vi.nm07ll.aa. r~~~wpuiiV~~~~~~19ai'.. i i 0fi Outp)utt Automatic T.ypewnftect A Fllexowriter untit types out the results of tle comjputation on paper, ready to be evaluated by the mathematician. The typewriter keys are actuated by sequences of electronic pulses, sent by the Control Unit from the I:igh-Speed Memory. Itl:.p'wSit P:hotoelteide U. I i. The input of numbers and instructions into Ihis machitne s accomplished by a high-speed lPhotoelectric Papers Tape Reader, which can'ead in six-level pulnched paper tape at a speed bf 200 claracters per second. Wtith such readn sp)eeds, computation in the machine need only wait a short time for incoming information. A light, shining through the lutnched |ioles, strikes photoelectric cells and is translated into electronic pulses, which are sent by the Control Unit to the H-igh-Speed Memory. Arith"Met;ic: Jnit The calculating element of the MIDAC is its Arithmetic Unit, which performs the operations of addition, subtraction, multiplication, and division oil operands called in from the Itigh-Sleed (Acoustic) Memory, and then sends the result back to storage for further processing. The Arithmetic Unit also can shift numbers right and left (multiplication by powers of two) and automatically scale numbers to a conventional standard form. Multiplication can be "roulnded" or "unroundedl.

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...I. F.... I t 1\\...AiII h..A4.Hi4P'4w.11~(A1 I Iil )IWX aI[!........ev.114v.uk3 ~{A miff I..iLh.r.s C) Q It ts Large Iu )r Storage Provides Easy IJUe of Su roId ine Subroutines, or pre-coded, pIre-tested program blocks, have beent found to b)e extremely impolltant il speeding the job of giving a computing machine instructions in its own language. Most previous con)puters have failed to use subroutines, or if they have used tleml, were forced to store their subroutines outsiole of the machine ot 1al el t lapc, junche l cars, oery other omedia. t matic call-in programs can Ibe used to operate these subroutines completely automatically. This saves programiming, time, an(1 (lecreases the cost of puttingy a p)roblemnl oil the machine......... a cost which has ruan' very hiIAg O other dcomputsers. Ii lid i n Relative A: resses iake S uroutine Readln Automatic Along withl the storage of subroutines ont tle drut, The relative address system autolmatically assigns MII>DAC possesses a "relative addressing" scheme proper acoustic memory addresses within the body of which allows subroutines to le coded once, independ- the subroutine, andl elitinates the need of a programnit of any specified position inl the memory, and after me1's (letertliling the absolute aldresses of the final storage oi the drumt to be called in to any acotstic stubroutine by hand. lllemory position.

Y A Special aq ase" Operation Aids in apid )ata Processi g All recent automatic comlluters have been able to modlify their own stored instruction program on the basis of previous results. Such cyclic program se(quelnces, or "iteration loop1s", are llelpful in halndling matrix manilulations, in processing large amnounts of (lata, a(nd in halndllng any large probl)ems of a cyclic natlure. NIDAC hal: I es been lblt witl a special "blase" operation ldesigned just for stuch iteration loops. This itnstruction performs an operation accoplllished in other computers only by a combination of instructions. Its special counting features, along with the relative address features, combine to save both storage and speed of operation in large probllems.'I'... C0 M0 " Builtl Ins'truetiaon Provides Speedy ]Binar y"Decimal Conversion Fee iVa V (, Iike tost recent electronic computers, MII)AC is a binary (base two) machine. However, special instructions in the MII)AC speed up the conversion of numbers from external decimal notation to the machine's internal binary system and vice versa. Thus, two conversion instructions, decimal-to-l)i - nary and binary-to-decimal, aid the MlII )AC progralmmer in translating his numbers from one form to another. T'lhis saves both machine andl programming time. An Input crConersionflTrans lbatiton Program Speeds Prog ram:ring Coding of i)rol)lems for MTIDAC, unlike similar tasks on most other machines, is greatly aided by an "input conlversionl-t'translation p)rogram" whiclh per — forms the complete task of translating the code for MI )A(C Ilrobllems fromi the external more familiar form into the binary language of the machine. (-.-925 -.6'723) (.j.-.321 As an example, if the machine is to be askedlthe simp)le question below, tlhe coder writes his instructions to the machine in the simplified form at the left, ratlter than tile more unfamliliar form at thle right, and the "input conversion-translation program" perforlms the complete translation for him..576) >.-327? —..... > - — ~-.3 2 7 IExternal Program (Decimal-Algebraic Code) Internal Machine Program (Binary Code)

i i i I l-I.I... Iackaged l[tnit s Irovide Ease of Maintenance Although "package(d units" have been sed to some extent on other computers, MIDAC has carried this efficient ")uildingt)lock" type of construe-: tion to its logical conclusion. T'he machine (except for the storage celements) is composed of only six different types of individual packages. Any unit can l)e elplaced by simply pulling it out and plugging in a duplicate. These packages are the result of circuit developments at the National Bureau of Standards in Washington, 1. C., at the Air Force Missile Test Center, PIatrick Air Force Base, Florida, and at the University of Michigan. The ir use as the basic elements of a computer provides ease of mainteInalce, convenience of cooling, rapid repair of machine failures when they occur, and mlakes possible rapid mass production of comp)uters when required. Each package contains no more than one t tbe and is a logical element in itself. There are six basic building block packages, three of which are made up of combinations of "and" and "or" gates. The otlher three are termination packages, relay driver packages for use with the magnetic drum, and delay line packages. Only one type of tube, one type of diode, and eight sizes of resistors are required with these units. Their use guarantees flexibility in making future engineering changes and additions that may be neetded in MIDAC.

""(oo..m to Grow Allows IFuture Increases in Memory Size without Internal Cire~uitry Chan es VWhen probllems increase in size beyond the )resent capacity of the machine, MID)AC (oes not become obsolescent. Instead, a simtlle addition of duplicate memory equip)ment, without changing any of the internall control circuits, will allow the machine to tmeet such new challenges. At present, MIDl)AC's acoustic memory contains 512 words of storage; however, its control circuits were planned to provide for expansion to 1,024 words. Similarly, its magnetic drum storage at p)resent is 6,144 words, but control circuits are built in so that the machine can later be expanded to 24,576 words of magnetic drum storage, without redesigning any of the control mechanism. Provisions are also available for addition of magnetic tape units without redesign of the basic logic. MIl)AC is now in operation at the University of Michigan's Willow Rlun Researcth Center at Willow Run Airport.

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