This report summarizes the discussion of the meeting for the benefit of those who may want to trace the development of thought on this subject

Mayer, Rollin P.

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I - — • Memorandum M-I469 I no Page 1 of 4 Dig i ta l Computer Laboratory Massachusetts I n s t i t u t e of Technology Cambridgej Massachusetts SUBJECT: WWII BLOCK DIAGRAMS MEETING OF APRIL 22, 1952 T o : WWII Planning Group From: R. P . Mayer Dates A p r i l 3 0 , 1952 Abs t rac t : This r e p o r t sumr.ari for t h e benefit of develoDment of thou. P r e s e n t : G. B r i g g s D. Brown S. Dodd R. J . H. The f i r s t part of t h i l d iscussion of methods of des ign! c o n t r o l . This c o n t r o l i s t o be fused j2Ji'k-fc&e--^±T]gTe-^register com-p u t e r that has been under i n v e s t i g a t i o n . In p a r t i c u l a r , a p rev ious-l y suggested method of opera t ing the s h i f t i n s t r u c t i o n was discussed. At the end of program timing t h e e l ec t ron i c r e g i s t e r conta ins the number which s p e c i f i e s the number of s h i f t s , so the e l e c t r o n i c r e g -i s t e r is used a s a counter u n t i l an overflow occurs , and then the number from AC i s t ransfer red t o the e l e c t r o n i c r e g i s t e r and shif ted t h e proper number of t imes. In t h i s system the sh i f t t akes a con-s t a n t number of s t e p s . The count-number i s usee to specify how many o f these steps should NOT s h i f t , so t ha t by the time the stepping i s completed, the d e s i r e d number of sh i f t s w i l l be performed. Another p roposa l was ske tched on the board showing how a se lec t ion matrix would be used t o s t a r t the chain of shift-command cores a t the proper p l a c e to provide t h e correct number of s h i f t s . Some other methods o f control l ing t h e shif t were mentioned b r i e f l y . I t was then suggested that these d e t a i l s concern*ng how t h e shift should operate are not important a t t h i s t ime. Severa l i d e a s were expressed as to where the p r o j e c t of designing a new com-p u t e r should b e g i n and how i t should p r o g r e s s . Some thought t h a t the problems to be handled by the computer should be analysed f i r s t , o thers f e l t that the components to be used rhould be discu&3B<jr f i r s t , s t i l l others f e l t t h a t the l o g i c a l design of the /p^u" t c# Securi ty Information » and i t e r should be SECURITYHNFORMATION APPROVED FOR PUBLIC RELEASE. CASE 06-1104.MM HNifcHi-t ^ » K i U U Memorandum 11-14.69 ^ ^ Page 2 of 4 a n a l y z e d f i r s t . The system under which we have been ope ra t ing u p "to now, and unde r which we w i l l probably cont inue to opera te , i s based on the prer . ise that we should s t a r t with the a b s o l u t e minimum number of components p o s s i b l e in a working computer and t h e n add new components to i t i n a s tep-by-s tep fashion, g e t t i n g c o n c r e t e f igures a s to how much complexity i s added a t each step a n d how much t ime i s gained a t each step as wel l as concre te f i g -u r e s on the number of components, r e l i a b i l i t y , e t c . , i f t h e s e are o b t a i n a b l e . Fol lowing th i s p rocedure , we should eventua l ly end u p w i t h a computer suitable f o r t h e task a t hand and yet con ta in -i n g components which we know a r e being used t o t h e i r maximum ef-f i c i e n c y . I t i s p o s s i b l e tha t t h i s technique w i l l r equ i re too much time in o r d e r to do a l l t h e required c a r e f u l ana lys i s a t e a c h step. An a l t e r n a t e approach i s to review very roughly the s p e e d requirements and s ta r t t h e program with a more or l e s s r e a l -i s t i c design of a complete computer. Then t h e add i t i ona l t ime can be spent in ana lyz ing and r e f i n i n g t h i s des ign . Following t h i s m e t h o d , R. E v e r e t t has cone up wi th some i d e a s which he explained t o u s as follows: Using some f i g u r e s for t h e probable frequency o f u s e of var ious in s t ruc t ions i n programs f o r which the computer i s designed and u s i n g some rough designs of simple computers, i t c a n be shown t h a t t h e average opera t ion in a o n e - r e g i s t e r computer w i l l have 9 s t o r a g e access t i m e s (AT) and 9 pu l s e times (TP) . A tv;o - r e g i s t e r computer will have 5 AT and 9 TP. A t h r e e - r e g i s t e r compute r will have 3^ AT and 9 TP. A computer with th ree r e g i s t e r s p l u s a program c o u n t e r will have 2^- AT and 8 TP. From t h i s analysis , i t looks as though a t l e a s t t h r e e r e g i s t e r s should be used, and probably three r e g i s t e r s p l u s a pro-g r a m counter. I f twe l a t t e r i s used, i t i s i n t e r e s t i n g t o no t ice t h a t nost of t h e t ime i s spent i n high-speed c a r r y during a mu l t i -p l y operation. High-speed c a r r y for other opera t ions i s u s u a l l y masked by access t o storage. I t would be d e s i r a b l e to speed up t h e high-speed c a r r y , and i f i t cannot be done by simply speeding-up t h e electronic c i r c u i t r y , t h e n i t may be necessary t o use the c a r r y f l ip-f lops w i th the s h i f t - a n d - c a r r y technique used in WWI. I f a matrix adder increases t h e speed, i t should be considered a l so . I t was mentioned t h a t t h e CADAC computer uses c r y s t a l m a t r i c e s and i s • i w j r e l i a b l e " . I t was suggested tha t S. Dodd s h o u l d inves t iga te the CADAC computer to l i n d ouL how r e l i a b l e it, i s i n terms of WWI r e l i a b i l i t y and WWII des i r ed r e l i a b i l i t y . I t would be nice to have a B-box t y p e ^ f order , bu t t h i s w o u l d seem to r e q u i r e a great d e a l of equipmearo^ (Perhaps some equipment can be saved if the B-box indicat^JqOfe programmed on t h e ins t ruc t ion p rev ious to t h a t on which i<CT$5n*ould be u s e d . ) APPROVED FOR PUBLIC RELEASE. CASE 06-1104.Memorandum M-14.69 *JkJr P a e e 3 of ( Since i t may be d e s i r a b l e to have a t l eas t two memory sys tems in the computer, i t may be worthwhile to consider using o n e memory e x c l u s i v e l y for opera t ions and t h e other exc lus ive ly f o r numbers, so t h a t a program counter would control one and a s e l e c t i o n r e g i s t e r the o the r . A computer designed in t h a t way c o u l d probably be made to o p e r a t e rather r a p i d l y , since each r e -w r i t e into s t o r a g e can be done while the o the r storage i s being u s e d . There a r e several poss ib le ways of modifying t h e oper-a t i o n s in such a s p l i t memory. One of t h e s torages could have o d d addresses, and the other could have even addresses . A B-b o x technique cou ld be used f o r modifying any i n s t r u c t i o n s . The o p e r a t i o n memory could be ar ranged so t h a t i t could be changed o n l y by large b l o c k t r ans fe r s from the drum. Perhaps the bes t s y s t e m is to have a t r a n s f e r - d i g i t s order (and other s p e c i a l o r -d e r s ) arranged t o actual ly modify a r e g i s t e r in the opera t ion memory. We shou ld be ca re fu l not to make such a system t o o complicated, b u t i t i s pos s ib l e t ha t the i n s t r u c t i o n s in t h i s computer could be f a s t enough (A or 5 microseconds) so t h a t i t w o u l d not need t o have s p e c i a l b u i l t - i n i n s t r u c t i o n s . This c o u l d mean t h a t t h e very complicated c e n t r a l control i s replaced b y a somewhat l e s s complicated method of opera t ing the d u a l -s t o r a g e system. We have heard a number of times about a deadl ine some-t i m e in June, J . Forrester was asked to c l a r i f y jus t what i s r e q u i r e d by t h i s deadl ine. By sometime In June , probably the end of June, v/e should know the kinds of physical components we need. For example: we s h o u l d know whether we are going to use t h e three-dimensional memory, the s t e p r e g i s t e r c o n t r o l , and the e l e c t r o n i c a r i t h m e t i c e l e m e n t . After t h i s , nine months can be s p e n t in deciding the number of components required and how they should be in te rconnec ted . I n t h i s calendar year we should develop t h e components and s e t t l e t h e block diagrams. In the fo l lov ing year , we should produce the f u l l design from t h e complete block diagrams. This means that by t h e end of June t h e mate r ia l s groups s h o u l d be able t o t e l l us what techniques ™il l be ava i l ab l e for us t o u s e and which techniques a r e not worth f u r t h e r i n v e s t i g a t i o n . I t i s necessary, however, for t h e block diagrams .group t o po in t o u t what kinds o f components a r e des i r ab le , so t ^ ^ the m a t e r i a l s g r o u p s can i n v e s t i g a t e such components and secy^Othey a r e worth c o n s i d e r i n g f u r t h e r , X r * ..;wi c|fe i ? a 11 APPROVED FOR PUBLIC RELEASE. CASE 06-1104.^WTRrTu IBML fe Memorandum M-H69 ^ \ Page 4 Of 4 I t was sugges ted that a t t h e next meet ing, on Thur sday , Reed and Je f f r ey should p resen t Reed's simple com-puter t o the group, showing both t h e equations and the block d i a g r a m s . The o b j e c t vd l l be t o show hov: the method of Boolean a l g e b r a can be a p p l i e d to the des ign of a computer. I t i s p lanned that some l i t e r a t u r e on Boolean algebra and on Reed's computer vdll be a v a i l a b l e before Thursday's meet ing. (TU t̂*, ft th ̂-tyJLA-R o l l i n P. Mayer RFM/NHT:bs APPROVED FOR PUBLIC RELEASE. CASE 06-1104.

WWII Block Diagrams Meeting of April 22, 1952

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WWII Block Diagrams Meeting of April 22, 1952

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