294 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 60 



subtracting-, testing, correcting, and shifting operations. Table 8 

 shows how 26,693,578 can be divided by 7,596 to obtain 3,514 as the 

 quotient with a remainder of 1,234. After an initial left shift, the 

 process involves subtracting the divisor 7,596 from columns 2 through 

 5 of the dividend until the remainder is negative. This indicates that 

 one too many subtractions has occurred, so the program adds the divi- 

 sor back and then shifts the remainder one position to the left. Then 

 the process repeats. Since a 1 is added in column 9 for each subtrac- 

 tion which leaves a positive remainder, the final result is that the quo- 

 tient (3,514) is in columns 6 through 9 and the remainder (1,234) is in 

 columns 2 through 5. 



^ABLE 7. — Steps in process of multiplying 3,514 by 7,596 to get 26,692,344 as a 

 computer might do this multiplication 



Steps 



1 Start 



2 Shift 



3 Add 



4 Add 



5 Add 



6 Shift 



7 Add 



8 Add 



9 Add 



10 Add 



11 Add 



12 Shift 



13 Add 



14 Shift 



15 Add 



16 Add 



17 Add 



18 Add 



Columns 



6 6 



6 7 



6 8 



6 9 



6 7 

 

 



7 5 



5 1 



2 7 



7 8 

 5 4 



3 



6 



8 2 



5 8 



8 6 



6 1 



1 9 



9 5 



7 1 



4 7 



2 3 



8 9 

 

 



9 6 

 9 2 

 8 8 



8 

 7 6 

 7 2 

 6 8 

 6 4 

 6 

 



9 G 

 6 



LOGICAL USES OF COMPUTERS 



So far we have considered digital computers only as they are fast 

 equivalents of a clerk with a calculator. The clerk functions were 

 assumed to be quite simple and the routine was spelled out in specific 

 detail. It was over 100 yeai-s ago that Lady Lovelace * said that a 

 digital computer "has no pretensions to originate anything. It can 

 do whatever we know how to order it to perform." The statement is 

 still true. It can be interpreted to indicate the limitations of com- 

 puters in that humans must think through in advance everything that 

 a computer might do and tell the computer specifically the course of 



* Her early Interest In computers Is considered on p. 282. 



