288 



ANNUAL REPORT SAOTHSONIAN INSTITUTION, 1960 



The speed of a digital computer means the speed at which it can 

 perform aritlmietic operations. This may be tens of thousands per 

 second. The size of a computer generally indicates the amount of 

 information that may be contained in its storage, possibly millions 

 of words. 



Note that the computer need do only a limited number of opera- 

 tions. In the program given above, the "operation" to be performed 

 in storage locations 000, 002, 004, 005, and 007 are all the same. They 

 differ only in the address of the number to be added to tlie number 

 already in the accumulator. Thus each instruction consists of two 

 parts, an operation portion and an address, or in other words, what 

 to do and wheref rom to do it. 



Numbers can be used to designate operations. Thus the add opera- 

 tion in drawers or storage locations 000, 002, 004, 005, and 007 can be 

 arbitrarily designated to the computer as "1," the sitbtract operation in 

 008 as "2," the multiply in 001 as "3," the store of 003 and 006 as "5," 

 and the decision operation in 009 as "7." If each word of a computer 

 consists of 10 decimal digits with the operation digit in the 6th posi- 

 tion and the address digits in the 8th, 9th, and 10th positions, then 

 the above compound-interest problem can be specified to a computer 

 as shown in table 1. This is a "program" for computer operation; 



* Tables 1, G, 7, and 8 and figure 1 are reprinted by permission from "Digital Computer 

 Primer," copyright 1959, McGraw-IIlll Book Co., Inc. 



