31 : 5/ Electronic Computers 



581 



The computer itself understands the steps which it should follow only 

 in terms of sets of two to four (decimal) digit numbers. These are hard 

 for the programmer to learn and remember, whereas sets of three letters 

 are much easier to remember, particularly if they resemble English 

 words. Various schemes have been developed to make it possible to 

 use abbreviations resembling English and algebraic symbols with which 

 to write these codes. For example, in one such code, CLA means clear 

 and add, MPY means multiply, FSB means floating (point arithmetic) 

 subtract, and LXD means load index from decrement. Another 



Figure 4. An analog computer to simulate peroxidase reactions. 

 An oscilloscope may be connected to display voltage at 

 terminals x, p, p' , and a. Clamps C hold terminals at ground 

 until time zero. Constants e, a , k + , &_, l + , and m+ may be 

 varied by twiddling knobs. The entire pattern repeats about 

 once a second. Note use of feedback loops to produce analogs 

 of the differential equations. 



