in the 8008 computer CPU. These two registers can be osed to directly "point" to a specific word in memory so that the computer may obtain or deposit information in a different pari of memory than that in which a program is actually being executed-The reader should recall that a special part of the central processor unit (CPU) termed the program counter is used to tell the computer where to

It has been said that the computer is the most versatile machine in existence and that its applications are limited only b> man's ability to develop progrjms that direct the operation of the machine.

obtain the next instruction while executing a program The program counter was effectively a "double word length" register that could hold the value of any possible address in memory. The program counter is always used to tell the machine where to obtain the next instruction. However, it is often desirable to have the machine obtain some information such as a "data word" — from a location in memory that is not connected with where the next instruction to be performed is located. This cam be accomplished by simply loading "register H " with the "high address" (page) portion of an address in memory, then loading register L" with 1 Fie "low address'1 portion of an address in memoiy, and then utilizing one of a class of commands that will direct the CPU to fetch information from or deposit information into the location in memory that is specified {"pointed to") by the "H" and "L" register contents. This information flow can be from/to the location specified in memory and any of the CPU registers.

At this time it would be beneficial for the reader to study Fig. 10. Fig, 10 is an expanded block diagram of Fig. 2(b) and shows the units of the computer which have been presented in the previous several pages.

Until now no mention has

The computer s great versatility comes about because the machine is capable of executing a large group of instructions in an essentially limitless series of combinations.

been made of how information is put into or received from a computer. Naturaliy, this is a very vital part of a computer because the machine would be rather useless if people could not put information into the machine upon which calculations or processing could be done, and receive information back from the machine when the operations!*) had been performed!

Communications between the computer and external devices - whether those devices be simple switches, or

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