Control signals .
So far we have talked about the program as a means of symbolic description of the algorithm. Now the concept of the program is meaningful way to the functioning of the CA, whose actions are initiated by a sequence of signals CU. If the control unit is designed to execute a single program and works without external influences, then we say that it has a rigid circuit or logic operation.
In another approach, CU provides control signals only when its input is present a special code of the current instruction program. Each command is divided into reading the code from an external data carrier and the actual execution. CU it plays the role of the transducer coded commands in the program control signals. Such an approach to N is called the principle of program management. It allows you to move on to implementing another algorithm, without any alterations were N. It's enough to write to the storage medium of the new program.
Work a simple jukebox - one of the most ancient manifestations of the principle of program management. The pins are located on a rotating drum, hurt when they move the vibrating plate to sound a different height. Strategically placed the pins you can play some tunes. To get the machine to perform a new melody, enough to place the pins differently. The principle of management software known to mankind has long been realized in the jukeboxes, toys, many mechanisms. As the media in such devices were used rotating disks and drums with holes or protrusions, gears, paper tape. Unfortunately, they all have a low speed.
On the way to a computer or the principle of in-memory program.