The basic computer consists of four blocks: processor, memory, input and output. Let’s consider the role these blocks play in information processing.
The peripheral devices bring information to the computer through the input, and gain information from the output. Memory is stores all the information processed by the computer and also the instructions that relate to information processing. Figure 1 shows the block diagram for a digital computer and the interaction between the processor and memory element.
Information is stored in the memory element in the form of bits or binary digits in registers containing several bi-stable storage elements. The length of each register and their number is determined in the specification of the computer. To select a register the processor should provide the address code which is decoded to open the selected communication channel. The length of the address code depends on the number of registers in the memory.
To perform fast characteristics the time-delay between presenting an address code, access time and reading the memory should be hundreds of nanoseconds. A large memory can be constructed from sub–units of LSI random access read write memory (RWM) modules. Other forms of memory are also required like read only memory (ROM) for keeping the information without any change, programmed read only memory (PROM), that allows the change of fixed information in accordance to versions of the system.
On the topic of processors, the specification of a processor is very specific. It depends on many factors and may vary greatly from model to model. However, there are some points that unify processors. Processors are carrying arithmetic and logical operations for data stored in the memory. The first processor gains the instructions of operations that must be performed with data. Afterwards the data should be found in the memory and brought to the processor to perform operations. The instructions of operations are stored as bits in corresponding registers.
Interaction processor and memory goes through the ports READ, WRITE, SELECT (each port has it’s own meaning). The SELECT port passes the access code to request the READ or WRITE channel between memory and processor. The processor contains the control unit and data paths. The control unit monitors the correct sequence of actions in the data path. The data path consists of the function unit, accumulator register, counter register and buffer register. Figure 2 shows the interconnection between the control unit and data path.