Basic function blocks of the computer
From a functional point of view, a personal computer can be represented as a microprocessor system containing four base units, or subsystems (Figure 1.8):
Fig. 1.8. Functional structure of the computer
• the central processor, which is responsible for performing the basic functions for organizing the processing of digital information;
• main memory block intended for storing and issuing digital information (commands and data) of executable programs. As a matter of fact, this unit ensures the normal functioning of the central processor and microprocessor system (computer) as a whole when executing programs;
• peripheral unit (external) devices, intended for entering the initial information, controlling the operation of the computer, displaying the results of processing and converting them to a form that satisfies the user's requirements;
• interface unit, which provides the interaction of devices and components of the microprocessor system, i.e. their coupling (alignment, compatibility) at the hardware, software and design levels.
Let's consider in general the separate functional blocks of the microprocessor system.
Central Processing Unit
There are three components in the processor:
• an operating device that executes a specific set of instructions (instructions): data transfer commands; commands of arithmetic, logical and bit operations; floating-point operation commands, unconditional control transfer commands and conditional branches; command of the organization of program cycles, stream processing of data, etc. The set of commands of modern processors counts several hundreds;
• the control device, whose main functions are to control the execution of commands, namely, the generation of the required sequence of control signals (micro-instructions performed on a single processor clock cycle). A set of micro-commands is a microprogram for this command. When executing individual microinstructions, informative signals (logical conditions, signs, flags) coming from the side of the operating device are used. Informative signals inform the control device of the status of the operating device;
• a memory device is a set of registers that form the processor's internal high-speed memory. Some registers are accessible to the programmer and are designed to store operands (processed data) and perform actions on them, generate addresses for interaction with the main memory and a number of other actions. Storing in the internal registers of operands greatly speeds up the execution of the program, since there is no need to access the main memory, which requires additional time. Another part of the registers, access to which can be limited and even excluded (software-invisible registers), is used by the processor for service (system) purposes. The memory device can also include the built-in cache memory that all modern processors have.
In addition to these basic devices, processors contain a number of specific devices used to implement various (processor) technologies.