Structure and function of a computer system

Structure

In general:-
Structure of a system or a sub-system is defined as the interconnection of its components.

Defining structure in terms of a hierarchical system:-
When a complex systems like computer is depicted as an hierarchical system then the interconnection of the components at a particular level of the hierarchy is defined as the structure at that level.

Structure of a computer

Structure of a CPU

Structure of a control unit

Topmost level components of computer structure are as follows:-

1. CPU(Central processing unit)/Processor
2. Memory
3. System bus
4. I/O
5. Communication lines
6. Remote devices

All these above components are explained below:-

CPU(Central processing unit)/Processor

A computer system can be seen as a centralized system where CPU lies at the center. It controls all other components of the computer system. It processes the data and all data transfer operations are routed via CPU(except DMA transfer technique).

Memory

Memory is a storage component of the computer system. All the instructions and data are stored here.

System bus

System bus is a combination of parallel wires. All the data movement from one address to other address among the componets of computer structure except remote devices is done via system bus.

I/O devices

These I/O devices moves data between the computer and external environment. Input devices send data to the computer system from the external environment.
For examples:- Mouse, Keyboard, Microphone, Camera, Scanner, etc.
While, output devices receive data from the computer system.
For example:- Monitor, Speaker, Printer etc

Communication lines

To communicate devices which are at remote places or can't be connected to system bus directly are connected to the computer via communication lines. These communication lines can be wired or wireless.
For example:- Ethernet cable, Bluetooth, WiFi, Wireless internet connection etc.

Remote devices

Those devices which communicates with the computer over communication lines are called remote devices.
Foe example a keyboard connected to the computer via bluetooth.

Computer structure

The structural components of cpu are as follows:-

1. Control unit
2. Register array
3. ALU(Arithmetic logic unit)
4. Internal bus

All these above components are explained below:-

Control unit

Contol unit manages all the resources of the computer system. All the instruction of the computer are achieved when sequence of some microoperations are are executed. This sequence of microoperations is controlled by control unit.

Registers array

Registers array has a number of arrays. It stores data temporarily before data is fed to ALU and after data is received from ALU. Registers are faster than memory but expensive.

ALU(Arithmetic logic unit)

All the data processing tasks are carried out in ALU.

Internal bus

It provides the connection between ALU and registers array for data movement inside CPU.

Structural components of CPU

The structural components of control unit are as follows:-

1. Address sequencer
2. CAR(Control address register)
3. Control memory
4. CDR(Control data register)

All these above components are explained below:-

Address sequencer

Address sequences generates the address of next microoperation in control memory.

CAR(Control address register)

Contol address register holds the address generated by address sequencer.

Control memory

Every computer has finite number of microoperations. Every microoperation is represented by string of 0's and 1's. This is called control word. These control words are stored in the control memory.

CDR(Control data register)

Control data register holds the control word provided by the control memory.

Structural components of control unit

Function

The operations performed by a system or a sub-system or a component is called its function.

All the functions of computer can be classified into following four functions:-

• Control
• Data processing
• Data storage
• Data transfer

All these functions are explained below:-

Control

A computer controls all its other functions like data transfer, storage and processing. A computer is connected to various peripherals. All these devices use resources like memory, ALU, registers, etc. Computer also make these resources available as per the instructions. In case of multiple request for a particular resource a computer decides how to handle requests coming for these resources.

Data transfer

Data has to be moved from one one location to another location in computer world for retrieval, processing or storing at some different location. Most frequent data tranfer routes are:-
memory-memory,
memory-peripherals,
memory-remote devices over communication lines,
peripherals-peripherals,
peripherals-remote devices over communication lines and
remote devices-remote devices over communication lines.

If the data transfer is between the computer and a device that is directly connected to it then it is called I/O communication or peripheral communication.
Here devices receive and send data over system bus.

If the data transfer is between the computer and devices which is connected to the computer with communication lines then it is called data communication.
Here devices receive and send data over communication lines.

Data storage

A computer stores data in its memory or registers. On the fly data (data which come for processing and are send) are stored temporarily. These data are stored in processor registers. While data which are to be retrieved or updated further are stored in its memory.

Data processing

Data are processed to obtain new data. All the data processing operation like arithmetic and logical operation are performed inside computer.

The differences between computer function and computer structure are as follows:-

Computer function	Computer structure
Definition
The operation perfomed by a computer is called computer function.	The interconnection of top-level componets of the computer system is called computer structure.
Control, data processing, data storage and data transfer are computer functions.	CPU, memory, system bus, IOP(Input-output processor), input devices, output devics, communication lines and remote devices are the components the computer structure.
Relation
Computer functions are realized by the computer structure.	Computer structure develops a system to provide computer functions.

Citation:-
Stallings, W. (2010). Computer Organization and Architecture: Designing for performance. Prentice Hall.