Introduction to Digital Computer Organization

The Organization of a Digital Computer

• A digital system is an interconnection of digital hardware modules that accomplish a specific information processing task. 
• Digital systems vary in size and complexity from a few integrated circuits to a complex system of interconnected and interacting digital computers. 
• Digital system design invariably uses a modular approach. The various modules of a digital system are constructed from such digital components as registers, decoders, arithmetic elements, and control logic. 
• The various modules of a digital system are interconnected with common data and control paths to form a fully functional digital system.

Here is a Presentation on Basic Computer Organization.

Hardware and Software:

• The digital computer is a digital system that performs various computational tasks on binary  digits - 0 and 1, called bits. 
• Information is represented in digital computers in groups of bits.
• In the simplest term, a digital computer is a fast electronic calculating machine that accepts digitised input information, processes it according to a list of internally stored instructions, and produces the resulting output information.

Fig.: Block Diagram of a Digital Computer

• Digital computers make use of both hardware and software to store and process data of various types.  
• The hardware consists of electronic components, input output devices, magnetic and optical storage media, electromechanical devices, and communication facilities.
• Software consists of instructions and data that the computer operates on to perform various data-processing tasks 
• A sequence of instructions to follow by the computer is called a program.
• System software is a collection of programs whose purpose is to make more effective use of hardware resources of the computer
• It is important to consider both hardware and software aspects of a digital computer in order to achieve a good understanding of computer systems.

Basic Building Blocks of a Digital Computer:

• The hardware of the computer is usually divided into three major parts - the Central Processing Unit (CPU), Random Access Memory (RAM) and Input and Output Processor
• The Central Processing Unit (CPU) contains an Arithmetic and  Logic Unit (ALU) for manipulating data, a number of Registers for storing data, and Control Circuits for fetching and executing instructions.
• The main memory contains storage for instructions and data. It is called as Random Access Memory (RAM) because the CPU can access any location in memory at random and retrieve the binary information within a fixed interval of time. 
• The Input and Output Processor (lOP) contains electronic circuits for communicating and controlling the transfer of information between the computer and the outside world. 
• The input and output devices connected to the computer include keyboards, printers, terminals, magnetic disk drives, and other communication devices

The Role of CPU:

• The Central Processing Unit (CPU) is the central or major unit of a computer that executes machine instructions and coordinates the activities of other units of a computer.
• The CPU is often called the Instruction Set Processor (ISP), or simply the Processor.
• It performs the tasks such as fetching, decoding, and execution of machine instructions in a program.
• Most of the computational operations are performed by the Arithmetic and Logic Unit (ALU) of the processor.
• Suppose two numbers are located in memory to be added, they are brought into the processor, and the addition is carried out by the ALU

Computer Organization & Architecture:

• The term Organization is concerned with the way the hardware components are connected together and operate to perform the various functionalities of a digital system. 
• Computer Organization refers to the formation of a digital computer by interconnecting its various operational units that realise the architectural specifications of the hardware components of the computer.
• The term Design is concerned with the hardware design of the computer. Once the computer specifications are formulated, it is the task of the designer to develop hardware for the system.
• The architectural design of a computer system defines the specifications of various functional modules, such as processor and memory, and structuring them together into a computer system.
• Computer Architecture is concerned with the structure and behaviour of a digital computer as seen by the user. It defines the internal architecture of a computer by specifying the information formats, the instruction set, and techniques for addressing the memory for storage and computation.