Digital Computers

A digital computer is a digital system that performs various computational tasks. The term "digital" implies that the information within the computer is represented by variables that take a limited number of discrete values. These values are processed internally by components that maintain a finite number of distinct states. For instance, decimal digits (0, 1, 2, ..., 9) provide 10 discrete values. The earliest electronic digital computers, developed in the late 1940s, were primarily used for numerical computations. From this application, the term "digital computer" emerged.

In practice, digital computers function more reliably if only two states are used. Due to the physical limitations of components and because binary logic (i.e., true-or-false, yes-or-no statements) aligns well with human reasoning, digital components are generally constrained to two values, which are binary.

Binary System

Digital computers use the binary number system, which has two digits: 0 and 1. A binary digit is called a bit. Information is represented in digital computers in groups of bits. Through various coding techniques, groups of bits can represent not only binary numbers but also other discrete symbols, such as decimal digits or letters of the alphabet. By effectively utilizing binary arrangements and coding techniques, groups of bits are employed to develop comprehensive instruction sets for performing diverse types of computations.

Binary to Decimal Conversion

In contrast to the common decimal numbers that use the base-10 system, binary numbers use a base-2 system with two digits: 0 and 1. The decimal equivalent of a binary number can be determined by expanding it into a power series with a base of 2. For example, the binary number $1001011_2$ can be converted to a decimal number as follows:

$1 \times 2^6 + 0 \times 2^5 + 0 \times 2^4 + 1 \times 2^3 + 0 \times 2^2 + 1 \times 2^1 + 1 \times 2^0$

$= 64 + 0 + 0 + 8 + 0 + 2 + 1$

$= 75$

Thus, the binary number $1001011_2$ represents the decimal number 75. However, the same group of seven bits could represent the letter 'K' when used with a binary code for the alphabet or a control code for specific logic decisions in a digital computer. In essence, groups of bits in a digital computer can represent many different things, similar to how letters in an alphabet construct different languages.

Computer System Components

A computer system is often divided into two main functional entities: hardware and software.

• Hardware: Consists of all electronic components and electromechanical devices that make up the physical entity of the device.
• Software: Comprises instructions and data manipulated by the computer to perform various data-processing tasks. A sequence of instructions is known as a program, and the data manipulated by the program is referred to as the database.

System Software

System software of a computer includes a collection of programs designed to make the computer more efficient. These programs are referred to as the operating system, distinguishing them from application programs written by users to solve specific problems. For example, a high-level language program written to meet particular data-processing needs is an application program, whereas a compiler translating the high-level language program to machine language is a system program. System software is crucial as it bridges the gap between user needs and hardware capabilities.

Major Parts of Computer Hardware

The hardware of a computer is typically divided into three major parts:

1. Central Processing Unit (CPU): Contains an arithmetic and logic unit for manipulating data, various registers for storing data, and control circuits for fetching and executing instructions.
2. Memory: Stores instructions and data, known as random-access memory (RAM) because the CPU can access any location randomly within a fixed interval.
3. Input and Output Processor (IOP): Includes electronic circuits for communication and control of information transfer between the computer and the outside world. Input and output devices connected to the computer include keyboards, printers, terminals, magnetic disk drives, and other communication devices.

Distinctions in Computer Hardware

When dealing with computer hardware, three areas are often distinguished:

• Computer Organization: Concerned with how the hardware components operate and are connected to form the computer system. It examines the organizational structure to ensure the parts function as intended.
• Computer Design: Focuses on the hardware design of the computer. After formulating computer specifications, the designer develops the necessary hardware, determining the components and their connections. This aspect is sometimes referred to as computer implementation.
• Computer Architecture: Involves the structure and behavior of the computer as perceived by the user. It includes information formats, the instruction set, and memory addressing techniques. The architectural design specifies the functional modules, such as processors and memories, and how they integrate into a complete computer system.