Image credit: National Instruments | Phoenix Contact USA | Nortech Engineering

Computers are digital devices used to process, store, and display information.  Computers can be considered programmable machines. Throughout modern history, the term "computer" has generally referred to a mechanical or digital device which is able to respond to and execute a specific series of instructions, known as a program. Modern computers are digital electronic devices and consist of two broad groups of components: hardware and software.

Hardware

Computer hardware refers to the physical wires, transistors, and circuits which facilitate processing of software code.

Depending on the machine's form factor, these components have the capability of appearing radically different. For example, a touchscreen tablet computer's input and output components are combined into one multipurpose display, while a desktop personal computer (PC) has discrete input, output, and processing units (a keyboard/mouse, monitor, and system unit or "tower," respectively).

A deconstructed tablet computer; the identical (yet different) components of a desktop PC.

Image credit: Nikkis | Microsoft

All general-purpose computers require the following hardware components:

CPU

The central processing unit (CPU) is the core of the modern computer and is responsible for executing stored instructions. CPUs are sometimes called processors or microprocessors. A computer may contain more than one CPU, in which case it is referred to as capable of multiprocessing.

CPUs consist of two important parts: the arithmetic logic unit (ALU) and a control unit (CU); they may also contain registers. The CPU's components are linked to other areas of the computer via electrical buses.

• The ALU performs logic and arithmetic operations and is capable of complex calculations, including equations, trigonometry, and logic functions.
• The control unit is responsible for fetching instructions from the computer's memory and delivering them to the ALU. The CU bridges most of the computer components, as it acts as an intermediary between the CPU, memory, and other units.
• Registers are storage areas which reside in the CPU. The control unit fills the registers with data for easy accessibility and to avoid the slower-reading memory areas.

The diagram below shows an oversimplified view of the components and operation of a CPU. Note that the memory unit almost always exists outside of the CPU, but is linked to it via the control unit. All of the components of this image are described in more detail below.

Image credit: Hey Plumpkin

Memory

A computer's memory stores data, whether temporarily or semi-permanently. Computer memory is comprised of semiconductor integrated circuits (IC) which store binary data in tiny memory cell transistors. Each memory cell is able to store a single bit (a single binary digit). Each cell may be read or written by the control unit.

Input

All computers contain one or more input devices, which include alphanumeric keyboards, pointing devices (such as mice or touchpads), and microphones. Input components are responsible for the flow of data, information, and instructions into a computer's processor.

Output

Output components display processed data and other information to the operator. These devices include video monitors and screens as well as printers.

Software

The term "software" refers to a set of readable instructions which directs a computer's processor to perform predefined operations. Because the processing unit can only understand and interpret binary code, a human-understandable source code — written in a programming language — acts as an intermediary between a human operator and the processor.  

Software as a broad term encompasses all non-physical ("non-touchable") components. This definition includes:

• System software, which provides a platform for running applications and operates the hardware on a basic level.  
• Application software, which refers to all useful scripts functioning beyond the basic operation of the hardware. This type allows the computer to perform useful tasks such as media creation, word processing, financial accounting, and gaming.
• Plugins (also known as extensions) modify or improve other pieces of software.
• Embedded software exists within embedded systems, such as those which reside in modern vehicles or televisions. Embedded software may be considered to combine certain features of system and application software within the same framework.

Complexity

While the examination of hardware and software alone gives the illusion that computers are simple devices, modern computers perform billions of binary operations per second and are capable of extremely complex processing. While small embedded computers are sometimes used only to perform basic mathematical calculations (as in a handheld calculator), multiprocessor machines have been used throughout the 20th and 21st century to perform complex tasks. As of 2012, single semiconductor processors are capable of executing well over 100 billion instructions per second (IPS).

Since the inception of the modern personal computer, both microprocessor speeds and the number of transistors per integrated circuit have increased exponentially. In accordance with Moore's Law, an observation stated in 1965, these two specification values have roughly doubled every two years, as shown in the graph below. This rapid development has largely defined technological and social change during the "Information Age" of the late 20th and early 21st centuries.

More information on processor speed can be found in the "Speed" section below.

Processor clock speeds (in Hz) since 1971.

Image credit: singularity.com

Applications

Computers are ubiquitous in modern society. They are found in applications ranging from "smart" toys and telephones to mission-critical military systems and spacecraft.

Industrial computers can be used for an equally diverse range of applications, depending upon the machine's processing power and the software it runs. Examples include:

• Machine control
• Computer-aided design (CAD)
• Device networking
• Data acquisition and analysis
• Computer-integrated manufacturing

The image below shows a screenshot of a welding software program, an example of an industrial computing application. Engineers can use this tool to calculate part dimensions, select recommended consumables, and plan processes.

Image credit: EWI

Types of Computers

Computers are generally classified by their form factor, which, as described above, can be radically different depending on the size and construction of the machine's individual components. Common types are listed in the table below.

Table image credits: Pixelvolt |  Windows Blogs | PCWorld | New Mexico State University

123rf | Newell High School | University of New Mexico | Seattle Times

Specifications

Storage

Computer memory is rated using the storage capacity in bits. Modern computers are specified in bytes, each of which consists of 8 bits.

Computer memory can be divided into two types: random access memory (RAM) and read-only memory (ROM).

RAM is a type of primary memory which can be directly accessed by the CPU. A computer's RAM capacity is significantly less than its ROM capacity (under 1 gigabyte [GB]) but is faster and easier to access. Machines with higher RAM capacities often operate faster than those with smaller ones.

ROM is used for longer-term data storage and includes hard drives and optical drive devices. Modern computers can typically store between 20-120 GB of data in read-only memory. Higher ROM capacity results in increased capability to store programs and files.

For more information about semiconductor memory, please visit the Memory Chips Selection Guide.

Speed

Processor speed, often referred to as clock rate, is measured in Hertz. Clock speed can generally be used to determine the machine's operating speed, although it is most helpful when comparing CPUs with similar architectures. For example, an Intel 486 CPU running at 1 GHz will run roughly twice as fast as a 486 rated to 500 MHz, but comparing the former machine to a 500 MHz processor with a different architecture will not result in a 2:1 speed ratio. This is due to the fact that overall speed is also determined by the computer's memory capability and structure.

Standards

Computers, especially those used for military and industrial applications, may be manufactured, programmed, and used according to various published standards. Example standards include:

• MIL-C-5414 - Air navigation computer, type MB-4A
• BS 5905 - Specification for computer programming language Coral 66
• CSA N286.7 - Quality assurance of analytical, scientific, and design computer programs for nuclear power plants

References

Shutha - The Computer (hardware, software, and operating systems)