Computing Hardware

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Chapter Overview

Digital data is represented by abstractions at different levels. At the lowest level all digital data are represented by binary data. Binary data is processed by physical layers of computing hardware, including gates, chips, and components. A logic gate is a hardware abstraction that is modeled by a Boolean function with values true (represented by a 0) and false (represented by a 1). A chip is an abstraction composed of low-level components and circuits that perform a specific function. A hardware component can be low level like a transistor or high level like a video card. Hardware is built using multiple levels of abstractions such as transistors, logic gates, chips, memory, motherboards, special purposes cards and storage devices. Applications and systems are designed, developed, and analyzed using levels of hardware, software, and conceptual abstractions.

A computer has several main parts. When comparing a computer to a human body, the CPU is like a brain. It does most of the 'thinking' and tells the rest of the computer how to work. The CPU is on the Motherboard, which is like the skeleton. It provides the basis for where the other parts go, and carries the nerves that connect them to each other and the CPU.



The motherboard is connected to a power supply, which provides electricity to the entire computer. The various drives (CD drive, floppy drive, and on many newer computers, USB drive) act like eyes, ears, and fingers, and allow the computer to read different types of storage, in the same way that a human can read different types of books.



The hard drive is like a human's memory, and keeps track of all the data stored on the computer. Most computers have a sound card or another method of making sound, which is like vocal cords, or a voice box. Connected to the sound card are speakers, which are like a mouth, and are where the sound comes out. Computers might also have a graphics card, which helps the computer to create visual effects, such as 3D environments, or more realistic colors, and more powerful graphics cards can make more realistic or more advanced images, in the same way a well trained artist can. All of these components are typically housed in a single enclosure called the computer case, which protects the internal components and provides airflow for cooling.


A computer case, also known as a computer chassis, tower, system unit, or simply case, is the enclosure that contains most of the components of a computer. Different form factors typically specify only the internal dimensions and layout of the case. Conversely, for rack-mounted and blade servers form factors may include precise external dimensions as well, since these cases must themselves fit in specific enclosures.




Computer cases usually include sheet metal enclosures for a power supply unit and drive bays, as well as a rear panel that can accommodate peripheral connectors protruding from the motherboard and expansion slots. Most cases also have a power button or switch, a reset button, and LEDs to indicate power status as well as hard drive and network activity. Some cases include built-in I/O ports (such as USB and headphone ports) on the front of the case. Such a case will also include the wires needed to connect these ports, switches and indicators to the motherboard.

Internal access

Tower cases have either a single side panel which may be removed in order to access the internal components or a large cover that saddles the chassis. Traditionally, most computer cases required computer case screws to hold components and panels in place (i.e. motherboard, PSU, drives, and expansion cards). Recently there is a trend toward "screw-less" cases, in which components are held together with snap-in plastic rails, thumbscrews, and other methods that do not require tools; this facilitates quick assembly and modification of computer hardware.

Power supply

A power supply unit (PSU) converts mains AC from a wall socket to low-voltage regulated DC power to operate the internal components of a computer and peripheral devices. Some power supplies have a switch to change between certain voltages. Other models have automatic sensors that switch input voltage automatically, or are able to accept any voltage between those limits.

The overall power draw on a PSU is limited by the fact that all of the supply rails come through one transformer and any of its primary side circuitry, like switching components. Total power requirements for a personal computer may range from 250 watts to more than 1000 watts for a high-performance computer with multiple graphics cards. Personal computers rarely require more than 300–500 watts. Power supplies are designed around 40% greater than the calculated system power consumption. This protects against system performance degradation, and against power supply overloading. Power supplies label their total power output, and label how this is determined by the amperage limits for each of the voltages supplied.

Some power supplies may have short circuit protection, overpower (overload) protection, over-voltage protection, under-voltage protection, over-current protection, and over temperature protection.

Expansion cards

The expansion card, also known as expansion board, adapter card or accessory card, is a printed circuit board that can be inserted into an electrical connector, or expansion slot on a computer motherboard, backplane or riser card to add functionality to a computer system via the expansion bus. Common expansion slot standards include PCI Express, PCI, and ExpressCard.


An expansion bus is a computer bus which moves information between the internal hardware of a computer system (including the CPU and RAM) and peripheral devices. It is a collection of wires and protocols that allows for the expansion of a computer.[1]

Physical construction

One edge of the expansion card holds the contacts (the edge connector or pin header) that fit into the slot. They establish the electrical contact between the electronics on the card and on the motherboard. Peripheral expansion cards generally have connectors for external cables.

Depending on the form factor of the motherboard and case, around one to seven expansion cards can be added to a computer system. When many expansion cards are added to a system, total power consumption and heat dissipation become limiting factors. Some expansion cards take up more than one slot space. For example, many graphics cards are dual slot graphics cards, using the second slot as a place to put an active heat sink with a fan.

Some cards are "low-profile" cards, meaning that they are shorter than standard cards and will fit in a lower height computer chassis. (There is a "low profile PCI card" standard that specifies a much smaller bracket and board area). The group of expansion cards that are used for external connectivity, such as network, SAN or modem cards, are commonly referred to as input/output cards (or I/O cards).

Expansion Card Types

Some expansion card types include:

Input and Output Peripherals

A peripheral device (often labeled I/O device or Input/Output device) is any equipment used to give a computer system more features. Input is anything that goes in and output is any thing that goes out. Any device for the computer that the computer can work without is peripheral equipment. This equipment is always separated from the central processing unit (CPU) by a device controller.

Peripheral equipment is necessary for people to interact with a computer system. Some peripheral equipment displays information (such as a computer monitor).


Some input devices include:


Some output devices include:


Input and Output devices

A central processing unit (CPU) is an important part of almost every computer. The CPU sends signals to control the other parts of the computer, almost like how a brain controls a body.

The speed that a CPU works at is measured in "Hertz", "Hz", however modern processors run so fast that "Gigahertz", "GHz", is used. One gigahertz is one billion hertz.

The desktop and server CPU market is controlled by two companies, Intel and Advanced Micro Devices (usually shortened to AMD). There are other CPU manufacturers but they have very limited users, due to their processors having a very specific application (such as use by the military or for low powered devices) or being too low in performance.

Types of CPUs

Most computer CPUs are based on the x86 instruction set architecture based on the Intel 8086 CPU introduced in 1978. The Intel 8086 was a 16-bit CPU, meaning it has an addressability of 16 bits or 64 KB.

Now, x86 typically refers to 32-bit CPUs and x86-64 refers to 64-bit CPUs. The main difference between these two processors is the structure. A 32-bit processor has an address space of about 4GB, which is why 32-bit processors can only support up to 4GB of RAM. This also means that a 32-bit CPU can handle fewer instructions at one time in comparison to a 64-bit CPU. A 64-bit processor has an address space of up to 192GB. The amount of memory that a processor can handle does not only depend on the processor however, but it also depends on the operating system of the machine. For example, a Windows 7 Basic OS with a 64-bit processor can only handle 8GB of memory. Compare that to Windows 7 Ultimate with a 64-bit processor, which can handle 192GB of memory.


Here are some of the basic things a CPU can do:

  • Add one number with another
  • Test to see if one number is bigger than another
  • Move a number from one place to another
  • Get a number from memory
  • Jump to another place in the instruction list
  • Execute Commands

Combining many simple instructions like these can make very complicated programs. This is possible because each instruction takes a very short time to happen. Many CPUs today can do more than 1 billion (1,000,000,000) instructions in a single second. In general, the more a CPU can do in a given time, the faster it is.

A CPU is built out of logic gates; it has no moving parts. The CPU of a computer is connected electronically to other parts of the computer, like the video card, or the BIOS. A computer program can control these peripherals by reading or writing numbers to special places in the computer's memory.

Multiple Cores

Newer processors have "Multiple Cores". This means that they have many processors built on to the same chip so that they can do more than one thing at once.

While the individual cores might be slower than a single core processor, all the cores can work together to go faster. This means that the GHz might be lower, however the overall speed of the processor will be higher.

To make an analogy, think of cars;

  • One car travelling at 100 miles per hour for an hour will cover 100 miles.
  • Four cars travelling at 70 miles per hour for an hour will cover only 70 miles each, but together they will cover a total of 280 miles.

In computing, memory refers to the physical devices used to store programs (sequences of instructions) or data on a temporary or permanent basis for use within the computer.

Characteristics of Memory

Evaluating and measuring certain core characteristics can differentiate storage technologies at all levels, including both primary and secondary storage. The characteristics are volatility, mutability, accessibility, addressability, capacity, and performance.


  • Non-volatile memory will retain the stored information even if it is not constantly supplied with electronic power. This makes it suitable for long-term storage of information.
  • Volatile memory requires constant power to maintain the stored information. The fastest memory technologies of today are, in general, volatile ones. Since primary storage is required to be very fast, it predominantly uses volatile memory.


  • Read/Write storage (mutable) allows information to be overwritten at any time. A computer without some amount of read/write storage for primary storage purposes would be useless for many tasks. Modern computers typically use read/write storage also for secondary storage.
  • Read only storage retains the information stored at the time of manufacture, and write once storage allows the information to be written only once at some point after manufacture. These are called immutable storage.


  • Random access memory allows any location in storage to be accessed at any moment in approximately the same amount of time. Such a characteristic is well suited for both primary and secondary storage.
  • Sequential access memory requires that accessing pieces of information be in a serial order, one after the other; therefore the time to access a particular piece of information depends upon which piece of information was last accessed.


  • In location-addressable memory, each individually accessible unit of information in storage is selected with its numerical memory address. Location-addressable storage usually limits to primary storage, accessed internally by computer programs, since location-addressability is very efficient, but burdensome for humans.
  • In file addressable storage, information is divided into files of variable length, and a particular file is selected with human-readable directory and file name. The underlying device is still location-addressable, but the operating system provides the file system abstraction to make the operation more understandable.
  • In content-addressable storage, each individually accessible unit of information is selected based on the basis of (part of) the contents stored there. Content-addressable storage can be implemented using software (computer program) or hardware (computer device), with hardware being faster but more expensive option. Hardware content addressable memory is often used in a computer's CPU cache.


  • The raw capacity is the total amount of stored information that a storage device or medium can hold. It is expressed as a quantity of bits or bytes.


  • Latency is the time it takes to access a particular location in storage. The relevant unit of measurement is typically nanosecond for primary storage and millisecond for secondary storage. It may make sense to separate read latency and write latency, and in case of sequential access storage, minimum, maximum and average latency.
  • Throughput is the rate at which information can be read from or written to the storage. In computer data storage, throughput is usually expressed in terms of megabytes per second or MB/s, though bit rate may also be used. As with latency, read rate and write rate may need to be differentiated. Also accessing media sequentially, as opposed to randomly, typically yields maximum throughput.
  • Granularity is the size of the largest "chunk" of data that can be efficiently accessed as a single unit, e.g. without introducing more latency.
  • Reliability is the probability of spontaneous bit value change under various conditions, or overall failure rate

Types of Memory

Primary Storage

Primary storage (or main memory or internal memory), often referred to simply as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in uniform manner.

Random Access Memory (RAM)

Random access memory (or simply RAM) is the memory or information storage in a computer that is used to store running programs and data for the programs. Data (information) in the RAM can be read and written quickly in any order. Normally, the random access memory is in the form of computer chips. Usually, the contents of RAM are accessible faster than other types of information storage but are lost every time the computer is turned off. Dynamic random access memory (DRAM) is the majority in computers.

Read-Only Memory (ROM)

Read-only memory (or simply ROM) is a type of computer memory. Unlike RAM, it keeps its contents even when the computer or device is turned off. Usually, ROM cannot be written to when the computer runs normally. ROM is used for important programs like the BIOS which tells the computer how to start, or the firmware of certain devices, which usually does not need to be modified. Usually, ROM comes on computer chips.

Secondary Storage

Secondary storage (also known as external memory or auxiliary storage), differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile. Per unit, it is typically also two orders of magnitude less expensive than primary storage. Modern computer systems typically have two orders of magnitude more secondary storage than primary storage and data are kept for a longer time there.

Examples of secondary storage include:

Abstraction And Hardware

The process of abstraction involves removing detail and generalizing functionality. It is used extensively in computing systems where:

  • bits are represented by transistors, capacitors, magnets, switches, and other physical components that have two states.
  • bit components are grouped together into computer chips, such as CPU and RAM chips.
  • computer chips are grouped together into logic boards, such as a motherboard.
  • boards are grouped together in cases to form the computing device.

Similarly data has multiple layers of abstraction:

  • bits are grouped into 8-bit bytes in the system on into 4-bix hex digits for viewing by humans
  • multiple bytes can be grouped to form data types like a floating point number or a pixel with millions of possible colors
  • multiple data types can be grouped into files to be managed, or into data units like SMS messages used to send texts.

Similarly software has multiple layers of abstraction:

  • Computer programs are written in high-level programming languages
  • The high-level language is translated by a software tool such as a compiler to binary
  • The binary program is passed to the computing device's operating system to be executed on the hardware described above.


Parts of this page are based on information from: Wikipedia: The Free Encyclopedia