GCSE Computing: Hardware

Contents

Keywords
The Central Processing Unit (CPU)

How it works

The fetch-execute cycle

Dual-core and quad-core processors

How common characteristics of CPU's such as clock speed, cache size and number of cores affect their performance

Summary
Memory

Units

Random access memory (RAM)

Read-only memory (ROM)

Virtual memory

ROM chips and flash memory

Flash memory

Change in Memory Technologies and Innovative Computer Designs
Summary
Binary Logic

NOT gate

AND gate

OR gate

Logic circuit's

Logic in Programming

Summary

Input and Output Devices

Input devices

Input devices for users with specific needs

Output devices

Output devices for users with specific needs

Summary

__________________________________________

Keywords

Computer architecture: The internal, logical structure and organisation of the computer hardware.

Binary: A number system consisting of two digits: 1 and 0

CPU (Central Processing Unit): A hardware that executes instructions. Contains the control unit, ALU and cache memory.

Control unit: A part in the processor that helps maintain the flow of data within the system.

ALU (Arithmetic Logic Unit): Performs all mathematical operations.

RAM (Random Access Memory): Stores data of programs currently being run - applications, etc.

ROM (Read-Only Memory): Memory that cannot be overwritten.

Cache memory: Special high speed memory used by the computer.

Flash memory: Solid-state memory use as low cost secondary storage i portable devices and as removable memory.

Solid states: Technology based on electronics with no moving parts like transistors and capacitors.

Secondary storage: Non-volatile storage used to store programs and files that need to be retained.

Fetch-execute cycle: The process of fetching the instructions from memory, decoding them and then executing them so that the CPU performs continuously.

Program counter (PC): Part of a CPU that contains the number of the next instructions to be fetched.

Register: A very fast memory location within a processor.

Decode: The CPU must now make sense of the instruction it has just been fetched.

Execute: The instruction can be carried out. The result of the instruction are then stored in another register. The cycle can begin again.

Clock speed: Maintains the computers speed - timing of the fetch-execute cycle to ensure instructions are processed in the correct order.

Clock chip: The electronic device in a computer that controls the timing of signals.

Bus: A part of the computer architecture that transfers data signals between the component and the computer.

Motherboard: The central printed circuit board (PCB) that holds the crucial components of the system.

Dual-core/quad-core: A CPU with multiple processors (dual meaning two processors; quad meaning four processors).

Volatile: Data lost when power is not supplied

Non-volatile: Date retained even if power is not supplied.

Virtual memory: A section of the hard disk used as if it were RAM to supplement the amount of main memory available to the computer. Used when there is not enough memory to tun the programs required.

Logic gate: A circuit that produces an output based on the input:

Not gate: A logic gate that outputs the opposite value to the input.

And gate: A logic gate that outputs 1 if both inputs are 1.

OR gate: A logic gate that outputs 1 if either, or both, of the two inputs are 1.

Truth table: A method of recording all the possible input combinations ad determining the output for each.

Logic circuit: A circuit made by combining a sequence of logic gates.

Boolean algebra: A method for expressing mathematically a log circuit.

Input device: A hardware device used to input data into a computer system for processing.

Keyboard: A device that uses labelled keys to enable data input into a computer.

Mouse: A device that controls the movement of a pointer on screen based on its own movement and allows the user to select an object by pressing the button.

Touch screen: A touch sensitive surface that allows the user to select , control or move objets by touching icons and symbols using fingers.

Microphone: A device for capturing sound.

Camera: A device to capture stills or moving images.

Bar code: A pattern of thin and thick lines representing a number than can be scanned by a reader for input into a computer system.

RFID (Radio Frequency Identification): Uses radio frequency to represent a number that an be scanned for input into a computer.

Sensor: A device that can detect physical conditions such as temperature, weight, light sound, etc.

Output device: A hardware device used to output data into a computer system for processing.

Monitor: A device that can display images and text.

Printer: A device to produce physical copies of output from a computer system.

Speaker: A device to output sound,

Actuator: A device to produce physical movement based on output from a computer.

Magnetic hard disk: Secondary storage device using magneto platters to store data and files.

Optical disk: Secondary storage device using lasers to read (and write) data to a reflective surface. For storing files to be distributed, transferred or for backup of important files.

CD: A type of optical device with a capacity of 700MB.

DVD: A type of optical device with a capacity of 4.7GB.

EEPROM: Electronically Erasable Programmable Read Only Memory.

The Central Processing Unit (CPU)

How it works

The CPU is the core of every computer system and has two main components: the control unit and the arithmetic and log unit (ALU). The control unit uses electrical signals to direct the system to execute the instructions in stored programs. The ALU carries out all the arithmetic ad logical operations, including addition, subtraction and comparisons (greater than; less than; equal to).

The CPU needs to access the main memory, RAM (random access memory), where programs are stored, and the cache memory, which is used to store data waiting to be processed. These two components are called primary storage and are part of the computer's processing capabilities. Primary storage are volatile data.

Hard drives and other devices like flash memory drives and solid-state drives are called secondary storage. Secondary storage is non-volatile data.

The fetch-execute cycle

The fetch-execute cycle is the number of the next instruction is taken from the PC. This instruction is taken from the PC. The instruction is fetched from the main memory and stored in a register on the CPU. Buses between the CPU and memory are used to transfer this. The PC can be incremented by 1 so it is ready for the cycle to begin again. This idea was created by Jon Von Neumann.

Cache memory is fast memory that is located close to the main CPU with dedicated connections so the CPU has fast access to the frequently used data.

Dual-core and quad-core processors

The clock speeds in use today are close to the limit for the existing technology so another way of improving, the multi-core processor: a dual-core processor simply means that two CPU's are working simultaneously; they may have their own cache memory or may share Level 2/3 ache, but they both follow the fetch-execute cycle meaning the computer can process more instructions.

How common characteristics of CPUs such as clock speed, cache size and number of cores affect their performance

The clock speed determines the rate at which instructions are carried out. The higher the clock speed, the faster each instruction is fetched and executed. Each tick of the clock is used to synchronise the processor. Each and every operation of the processor takes a fixed number of ticks. Therefore, if the clock is ticking faster, the more instructions are processed.

The CPU cache is a memory buffer that sits between the processor and the main memory. The bigger the cache, the more space there is to store instructions that the processor needs, and so the more likely it is that when an instruction needs to be fetched, it will already be in the cache. Therefore, having a larger cache size on the CPU can improve the performance of the computer.

The number of cores can affect the performance of the computer because a core fetches and decodes instructions. So if you add more than one it will increase the speed of performance and mean that it will help create a faster computer system. So the higher the number of cores, the better the performance of the computer.

Memory

(Binary Digit): Is logical 0 and 1, representing a passive or active state (on or off)
Nibble: 4 bits
Byte: 8 bits (the smallest unit that can represent a data item or character)
Kilobyte (KB): 1024 Bytes
Megabyte (MB): 1024 Kilobytes
Gigabyte (GB): 1024 Megabytes
Terabyte (TB): 1024 Gigabytes
Petabyte (PB): 1024 Terabytes

Random access memory (RAM)

RAM is the main memory in the computer. It is required for the operating system, applications and data in use. The more RAM available to the computer, the more programs and data can be held, creating a better performance. Random Access Memory allows data items to be read and written in approximately the same amount of time regardless of the order in which data items are accessed. RAM is volatile, meaning that when you switch off your computer, information under this specification is deleted.

When a program is loaded, it is copied from the hard disk or any secondary storage into the RAM. The CPU can not access the data and instructions. This data is copied from secondary storage device because access to the data is extremely slow. Secondary storage is needed to keep copies of files and programs because RAM is volatile storage.

Read-only memory (ROM)

RAM chips in RAM use transistors to hold a charge that represents the data, but require power to maintain this charge. By connecting transistors in a certain manner, they can retain stored data - this is called read-only memory (ROM). Read-Only Memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM can only be modified slowly, with difficulty, or not at all, so it is mainly used to distribute firmware. Doing so makes it non-volatile. It is often used in start-up sequences and protocols as it cannot be overwritten by the computer.

Virtual Memory

Virtual memory is an imaginary memory area supported by some operating systems (hard disk) in conjunctions with the hardware. Hard disks are vast storage devices. We can use a small part of this for RAM - when RAM is full, it temporarily consumes extra space form the hard drive - an overflow of RAM. Switching between programs is now significantly slower because the computer is transferring data between the main memory and the hard disk.

ROM chips and flash memory

ROM chips follow the principle of using a group of transistors wired together so that they can retain information - these chips create the difference between RAM and ROM! This memory uses large electric currents to force electrons through a barrier and trap them in a layer on the other side of the barrier until they are rest. The 'flash' of electric current used to achieve this gives the name of this type of memory - flash memory. An acronym for this action is EEPROM - Electronically Erasable Programmable Read Only Memory, also a replacement for a hard drive.

Flash memory

Flash memory is often used as a removable memory, such as USB memory sticks, the main secondary storage in large installations. It provides low cost, portable and removable storage for a range of devices: mobile phones, cameras, laptops and USB's to transfer and store personal files.

Flash memory is not as fast as RAM, but is faster than a magnetic hard disk.

Change in Memory Technologies and Innovative Computer Designs

Storage in computer systems, in particular portable ones, can be much smaller.Cache memory built into the CPU can make data transfers between the processor and RAM more efficiently, allowing increases in their performance.

Faster read/write times allows increasing performance of computer systems.

Less power consumption allows mains computers to consume less electricity and portable computing devices to last longer on battery power or use smaller batteries.

Lower costs making it affordable to install significant amounts of RAM in basic computer systems.

Memory capacity equals to storage becoming an alternative to hard drives in smaller systems.This means that a computer can start operating far more quickly when it starts up the data can be copied into RAM.

Binary Logic

Binary logic determines itself using two states - on or off, true or false, 0 or 1 - using transistors and capacitors to store data. It is possible to wire transistors together to carry out simple logical calculations - these are called logic gates.

Logic gates are expressed using truth table to display all the different possibilities of every combination.

Algebraic variables, such as A, B, C… are used as inputs; whereas variables such as P, Q, R are outputs.

NOT gate

The NOT gate is very simple - the output is also opposite to the input, for example, if the input is 0/off, then the output becomes 1/on; similarly, if the input is 1/on, then the output is 0/off. (See clippings for diagram and truth table).

AND gate

The AND gate illustrates that the output can only be 1/on if both inputs are 1/on, otherwise all other combinations equal 0/off. (See clippings for diagram and truth table).

OR gate

The OR gate shows that only one input needs to be 1/on for the output to be 1/on. If all inputs are 1/on, then the output with also be 1/on. If inputs are 0/off, then the output will become 0/off. (See clippings for diagram and the truth table).

Logic circuit's

Using the fundamental gates, you can create complex logic circuits. Examples of complex logic circuit's include NAND, or NOT AND, made of an AND gate, followed by a NOT gate.

The truth table of a logic circuit (NAND) can be determined by beginning with all the possible input combinations for A and B, then, using the first output, R from the AND gate, we can determine the output to the NOT gate. (See clippings below for diagram and truth table - Extra example provided).

Logic In Programming

Understanding Boolean algebra is needed in order to use many facilities within programming languages. Writing a program requires the identification of a logical process that the computer can follow. To do so, providing suitable Boolean expressions help the computer to make decisions about the next course to be taken.

Input and Output Devices

Without a way to retrieve and extract data form a computer would make one. A typical home has multiple devices that use computer technology. What is important is that we supply a computer system with the most appropriate input and output devices for the situation, in order for it to function effectively.

Input devices

Keyboard: A keyboard is used for data entry into a computer. Standard laptop and desktop 'qwerty' keyboards are used, but devices such as tablet computers and mobile phones often have a modified on-screen keyboard that will adapt to the type of input expected.

Mouse: Using sensors to track movement, it translates this to a moving pointer on the screen. This pointer can then be used to select items to open, move or edit. The trackball is often regarded as a as a variation on the mouse to control a pointer.

Touch screen: A touch screen is were the user touches an icon or symbol to sleet it directly on screen. They are used in tablet computers, kiosks, smart phone, supermarket checkouts, etc. A touch pad is an earlier alternative that uses a touch sensitive pad with printed symbols to represent items - these were often used where a keyboard or other input device would be difficult to use or subject to damage.

Microphone: Most personal computer systems have a microphone for inputting research, communication or direct voice commands to the system. These systems often only recognise numbers or basic words, but do manage to deal with a wider range of commands.

Camera: Some form of image or video input is usually found on a modern personal computer for use in taking photographs or video conferencing.

Bar code scanner: A bar code is a pattern of different thickness lines that can be scanned to identify an item. A light is reflected back to the scanner, which detects the pattern of thick and thin lines that identify as a figure. This numb can then be used to identify an item in a database.

RFID reader: Radio Frequency Identification is an electronic version of a bar code. It uses radio frequencies to transfer information to a reader. As with a barcode, the number is looked up in a database to return information about the item. Unlike barcodes, these devices do not require line of sign and can be read at distances of around ten metres.

Sensors: They are a variety of sensors that are used in a wide range of applications, which include light, pressure, accelerometers (used in hand held games and mobile phones) and motion sensors. Gesture based interfaces frequently use motion sensors and are a common form of input into games systems.

Input devices for users with specific needs

Eye-typer: for users with limited physical mobility, this device uses a camera to track the movement of the user's eye and an detect which key the user is looking at. A slow blink is used to select the key in order to type commands into a computer stem.

Puff-suck switch: this device is a switch hat can be operated by blowing or sucking into a small tube and is used by those with severely limited physical mobility. The software then interprets the actions to take.

Voice input: For those who find it difficult to operate a keyboard, spoken commands can be translated into text by software and used to communicate or instruct the computer to take actions.

Joystick: For those with limited movement, a joystick requiring less physical movement than a mouse can guide the pointer on screen to select commands to be carried out the by computer.

Foot mouse: For those who have limited hand movement, this device is a track ball device that can be operated with the foot.

Braille keyboard: This keyboard has raised embossed patterns on each key that match the standard braille characters and can be used by the blind or those with a visual impairment to type text and commands into a computer.

Output devices

Monitor: The most likely output from a system will be some form of visual message, text image or video and that required a monitor. The LCD and LED type of monitor is the most common form ( used to be CRT - Cathode Ray Tube monitors). Hand held devices include a touch screen type of display so that the input and output are through the same device.

Printer: A printer is a common accessory to a computer system that allows the production of hard opt evidence. The variety of printers include monochrome and colour last printers for fast and economical output; or ink-jet printers, for high quality images (photographs); thermal printers for silent and slow production; finally, 3D printers.

Speakers: Music, or sound files, are often handled thorough speakers, or headphones. The visually impaired user often replies on speakers or headphones to obtain feedback from a computer device. Sound output is also used as a warning - hospital monitors.

Actuators: A computer controlled device that a make a mechanical adjustment to a system. These are a fundamental part of an aeroplane control system -sensors monitoring various factors that will automatically apply adjustments to the wings (flaps) or engines to maintain the required performance.

Output devices for users with specific needs

Screen readers: there is a range of devices see to read a computer screen to assist people with a wide range of simple magnification software to enlarge visual text, speech output software that reads text and outputs through standard speakers or headphones. and devices that read text and convert this to a braille interface with raised symbols.

Actuators: These devices create a physical movement i response to a computer command and the are incorporated into a range of everyday or specialist devices so that those with a limited physical mobility can operate them using a suitable input device.

Voice synthesisers: Spoken output from a computer can be used for those unable to communicate verbally. These devices can 'read' text input with other devices and output synthesised voice to communicate with others.

Secondary Storage

It is difficult to rewrite programs and data every time something needs to be processed. Most computing needs require general purpose computer capable of reforming a ran of tasks. RAM is volatile so all collected data is lost. ROM is not volatile, but only maintains pre-programmed instructions so an adjustments are not saved - secondary storage is additional storage facilities added to a computer system to store data and programs when power is switched off.

Magnetic hard disk

A magnetised rigid plate or stacks of plates with heads to read the data as he platers spin around. The magnetic hard disk is a reliable and cost-effective solution, providing high capacity at low cost. The hard disk is used in mod personal and commercial computer systems. It storied the operating system, installed applications or programs and users' data. It can also be used as a portable, external device to transfer large amount of data or to act as a backup for important data.

Optical disks

The CD-ROM and DVD-ROM are written at manufacture and are used to distribute programs, video or data that is read only. CD-DW and DVD-RW devices have the ability to be written to and are used as secondary storage to transfer files between computers. Both of these types of optical storage use light from lasers to detect reflections from the surface of the data are on the CD/DVD surface. In DVD-ROM's this is a manufactured raised area on the reflective layer in the disk. In RW media the writer is able to modify the surface of the media using a laser. The surface has a dye layer that is changes by shining a laser light at it and it is this colour difference that is detected when it is read.

A CD typically hold 700MB of data; a DVD with hold 4.7GB of data. They expensive and robust, though data storage is not permanent as the dye layer in RW media does deteriorate over time and during the re0writing process, but are a good medium for transferring personal files, or otherwise, but this method is slower compared to other portable media like flash drives.

Flash memory (solid state memory)

A common form of personal portable file storage and often uses a USB conniption to a computer. Flash memory is an electronically erasable programmable read only memory device (EEPROM) and in different formats, it is used as memory to store images within digital cameras, mobile phones, MP3 players and tablet computers. Solid-state flash memory has better access ties than magnetic disks - no moving parts and uses significantly less power. Flash memory, however, is currently not able to store the size of storage offered by magnetic hard disks and, while relatively inexpensive at low capacity, it becomes significantly more expensive s a replacement for a higher capacity storage device.

Things to consider when choosing secondary storage:

Capacity - how much data does it need to hold?

Speed - how quickly can data be transferred

Portability - does it need to be portal or used to move data from one system to another?

Durability - does it need to be transported and if so, it is easily damaged?

Reliability - does it need to be able to be used repeatedly without failing?

Hardware Topic Summary

The Central Processing Unit (CPU)

The purpose of the CPU is to:

Control the movement of data and instructions

Fetch data and instructions from the memory before decoding and executing these instructions, also known as the fetch-execute cycle

Perform arithmetic operations using ALU

The purpose of the CPU depends on the:

Processor speed

Bus speed

Amount of cache available

Number of core processors

Memory

A computer uses two main types of main memory:

RAM (random access memory). This is a volatile memory and needs power to retain content.

Cache memory is a fast form of RAM, used by the computer for fast access to data.

ROM (read only memory). This is non-volatile memory that retains content without the need of a power supply.

A computer also uses:

Virtual memory is when a computer uses a section of the hard disk to supplement the main memory

Flash memory is a sold-state memory that is used in portable devices or removable devices to store data. It is secondary storage with slower access times than RAM, but faster times than a magnetic disk.

Binary Logic

Computers use binary because it more comprehendible to understand the current state (on/off; 1/0).

The von Neumann principle is the foundation of modern digital computing. His architecture uses of binary for data and instructions which are indistinguishable from each other and stored in the same place in memory.

Three fundamental logic gates are AND, OR and NOT - these gates can be combined to make logic circuits.

Truth tables are used to express the different combinations available creating using all components/values provided in the circuit.

Boolean algebra is used to write down logic circuits as simple mathematic expressions - it is also used within programs to determine the outcome of a comparison or to determine the next step in the sequence.

Input and Output Devices

These input and output devices are merely a sample of the wide variety that are in use and there is a range of specialise devices tailored to specific applications that have not been mentioned. What is important is that the device chosen is appropriate to the situation.

Secondary Storage

Secondary storage is needed to store programs, data and other files that would others be lost when the power is turned off.
Magnetic hard disks are relative slow to access, but have a large capacity and are commonly used within personal and commercial computer systems to store operating systems and other files and programs.
Optical disks (CD and DVD) are used to distribute programs, video and large data files as ROM. CD and DVD-RW are used to store backup copies of personal files or software and to transfer files. They are relatively slow, but also inexpensive, reliable and robust. They have capacities of 700MB (CD) and 4.7GB (DVD).
Flash (solid-state) memory is very flexible and can store many GB of data. It is relatively inexpensive with good access times. It is used to store data in cameras, mobile phones, portable devices and tablet computers as well as with USB interfaces for storage and transfer of personal files between systems or for backup. Portable flash memory devices are generally quite small, robust and easy to use, requiting no set up or driver software.

	Created by Yasmin F about 11 years ago

	Copied by Daniel Quick over 9 years ago

One of seven workbooks to tackle GCSE Computing, step by step.