Computer Science Flashcards
(107 cards)
1
Q
Registers
A
A fast access storage location found in the CPU where data or control information is temporarily stored.
2
Q
Program counter (PC)
A
A counter that keeps track of the memory address of which instruction is to be executed next.
3
Q
Memory address register (MAR)
A
Holds the address in the main memory that is to be read to or written from.
4
Q
Current instruction register (CIR)
A
A temporary holding area for the instruction that has just been fetched from memory and is being decoded and executed.
5
Q
VN Architecture Characteristics
A
Binary format, fetched from main memory,, fetched one at a time, one instruction is decoded before another is fetched (as and when required).
6
Q
Von Neumann Architecture def
A
The design on which general purpose computers are based. Von Neumann architecture provides a simple explanation of the construction of the CPU and its relationship with other components of the computer.
7
Q
Control Unit def
A
Control Unit – directs the flow of instructions and / or data and coordinates the other parts of the CPU. It generates clock ticks (controls the clock).
8
Q
Arithmetic Logic Unit def
A
Arithmetic Logic Unit – the ALU performs all the calculations and logical operations in the CPU.
9
Q
Memory def
A
Memory – used for temporary storage of currently running programs and data.
10
Q
Address bus def
A
Address bus - when data is saved or loaded from memory, the address at which it is to be stored or loaded from must be sent. The storage address of data always travels in one direction along an address bus.
11
Q
Data bus def
A
Data bus - data will then need to be moved between several parts of a computer. The path along which data travels is called a data bus.
12
Q
Control bus def
A
Control bus - the controller uses the control bus to send control signals to different parts of the computer.
13
Q
Bus def
A
Buses allow data to be transferred to different parts of the computer
14
Q
Fetch def
A
The fetch cycle takes the instruction from the main memory using the address, and stores it in the current instruction register, and moves the program counter on one so that it points at the next instruction.
15
Q
Execute def
A
The control unit authenticates the instruction in the current instruction register. The instruction is decoded to determine the action that needs to be carried out.
16
Q
Decode def
A
The actual actions that happen during the execution cycle depend on the instruction itself.
17
Q
Cache def
A
Cache – incredibly fast, but very expensive volatile memory used in the CPU. The cache temporarily holds data and instructions that are used frequently. It consists of a small number of store locations that can be accessed very quickly by the CPU; it is quicker than RAM.
18
Q
Cache affecting performance
A
More cache memory improves performance as it can provide instructions and data to the CPU at a much faster rate than other system memory such as RAM. In addition, more cache memory will allow more instructions that are repeatedly used by the CPU to be stored in cache and therefore increase the hit rate, improving the performance of the processor as a result.
19
Q
Clock speed def
A
Clock speed – the number of fetch-decode-execute cycles that the CPU can carry out per second. This is usually measured in Hertz.
20
Q
Clock speed affecting performance
A
The faster the clock speed, the faster the computer can run the fetch-decode-execute cycle and therefore process more instructions in any given period. However, the faster the clock speed, the more power is generally required, which creates greater requirements for heat dissipation and can place more strain on battery life.
21
Q
Cores def
A
Cores – some processors have multiple processors (known as cores) which can run in parallel, sequentially or can multitask.
22
Q
Cores affecting performance
A
In a single-core CPU each instruction is processed one after the other, whereas in a dual-core CPU, two instructions may be processed at the same time. In theory, a dual-core CPU should mean that the computer can process instructions twice as fast as a single-core CPU. Performance may be affected where one core is waiting on the result of another and therefore cannot carry out any more instructions, leading to the performance being no better than a single-core processor.
23
Q
RISC def
A
RISC processors can process a limited number of relatively simple instructions. To carry out more complex commands, the problem is broken down into a longer list of simpler instructions. The advantage of this is that a RISC processor can process these simpler instructions quickly. Processing simpler instructions also requires less circuitry to decode and execute these instructions, which in turn means less power consumption and therefore less heat being generated.
24
Q
CISC def
A
CISC processors can process a large number of complex instructions. This allows the processor to understand and carry out complex tasks with only a few instructions. The advantage of this is that a CISC processor can process complex instructions, without having to break them down into many simpler instructions. Processing complex instructions, however, requires more circuitry to decode and execute these instructions, which in turn means more power consumption and therefore more heat being generated. Because of this, CISC CPUs will usually come with a heat sink or fan embedded.
25
RISC and CISC advantages and disadvantages
In order to handle complex instructions CISC CPUs are physically larger to accommodate more complex circuitry. RISC CPUs are designed to use less power and run cooler, meaning that they can be used in smartphones that do not have dedicated cooling systems such as fans.
RISC CPUs tend to be cheaper to mass produce. RISC CPUs run at lower clock speeds than CISC CPUs. They can perform simple tasks more quickly than CISC CPUs but are generally not used to carry out complex instructions.
26
Input device def
An input device allows data, such as text, images, video, or sound, to be entered into a computer system.
27
Keyboard
Computer keyboards are used to input data and commands into the computer by pressing the keys. Computer keyboards are common in the workplace and are usually used together with a mouse.
28
Graphics tablet
A graphics tablet is an input device that converts hand drawn artwork into a digital image. A graphics tablet is a flat touch sensitive surface. The user draws using a stylus as if they were drawing on a piece of paper. The image is transferred to the computer screen and can be stored, edited, and printed.
29
Mouse
A mouse is an input device that allows the user to control the co-ordinates and movements of a cursor on the computer screen. The left button is used to select items and the right button is used to access menus (these can be changed around in settings). Most mice now use a laser to track location on a smooth surface and mice can be wired or wireless.
30
Touchpad
A touchpad is a flat control surface used to move the cursor and perform other functions on a computer. Touchpads are commonly found on laptops and replace the functionality of a mouse. A touchpad is designed to be controlled with your finger.
31
Scanner
Scanners convert documents and images into digital files. Scanners can be run with additional software such as an optical mark reader (OMR) or optical character recognition (OCR). One example would be using OCR software in the computer to read handwriting and convert it into digital text.
32
Digital Camera
A digital camera is an input device that captures images (and sometimes videos) digitally. A digital camera uses an image sensor and a chip to capture an image, as opposed to the film used in traditional cameras.
33
Microphone
A microphone is an input device that receives analogue sound waves and converts them into electrical signals understood by the computer. Microphones play an important role in speech recognition.
34
Interactive whiteboard
An interactive whiteboard is usually used in classrooms. This device was developed long before touch screens. It is cheaper than touch screens and differs from normal screens as it can be used in plenty of ways when paired with a projector. It can be used for navigation systems or to write/design with your fingers or a stylus.
35
QR code scanner
QR code scanners, as seen on smartphones, can scan QR codes by taking a picture of them. The QR codes normally hold more data than barcodes, e.g., web addresses, contact details, calendar registrations and details of goods in factories and warehouses.
36
Barcode scanner
A barcode is a code that can be read by a machine. The code is represented by a series of black and white lines. These lines represent numbers from 0 to 9. The use of barcode scanners speeds up the process of data input into a system, e.g., scanning items at a check out desk in a supermarket.
37
Output device def
An output device is a piece of hardware that receives data from the computer to display either as an image, video, text, or sound.
38
Monitor
A monitor is an electronic visual computer display. It includes a screen and the case in which all circuitry is enclosed. Most monitors used with devices such as laptops, PDAs and desktop PCs are made using LCD screens as they are lighter and more energy efficient.
39
Speaker
Speakers are used to produce audio output that can be heard by the listener. When they receive audio input from a device, the electromagnetic waves are converted into sound waves. This input may be in either analogue or digital form. Analog speakers simply amplify the analogue electromagnetic waves into sound waves. Digital speakers must first convert the digital input into an analogue signal, then generate the sound waves.
40
Printer
A printer is an output device that prints paper documents. This includes text documents, images, or a combination of both. The two most common types of printers are inkjet and laser printers. Inkjet printers are commonly used by consumers, while laser printers are a typical choice for businesses.
41
Projector
A projector is an output device that projects an image onto a large surface, such as a white screen or a wall. It may be used as an alternative to a monitor or a television when showing video or images to a large group of people.
42
Touch screen
A touch screen is a digital visual display that also works as an input device that responds to the user's touch. It allows users to make selections by touching the screen. A touch screen can be categorised as both an input and an output.
43
RAM def
RAM is used for the temporary storage of currently running programs (instructions) and data, e.g. the operating system, a text editor program, or a spreadsheet. It consists of many store locations, each of which is identified by a unique address. The data in each store location can be changed. RAM is volatile – data is lost when the power is switched off. Random access memory.
44
ROM def
ROM is used for the permanent storage of data. The data in each store location cannot be changed. ROM is non-volatile or permanent – data is not lost when the power is switched off.
45
BIOS
It is a low-level program that handles input and output operations relating to the system's keyboard and screen. It provides an interface between the hardware and the operating system. One of its primary functions is loading and executing the bootstrap loader – the program that loads the operating system.
46
Flash memory
Flash memory is used for the permanent storage of data. However, the data stored in flash memory can be changed. Flash memory is permanent – data is not lost when the power is switched off. Stores BIOS sometimes.
47
Optical storage – CD/DVD/Blu-ray
Laser beams are projected onto a disc and if light is reflected, then data is read as a 1. If light is not reflected, data is read as a 0.
48
Magnetic storage – disk/type
Data is stored and read using a read-write head and magnetic platter.
49
Solid state storage – Flash/Solid state drive (SSD).
The technology is called solid state as it doesn't have any moving parts. Data is stored on circuitry known as flash memory chips. Its low power consumption and high-speed access is advantageous.
50
Secondary storage def
Secondary storage is non-volatile, long-term storage that is not directly accessed by the CPU. The computer uses its input and output channels to transfer the data from secondary to primary storage when needed for processing. Data from the memory is written in the secondary storage when the data is no longer being actively used, for retrieval at a later period. The time a computer takes to access data stored on secondary storage is longer than the time it takes to access data from memory.
51
HDD
HDD have a fast transfer rate and a moderately fast access time providing a good compromise between storage capacity, performance and cost. However, their speed does not come close to the speed of RAM, the CPU or that of a solid-state drive. HDD are a magnetic medium and store data on a hard drive platter. Data is read and saved using an arm that has a special read / write head at the end. As the disk spins, the arm travels across the disk. Each sector on the platter can store data and the movement of both the disk and the read / write head means that every sector on the hard drive can be reached. The faster the platter spins, the faster data can be read from the disk. This speed is measured in revolutions per minute or RPM. A common speed for HDDs is 7,200 RPM.
52
SSD
A solid-state drive features a non-mechanical design of NAND mounted on a circuit board. NAND flash memory is a type of non-volatile storage technology that does not require power to retain data. Computers with SSDs have quicker boot time than those with HDDs. SSDs do not require defragmentation, consume less power than HDDS, and are lighter and smaller than HDDS. SSDs offer cost savings in the long run for businesses with lower energy usage and greater productivity. With no moving parts they are more robust than HDDs and run at near silent operation.
53
CD / DVD / Blu-ray Disk
Optical drives work by using lasers to store data, burning microscopic indentations into an optical disk such as a CD. The pattern of indentations is created in a spiral pattern, starting in the middle of the optical disk. The indentations and their absence create pits and lands, 0s and 1s retrospectively. A DVD uses the same techniques to store data, but the data is stored in two layers increasing the capacity of the storage medium. On Blu-ray disks the pits and lands are closer together, meaning that the laser’s wavelength is shorter (blue).
54
Comparison between HDD and SSD
Storage capacity – HDD has greater capacity.
Speed of access – SDD provides faster access to data.
Durability – SSD is more durable.
Cost – per unit of storage is cheaper for HDD.
55
Comparison between optical and SSD
Storage capacity – SSD has greater capacity.
Speed of access – SSD provides faster access to data.
Durability – Optical drives are less durable.
56
Comparison between HDD and optical
Storage capacity – HDD has greater storage capacity.
Speed of access – HDD is faster to access data.
Durability – optical drives are more durable
57
Prefix order
Kilo, mega, giga, tera, peta, exa, zetta, yotta
58
GPU def
It generates and controls the output to the screen. Graphics cards can be either integrated or discrete.
59
Intergrated GPU
An integrated graphics card is placed on the same chip as the CPU. The integrated card relies on the system’s memory for graphics processing. The card uses less power and generates less heat than a discrete graphics card. It is cheaper
60
Dedicated GPU
A discrete graphics card is separate from the CPU and has its own independent memory (VRAM) to provide high graphics processing power. The discrete card uses more power and generates a significant amount of heat.
61
Sound cards def
Sound cards may be on the motherboard or designed to fit a PCI slot. They enable the computer to output sound through speakers, record sound from a microphone and manipulate sound stored on a disk. Sound cards convert analogue input signals into digital data and reverse this process for audio output.
62
Motherboard def
The motherboard is the main circuit board of a computer. The CPU and ROM will be mounted on the motherboard, which also provides RAM expansion slots, USB ports, PCI slots for expansion cards and controllers for devices such as the hard drive, DVD drive, keyboard and mouse.
63
Embedded systems def
An embedded system is a combination of software and hardware that performs a specific task rather than a general-purpose computer that is designed to carry out multiple tasks. Embedded systems are included as part of a complete device, often with hardware and mechanical parts. As the systems carry out specific tasks, they can be designed to be small and have a low cost. Mass-production of embedded systems can save large amounts of money.
64
Embedded systems software
The software written for an embedded system is called firmware. The instructions are stored in read-only memory or in Flash memory. The software runs with limited computer hardware resources, little memory, and no peripherals. Most embedded systems are reactive – they react to conditions such as temperature, weight, vibration, and air quality. These systems detect external conditions and react to them by recording data, turning motors on or off, sounding an alarm or sending a message to another processor.
65
Embedded systems examples
Washing machine, calculators, CT scanners
66
Embedded systems reliability
Reactive embedded systems often control real time events so must be completely reliable. For example, drivers rely of the anti-lock braking system of their car working correctly to avoid accidents on the road. When an embedded system performs operations at high speed, and if it is reliable, it can be used for real-time applications. If the size of the embedded system is small and power consumption is very low, the system can be easily adapted for different situations
67
Network def
A network consists of two or more computer systems that are connected together to allow them to share resources and exchange information. There are many advantages and disadvantages of using a computer network over a stand-alone computer.
68
network advantages
Share hardware resources, such as printers, scanners and back up facilities.
Share software that is licensed for use over a network.
Share data/files that are stored centrally on a server.
Easier for internal communication/can send email.
Easier to monitor network activity of user accounts.
Centrally controlled security.
69
network disadvantages
Security problems – if a virus is introduced to a single computer it can spread throughout the entire network.
Hackers can gain access to data more easily with machines being connected to the Internet.
If the server is down, all workstations on the network are affected.
Initial cost of servers, communication devices etc can be expensive.
70
LAN def
A LAN is a network in which the computer systems are all located relatively close to each other, for example in the same building or on the same site, such as a school.
71
WAN def
A WAN is a network in which the computer systems are all located relatively far from each other, for example in different buildings all over the country or in different countries altogether. The Internet is an example of a WAN. Note that many LANs could be linked using a WAN.
72
Hubs
A hub allows any two computers connected via the hub to send data to each other. A simple hub can only deal with one link at a time. If many computers are connected to the same hub then performance can be slow.
73
Switches
A switch or switched hub analyses each packet of data and sends it to the intended computer. A switch allows many connections at the same time and are therefore more efficient.
74
Managed switches
A managed switch allows the network manager to adjust each port on the switch to enable monitoring and configuring of the network. It provides control over how data travels across the network and which users can have access to the data.
75
Routers
Routers are sophisticated switched hubs. The router stores the addresses of all the computers on the network. It can then forward this data to the correct destination via an appropriate route over the network.
76
Wireless access points
Wireless access points are hubs that allow wireless connections to a network. Any computer with a wireless network interface can connect to the network.
77
Bridges
A bridge is a device that connects two networks which use the same base protocol, e.g. linking twos LANs together.
78
Gateways
A gateway joins two networks that use different base protocols, e.g. connecting a LAN to a WAN.
79
Topology def
A network topology is the physical or theoretical layout of computer systems on a network, including cabling and other hardware such as switches and peripherals.
80
Bus topology
It is easy to implement and add more computer systems to the network. Quick to set up – well-suited for temporary networks.
Cost-effective – less cabling. It is difficult to troubleshoot the bus. Limited cable length and limited number of stations – performance reduces as additional computers are added. If there is a problem with the main cable or connection, the entire network goes down. Low security – all computers on the bus can see all data transmissions. Proper termination is required. Data collisions are more likely, which causes the network to slow down. A collision is when two computers try to send a data packet at the same time. This causes the data packets to collide and become corrupted.
81
Ring topology
Data is quickly transferred without a bottleneck – consistent data transfer speeds.
The transmission of data is relatively simple as data packets travel in one direction only.
Adding additional nodes has little impact on bandwidth. It prevents network collisions. If any of the computer systems fail, the ring is broken, and data cannot be transmitted efficiently. If there is a problem with the main cable or connection, the entire network goes down. It is difficult to troubleshoot the ring.
Because all nodes are wired together, to add a another you must temporarily shut down the network.
82
Star topology
Its performance is good/has a fast network speed. It is easy to set up. Possible to add more computer systems without having to take the network down. Any non-centralised failure will have little effect on the network. There are minimal network collisions.
Has better security. Expensive to install – more cabling is required. Extra hardware is required, such as a hub.
If the central node fails then there will be no access to the network.
83
Mesh topology
Data can be transmitted from different nodes simultaneously. Mesh topologies can withstand high traffic.
Each connection can carry its own data load.
If one node fails, there is always an alternative present, so data transfer isn’t affected. A fault can be diagnosed easily.
Expansion and modification in topology can be done without disrupting other nodes.
Provides high levels of security and privacy.
Installation and configuration can be difficult as the network grows. Cabling costs are high.
There is a high chance that many of the network connections will be redundant.
Set-up and maintenance of mesh topologies is very difficult. Administration of the network is difficult.
84
Protocol def
Network protocols are essential if computers on networks are to communicate. Without shared common protocols, computers would not be able to communicate. A protocol is an agreed format, which allows two devices to communicate. Put simply, a protocol is a set of rules.
85
Ethernet
A wired (cable connection) protocol.
86
Wi-Fi
Wireless. The two common standards are Bluetooth and 801.11.
87
TCP/IP
Transmission control protocol / Internet protocol. This is the basic communication language or protocol of the Internet.
88
IMAP
Internet message access protocol. This protocol transfers emails between computer systems via the Internet. The IMAP protocol is generally used for email retrieval and storage as an alternative to POP3.
89
SMTP
Simple mail transfer protocol. Mail servers use SMTP to send and receive mail messages. Mail applications typically use SMTP only for sending messages to a mail server.
90
HTTP
Hypertext transfer protocol. This protocol allows webpages to be shared across different computers and browsers.
91
POP3
Post office protocol 3. This protocol is for receiving email. An email is received and stored by an email server with a client downloading messages when ready.
92
5 Layers
Physical layer
Data link layer
Network layer
Transport layer
Application layer
93
Physical layer
The physical layer transmits the raw data. It consists of hardware including cables and switches. This layer deals with all aspects of setting up and maintaining a link between the communicating computers.
Physical connection using a NIC to connect to the internet.
94
Data link layer
The data link layer sends data from the network layer to the physical layer. It divides the data to be sent into data frames. A data frame consists of a link layer header followed by a packet. This layer handles the acknowledgements sent from the receiver and ensures that incoming data has been received correctly by analysing bit patterns in the frames.
Ethernet Protocol
95
Transport layer
The transport layer ensures that data is reliably transferred from one point to another without errors. The transport layer is responsible for making sure data is sent and received in the correct order. The transport layer is implemented in the sending and receiving computers, but not in the routers on the path between them. It acts as an interface between the communicating computers and the network.
Transmission Control Protocol (TCP)
96
Application layer
The application layer provides interfaces to the software to allow it to use the network. Examples of software include email, file transfer protocol (FTP) and the World Wide Web (WWW).
Hypertext Transfer Protocol (HTTP)
Simple Mail Transfer Protocol (SMTP)
File Transfer Protocol (FTP)
97
Network layer
The network layer is responsible for the addressing and routing of data. Routers belong to the network layer as they use logical addresses to direct the data from the sender to the receiver. A router determines the path the data should take based on network conditions. Routers manage traffic problems on the network, for example the routing of packets to minimise congestion of data.
Internet Protocol (IP)
98
Connectivity def
Connectivity is important for the transfer of data. Without connectivity, data could not be easily exchanged between computers without the use of removal storage media. To connect a computer system to a network, a Network Interface Card (NIC) is required. One method of connection is provided through a physical hardware port, which allows a cable to connect your computer system to the network. Wired connections use a connection protocol such as Cat6 cabling using Ethernet.
99
Physical connections
A copper cable, with typical data transfer speeds of between 100 Megabits per second (Mb) and 1 Gigabit per second (Gb)
a fibre-optic connection, which has typical data transfer speeds of between 1 and 10 Gb
100
Wi-fi
Wi-Fi connections have typical data transfer speeds of 54–108 Mb but can go much higher. However, this can be severely affected by the distance between the device providing the Wi-Fi connection and the computer system. The data transfer speed can also be severely affected by atmospheric conditions, such as the weather, and building infrastructure. However, one of the benefits of a Wi-Fi connection is the flexibility of being to be able to work anywhere that offers Wi-Fi Internet access.
101
Circuit Switching def
Circuit switching is a type of networking technology that provides a temporary but dedicated link between two computer systems, or nodes, regardless of the number of switching devices through which the data has to travel. During the connection, no other data can be transmitted along the same route.
102
Packet Switching def
Packet switching is the process of delivering packets from one computer system to another using a designated device, such as a switch or a router. Packets are provided to a network for delivery to a specified destination. Each data packet is redirected by a computer system along the network, until it arrives at its destination. Data may be split up into a number of packets. These packets are transmitted over a network and may take different routes to their destination. When all the packets have arrived, the data is reassembled. The internet is an example of a packet-switching network.
103
Routing def
Routing is the name given to the method of selecting paths along which packets are sent on a computer network. Specialist computer systems such as routers, switches, bridges, firewalls and ports construct a routing table in their memory. This stores the best routes for a packet to reach a specific destination.
104
DNS def
A Domain Name System (DNS) is a distributed database that matches IP addresses to computer system resources.
105
Overflow def
If the result of an addition or shift process results in a number that is too big to fit in the register being used, then overflow has occurred.
106
Raster graphics
Raster graphics are made up of dot matrix data structures representing a grid of pixels. A pixel, pel or picture element is the smallest portion of an image or display that a computer can display. Pixels are arranged in a two-dimensional grid. Pixels are often in many different colours. It is possible to edit each individual pixel. Raster graphics cannot be scaled up without a loss of quality. A raster image is also called a bitmap image. A black and white bitmap image will store a 1 for a black pixel and a 0 for a white pixel.
107
Vector graphics
Unlike raster graphics, vector graphics are made up of points, lines and curves that are based on mathematical equations rather than pixels. Vector graphics can be enlarged without any distortion, meaning that the graphic can be used in many different sizes. This is often useful for an image such as a logo which may be used on a small article of clothing or a billboard advertisement. The mathematical nature of a vector graphic means that they have low file sizes regardless of their high quality and flexibility.
