Computing GCSE -OCR J277- Key Terms

What is the CPU?

Central Processing Unit
Processes all information

What is the fetch-execute cycle?

1. Fetch The next instruction from memory

2. Decode the Instruction

3. Get data if needed

4. Execute the instruction (repeat)

What is the ALU?

Arithmetic logic unit. Part of the CPU that carries out two types of operations: calculations & decisions.

What is the CU?

Control unit. It manages the instructions.

What is cache?

Temporary memory. Small amount of high-speed RAM (Random access memory), built into the CPU. Allows faster processing as processor doesn't have to wait for data to be fetched from RAM.

What is a register?

small amount of high-speed memory within the CPU. Store information such as:
Address of next instruction,
Current instruction being decoded,
Results of a calculation.

What is the MAR?

Memory address register and holds the address of the current instructions that is to be fetched from memory or addresses where data is to be transferred.

What is the MDR?

Memory Data Register
Holds the content found at addresses held in the MAR, or data which is to be transferred to primary memory.

What does the program counter do?

Holds the memory address of the instructions to be fetched from primary memory.

What does the Accumulator (ACC) do?

Holds the data being processed and the results.

What is clock speed?

It is how many fetch-decode execute cycles can be completed per second (Hertz). Bigger the number the faster & more cycles. 1GHz \= 1,000 MHz or 1,000,000,000 Hz/cycles.

How does cache size affect the performance of the CPU?

The bigger the cache, the less time a processor has to wait for instructions to be fetched.

What is a core inside a CPU?

A processing unit within a CPU is known as a core. Each core is capable of fetching, decoding and executing its own instructions.

How does the number of cores affect CPU performance?

More cores a CPU has, the greater number of instructions the CPU can process at a time.

What is an embedded system?

Embedded system is a small computer system that forms part of a LARGER SYSTEM. e.g.:
Central heating systems,
Dishwasher,
TV,
Digital phones,
GPS systems.

what are typical characteristics of embedded systems?

Limited number of functions - making them cheaper to build & design,
Tend to require less power,
Don't require high processing power.

What is primary storage?

Built inside the computer. Data can be read & written quickly.

What are the two types of primary storage?

Random Access Memory (RAM) and Read Only Memory (ROM). Both are limited in size.

What is the purpose of RAM?

Contains instructions & data currently in use, however it is volatile. Data can be changed and re-written to.

What is the purpose of ROM?

Contains instructions & data that a computer needs to run, such as BIOS. ROM is non-volatile. Data on ROM can not be changed.

What is virtual memory?

The use of secondary storage as additional primary memory.

Why is virtual memory used?

When RAM is "filled up" (data greater than amount of RAM) computer uses secondary storage to store data temporarily. It allows swapping - data not in use goes to hard drive when needed goes back to RAM and swapped with unused data on RAM.

What is a side affect of using virtual memory?

It causes the computer to run slower as it had to wait for data to be swapped. - secondary storages have slower access times.

What is secondary storage?

A device intended to permanently hold (store) data as it doesn't get lost when a computer turns off.

What are the three common types of secondary storage?

Magnetic, optical & solid state.

What is an example of all three secondary storages?

Magnetic - Magnetic tape, floppy disks & hard-disk drives,
Optical - Blue ray, DVD & CD,
Solid state - USB pens, SD cards & solid state drives.

What is advantages and disadvantages of optical storage?

Advantages - Low cost, portable, Reliable, long life.
Disadvantages - low storage & speed, easy to scratch, data can not be over written.

What is advantages and disadvantages of magnetic storage?

Advantages - Large capacity, low cost, long life, reliable.
Disadvantages - Not durable, not portable, Slow.

What is advantages and disadvantages of solid state storage?

Advantages - High speed, portable, durable, reliable.
Disadvantages - Low storage for price, high cost.

What is a bit?

A binary digit, a 1 (on) or a 0 (off):

How many bits are in nibble, byte & kilobyte?

4, 8 & 1000

How many Kilobytes(KB) are in a Megabyte?

1000(KB)

How many megabytes(MB) in a gigabyte?

1000(MB)

How many Gigabytes(GB) in a Terabyte?

1000(GB)

How many terabytes(TB) are in a petabyte?

1000(GB)

Why must data be stored in binary format?

computers use electronic circuits (transistors) that function as switches that can be turned on or off. We use a binary form to represent these two states (1 or 0)

How do you calculate sound file size?

Sample rate x duration(s) x bit depth

How do you calculate image file size?

Colour depth x image height(PX) x image width (PX).

How do you calculate text file size?

bits per character x number of characters.

What is 01111100 (binary) in denary?

128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
0 | 1 | 1 | 1 | 1 | 1 | 0 | 0|
\= 64 + 32 + 16 + 8 + 4 + 2 + 1 \= 127

what is 46 in binary?

128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
0 | 0 | 1 | 0 | 1 | 1 | 1 |0 |
\= 00101110

how does a overflow error occur?

Occurs when the largest number exceeds the number of bits that it can handle or if 3 1's are added together.

what does 00111010 + 10001011 \=?

0 0 1 1 1 0 1 0 1 0 0 0 1 0 1 1 + 1 1 0 0 0 1 0 1 = 128+64+8+2=202

How do u binary shift?

U shift all 1's either left or right for multiply or divide. Lose any overheads.

What is a network?

Two or more computers connected together in order to share files & resources.

What are some advantages of a network?

Sharing devices e.g a printer saves money, Files can be easily shared between them, saves money by sharing network license & data is easy to backup as all data is stored in a file server.

What are disadvantages of a network?

Purchasing network cables & file servers can be expensive, Managing a large network is hard - needs training - needs to be employed, viruses can be spread through the network easily, if file server breaks down all files on server become inaccessible.

What is a hub & what is it used for?

A physical layer network device used to connect multiple devices in a network - normally in a LAN.

What is a router and what is it used for?

Sends and receives data on a network. It can combine functions of a hub and a switch and connect with these devices to improve internet access.

What are the two types of compression?

lossy and lossless

What is lossy compression?

Data is removed and discarded therefore reducing the size of the file. Image can be compressed by reducing range of colours. Sound files can be compressed by reducing bit depth.

What is lossless compression?

Files reduced without losing data but doesn't achieve same amount of compression. e.g text files.

How is Sound Sampled and Stored Digitally?

1. Sound is recorded by a microphone as an analogue signal

2. Analogue is converted to digital (binary) so that the computer can read and store the file. (it uses an Analogue to Digital Converter)

What is the effect of sample rate, duration & bit depth on playback quality?

Higher the sample rate the better quality but more storage it uses.
Longer the duration the larger the file size.
Higher bit depth (number of bits available to store each sample) more accurate the sound is but the larger the file size.

What is sample rate measured as?

Hz

How do you work out the size of a sound file?

Sound File size \= sample rate X duration (S) X Bit Depth / 8

How do you work out the size of a image file?

Image file size (in bytes) \= Colour depth x image height (px) x image width (px) / 8

How to work out the size of a text file?

Text Files size (in bytes) \= Bites per character X number of characters /8.

What does LAN stand for and what is it?

Local Area Network - A network over a small geographical location

What does WAN stand for and what is it?

Wide Area Network - A network over multiple geographical sites

What is examples of LAN?

small businesses & organizations, schools & homes.

What is examples of WAN?

Banks, internet, large businesses & organizations.

What are advantages of LAN?

Faster, low setup cost, more secure, require low maintenance - require hub & switch.

What are advantages of WAN?

Cover large distance, require router & modem.

What makes a network slower?

More devices cause higher chance of data collisions,
Bandwidth of transfer medium - ethernet or wireless etc - determine how much data can travel at once.

peer-to-peer network

All computers are equal connected through a hub. Printers can be added to any of the machines. Access can be given to anyone only need a password.

Client Server

Most common for organizations, one or more computer designated as server which provide services for other machines on network.

What is a network switch?

Records which computers are connected to which ports. Switch forwards traffic to correct place. - increases network speed.

What is a wireless access point?

Uses radio transceivers to allow wireless connections to a network. Creates own wireless network then sends traffic to main wired network. Can also extent range of wireless network

What is a NIC (network interface card)?

Hard wired with a unique MAC address. Allows network to tell devices apart.

What is transmission media?

Method to carry data signals from one computer to another, either wired or wireless.

What is the internet?

Network made up of multiple networks.
Infrastructure - facility for sharing data between computers.

What is the world wide web?

Collection of web pages hosted on the internet.

What is a Domain Name System?

Turns URLs into IP addresses. Made up of multiple domain name servers.

What is hosting?

You are the place where online data is stored.

What is the cloud?

A file server accessible via the internet. Remote offering storage space for files.

What are advantages of the cloud?

access files from any location with any device, access be given to others, reduces need to create backups.

What are disadvantages of the cloud?

No guarantee over security, requires internet access, ownership issues, responsible of data security, no guarantee of backups.

What is a star topology?

Network where each node is connected to a central switch

What is a node?

Any device connected to a network.

What is a mesh topology?

Network where each node is directly connected to all other nodes.

Advantages of a star topology?

If one node fails won't cause chain reaction - all separate, new nodes can be added easily, high performance - message sent directly to recipient.

Disadvantages of star topology?

Network fails if switch does, requires a lot of cables, expensive.

What are advantages of mesh topology?

messages received quickly if route is short, message always get through as multiple routes to travel, multiple connections \= multiple transmissions and receivers, new nodes added without affecting others.

What are disadvantages of mesh topology?

Full mesh can be impractical to set up because of large number of connections needed, high maintenance.

What are advantages of using WiFi?

New nodes can be added without affecting other devices, users can move around freely and stay connected.

What are disadvantages of WiFi?

Limited range, can sufferer interference from other device, signal blocked by walls, limited amount of bandwidth to share between devices, WiFi signals can be intercepted by unauthorised users.

What are advantages of ethernet?

cheap, reliable, stable, low maintenance, faster transfer of data, higher security (data can't be intercepted),

What are disadvantages of ethernet?

Has to stay in place, can be a eye saw if many, high maintenance if server is needed (multiple).

What is encryption?

Process of disguising a message so that only intended recipient can read it. Requires a key.

What is IP addressing?

Addresses used to identify a packet's source and destination host computer. Addressing rules also organize addresses into groups, which greatly assists the routing process.

What is static & dynamic IP addressing?

Node given a static address always keeps the same where as dynamic has a different address assigned to it each time it connects to the network.

What is IPv4 & IPv6?

IPv4 uses 4 sets of digits where as IPv6 uses 6 sets of 3 numbers.

What is a MAC address and use?

Unique serial number assigned to each Network Interface card.

What is an advantage of Bluetooth?

Low cost to setup, little power for connection, easily setup with other Bluetooth devices.

What is a disadvantage of Bluetooth?

Short range, low level security, low data transmissions.

What is a protocol?

Rules in networks that control network communications

What do you use DNS (Domain Name System) for?

Translating domain names into a IP address.

What do you use TLS(Transport Layer Security)/SSL(Secure Sockets Layer) for?

Cryptographic protocols designed for secure communication.

What do you use FTP (File Transfer Protocol) for?

Copying files from one host to the other.