OCR GCSE computer science paper 1

what is the purpose of the CPU?

to process data by following the fetch-decode-execute cycle, it's incharge of searching, sorting, calculating and decision making

what happens at the fetch stage?

the CPU fetches data and instructions from RAM and then stores them in it's own temporary memory called registers

what happens at the decode stage?

the CPU understands what the instructions mean, the CPU decodes the instructions and gets to the next step

what happens at the execute stage?

the CPU carries out the instructions on the data

define bus

information travels along a bus from one part of the CPU to another

define address bus

a one way bus that requires data from an address in memory

define data bus

moves data in both directions as data is both read and written to memory

define control unit

responsible for timing on the CPU, uses the clock to ensure operations happen in the correct sequence

define arithmetic logic unit

does all arithmetic calculations and logical operations

define registers

Small temporary storage spaces inside the CPU

define accumulator

stores the results from the ALU temporarily until they're written to memory

define program counter

stores the memory address of the next instruction, is incremented by 1 at each new cycle

define instruction register

current instruction is stored in this register

define memory address register

stores the memory address of the current instruction being executed

define memory data register

stores the data that was read/written to memory

what is the function of the ALU?

performs basic arithmetic operations (addition, subtraction, multiplication, and dividion) and logical operations (AND, OR, NOT).

what is the function of the control unit?

manages and monitors hardware, manages the input and output signals, uses clock signals to synchronise the running of the fetch-decode-execute cycle

what is the function of the cache?

a small amount of storage that temporarily holds instructions that the CPU is likely to reuse, it's close to the CPU and so is fast to access

what are the 3 factors affecting CPU performance?

clock speed, cache size, number of cores

How does clock speed affect CPU performance?

the speed of the f-d-e cycle is determined by the CPU's clock chip, the clock speed is measured in hertz (cycles per second), the greater the clock speed, the more instructions are processed per second

what's the issue with increasing clock speed?

the CPU can overheat (overclocking), so you need to use heat syncs

How does cache size affect the performance of the CPU?

if the cache is larger it's more likely the next required instruction has already been transferred from the RAM to the CPU, improving process time

how does the number of cores affect the CPU?

they can carry out parallel processing - the same program can have two instructions carried out at once. they can carry out multi-tasking - different program's instructions are carried out at the same time

what is an embedded system?

An embedded system is a small computer that forms part of a larger system. it takes input, processes data and delivers an output. it doesn't need an operating system, the input is just a button or set a control, makes devices easier to use and increases reliability

what is primary storage? and examples

memory areas that the CPU can access very quickly, has fastest read/write speeds, mostly volatile. eg. CPU registers, cache, RAM, ROM

what is secondary storage? and examples

non-volatile where all data is stored when not in use, read/write speeds are much slower. eg. solid state, CD, SD cards

what is tertiary storage?

used for long term data storage, mainly used for archives and backups of massive amount of data

what is RAM needed for?

stores programs currently in use, helps to enable 'multi-tasking' (by copying data needed so it's passed through the CPU), stores all instructions from open programs

properties of RAM?

volatile (loses data when no power), faster than hard drive, internal

how does RAM store data?

uses capacitors and transistors, capacitor is a 1 or 0, transistors tell computer what's in capacitors

properties of dynamic RAM?

1 transistor, 1 capacitor per bit, limit to how fast data can be read, power is always needed

properties of static RAM?

4-5 transistors wired together for each bit data, doesn't lose its charge, much faster, but more expensive, needs constant power

what is the purpose of ROM?

stores BIOS and boot up program

what are the properties of ROM?

it's a memory chip, non-volatile (stores data without power), primary storage (directly accessed by the CPU), fast access rates

what type of memory do modern ROM chips use?

flash memory

how does flash memory work?

a large electrical current forces electrons through a barrier into fixed positions, the different arrangements give data

what is virtual memory?

a small portion of secondary storage which acts as RAM in the event of the RAM becoming full

Why is virtual memory needed?

it allows the computer to continue to function even though the RAM is full (albeit much slower)

what happens to the performance of the CPU with smaller/larger amounts of RAM?

smaller = limited multitasking and greater use of slower virtual memory

larger = greater storage of programs, faster performance, effective multi-tasking

what is cache memory?

a small amount of memory located next to the CPU, it stores frequently used instruction, it supplies the CPU with data at high speeds

properties of cache?

small capacity, volatile, used in f-d-e cycle

how does magnetic storage work?

it uses different patterns of magnetisation in a magnetisable material to store data. magnetised points represent 1 and demagnetised points represent 0

how does optical storage work?

a laser is used to burn 'pits' into shiny surfaces. a laser is used to read it, when it hits 'land' the beam is reflected (0), when it hits a 'pit' it isn't reflected (1)

how does solid storage (flash) work?

a large electrical current forces electrons through a barrier into fixed positions, the different arrangements give data

what is the use, capacity, speed, portability, durability, reliability and cost for hard disk (hard drive)?

desktop computers to store large files, programs and operating systems; 750GB - 3TB (large); fast read/write speeds; heavy; dropping can cause damage; can be reused but has has a limited life; quite cheap

what is the use, capacity, speed, portability, durability, reliability and cost for magnetic tape?

backing up vast amounts of data;; 1 - 5TB (very large); fast write speeds but slow read speeds; small and light but reading device is heavy; fairly durable; can be used again and again; cheap

what is the use, capacity, speed, portability, durability, reliability and cost for CD-ROM?

storage of small media files and documents; 650MB (small); moderate read/write speeds; portable and light; can be scratched/snapped but fairly durable; CD-R are written ones but CD-RW can be reused; very cheap

what is the use, capacity, speed, portability, durability, reliability and cost for blu-ray/DVD-ROM?

storage of larger media files and documents; 4.37GB (DVD) 25GB(blu-ray) (small); moderate read/write speeds; very portable and light; fairly durable but can be scratched; DVD-Rs are written once but can be re-read; very cheap

what is the use, capacity, speed, portability, durability, reliability and cost for solid state drive?

desktop computers, laptops and tablets store large files, programs and operating systems; 64GB - 480GB (moderate); super fast read/write speeds; very small and lightweight; no moving parts so is durable; can be reused many times; very expensive

what is the use, capacity, speed, portability, durability, reliability and cost for flash SD cards?

in phones, cameras - can function on the move; 16GB-64GB, super fast read-write speeds; extremely portable; no moving parts so is durable; can be reused many times; expensive

what is the use, capacity, speed, portability, durability, reliability and cost for flash memory stick?

backing up/transferring documents and small media files from computer to computer; 1GB-64GB, super fast read/write speeds; extremely portable; no moving parts so is durable; expensive

what is the use, capacity, speed, portability, durability, reliability and cost for a NAS drive?

a stand alone external hard drive at the centre of a network allows users to read/write files; 750GB-3TB (large); high read/write speeds but the network can cause slow access speeds; very heavy; dropping causes damage; can be reused; hard disk = cheap SS drive = expensive NAS enclosure = expensive

what is the use, capacity, speed, portability, durability, reliability and cost for cloud storage?

stores documents and media files; unlimited capacity if you pay; depends on bandwidth/network speeds; isn't physical; durable and reliable if payments are made and company looks after deives; can be issues with data protection laws; expensive depending on the service but is usually free for a few GB

how many bits are in a nibble?

4

how many nibbles are in a byte?

2

how many bits are in a byte?

8

how many bytes are in kilobyte?

1024 (1000 in calculations)

how many kilobytes are in a megabyte?

1024 (1000 in calculations)

how many megabytes in a gigabyte?

1024 (1000 in calculations)

how many gigabytes in a teabyte?

1024 (1000 in calculations)

what is a network?

where two or more computers/devices are connected to share resources

what devices can be in a network?

PC, laptop, tablets, smart phones, servers, printers, smart TV

what is a LAN?

local area network; a collection of computers and peripheral devices connected together over a small geographical area, all the hardware is owned by the company who use it

how are devices connected into a LAN, who's responsible for the cost and maintenance?

using copper Ethernet cables or wi-fi; the company

advantages of a LAN?

files can be shared as they're stored on a file server; peripheral devices can be shared; user profiles can be managed centrally; software can be installed centrally; files can be backed up centrally

disadvantages of a LAN?

viruses can be spread easily; server failure can cause network failure; costly to install as you need cables and specialist staff

what devices do you need to make a LAN?

2+ computers (each with an NIC), data transfer media, hub/swuitch, router, WAP

pros of WAP

can add new nodes easily, public can access network with permission

cons of WAP

can suffer interference, security threats

what is the purpose of a router?

to manage the data packets enabling them to be sent between networks, over the internet

what is the purpose of a switch?

to connect nodes, it's intelligent as it can create and connect to different segments of the network, reducing traffic as the packets aren't broadcast to the whole network

what is the purpose of a NIC?

convert the data signals from nodes into data signals that can be transferred across the network

define client server network

managed by a server, connected devices are called clients, files and software are centrally stored on the server rather than individual computers, the server processes and responds to requests from clients, server stores users profile passwords

pros of a client server network?

faster and easier to centrally update and backup, easier to manage network security centrally, easier to find files as they're centrally stored

cons of a client server network?

expensive to set up, need specialists to maintain, if the server goes down clients loses their work, server can be overloaded if too many clients are accessing at once

define peer to peer network

all the devices are equal, connecting to one another without the need of a serve, store files on individual devices and can share them with other

pros of a peer to peer network?

easy to maintain, don't need expertise or expensive hardware, if one device fails the whole network isn't lost, cheaper to set up

cons of a peer to peer network?

no centralised management, devices need updates and backup individually, peer machines are less reliable

what does a topology of a network affect?

cost, performance, ease of set-up

star topology

pros of star topology

fast network as few collisions, can add new PCs easily without disturbing the network

cons of star topology

expensive as lots of cables and extra hardware, if server/switch fails the network may go down

definition of mesh topology

a fully connected network where every node is connected to all others

mesh topology

pros of mesh topology

there's multiple routes for the data if there's heavy traffic or a cable break

cons of mesh topology

expensive due to all the cabling but they can be wireless

what three factors affect network performance?

bandwidth, latency, errors in transmission

what is bandwidth?

how much data can be sent in a second, higher it is faster the data is transferred

what is latency?

the delay between a signal being sent and received

what are transmission errors?

how reliable packets are transmitted, noise and distortion can cause data to be retransmitted

how does number of devices/users affect network performance?

maximum bandwidth is shared between all connected devices so more devices = less everyone gets

how does transmission media affect network performance?

wifi results in slower transfer speeds

how does interference affect network performance?

wireless and some wired networks are prone to electromagnetic interference which can corrupt data

how do obstacles affect network performance?

such as thick brick walls, can prevent radio waves from travelling

what is a WAN?

a collection of computers and networks (LANs) connected together over a wide geographical area, connected using resources from a third party

how are WANs connected?

fibre optic cables, leased telephone lines, satellites, radiowaves

pros of WANs?

allows workers to collaborate when far away, enables LANs to be connected, enables data to be shared between LANs

cons of WANs?

expensive to hire bandwidth from telecom operator, cables can go wrong, the organisation doesn't own the transmission media so is reliant on external suppliers to fix issues

what is the internet?

the largest WAN, the name given to the infrastructure

what are three key elements of the internet?

DNS, hosting, the cloud