1
Q
Computer system
A
A combination of hardware and software components that allow the input, processing and output of data
2
Q
What does a computer system do?
A
Its components work together to form a working solution to a problem
3
Q
Hardware
A
The physical components of a computer system
4
Q
Software
A
Programs that run on a computer system
5
Q
What are the four main components of a computer system? The optional fifth component?
A
- Input
- Processing
- Output
- Storage
- Communication
6
Q
What are some examples of computer systems other than PCs? (3)
A
- Mobile phones
- Cash machines
- Engine management systems in modern cars
7
Q
Auxiliary device
A
A piece of equipment that can be connected to a computer and used with it e.g. a printer
8
Q
Peripheral OR Peripheral device
A
An auxiliary computer device which provides input, output or storage functions for a computer, without providing computing-intensive functionality
9
Q
What are some examples of peripherals? (6)
A
- Mouse
- Keyboard
- Printer
- Webcam
- External drives
- CD-ROM
10
Q
Input device
A
A hardware device that takes real-world data and converts it into digital form
11
Q
What are some examples of input devices? (6)
A
- Keyboard
- Mouse
- Sensors (e.g. those in touchscreens)
- Microphone
- Camera
- Scanner
12
Q
Output device
A
A hardware device that presents digital data stored on a computer in a meaningful form
13
Q
What are some examples of output devices? (5)
A
- Monitors (e.g. CRT, TFT)
- Printers (e.g. laser, inkjet)
- Speakers
- Lights (e.g. LEDs)
- Actuators (motors which perform mechanical actions)
14
Q
Reliability
A
How much a system can be depended upon to be available when needed
15
Q
Why is the reliability of a computer system important?
A
There could be health and safety implications if certain systems failed e.g. if a hospital system failed, people could die.
16
Q
What are the two ways of measuring reliability?
A
- Availability: the proportion of time a system is operational, usually expressed as a percentage over a period of time
- MTBF: Mean Time Between Failure, how long a system is expected to last
17
Q
Robust
A
Describes a system that is resilient to failure
18
Q
Fault-tolerant
A
Describes a system where redundant components stop a single failure from bringing the whole system down
19
Q
Hardware redundancy
A
Where spare hardware components are built into a system so that, in the event of a component failing, the system can swap over to the spare
20
Q
What should a company do when reliability is extremely important? (2)
A
- Build in hardware redundancy
2. Back up data regularly
21
Q
CPU
A
Central Processing Unit: executes programs and manages the rest of the hardware
22
Q
What does the CPU do? (4)
A
- Executes programs using the fetch-execute cycle
- Fetches data from main memory
- Performs calculations
- Manages the movement of instructions and data to and from peripheral devices using system buses
23
Q
What are the three main units of the CPU?
A
- Arithmetic and Logic: performs arithmetic and logic operations
- Control: controls the actions of other components
- Registers: temporary storage within the CPU, which can be accessed at a high speed
24
Q
What happens when a program runs? (4)
A
- A copy of the program is loaded into the main memory, from where it can be accessed by the processor
- The processor is given the program’s start address in memory
- The processor executes the program one instruction at a time following the fetch-execute cycle
- Once completed, the program is removed from main memory
25
What are the steps of the fetch-execute cycle? (3)
1. Fetch an instruction from main memory
2. Decode the instruction
3. Execute the instruction
26
Why doesn't the processor get instructions straight from the disk?
Accessing a hard disk is very slow compared to accessing main memory
27
Clock speed
How many instructions a processor can execute per second, measured in Hertz
28
Factors that affect CPU performance (4)
1. Clock speed
2. Amount of cache memory
3. Number of cores
4. Slow components
29
Multi-core processor
A single component with two or more cores
30
Core
Processing unit
31
How can multi-core processors be utilised effectively?
By writing multi-threaded software i.e. software that divides tasks up between cores
32
RAM
Random Access Memory: used in main memory. It is volatile, and data is retrieved at the same speed regardless of location
33
Random access
Data can be retrieved from any location in any order
34
Volatile
Unsaved contents are lost when the power is turned off
35
What happens when the computer is running low on RAM?
Virtual memory can be used to compensate, although the computer may run slower or even crash if disk storage is close to full
36
Virtual memory
Allows a computer to compensate for RAM shortages by temporarily transferring pages of data to disk storage
37
Cache memory
Much faster than main memory, used to store frequently used instructions or data
38
How many levels of cache memory are there?
3
39
What happens as the level of cache memory increases? (3)
1. Cost decreases
2. Speed decreases
3. Memory size increases
40
L1 cache
Built onto the core and stores the most critical files
41
L2 cache
Located either on the core, or on a separate chip with a high-speed alternative bus, thus avoiding main bus traffic
42
L3 cache
Shared between cores, serving to reduce the number of calls to main memory and interaction between cores. May be significantly slower than L1 and L2, but usually twice the speed of RAM
43
Levels of cache memory stats in an Intel i7 CPU vs. RAM storage space
Intel i7
L1: 32Kb
L2: 256Kb
L3: ~8Mb
RAM
- 4Gb is the minimum these days
- 8Gb becoming more common
44
How are computer components connected?
By system buses, wires built into the lines on the motherboard
45
What are the three main buses?
Address: one-way, used to send a memory address from the CPU to the RAM
Data: can be used to send back an instruction from the RAM to the CPU. Two-way, as the CPU may need to get more data from the RAM
Control: carries signals to show if the Address or Data buses are already in use
46
Why is the control bus needed?
Only one component can transmit along a bus at any one time
47
Arrange the following in decreasing order of memory speed:
1. Main memory
2. L2 cache
3. Disk
4. L1 cache
4 2 1 3
48
An idea of the difference in memory speeds for the following:
1. L1 cache
2. L2 cache
3. Main memory RAM
4. Disk
L1: Picking up a book on your desk (~3s)
L2: Getting up to get a book off a shelf (~15s)
RAM: Walking down a corridor to another room (several minutes)
Disk: Walking the British coastline (~1 year)
49
ROM
Read-Only Memory: non-volatile memory used in hard-wired programs e.g. a bootstrap loader. Has come to include memory that is read-only in normal operation, but can still be reprogrammed e.g. EEPROM
50
Bootstrap loader
A program which loads the operating system, starting up the computer
51
Non-volatile
Retains data even when there is no power
52
EEPROM
Electrically Erasable Programmable ROM: used to store relatively small amounts of data e.g. in the bootstrap loader. Individual bytes can be reprogrammed through the application of high voltage
53
Secondary storage
Non-volatile storage devices. Not directly accessible by the CPU, but instead accessed through main memory
54
Factors to take into account when deciding on a type of secondary storage (6)
1. Capacity: space for files
2. Speed: for access, often linked with capacity
3. Portability: can it be carried away? What can it fit into?
4. Durability: how long will it last?
5. Reliability: how easily is it damaged?
6. Cost
55
What are two types of hard drives?
1. HDDs
| 2. SSDs
56
HDD
Hard Disk Drive: a secondary storage drive which uses rotating disks covered in magnetic material to store and retrieve data
57
```
HDD
Cost:
Capacity:
Speed:
Reliability:
Deterioration pattern:
```
Cost: cheap
Capacity: high - several terabytes not uncommon
Speed: slower than SSDs
Reliability: less reliable than SSDs due to moving parts
Deterioration pattern: slow down with age
58
SSD
Solid State Drive: a secondary storage drive which is completely electronic, with no moving parts
59
```
SSD
Cost:
Capacity:
Speed:
Reliability:
Deterioration pattern:
```
Cost: more expensive than HDDS - large disks very expensive
Capacity: smaller capacity than HDDs, although 1 Tb is becoming more common
Speed: fast
Reliability: very reliable - no moving parts means it is more robust and less power used
Deterioration pattern: work at the same rate until failure
60
Why is it important not to get close to filling any kind of hard drive?
Your computer will begin to slow down, and will eventually crash
61
Is an internal drive a peripheral? Why?
No, because:
1. Software programs are retrieved from it during runtime
2. Virtual memory allows data pages to be stored on it temporarily
62
What are three methods of data storage?
1. Magnetic
2. Optical
3. Solid state
63
Give three types of magnetic storage
1. Hard disk drives
2. Magnetic tape drives
3. Floppy disks
64
```
Internal hard disk
Capacity:
Speed:
Portability:
Reliability:
Durability:
Uses:
```
Capacity: up to 8 Tb
Speed: fast
Portability: not designed to be portable - directly attached to the computer chassis
Reliability: fairly reliable
Durability: vulnerable to damage if dropped. Affected by heat and magnetic fields
Uses: inside a PC as secondary storage
65
```
External hard disk
Capacity:
Speed:
Portability:
Reliability:
Durability:
Uses:
```
Capacity: up to 8 Tb
Speed: slower than internal hard disk, faster than CDs and DVDs
Portability: fairly portable - normally larger than a CD or USB
Reliability: fairly reliable
Durability: vulnerable to damage if dropped. Affected by heat and magnetic fields
Uses: supplementary storage for a PC when lots of storage space needed
66
```
Magnetic tape
Capacity:
Speed:
Portability:
Reliability:
Durability:
Uses:
```
Capacity: up to 6 Tb
Speed: slow
Portability: rarely used as portable storage
Reliability: fairly reliable
Durability: wears out with repeated use. Affected by heat and magnetic fields
Uses: network backups and archiving
67
What are the three main parts of magnetic media storage?
1. Magnetic medium: covered in or contains a magnetic substance e.g. iron oxide, chromium oxide
2. Read-write head: reads and writes data to the media
3. Actuator: a motor that moves or controls something
68
Where is the magnetic media on a:
1. Hard disk?
2. Tape?
HDD: in circular tracks on the surface of the disk platters
Tape: in lines along the length of the tape
69
How does the read-write head work?
It creates a magnetic field over the location on the medium and magnetises the individual dots of magnetic material in binary patterns, storing the data
70
How does an actuator work in a:
1. Hard disk?
2. Tape?
HDD: makes the read-write arm move across the disk platters
Tape: moves the tape to the heads
71
What happens when a magnetic hard disk crashes?
The arm crashes down onto the disk platters
72
Give three types of optical storage
1. Compact Discs (CDs)
2. Digital Versatile Discs (DVDs)
3. Blu-ray discs
73
```
CD
Capacity:
Speed:
Portability:
Reliability:
Durability:
Uses:
```
Capacity: 650 Mb
Speed: slower than external hard disk, faster than tape
Portability: fairly portable - easily fits into a bag
Reliability: not very reliable - easily scratched, quality can start degrading after just 18 months
Durability: scratching can lead to corrupted data. Affected by heat
Uses: CD-ROMs for software distribution, CD-R(W)s for backups or archiving
74
```
DVD
Capacity:
Speed:
Portability:
Reliability:
Durability:
Uses:
```
Capacity: 4.7 Gb (single layer), 9.4 Gb (double layer)
Speed: slower than external hard disk, faster than tape
Portability: fairly portable - easily fits into a bag
Reliability: not very reliable - easily scratched, lifespan of 2–15 years
Durability: scratching can lead to corrupted data. Affected by heat
Uses: used instead of CDs when higher capacity needed
75
```
Blu-ray Disc
Capacity:
Speed:
Portability:
Reliability:
Durability:
Uses:
```
Capacity: 25 Gb (single layer), 50 Gb (double)
Speed: slower than external hard disk, faster than tape
Portability: fairly portable - easily fits into a bag
Reliability: not very reliable - easily scratched, quality degrades over time
Durability: scratching can lead to corrupted data. Affected by heat
Uses: used to store very high quality, high-definition (HD) video
76
How is data read from optical storage media?
A laser reflects off of dots on the surface of the medium, and a sensor detects the patterns in the data. They are random access
77
How is data written to writable optical storage media?
The laser beam is used in high-power mode to mark the surface of the disk, making dots. This process is known as "burning" data onto the disk
78
Give three formats of optical discs
1. Read-only
2. Recordable
3. Rewritable
79
Read-only optical discs:
1. What does "read-only" mean?
2. What are they denoted by?
1. Data is written onto the disc during the manufacturing process. This data cannot be altered
2. ROM
80
How much data can a CD-ROM hold?
Around 800 Mb of data
81
Recordable optical discs:
1. What does "recordable" mean?
2. What are they denoted by?
1. Data can be written to them using a disc burner, but cannot be erased
2. R
82
Disc burner
A special disk drive which burns data onto an optical storage device
83
Why can't CD-Rs and DVD-Rs be reused?
When they are burnt, the laser makes permanent marks on the metal layer
84
Rewritable optical disks:
1. What does "rewritable" mean?
2. What are they denoted by?
1. Data can be burnt onto them and also erased, making the disks reusable
2. RW
85
Why can CD-RWs and DVD-RWs be reused?
When they are burnt, the laser makes marks on the metal layer, but in a way that can be undone
86
DVD-RAM disc
A type of rewritable DVD
87
How are DVD-RAMs different from normal DVD-RWs? (3)
1. They are much higher quality
2. In addition to this, they can also store data reliably for up to 30 years
3. This means that they are often used for video and data backups and archiving
88
Why do Blu-ray discs have a much higher storage capacity than CDs and DVDs? (3)
1. The laser used to read the disc uses blue light instead of red light
2. Blue light has a shorter wavelength than red light (used with CDs and DVDs)
3. This means that more data can be placed closer together on a Blu-ray disc than on a CD or DVD
89
What kind of memory is used in solid state storage devices?
Flash memory
90
Flash memory
An electronic, random-access, non-volatile computer storage medium that can be electrically erased and reprogrammed
91
What is flash memory developed from?
EEPROM
92
Fill in the blanks:
Although flash memory is a ________ form of RAM, it will not replace the RAM found in _____________ because its ___________ is much slower.
1. Non-volatile
2. Main memory
3. Access speed
93
Give three types of flash storage devices
1. Solid state drive
2. USB memory stick
3. Memory card
94
```
Internal solid state drive
Capacity:
Speed:
Portability:
Reliability:
Durability:
Uses:
```
Capacity: up to 2 Tb
Speed: very fast
Portability: not portable - built into system
Reliability: very reliable
Durability: very durable - can be dropped without damaging contents. Not affected by magnets or heat
Uses: notebooks, tablets, slim laptops
95
```
External solid state drive
Capacity:
Speed:
Portability:
Reliability:
Durability:
Uses:
```
Capacity: up to 2 Tb
Speed: fast - when using Thunderbolt speeds, can come close to the speed of an internal drive
Portability: fairly portable - normally larger than a CD
Reliability: very reliable
Durability: very durable - can be dropped without damaging contents. Not affected by magnets or heat
Uses: external data storage
96
Thunderbolt
The brand name of a hardware interface that allows the connection of external peripherals to a computer
97
```
USB stick
Capacity:
Speed:
Portability:
Reliability:
Durability:
Uses:
```
Capacity: up to 1 Tb for USB 3.0
Speed: slower than hard disk, faster than CDs and DVDs
Portability: very portable - easily fits on a keyring
Reliability: very reliable, although files can become corrupted if the stick is not ejected correctly
Durability: very durable - not affected by magnets or heat. The USB connector can be snapped off, rendering the device unusable
Uses: personal, moving files between computers
98
How do USB sticks work?
Each USB stick has some flash memory connected to a USB interface. When plugged into a computer, it appears as a drive. Files can then be added or erased
99
What are flash memory cards used for?
It is used in devices where compact, non-volatile storage is needed (e.g. cameras, mobile phones, MP3 players)
100
What is one of the most common memory card formats used in cameras?
The SD card
101
SIM card
Subscriber Identity Module card: put into a phone, containing a phone number
102
Besides a SIM card, what do many phones also have?
Extra memory cards to store music, video, photos, etc., such as micro-SD cards
103
Smart card
A card with flash memory
104
What have smart cards replaced and why?
Smart cards have replaced the use of magnetic strips, as they are more reliable and have a much larger storage capacity
105
What are three areas of hardware development in memory?
1. Capacity and density: how much can be stored in a certain amount of space
2. Speed
3. Price
106
Hardware developments in memory: Capacity and Density (4)
1. You can now buy 64Gb SD cards for cameras where 4Gb was previously considered high capacity.
2. Higher density means that devices have higher capacity in the same amount of space, or the same capacity and get smaller.
3. This can be seen in phones, which have become smaller and lighter and yet can store more data.
4. The capacity of main memory has also increased, so computers can run more applications at the same time, and even complex games can run easily on today's "basic" computers.
107
Hardware developments in memory: Speed (4)
1. Although flash memory is much slower than RAM, it is significantly faster than HDDs.
2. This means that bulky and sensitive hard disks can be replaced with smaller, lighter, faster and more reliable flash memory.
3. Computers can start up quicker, as this is dependent on how long it takes to load the OS from secondary storage into RAM.
4. So now there are notebooks that can be slipped into pockets, tablet PCs and smartphones that behave like computers.
108
Hardware developments in memory: Price (3)
1. Flash memory is becoming cheaper and easier to produce, meaning that devices using it have become cheaper as well.
2. The lower cost of memory improves the capacity of gadgets e.g. MP3 players, handheld game consoles, phones, etc.
3. As the cost of RAM has dropped as well, a £500 PC today has more RAM and more storage space than a £500 PC just a couple of years ago.
109
For each of the following features of a modern phone, show whether it is input (I), output (O) or both (B):
1. Vibration alert
2. Touchscreen
3. Microphone
4. Speaker
Vibration alert: O
Touchscreen: B
Microphone: I
Speaker: O
110
Give three developments that have made modern smartphones possible in the last decade
1. More powerful processors have enabled phones to become minicomputers
2. Solid state memory means that phones are less bulky and can store more
3. Touchscreen technology has become cheaper and more reliable
111
```
Which of the following two computers is likely to be faster and why?
#1: quad-core, with a clock speed of 2 GHz
#2: single core, with a clock speed of 4.1 GHz
```
```
#1 should be faster.
Although #2 has a higher clock speed, #1 has four cores, meaning that it can process four sets of instructions at a time. Provided that the software is multi-threaded, the speed of #1 can approach four times the clock speed, making #1 the faster processor overall.
```
112
What are four factors that affect a computer's speed?
1. Clock speed and number of cores
2. Sufficient RAM
3. Cache memory
4. Secondary storage method
113
Factors in computer speed: Clock speed and number of cores (3)
1. A higher clock speed means that more instructions can be completed more quickly.
2. However, a slower clock speed with more cores means that instructions can be executed simultaneously.
3. Provided that the software has been written to accommodate multiple cores, this will result in a faster machine overall.
114
Factors in computer speed: Sufficient RAM (3)
1. When working on a computer, all of the open applications and processed data are stored in the RAM.
2. If the RAM is filled, part of the hard drive is used as virtual memory. This acts as additional RAM.
3. However, as hard drives are much slower than RAM, using virtual memory will have a detrimental effect on the computer's performance.
115
Factors in computer speed: Cache memory (4)
1. As the development of RAM has not kept up with that of processors, computers use the very fast, expensive cache memory.
2. This is supplied in levels depending on speed and proximity to the processor e.g. L1, L2 and L3, with L3 being the slowest.
3. Frequently used instructions are stored in cache, speeding up the computer considerably. The more cache supplied, the faster the system will run.
4. However, this will increase the cost of the computer.
116
Factors in computer speed: Secondary storage method (3)
1. SSDs are faster than HDDs as they have no moving parts, thus speeding up a computer.
2. However, SSDs are more expensive and have less capacity than HDDs.
3. In addition to this, as soon as the SSD starts to get close to full it will begin to slow down due to the way that they work.
Computer Science GCSE
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