GCSE Computer Science - OCR J277 Flashcards
FLASHCARDS MADE MYSELF WITH AID OF SOURCE BOOK: COMPUTER SCIENCE GCSE (9-1) FOR OCR J277 STUDENT BOOK BY DAVID WALLER
1
Q
What does CPU stand for?
A
Central Processing Unit
2
Q
What is the purpose of the CPU?
A
The CPU is responsible for executing the instructions given to it in a program. It is the component of the computer that controls the other devices, executes the instructions and processes the data.
3
Q
What was the name of the first computer?
A
ENIAC
4
Q
Where does data processing take place?
A
CPU
5
Q
What is Von Neumann architecture?
A
The way the CPU is designed and executes the program instructions. It is a ‘stored program’ computer where both the program and the data are stored in the memory.
6
Q
What year did John von Neumann propose his ‘stored program’ computer design?
A
1945
7
Q
What problem did Von Neumann architecture solve in 1945?
A
Prior to 1945, computers had to be rebuilt for each new program that was needed.
8
Q
What does ‘execute’ mean in a computer science context?
A
To run a computer program or process.
9
Q
What is the bus in Von Neumann architecture?
A
A bundle of wires carrying data from one component to another or a number of tracks on a printed circuit board (PCB) fulfilling the same function.
10
Q
What does PCB stand for?
A
Printed Circuit Board
11
Q
What does RAM stand for?
A
Random Access Memory
12
Q
What is RAM?
A
Memory that can be used by computer programs to store data and instructions, but all of its data is lost when the computer is switched off.
13
Q
What is a collection of wires that carry signals or communications between the various components of a computer system called?
A
A bus
14
Q
What does the control bus connect?
A
The control unit (CU) with the other components of the CPU and devices in the computer system.
15
Q
What does the control unit use the control bus for?
A
To send instructions to other components of the computer.
16
Q
What is the data bus used for?
A
The transfer of data between the CPU and the RAM and the address bus for the CPU to access memory locations in the main memory.
17
Q
What happens before the fetch-decode-execute cycle starts?
A
The program instructions are copied from a storage device such as a hard disk drive or DVD to the primary storage or RAM.
18
Q
What is the fetch-decode-execute cycle?
A
The way in which the Von Neumann architecture executes the program instructions.
19
Q
What happens during the fetch part of the fetch-decode-execute cycle?
A
Instructions and data are moved from the RAM to the CPU.
20
Q
What happens during the decode part of the fetch-decode-execute cycle?
A
The control unit (CU) decodes or interprets the instructions and decides what action to perform.
21
Q
What happens during the execute part of the fetch-decode-execute cycle?
A
The decoded instructions are now carried out by the control unit (CU). If a calculation needs to performed then it instructs to ALU (Arithmetic Logic Unit).
22
Q
What does ALU stand for?
A
Arithmetic Logic Unit
23
Q
What is the function of the ALU?
A
To perform arithmetic and logical operations. It carries out activities such as:
1. addition and subtraction
2. multiplication and division
3. logical tests using logic gates (Boolean logic)
4. comparisons, such as whether one number is greater than another
24
Q
What does CU stand for?
A
Control Unit
25
What are control signals?
Electrical signals that are sent out to all of the devices to check their status and give them instructions.
26
What is a register?
A storage location that is inside the CPU itself and stores the instructions and data that are currently being used in the fetch-decode-execute cycle.
27
What is the purpose of the CU?
The CU coordinates the actions of the computer and controls the fetch-decode-execute cycle by sending out control signals to the other parts of the CPU such as the ALU and registers. It also sends signals to other components of the computer system such as the input and output devices. The 2 main elements of the CU are the clock and the decoder.
28
What are the 2 main elements of the CU?
The clock and the decoder.
29
What is clock speed measured in?
Cycles per second
30
What is the rate of one Hertz?
One cycle per second
31
What is the rate of one megahertz (MHz)?
One million cycles per second
32
What is the rate of one gigahertz (GHz)?
One billion cycles per second
33
What are the common rates (in GHz) in most home computers?
Rates of between one and three GHZ
34
Why does the clock in the CU send out pulses?
Pulses are sent out to the other components to coordinate their activities and ensure instructions are carried out and completed.
35
What controls the timing of the pulses sent out by the CU's clock?
A vibrating quartz crystal
36
How many instructions can be carried out with each pulse of the clock?
One
37
How does the clock speed impact the CPU speed?
The higher the clock speed, the faster the CPU will be able to carry out the program instructions.
38
What is the function of the decoder in the CU?
The decoder is the part of the CU that decodes the program instructions to work out what they mean and decide what actions should be taken. It then sends control signals to the other components to carry them out.
39
True or false: Registers can be accessed faster then RAM.
True
40
What is the function of registers?
Registers are storage locations within the CPU. The function of these registers is to store instructions and data that are currently being used in the fetch-decode-execute cycle.
41
What are general purpose registers used for?
The quick storage of data items.
42
Name the 4 main registers which are not general purpose registers as they serve specific functions:
1. the accumulator (A or ACC)
2. the program counter (PC)
3. the memory address register (MAR)
4. the memory data register (MDR) or memory buffer register (MBR)
43
What are storage locations in Von Neumann architecture?
Places in RAM where a single piece of data can be kept until they are needed.
44
What does the CPU consist of?
1. control unit (CU)
2. arithmetic and logic unit (ALU)
3. registers
45
How does the CPU control the activities of the CPU?
By sending out control signals.
46
What is the function of the ALU?
To carry out arithmetic and logic operations.
47
What are registers?
Registers are the memory stores within the CPU, which can be accessed faster than RAM.
48
What is overclocking?
The process of increasing the clock speed to a higher level than that recommended by the manufacturer.
49
What are the risks of overclocking?
Overclocking causes an increase in heat and can result in instability and permanent damage to the processor.
50
What is a heat sink?
A metal device, glued to the CPU chip with thermally conducting paste, to transfer the heat away from the chip.
51
What does clock speed control?
The rate at which instructions are processed.
52
How does clock speed impact the rate of processing?
The faster the clock speed, the faster the rate of processing.
53
What is the problem with microprocessors with clock speeds of 9 GHz?
They require cooling by liquid nitrogen.
54
What are the limitations of increasing clock speed to increase processing speed?
1. Microprocessors with clock speeds of 9 GHz require cooling by liquid nitrogen.
2. The microprocessor generates a large amount of heat and this heat increases with clock speed. Although heat is dissipated by a fan and heat sink to prevent it from malfunctioning (and eventually melting) there are limits to the rate of cooling.
55
When do bottlenecks occur?
Bottlenecks occur when one component cannot work as fast as other components and so hinders progress.
56
True or false: It is far quicker to fetch instructions from RAM than from a hard disk drive.
True. However, (while it is quicker to fetch the instructions) the RAM is still far slower than the CPU and then the instructions still need to be transferred through the data bus. This is why cache needed to be created as a solution.
57
Why is the speed of processing limited by RAM?
RAM supplies the instructions regardless of how much clock speed is increased or how many cores are used. This is why cache needed to be created as a solution.
58
What is cache?
Memory used to store recently used data and data likely to be frequently used so that they can be accessed more quickly.
59
What is the difference between data and instruction caches?
Data caches have to be read and written to but instruction caches just have to be read by the CPU.
60
Where are caches located?
On the processor chip.
61
Which level of cache is the fastest?
There are 3 levels of cache. Level 1 is both the fastest and the smallest.
62
Which level of cache is the smallest?
Level 1
63
Which level of cache is the slowest?
There are 3 levels of cache. Level 3 is the slowest.
64
Which year did manufacturers introduce multi-core processors?
2006
65
Why does a multi-core processor have a faster processing speed?
A multi-core processor has more than one CPU.
66
What is a processor with one core called?
Single-core processor
67
What is a processor with two cores called?
Dual-core processor
68
What is a processor with four cores called?
Quad-core processor
69
What is a processor with 5 cores called?
Penta-core processor
70
What is a processor with 8 cores called?
Octa-core processor
71
What is a processor with 10 cores called?
Deca-core processor
72
What is parallel processing? HINT: OPPOSITE OF MULTI-TASKING
When the processor cores work on different parts of the same program.
73
What is multitasking? HINT: OPPOSITE OF PARALLEL PROCESSING
When the processor cores work on different programs at the same time.
74
What are the advantages of multi-core processors over single core processors?
1. the cores can work together on the same program; this is called parallel programming
2. the cores can work on different programs at the same time; this is called multi-tasking
75
Why can clock speed not be increased indefinitely?
Because of the extra heat that is generated.
76
What is a multi-core processor?
A processor with multiple CPUs.
77
What limits the processing speed of the CPU?
The CPU's processing speed is limited by the speed that data can be supplied by the slower RAM.
78
What does cache memory store?
Regularly used items of data so that they can be accessed more quickly.
79
What happens when RAM is full? (Where will the operating system store data?)
When RAM is full, the operating system will store data on an area of the hard disk drive known as virtual memory.
80
What is an embedded system?
A computer system built within a larger device to carry out specific tasks. They are generally limited to a certain number of tasks, unlike general purpose computer systems such as laptops and desktops.
81
Give an example of an embedded system:
1. washing machines
2. dishwashers
3. microwaves
4. digital cameras
etc.
82
True or false: all the components in an embedded system, including the microprocessor, memory and input and output devices are on a single printed circuit board. The memory contains the program and the board is merely a component built into a larger device hence the name 'embedded'.
True.
83
Why are the programs in an embedded system often written in an assembly language, rather than a higher level programming language?
So that the hardware components can be more easily controlled.
84
What is an embedded system?
A computer system built into a larger device that carries out a limited number of functions. All of the components (memory, microprocessor, input/output devices) are stored on a single PCB, with the memory containing the program.
85
What is a PCB?
A PCB (Printed Circuit Board) is the base that supports the wiring and electronic components that are soldered to it or fit into sockets on the board.
86
What is hardware?
The physical components making up the computer, and its peripheral devices.
87
What is primary storage?
Storage that can be accessed directly by the CPU, usually referred to as 'memory'.
88
What is secondary storage?
Permanent storage for data that does not need to be frequently accessed.
89
Why is RAM used by the CPU?
It takes a long time to fetch data and program instructions from the hard drive. Therefore, they are stored in RAM, a temporary store of data, so that the information can be retrieved quickly by the CPU when required for the program it is running.
90
Why does each byte of date have an address?
So that the CPU knows where to store and retrieve the instructions and data.
91
Why is RAM said to be 'Random Access'?
Because each memory location can be accessed in any order if the 'address' of that location is specified. This speeds up data retrieval as the CPU can go to any location and does not have to start each time at the first location and go through them in order until it finds the correct one. This is called serial access.
92
What is serial access? HINT: RANDOM ACCESS MEMORY
When the CPU has to search each memory location by starting at the first location and and going through them in order until it finds the correct one.
93
What does it mean to say RAM is volatile?
RAM is said to volatile because if there is no electrical power then the RAM will lose all of its data.
94
What are the different types of RAM?
DRAM and SRAM
95
What does DRAM stand for?
Dynamic RAM
96
What does SRAM stand for?
Static RAM
97
Why is DRAM used as the main memory store, despite being slower than SRAM?
Because it is cheaper.
98
True or false: DRAM is slower than SRAM.
True. Despite DRAM being slower than SRAM it is still used as the main memory store because it is cheaper.
99
How large is a byte?
8 bits
100
What is an address?
A number assigned to the storage location so that it can be accessed.
101
What does volatile mean?
Data is permanently lost when the power is switched off.
102
What does BIOS stand for?
Basic Input/Output System
103
What is the function of the BIOS?
The BIOS system controls the computer when it is first switched on. It tests the system hardware and loads the operating system. It is specially written for each motherboard and performs any other operations that are needed by that particular motherboard.
104
What does ROM stand for?
Read-Only Memory
105
What is ROM? HINT: THINK IN TERMS OF HARDWARE
ROM is an integrated circuit on a chip. It is programmed with specific data to perform a particular function then it is manufactured.
106
List the functions of the BIOS:
1. the BIOS controls what happens when the computer is first switched on
2. the BIOS checks the hardware devices to ensure there are no errors
3. the BIOS loads basic software so that it can communicate with these hardware devices. It then locates and passes control to the operating system.
107
What does it really mean to say that ROM is 'Read-Only'?
The data can be read but it cannot be changed; the computer cannot write to the chip, unlike RAM.
108
ROM is non-volatile. What does non-volatile mean?
ROM is non-volatile as the data is not lost when the power is turned off.
109
What does RAM act as?
A temporary store of program instructions and data.
110
What is RAM made up of?
RAM consists of billions of memory locations with unique addresses which can be accessed in any order.
111
What is ROM used to store?
Basic information and instructions that a computer needs when it is starting up (booting).
112
What are applications?
Programs that are called up by the systems software and which perform specific tasks.
113
When could RAM become full?
When the computer is running the operating system and several applications.
114
Explain the 4 steps of the computer calling in virtual memory and swapping in and out data stored in RAM.
1. a process running on the computer may need to store data in the physical memory.
2. if there is no free memory, the memory manager will 'swap out' some of the data stored in RAM to the swap area on the hard disk drive and 'swap in' the requested data into the now free area.
3. usually the least recently used stored data is swapped out.
4. if data is swapped out and then is needed again, it is swapped back in, from the swap area, at the expense of the data.
115
True or false: the size of the area on the hard disk drive to be used for virtual memory can be set by the user.
True
116
What are the three main disadvantages of virtual memory?
1. the read/write speed of a hard drive is much slower than RAM, as the technology of a hard drive is not geared towards accessing multiple small pieces of data at a time.
2. if the system has to rely too heavily on virtual memory, there will be a significant performance drop.
3. often the operating system has to constantly swap information back and forth between RAM and the hard disk drive, which operates all of the time. You can hear the disk drive operating continuously. This is called 'disk thrashing' and significantly slows down the execution of programs.
117
What is virtual memory?
Virtual memory is the use of secondary storage as additional primary memory.
118
What is disk thrashing?
Often the operating system has to constantly swap information back and forth between RAM and the hard disk drive, which operates all of the time. You can hear the hard disk drive operating continuously. This is called 'disk thrashing' and significantly slows down the execution of the programs.
119
Why will inserting more RAM significantly improve the performance of a computer?
The more RAM a computer has then the less virtual memory will be needed. Virtual memory has a much slower read/write speed as the technology of a hard drive is not geared towards accessing multiple small pieces of data at a time.
120
What is execution?
When a program or part of a program is run by the computer.
121
What are secondary storage devices?
Devices that store information but which do not lose the data when they are switched off; usually not on the main circuit (motherboard).
122
What is optical storage?
Storing data using optical devices such as CDs and DVDs.
123
What is solid state storage?
Storing data using devices such as flash memory. This is sometimes called 'electrical' storage.
124
What are the three types of secondary storage?
1. magnetic storage
2. optical storage
3. solid state storage
125
What are the three types of secondary storage?
1. magnetic storage
2. optical storage
3. solid state storage
126
Why do we use secondary storage devices?
Because RAM is volatile, data must be stored on devices called secondary storage devices so that the data is not lost when the power is turned off.
127
How does optical storage work?
Optical storage uses light from lasers to read and write data on discs. To write data to a disk, a laser beam encodes data onto a disk via burning pits onto the disk's surface in a spiral track.
128
How much data can a CD typically store?
CDs typically store 700MB.
129
How much data can a DVD typically store?
DVDs typically store 4.7 GB.
130
What does CD stand for?
Compact Disk
131
What does DVD stand for?
Digital Versatile Disk
132
How much data can a Blu-ray disk typically store?
128 GB
133
Give two advantages of optical storage:
1. cheap
2. easy to transport from one site to another
134
Give five disadvantages of optical storage devices:
1. less storage space than hard disk drives
2. slow access speeds
3. stored data degrades over time
4. risk of disk scratching
5. data cannot be written over unlike with hard disk drives
135
Give three examples of magnetic storage devices:
1. hard disk drives
2. magnetic tape
3. floppy disk drives
136
What do hard disk drives consist of and how do they work? HINT: THINK HARDWARE
Hard disk drives consist of stacks of non-removable disks coated with magnetic materials. The disks spin and read-write heads move across them. Electro-magnets in the read-write heads read and write the data.
137
What is magnetic storage?
Storing data using magnetic media such as a hard disk drive.
138
When is magnetic storage most suitable?
Hard disk drives are suitable for the storage and backup of large amounts of data that do not need to be transported.
139
When is optical storage most suitable?
Optical disks are most suitable for distributing program files and images, and backing up data which can then be stored at another site.
140
Give two disadvantages of magnetic storage:
1. not very portable
2. susceptible to physical knocks that may cause the read-write heads to hit the disks and corrupt data
141
Give four advantages of magnetic storage:
1. very fast access speeds
2. random access: data can be read instantly from any part of the disc
3. low cost
4. can store large amounts of data; hard disk drives that store terabytes of data are common in most home computers
142
What does SSD stand for?
Solid State Drive
143
What does SD card stand for?
Secure Digital card
144
Give five examples of solid state storage:
1. SSDs
2. SD cards
3. Micro SD cards
4. SDXC (extended capacity) cards
5. USB drives
145
How much data can an SD card typically store?
4 - 32 GB
146
How much data can a Micro SD card typically store?
4 - 32 GB
147
How much data can an SDXC (extended capacity SD card) store?
2 TB
148
How much data can a USB drive typically store?
256 GB - 1 TB
149
When is solid state memory most commonly used?
Data storage in cameras, mobile phones and embedded devices. It is also increasingly used as the main secondary storage device in computers, especially in laptops as SSDs.
150
What is the main secondary storage device used by the MacBook Air?
SSD
151
When are solid state drives most suitable?
Solid state memory devices are ideal for transporting data as they are light and have no moving parts which could be damaged.
152
Give four advantages of solid state storage:
1. very fast access speed; much faster than optical discs
2. portable - small and light
3. quiet
4. has no moving parts that could be damaged if the device was knocked or dropped and therefore there is less chance of losing data
153
Give three disadvantages of solid state storage:
1. more expensive than a HDD or optical disc
2. less storage capacity than a HDD
3. limited number of erase/write cycles, up to 100000 for high quality SSDs and so it cannot be used indefinitely
154
Analyse magnetic storage devices in terms of capacity, speed, portability, durability, reliability and cost:
1. capacity - very large
2. speed - fast
3. portability - not very portable as physical knocks may cause the read-write heads to hit the discs and corrupt the data
4. durability - very durable
5. reliability - very reliable
6. cost - very low
155
Analyse optical storage devices in terms of capacity, speed, portability, durability, reliability and cost:
1. capacity - low
2. speed - slow
3. portability - more portable than HDD but discs are still relatively slow
4. durability - easily scratched and data can be damaged. Data cannot be overwritten
5. reliability - very reliable if not scratched
6. cost - very low
156
Analyse solid state storage devices in terms of capacity, speed, portability, durability, reliability and cost:
1. capacity - large (usually around 1TB)
2. speed - very fast
3. portability - very portable
4. durability - lower than a HDD, limited number of erase/write cycles
5. reliability - very reliable, data is not affected by magnetic fields as it is in HDD
6. cost - most expensive but becoming cheaper
157
What is cloud storage?
Off-site storage accessed over the internet.
158
What are bits (also known as binary digits)?
0 and 1
159
Explain how the CPU carries out the program instructions.
The CPU carries out all of the program instructions by carrying out millions of calculations each second. These calculations are performed by billions of transistors acting as switches. The transistors are either on or off - they have two states, they either transmit an electric current or they do not.
160
What are computer programs made up of?
Lists of instructions switching transistors off or on (to be represented by 0 and 1).
161
What do binary digits represent?
They are 0 and 1 and represent the codes for instructions and data.
162
How many bits in a nibble?
4
163
How many bits in a byte?
8
164
How many bytes in a KB?
1000 bytes
165
How many KB in a MB?
1000 KB
166
How many MB in a GB?
1000 MB
167
How many GB in a TB?
1000 GB
168
How many TB in a PB?
1000TB
169
What is the acronym for remembering the increasing order of file size? BITS --> PETABYTES
Bold - BIT
Blue - BYTE
Kites - KILOBYTE
Make - MEGABYTE
Great - GIGABYTE
Toy - TERABYTE
Planes - PETABYTE
170
What does KB stand for?
Kilobyte
171
What is the magnitude of a KB? HINT: IN TERMS OF 10 TO THE POWER OF N
10^3 bytes
172
What does MB stand for?
Megabyte
173
What is the magnitude of a MB? HINT: IN TERMS OF 10 TO THE POWER OF N
10^6 bytes
174
What does GB stand for?
Gigabyte
175
What is the magnitude of a GB? HINT: IN TERMS OF 10 TO THE POWER OF N
10^9 bytes
176
What does TB stand for?
Terabyte
177
What is the magnitude of a TB? HINT: IN TERMS OF 10 TO THE POWER OF N
10^12 bytes
178
What does PB stand for?
Petabyte
179
What is the magnitude of a PB? HINT: IN TERMS OF 10 TO THE POWER OF N
10^15 bytes
180
True or false: Transistors act as switches which either conduct electricity (represented by the binary digit 1) or they do not (represented by the binary digit 0). The system consists of these two states, so is called a binary system.
True
181
What does it mean to say a number system is base 10?
Each place value is 10 times bigger than the place to its right.
182
Which number system do we use?
Denary
183
Which base does denary use?
Base 10
184
What are place values?
A place value is the value that a digit's position in a number gives it. For example (for decimal) in the number 356, the digit 5 has a value of 50 whereas in the number 3560, the digit 5 has a value of 500.
185
What does it mean to say a number system is base 2?
Each place value is 2 times bigger than the place to its right.
186
Which base does binary use?
Base 2
187
Which number system does a binary system use?
Binary
188
What is the denary equivalent of 2^0 bits in a byte?
1
189
What is the denary equivalent of 2^1 bits in a byte?
2
190
What is the denary equivalent of 2^2 bits in a byte?
4
191
What is the denary equivalent of 2^3 bits in a byte?
8
192
What is the denary equivalent of 2^4 bits in a byte?
16
193
What is the denary equivalent of 2^5 bits in a byte?
32
194
What is the denary equivalent of 2^6 bits in a byte?
64
195
What is the denary equivalent of 2^7 bits in a byte?
128
196
How many bits does one binary number have? FOR EXAMPLE: 10011010
8
197
What does MSB stand for?
Most Significant Bit
198
What is the MSB?
The bit with the largest value, farthest to the left.
199
What does LSB stand for?
Least Significant Bit
200
What is the LSB?
The bit with the lowest value, farthest to the right.
201
What are bits?
BInary digiTs - they have single binary values of either 0 or 1.
201
What is an integer?
A whole number without decimals (can be positive or negative).
202
What are the three rules of binary addition?
0 + 1 = 1
0 + 0 = 0
1 + 1 = 0 CARRY THE 1
1 + 1 + 1 = 1 CARRY THE 1
203
What is an overflow error?
When a calculation produces a result that is greater than the range of values that the computer can represent or store.
204
What is the most famous example of an overflow error?
The crash of the Ariane 5 space rocket launched by the ESA (European Space Agency) in 1996.
205
True or false: Binary numbers can only be added and subtracted.
False. Addition, subtraction, multiplication and division can be carried out on binary numbers in the same way as denary ones.
206
What base does the hexadecimal system use?
Base 16
207
What is A in hex?
10
208
What is B in hex?
11
209
What is C in hex?
12
210
What is D in hex?
13
211
What is E in hex?
14
212
What is F in hex?
15
213
How many digits are in the hexadecimal system?
16 digits - 0 to 15
214
List the hexadecimal digits:
0 1 2 3 4 5 6 7 8 9 A B C D E F
215
True or false: Computers understand hexadecimals.
False. Computers only understand and use the binary system.
216
Why do we use hexadecimal numbers?
Human limitations - we get confused by large binary numbers so we simplify them by representing them in hex notation. Saves time.
217
How many bits in a colour code?
24 bits
218
How are colour codes represented?
Hexadecimal numbers - far easier to represent the codes as 6 hex numbers than 24 binary ones. EXAMPLE OF A COLOUR CODE: #CC3399.
219
Why are # signs placed before hexadecimal numbers?
To let people know that the number is a hexadecimal number.
220
Give 2 examples of when hexadecimals are used:
1. Error messages
2. Assembly language programming
3. Colour codes
4. Short-hand for binary numbers
220
Give 4 examples of when hexadecimals are used:
1. Error messages
2. Assembly language programming
3. Colour codes
4. Short-hand for binary numbers
221
ASCII - What is 'A'?
65. You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
222
ASCII - What is 'a'?
97. You can work out any lowercase letter from this by counting up to the letter (ie. z is 122) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
223
ASCII - What is '0'?
48. You can work out any number 0-9 from this by counting up to the number (ie. 9 is 57) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
224
ASCII - What is ' '? HINT: SPACE
32. Convert to binary if needed in that form.
225
ASCII - What is DEL?
127 -> 01111111
226
What is a character set?
The list of binary codes that can be recognised by the computer hardware and software as being usable characters.
227
Why was ASCII created as the first common encoding system for text?
Different manufacturers used to use their own codes for their computers. However, they soon realised that if computers wanted to share information, they needed to also share a common encoding system for text.
228
What does ASCII stand for?
American Standard Code for Information Interchange
229
How many bits does ASCII use?
7 bits. It can represent 128 possible code sequences - these represent English characters and control actions (backspace, shift on, etc.).
230
What is pseudocode?
A language that is similar to real programming language, but is easier for humans to understand although it doesn't actually run on a computer. It can be easily converted to a regular programming language.
231
Why was Extended ASCII created?
ASCII had 92 printable characters but there was always a need for more to accommodate foreign languages, mathematical symbols and special symbols for drawing pictures.
232
How many bits does Extended ASCII use?
Extended ASCII uses the full 8 bits and was created to cater for foreign languafgees and graphics characters.
233
How many codes are in the character set allowed by Extended ASCII?
256
234
What can Unicode represent?
Unicode can represent characters in all known languages and writing systems.
235
Why was Unicode introduced?
The Unicode Consortium introduced Unicode due to too many different versions of Extended ASCII developed by different manufacturers such as IBM and Apple.
236
How many codes are in the character set allowed by ASCII?
128
237
How many bits does Unicode use?
16 bits.
238
How many codes are in the character set allowed by Unicode?
Unicode uses 16 bits, allowing the use of over 65,000 characters.
239
What is a pixel?
A pixel is the smallest possible dot on a computer screen, represented by a number of bits.
240
What are images made up of?
A digital image is composed of many small points of colour or picture elements, pixels for short.
241
How is the size of an image given?
The number of pixels in the width and then the number of pixels in the height. For example, 640 x 480 or 2048 x 1536.
242
How does resolution affect image quality?
Higher resolution, better image quality.
243
What is resolution?
The number of pixels per square inch on the computer screen. The higher the resolution, the better the picture.
244
What is colour depth?
The number of bits used to encode the colour of each pixel.
245
How many colours can be used in an image/graphic if only one bit is used to encode each pixel?
Only two colours can be used (2^1). The 0 represents black and the 1 represents white.
246
A colour depth of three would allow how many colours to be used?
2^3 is 8. So 8 colours could be used.
247
What is the current standard for colour depth (in bits) when representing images?
24-bit representation. This means that the colour data for each pixel is encoded in 24 bits with 8 bits used for each of the primary colours: red, green and blue. Each colour in the palette is a combination of these in different proportions.
248
How many colour variations are allowed by 8-bit encoding?
Using 8-bits allows 256 different levels of each red, green and blue. Therefore 256 x 256 x 256 = 16,777,216 different colour variations are possible. This number of bits produces such a realistic image it is described as being 'true colour'.
248
In computer science, what are the primary colours?
Red, green and blue
249
I know the number of bits. How can I find the equivalent number of bytes?
Divide the number of bits by 8.
250
I know the number of bytes. How can I find the equivalent number of kilobytes?
Divide the number by 1000.
251
How does colour depth and number of pixels impact file size?
As the number of pixels and colour depth increase, then so will the size of the image file.
252
What is the equation for calculating file size of an image?
W x H x CD (Width x Height x Colour Depth used)
253
How does image quality impact file size?
Better image quality, greater file size.
254
Why is image quality often reduced before transmitting an image electronically?
To reduce the amount of time it will take to download the image after transmitting - there is always a compromise between file size and image quality. Lower image quality = faster download speeds.
255
What is metadata?
Data about data. Included in many files, in addition to the stored data, is information about the file.
256
Give 2 examples of metadata:
1. When the file was last saved
2. Who created the file
3. What the file is named
4. When the file was created (date/time)
257
What does Exif stand for?
EXchangeable Image File format. The metadata stored in a digital image file contains descriptive and technical information (such as point of capture) and the data is stored in the Exif format.
258
What data could be stored in Exif for image files?
1. Make and model number of the camera
2. Aperture setting
3. Speed settings
4. Dimensions of the image and the resultant file size
259
What is sound caused by?
Vibrations travelling through a medium such as air, water or metal. These vibrations compress and then pull apart the air molecules thus causing changes in air pressure.
260
Vibrations travel out in waves - what are these called?
Sound waves
261
What do the sound wave vibrations cause in terms of air pressure?
Continuous changes to air pressure. These are shown on analogue diagrams.
262
What are analogue recordings?
Recording methods that try to capture the continuous changes in air pressure by trying to convert all of the changes to analogous changes in voltage.
263
Give 2 examples of analogue recordings?
1. vinyl albums
2. audio cassettes
These can capture the continuous changes in air pressure as minute changes in voltage.
264
Why do computers not use analogue recordings?
Computers are digital. They cannot represent continuous, minute changes in voltage; each transistor is either on or off, nothing in between.
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What does analogue mean?
Data which can use any value in a continuous range.
266
What is sampling?
Making a physical measurement of the amplitude of the wave at set time intervals and then converting the measurements to digital values.
Think of it as similar to making an animation - the smaller the changes between each sample and the greater number used each second, the more realistic the animation.
267
What are the advantages of digital sound files? HINT: ANSWER NAMES 7
1. it can be edited and manipulated easily by computer equipment
2. it is more portable; it can be carried on a memory stick or SD card while a vinyl record or tape are not as portable
3. it can be played over and over again without deterioration. LPs and tapes deteriorate.
4. it can be easily copied on a computer. Expensive equipment is needed to copy a vinyl record.
5. digital audio files can be easily emailed, downloaded and streamed by users.
6. equipment to record and process digital sound is relatively cheap.
7. it has allowed people to produce their own commercial music at home.
268
What are the advantages of digital sound files? HINT: ANSWER NAMES 7
1. it can be edited and manipulated easily by computer equipment
2. it is more portable; it can be carried on a memory stick or SD card while a vinyl record or tape are not as portable
3. it can be played over and over again without deterioration. LPs and tapes deteriorate.
4. it can be easily copied on a computer. Expensive equipment is needed to copy a vinyl record.
5. digital audio files can be easily emailed, downloaded and streamed by users.
6. equipment to record and process digital sound is relatively cheap.
7. it has allowed people to produce their own commercial music at home.
269
What are the two factors that impact how accurately a digital recording will match the original sound?
Sample rate and bit depth
270
What is sample rate?
The number of samples taken each second. The higher the sample rate, the more accurately the sound will be represented.
271
For CDs, what is the average sample rate?
44,100 samples per second (44.1KHz)
272
For Blu-ray audio, what is the average sample rate?
96,000 samples per second (96KHz)
273
How many KHz is one sample when converting audio to digital form?
1000
274
What is bit depth when converting audio to digital format?
The number of bits used to encode each sample.
275
How does increasing bit depth impact digital audio quality?
Higher bit depth = more bits used to encode each sample = more accurate representing of range of sound = better audio quality
276
What is the dynamic range?
The range of volume of sound in music.
277
For CDs, what is the bit depth used for digital audio?
16 bits
278
For CDs, what is the bit depth used for digital audio?
16 bits
279
What is the equation for calculating digital audio file sizes?
sample rate x bit depth x length in seconds (x number of channels (mono or stereo) if applicable)
280
What is compression?
Reducing the size of a file so that it takes up less storage space or bandwidth when it is transmitted.
281
What are the benefits of compression? HINT: ANSWER NAMES 5
1. it uses less internet bandwidth when files are downloaded
2. transfer speed is quicker
3. takes up less storage space on the servers of storage providers
4. smaller files reduce congestion on the Internet, which is good for everyone
5. it makes audio and video files suitable for streaming
282
What is lossless compression?
Compression where a compressed file can be decompressed to the original without any loss of data - all information will remain intact.
283
What is lossy compression?
Compression where data is lost in the compression process and when the file is decompressed it will not contain all of the original information.
284
What is a server?
A computer that provides files on demand to client machines.
285
What is redundancy?
The number of items of data in a file which are repeated.
286
Why are lossless compression rates of 50% relatively easy to achieve with text files?
They have lots of repeated items (words) and characters which are redundant and can be compressed.
287
How does lossy compression reduce file size?
By throwing out some of the data - this is irreversible.
288
Why is lossy compression unsuitable for text or program files?
File size is reduced by throwing out data - a book with missing letters would be unreadable, a program with missing letters/formatting would be inexecutable
289
Why is lossy compression more useful for graphic and audio files?
Because they contain lots of information that can be discarded.
290
What are RAW files?
Image files that have not been compressed and which contain all of the colour data are called RAW files.
291
True or false: RAW in RAW files is an acronym.
False. RAW is not an acronym, it just means that the files is as it was when produced by a camera sensor and has not been compressed in any way.
292
What exactly happens during lossy compression? HINT: WHAT DOES THE ALGORITHM DO?
The algorithm analyses the image and finds areas where there are only slight differences that we might not be able to distinguish. It then gives these the same value so that it can rewrite the file using fewer bits.
293
What does JPEG stand for?
Joint Photographic Experts Group - known for '.jpeg' files.
294
What does WAV stand for?
Waveform Audio Format - known for '.wav' audio files.
295
What are WAV files?
Digital audio files that contain all of the sound data.
296
How many MB would generally be in a 3 minute WAV file?
30 MB WAV file
297
How many MB would generally be in a 3 minute MP3 file?
3 MB MP3 file
298
How large is a WAV file compared to an MP3 file?
MP3 files are often about 1/10th the size of WAV files.
299
What do computer networks enable? Give at least 2 examples of possible uses. HINT: ANSWER GIVES 5.
Computer networks allow computers and devices to share data. This includes:
1. computer-to-computer communication
2. mobile phone networks
3. computers communicating with devices such as printers, mice and keyboards
4. smart televisions
5. tablets and media players downloading videos and music and playing them through external devices such as speakers and digital projectors.
300
What does LAN stand for?
Local Area Network
301
When are LANs used?
Computers in a site such as an office building use an LAN to connect with each other.
302
What is a LAN?
An LAN is a computer network for data transmission within a small geographical area such as a home, office or school or a group of buildings on a site.
303
What does WAN stand for?
Wide Area Network
304
When are WANs used?
WANs are used for connecting LANs over a large geographical area.
305
What is a WAN?
A WAN is a network that connects separate LANs over a large geographical area. This ensures that computers in one location can communicate with computers and users in other locations.
306
True or false: The internet is a huge WAN.
True.
307
What are the two network types?
Client-server networks and peer-to-peer networks
308
When are peer-to-peer networks used?
Peer-to-peer networks are used to connect a small number of devices, for example in a home or office where there are just a few users.
309
Give two advantages of peer-to-peer networks:
1. easier to set up and maintain
2. cheaper
310
Give two disadvantages of client-server networks:
1. more expensive to set up and maintain as a more powerful computer is required to act as the server and network software is required
2. specialist knowledge is needed to administer the network
311
In client-server networks, what are the servers?
The computers that control access to the network.
312
In client-server networks, what are the clients?
The computers on which the users work - computers that act as a desktop for the users and which relies on a server for its operations.
313
Explain how a client-server network works.
In a client-server network there are two types of computers: the computers that control access to the network (servers) and the computers on which the users work (clients).
From the client machines, the users log into the network servers in order to be able to access programs and peripherals to save data on the servers.
The server is therefore responsible for the security of the network, expecting users to log in with a username and password. As all files are stored on the server the data can be backed up centrally.
314
True or false: In a peer-to-peer network, all computers are equal.
True. The computers are simply connected together without any one computer having superiority over the others.
315
Explain how a peer-to-peer network works.
In a peer-to-peer network, the computers are simply connected together without any one computer having superiority over the others. All of the computers on a peer-to-peer network are equal.
Through sharing rights granted by the users any computer can share thee programs of another, save data onto their hard disk and use printed connected to them.
Each computer acts as both a client and a server and can communicate directly with all of the others.
Security is distributed and the users of each computer have to be able to grant access rights to its resources and allot passwords.
As data is stored on all f
316
Explain how a peer-to-peer network works.
In a peer-to-peer network, the computers are simply connected together without any one computer having superiority over the others. All of the computers on a peer-to-peer network are equal.
Through sharing rights granted by the users any computer can share thee programs of another, save data onto their hard disk and use printed connected to them.
Each computer acts as both a client and a server and can communicate directly with all of the others.
Security is distributed and the users of each computer have to be able to grant access rights to its resources and allot passwords.
As data is stored on all of the computers and is not held centrally, all the users are responsible for backing up procedures.
317
What does a computer need to connect to a network?
A computer needs some hardware and also some software that allows it to communicate with the other computers.
318
What are the most commonly used cables to connect devices?
Twisted pair cables
319
What are twisted pair cables?
Cables in which pairs of copper wires are twisted together and carry electrical signals.
320
What are optical fibre cables made of?
Glass
321
What are microwaves in computer science?
Electromagnetic waves that can be used to carry data between computers.
322
What are protocols?
Agreed rules for requesting and sending data across networks.
323
What is the motherboard?
The main printed circuit board of the computer; it has connectors that other circuit boards can be slotted into.
324
What are optical fibre cables?
Cables which are made of glass and transmit information encoded in beams of light. They are much faster than twisted pair cables at transmitting data.
325
What does NIC stand for?
Network Interface Card
326
What is the NIC (Network Interface Card) also known as?
Network adapter
327
What does the NIC/Network adapter do?
It is a component that connects a computer to a network. It formats the data sent from the computer into a required format according to the protocols (rules) of the network.
328
Where is the NIC built into?
The motherboard
329
True or false: NICs support both wireless and wired connections.
True
330
What does MAC stand for?
Media Access Control
331
Every NIC is created with a hardware number permanently burned into it. What is this called?
The MAC (Media Access Control) address.
332
What is the purpose of a MAC address?
Every MAC address is unique so that all data on a network can be sent to the correct component . MAC addresses are 48 bits in length, usually displayed as a 12-digit hexadecimal number.
333
What do network switches allow?
Network switches allow individual devices to connect to a network using cables.
334
How do network switches work? HINT: 5 POINTS
1. all of the computers on a network plug into a port on the switch using a cable.
2. switches read the messages passing through them.
3. they can read the destination addresses and send them to only the intended computers.
4. they can do this because they build up a table of MAC addresses on the network to cut down on unnecessary network traffic.
6. switches can send and receive information at the same time.
335
What is network traffic?
The overall network usage caused by all of the data that is being transmitted at a given time.
336
What do computers need an NIC or network adapter for?
To connect to a network.
337
What are switches used for?
To allow messages to be transmitted between computers in a single network.
338
What are routers used for?
To transmit messages between computers on different networks.
339
Give two ways to carry data across a network:
1. cables
2. radio waves
340
Why are routers similar to switches?
Routers and switches both read the address information and forward the messages to the correct network. A switch does this within a single network, but a router does this across several networks.
341
What are routers commonly used for in the home?
Routers are commonly used in the home to allow many computers to access one internet connection. The router links the home network to the Internet. The router will transmit the incoming web pages, streamed audio, etc. to the correct computer on the network.
342
What does WAP stand for?
Wireless Access Point
343
What do wireless access points allow?
Wireless access points allow wireless devices to connect to a wired network.
344
How do wireless access points work?
Wireless access points convert data they receive through cables into a wireless signal (and vice versa) to allow wireless devices to connect to a wired network.
345
True or False: Wireless access points can direct messages to particular devices
False. Unlike switches, they CANNOT direct messages to particular devices.
346
What is a web server?
A computer that can serve world wide web pages to other computers that request them.
347
What is the Ethernet?
A set of technical standards for connecting computers.
348
What is frequency?
The number of waves per second.
349
What is Wi-Fi?
A set of technical standards or protocols for short-range connection of digital devices using radio waves.
350
What is bluetooth?
A set of technical standards or protocols for short-range connection of digital devices using radio waves.
351
What is bandwidth?
Bandwidth is the amount of data that can pass through a transmission medium per second.
352
What is bandwidth measured in?
Bits per second (bps) or megabits per second (Mbps) - bandwidth is a measure of how many bits can get through a particular point in a second.
353
How does a copper wire carry data?
Copper wires carry the data as electric currents.
354
How does a fibre optic cable carry data?
Fibre optic cables transmit data as pulses of light generated by a LED or laser.
355
What does LED stand for?
Light Emitting Diode
356
Name 3 advantages of fibre optic cables over copper wire cables:
1. Far greater bandwidth
2. Can carry signals much faster
3. Can travel over greater distances without needing to be boosted
357
True or False: Radio waves are a type of microwave.
True.
358
What do microwaves consist of?
Electromagnetic radiation travelling in waves with a frequency higher than 1 GHz.
359
Radio waves can transmit data across networks in what range of frequencies?
Radio waves are used to transmit data across networks in frequencies of between 2.4 and 5 GHz.
360
What is The Internet?
The Internet is a global system of interconnected computer networks which serves billions of users worldwide - this makes it a wide area network.
361
Name 2 services The Internet provides:
1. Email
2. World Wide Web (www)
362
Who first proposed the World Wide Web?
British scientist, Tim Berners-Lee
363
When was the World Wide Web proposed by Tim Berners-Lee?
1989
364
When was the first website launched?
Time Berners-Lee launched the first website in 1990.
365
What is a host?
A host is a computer which can be accessed by users working at remote locations using networks, including the internet.
366
What do web hosting companies do?
Web hosting companies rent space on their servers where people can develop their own websites that can be accessed by users all over the world using the World Wide Web.
367
How many host computer systems were there in 1969?
4 - today there are 10s of millions.
368
When was The Internet Society established?
1992
369
Why was The Internet Society established?
It was established to oversee the policies and protocols that define how we use and interact with the Internet.
