1.2- Memory and Storage

Question 1

Characteristics of primary storage?

Answer 1

Volatile
Small capacity

Question 2

Characteristics of secondary storage?

Answer 2

Non-volatile
Large capacity

Question 3

Why do computers need primary storage?

Answer 3

A computer needs primary storage because access times are considerably faster than secondary
This means the time taken to complete operations such as the Fetch-Execute Cycle is dramatically reduced

Question 4

What is primary storage used for?

Answer 4

Primary storage holds the data and instructions that the CPU needs to access whilst the computer is turned on

Question 5

Where is primary storage found in the computer?

Answer 5

Due to the fast access times, primary storage is used as short term, working memory, in hardware that is directly connected to the CPU such as RAM, and components that reside inside the CPU such as Cache and Registers

Question 6

What are the limitations of primary storage?

Answer 6

Performance of primary storage means a much higher cost which limits the amount that is used

Question 7

What is RAM?

Answer 7

RAM (Random Access Memory) is primary storage that is directly connected to the CPU and holds the data and instructions that are currently in use

Question 8

What are the characteristics of RAM?

Answer 8

RAM is volatile which means the contents of RAM are lost when the power is turned off
For the CPU to access the data and instructions they must be copied from secondary storage
RAM is very fast working memory, much faster than secondary storage
RAM is read/write which means data can be read from and written to
In comparison to ROM, it has a much larger capacity

Question 9

What is ROM?

Answer 9

ROM (Read Only Memory) is primary storage that holds the first instructions a computer needs to start up (Bootstrap)

Question 10

What are the characteristics of ROM?

Answer 10

ROM contains the BIOS (Basic Input Output System)
ROM is a small memory chip located on the computers motherboard
ROM is fast memory, much faster than secondary storage but slower than RAM
ROM is non-volatile which means the contents of ROM are not lost when the power is turned off
ROM is read only which means data can only be read from
In comparison to RAM, it has a much smaller capacity

Question 11

What is virtual memory?

Answer 11

Virtual memory is an extension of primary storage (RAM) located on secondary storage
In situations where RAM is close to being full, virtual memory can be used so that the computer remains operational

Question 12

How does virtual memory work?

Answer 12

Programs and data not currently being executed are transferred to virtual memory
Programs and data are transferred back to RAM when they are needed

Question 13

What are the downsides to virtual memory and how can you fix this?

Answer 13

Virtual memory is much slower than RAM and it’s use will impact negatively on system performance
To avoid the use of virtual memory, increase the size of the RAM

Question 14

What happens when you turn a computer on?

Answer 14

When computer first turns on and receives power, no instructions in CPU
Loads operating system so you can start using it
Operating system is stored on hard drive
Computer does not know that hard drive exists when first turned on
Cannot look for the operating system in hard drive and load into RAM
ROM is solution, contains bootstrap, set of initial instructions placed on it during manufacturing
First initial instructions perform a power on self test NOT GCSE known as the post
- Sends signals to other kinetic components EG harddrive
- Post wakes up other kinetic components, makes CPU aware of its existence
Now that the computer is aware of the hard drive and software on it, it can load instructions into RAM and start the process of booting up OS.

Question 15

What is cache memory?

Answer 15

Cache memory is a small amount of very fast memory inside or very close to the CPU (Central Processing Unit).
The purpose of cache memory is to store instructions and data that the CPU is likely to reuse. This means:
- The CPU can access this information faster than if it had to get it from the main memory (RAM).
- It helps the computer run quicker and more efficiently.

Question 16

What are the advantages of cache memory?

Answer 16

1.Faster Access Speed
2.Improves CPU Performance
3.Reduces Latency- Cache helps reduce the delay (latency) when the CPU needs data, especially for repeated instructions.

Question 17

What are the disadvantages of cache memory?

Answer 17

1.Very Expensive
2.Limited Size
3.Complex to Manage- It’s harder for the system to decide what data to store in cache to make the best use of the small space.

Question 18

What is secondary storage?

Answer 18

A computer needs secondary storage for long term storage of programs and data that are currently not in use

Question 19

Why is secondary storage needed?

Answer 19

Secondary storage is needed as ROM is read only and RAM is volatile
Secondary storage holds the programs and data whilst the computer is turned off (non-volatile)

Question 20

What is secondary storage perfect for?

Answer 20

Performance of secondary storage is slower than primary storage but capacity is much higher which makes it perfect for backup & archive of data files

Question 21

What are the characteristics of secondary storage?

Answer 21

Capacity - What is the maximum amount of data that can be stored?
Speed - How fast can data be read from and written to? (R/W)
Cost - How much does it cost?
Portability - How easy is it to move around? What is the physical size? Weight?
Durability - How robust is the storage?
Reliability - What is the probability that the device will consistently perform its function?

Question 22

What is magnetic storage?

Answer 22

Magnetic storage is a type of non-volatile media that uses magnets (polarity) to store binary 0s and 1s.

Question 23

What are the advantages of magnetic storage?

Answer 23

Capacity- High storage
Cost- Low per gigabyte
Speed- moderate read/write access

Question 24

What are the disadvantages of magnetic storage?

Answer 24

Durability- moving parts can get damaged if dropped
Portability- heavy and bulky making them less convenient for transport
Reliability- prone to mechanical failure
Noise- Loud spinning disks

Question 25

What are the advantages of solid state storage?

Answer 25

Capacity- Medium/High storage Speed- Very fast read/write access Durability- no moving parts Portability- small and no moving parts Noise- silent

Question 26

What is solid state storage?

Answer 26

Solid state storage is a type of non-volatile media that uses electronic circuit to store binary 0s and 1s.

Question 27

What are the disadvantages of solid state storage?

Answer 27

Cost- very high per gigabyte Reliability- limited read/write cycles

Question 28

What is optical storage?

Answer 28

Optical storage is a type of non-volatile media that uses lasers to burn the surface of a disk, creating pits and lands suitable for storing binary 0s and 1s.

Question 29

What are the advantages to optical storage?

Answer 29

Cost- very low per gigabyte Durability- no moving parts Portability- small and no moving parts Noise- silent

Question 30

What are the disadvantages to optical storage?

Answer 30

Capacity- very low Speed- very slow read/write access Reliability- prone to scratches

Question 31

What is an example of magnetic storage and what is its capacity?

Answer 31

Hard Disk Drive (HDD) Capacity: 500GB-8TB (consumer-grade)

Question 32

What is an example of solid state storage and what is its capacity?

Answer 32

Solid-state drive (SSD) Capacity: 128 GB-2TB (consumer-grade) USB Flash drive Capacity: 8GB-256GB (common sizes)

Question 33

What are examples of optical storage and what are their capacities?

Answer 33

Compact disk read only (CDR) Capacity: 700 MB Compact disk read write (CD RW) Capacity:700 MB Digital versatile disk read only (DVDR) Capacity: 4.7 GB- 9GB Digital versatile disk read write (DVDRW) Capacity: 4.7 GB- 9GB Bluray Capacity: 25 GB- 50 GB

Question 34

For an army laptop what type of secondary storage would be best?

Answer 34

The army would like a new portable computer than can used whilst 'in the field', it must be robust enough to withstand a few bumps and easy to transport to new places. Money is no object In this scenario a solid state device would be most suitable A solid state device has a high durability which means it can withstand any bumps or drops, it is small in size and weight which is perfect for a device that needs to be portable and because money is no object, the high cost is not a concern

Question 35

Units in computing?

Answer 35

Bit (b)- A single binary digit (1 or 0) Nibble- 4 bits Byte (B)- 8 bits Kilobyte (kB)- 1000 bytes Megabyte (MB)- 1000 kilobytes Gigabyte (GB)- 1000 megabytes Terabyte (TB)- 1000 gigabytes Petabyte (PB)- 1000 terabytes

Question 36

What are some examples of units in storage of common things?

Answer 36

1 character of text - 1 byte A full page of text- 30 kB One small digital colour photograph- 3 MB Music CD capacity- 650 MB DVD capacity - 4.5 GB Hard disk capacity -1 TB

Question 37

What is the difference between denary and binary numbers?

Answer 37

Counting in binary is similar to counting in denary, but the place values from right to left increase by powers of 2 (for example 1,2,4,8 etc), instead of powers of 10 (1,10,100,1000).

Question 38

How many numbers can you represent with 8-bit binary?

Answer 38

All the numbers from 0-255

Question 39

How do you convert numbers from binary to denary using a table?

Answer 39

1. Draw up a table with binary place values in the top row. Start with 1 at the right, then move left, doubling each time. 2. Write the binary number into your table 3. Add up all the numbers with a 1 in their column:

Question 40

How do you add binary numbers?

Answer 40

First put the binary numbers into columns. Starting from the right, add the numbers in columns When you have 1 + 0 = 1 0 or 1 + 1 = 1 1 carry the one into the next column

Question 41

What are overflow errors?

Answer 41

Sometimes, during binary arithmetic, you will get a result that requires more bits than the CPU is expecting - this is called overflow. Computers usually deal with these extra bits by storing them elsewhere- leading to a loss of data and a loss of accuracy in your answer. It could also cause software to crash if it does not have anywhere else to store it. Overflow flags are used to show that an overflow error has occurred.

Question 42

What is a binary shift?

Answer 42

A binary shift moves every bit in a binary number left or right a certain amount. Gaps at the beginning or end of the number are filled in with 0’s. The direction of the binary shift indicated whether it multiplies or divides the binary number:

Question 43

What do left (logical) shifts do?

Answer 43

Left shifts multiply a binary number, for every place a bit is shifted left, the number is doubled.

Question 44

What do right binary shifts do?

Answer 44

Right shifts divide a binary number, for every place a bit is shifted right, the number is halved. If a number is shifted 3 places right, it would be halved 3 times (i.e divided by 23 = 8), or if a number is shifted 3 places to the left, it would be doubled 4 times, (i.e multiplied by 24).

Question 45

What is hexadecimal?

Answer 45

Hexadecimal (hex) is another number system used regularly in programming. Hex uses a combination of digits and letters in order to represent a number. Hexadecimal (base-16) uses 16 different digits. A single hex character can represent any denary number from 0-15. To represent 0-15 in binary would require 4 bits (a nibble), so each hex digit equates to a nibble in binary.

Question 46

What are the values for hexadecimal?

Answer 46

0 = 0 1=1 2=2 3=3 4=4 5=5 6=6 7=7 8=8 9=9 10= A 11= B 12= C 13= D 14= E 15= F

Question 47

Why do programmers prefer hex over binary?

Answer 47

It is much easier to remember large numbers in hex - they are far shorter than binary numbers. Due to hex numbers being shorter, there is less chance of input errors. It is easier to convert between binary and hex, than binary and denary.

Question 48

Convert the binary number 10111001 into hexadecimal.

Answer 48

Firstly, split the binary number into nibbles: 1011 and 1001 For each nibble calculate its designated hexadecimal value: 1011 = 8 + 2 + 1 + 1 = 12, which in hexadecimal is B. 1001 = 8 + 0 + 0 + 1 = 9, which in hexadecimal is 9. Finally, put the hex values together to get the whole number 10111001 = B9 in hexadecimal.

Question 49

What are character sets?

Answer 49

Computers are unable to process these characters directly as they only process binary code. They need a way of converting these characters into binary code and vice versa. They can do this using character sets. Character sets are collections of characters that a computer recognises from their binary interpretation.

Question 50

What happens when you press a button on your keyboard?

Answer 50

Pressing a button on your keyboard sends a binary signal to the computer telling it which key you pressed. The computer then uses the character set to translate the binary code into a specific character.

Question 51

What is ASCII?

Answer 51

ASCII - American Standard Code for Information Interchange Most commonly used character set in the English speaking world. Each character is given a 7 bit binary code- this means that it can represent a total of 128 different characters. An extra bit (0) is added to the start of each binary code for each ASCII character, which means that they fit nicely into 1 byte. The codes for numbers, uppercase and lowercase letters are ordered (A comes before B, which comes before C etc) with symbols scattered around.

Question 52

What is Unicode?

Answer 52

Comes in several different forms and tries to cover every single possible character or symbol that might be written. Unlike ASCII, Unicode uses multiple bytes per character, each character has 16 bits. The best thing about Unicode is that it covers all major languages, even those in a completely different character set, such as Chinese or Greek. The first 128 codes in Unicode are the same as in ASCII.

Question 53

How to calculate size of text file?

Answer 53

File size (in bits) = number of bits per character x number of characters

Question 54

What is a bitmap graphic?

Answer 54

Bitmap graphic is a digital image, which is divided into a grid of picture elements called pixels.

Question 55

What is a pixel?

Answer 55

A pixel is the smallest addressable part of an image.

Question 56

What is colour depth?

Answer 56

Colour depth is the number of bits used to represent a colour value of a single pixel in an image.

Question 57

How do you calculate the number of colours that can be displayed in a picture?

Answer 57

Number of colours = 2 to the power of n (n = number of bits per pixel)

Question 58

What is image resolution?

Answer 58

Image resolution is the number of pixels in the image

Question 59

How do you calculate memory required for an image?

Answer 59

Memory required = Total number of pixels x number of bits per pixel from colour depth.

Question 60

What is metadata?

Answer 60

Metadata is a set of standardised information about a picture. The term means data about data.

Question 61

What are some examples of metadata?

Answer 61

author name, location, camera settings, depth, resolution, width/height

Question 62

Explain why metadata is needed?

Answer 62

Metadata is stored with the image to provide information for the computer, so it knows how to store and display the image and to provide information for the viewer so that the viewer knows information about when and how the photo was taken.

Question 63

What is frequency?

Answer 63

number of times sound waves vibrate per second – measured in number of cycles per sec (hertz)

Question 64

How do you record sound?

Answer 64

Microphone (transducer)converts sound waves to electrical voltage signals Resulting signal is an analogue (or continuous) signal. Computers are digital so need to convert this analogue signal to a digital signal (binary) for a computer to process. Sampling – converting an analogue sound signal into a digital file containing binary numbers Done by ADC (Analog-to-Digital Converter)

Question 65

What is sampling?

Answer 65

Sampling involves measuring the amplitude of a wave at regular intervals. These are then quantised (rounded) into one of a set number of values and then these values are stored in the computer as binary numbers as a binary file.

Question 66

How can you improve accuracy of sound?

Answer 66

By taking samples at more frequent intervals, the digital signal will come closer to the actual analogue signal. By increasing the bit depth, the digital signal will come close to the actual analogue signal, as there are more amplitude values that are able to be recorded.

Question 67

What is sampling rate?

Answer 67

Sampling rate - the number of times the sound is sampled per second, measured in Hertz (Hz) or Kilohertz (kHz)

Question 68

What is sampling (bit) depth?

Answer 68

the number of bits used to represent each sample in a digital recording or image

Question 69

How do you calculate the size of a sound file?

Answer 69

Size of sound file = Sample rate x sampling depth x duration (in seconds)

Question 70

What is data compression?

Answer 70

Data compression is when we make files smaller , while trying to make the compressed file as true to the original as possible.

Question 71

Uses of data compression?

Answer 71

Smaller files take up less storage space on a device Streaming and downloading files from the Internet is quicker as they take up less bandwidth Allows web pages to load quicker in web browsers Email services normally have restrictions on the size of the attachment you can send, compressing the file allows you to send the same content with a much smaller file size

Question 72

What is lossy compression?

Answer 72

Lossy compression works through run length encoding. works by permanently removing data from the file which limits the number of bits the file needs, reducing its size. (examples are mp3 (audio), AAC (audio) and JPEG (image).

Question 73

What is lossless compression?

Answer 73

Lossless compression works by temporarily reducing file data to store the file and then restoring it to its original state when it is opened. (examples are FLAC (audio), TIFF (image) and PNG (image).

Question 74

Pros to lossy compression?

Answer 74

Greatly reduces file size, meaning more files can be stored Take up less bandwidth so they can be downloaded and streamed quickly Commonly used- lots of software can read files

Question 75

Cons to lossy compression?

Answer 75

Loses data- the file cannot be turned to the original Cannot be used on text or file messages as these files need to retain all the information of the original. Worse quality than the original- but usually unnoticeable

Question 76

Pros to lossless compression?

Answer 76

Data only removed temporarily - no reduction in quality, the compressed file should look/sound like the original Can be decompressed- turned back into original Can be used on text/software files

Question 77

Cons to lossless compression?

Answer 77

Only slight reduction in file size - so lossless files still take up lot of storage space