Memory and storage

Question 1

Primary storage

Answer 1

Primary storage refers to the memory areas that the CPU can access very quickly. They are volatile with the exception of ROM. They have much faster access speeds than secondary storage. Due to the higher performance primary storage costs more per GB than secondary storage.

Question 2

Random access memory (RAM)

Answer 2

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.
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.

Static RAM - use transistors to store data.
Dynamic RAM - use capacitors to store data.

Question 3

Read only memory (ROM)

Answer 3

ROM (Read Only Memory) is primary storage that holds the first instructions a computer needs to start up (Bootstrap).
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 4

Virtual memory

Answer 4

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.
Programs and data not currently being executed are transferred to virtual memory.
Programs and data are transferred back to RAM when they are needed.
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 5

Secondary storage

Answer 5

A computer needs secondary storage for long term storage of programs and data that are currently not in use .
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).
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 6

Advantages and disadvantages of Magnetic storage

Answer 6

Advantages -
capacity - high storage
cost - low per gigabyte
speed - moderate read / write access

Disadvantages -
durability - moving parts can get damaged if dropped
portability - heavy and bulky making them less convenient for transport
reliability - prone to mechanical failure (moving parts)
noise - loud (spinning discs)

Question 7

Advantages and disadvantages of optical storage

Answer 7

Advantages -
cost - low per gigabyte
durability - no moving parts
portability - small and no moving parts
noise - silent

Disadvantages -
capacity - very low
speed - very slow read / write speed
reliability - prone to scratches

Question 8

Advantages and disadvantages of Solid state storage

Answer 8

Advantages -
capacity - medium / high storage
speed - very fast read / write access
durability - no moving parts
portability - small and no moving parts
noise - silent

Disadvantages -
cost - very high per gigabyte
reliability - limited read / write cycles

Question 9

magnetic storage

Answer 9

Magnetic devices such as hard disk drives use magnetic fields to magnetise tiny individual sections of a metal spinning disk. Each tiny section represents one bit. A magnetised section represents a binary ‘1’ and a demagnetised section represents a binary ‘0’. These sections are so tiny that disks can contain terabytes (TB) of data.

Question 10

optical storage

Answer 10

Optical devices use a laser to scan the surface of a spinning disc made from metal and plastic. The disc surface is divided into tracks, with each track containing many flat areas and hollows. The flat areas are known as lands and the hollows as pits.

When the laser shines on the disc surface, lands reflect the light back, whereas pits scatter the laser beam. A sensor looks for the reflected light. Reflected light (lands) represents a binary 1, and no reflection (pits) represents a binary 0.

Question 11

solid state storage

Answer 11

Solid state storage is a type of non volatile media that uses electronic circuits to store 0s and 1s. Most SSDs use a type of flash memory. They have no moving parts and are used for the same purpose as HDDs for internal / external storage.

Question 12

BIOS

Answer 12

basic input output system - it is software stored on a small memory chip on the motherboard

Question 13

bootstrap

Answer 13

the first piece of code that runs when a machine starts

Question 14

POST

Answer 14

power on self test - is the initial set of diagnostic tests performed by the computer right after it turns on

Question 15

Units of capacity

Answer 15

The capacity of a device is how much data it can store. It is important to know the units of capacity so that we can compare the capacity of different devices.

The smallest unit of data that we can store is called a binary digit, or a bit for short.
The value of a bit can be either a 0 or a 1.

Because a bit is so small, we do not usually use it to measure data.
Instead, we group bits into larger groups such as:
Nibble (4 bits).
Byte (8 bits).

Question 16

Denary

Answer 16

In everyday life, we use a denary number system.
We use 10 symbols to represent each digit.
Each digit’s place value is multiplied by 10 as we move from right to left.

Question 17

Binary

Answer 17

Only 1 and 0 are used in binary.
Each digit’s place value is multiplied by two as we move from right to left.

Question 18

Hexadecimal

Answer 18

Hexadecimal uses 16 different symbols for each place.
Hexadecimal uses the digits 0-9 then A-F:
A = 10 in denary, B = 11…
Each digit’s place value is multiplied by 16 as we move from right to left.

Question 19

Binary to hexadecimal

Answer 19

Binary can be converted to hexadecimal by grouping into groups of 4 bits:
Start grouping from the right-hand side.
Convert each 4 bit group separately.

Question 20

Hexadecimal to binary

Answer 20

Hexadecimal can be converted to binary by splitting each digit into 4 bits:
Separately convert each hexadecimal digit into 4 bits of binary.
Put all of the 4 bit groups together.

Question 21

Advantages of hexadecimal

Answer 21

An 8-bit binary number can be represented by two hexadecimal digits.
This means you can reduce processing time with hexadecimal than with binary.
Hex is easier and faster to write two digits than the full binary sequence.
It is easier for a human to process hexadecimal than binary.

Question 22

HTML colours

Answer 22

In HTML, colours are defined by how much red, green and blue (RGB) there is on a scale of 0 to 255.
0 to 255 is the range of numbers that can be represented as a single byte.
This means we use 2 hexadecimal digits to represent each RGB value.
HTML colour codes start with a hash symbol followed by 3 pairs of hexadecimal numbers like #00FF00.

We can break down the HTML colour code #00FF00 in the following way:
The red value is 00, which means we have 0 units of red.
The green value is FF, so we have 255 units of green.
The blue value is 00, so we have 0 units of blue.
The colour code #00FF00 corresponds to a bright green colour.

Question 23

MAC addressing

Answer 23

A MAC address is a number that uniquely identifies a networked device.
A MAC address is made up of 48 bits which are shown as 6 groups of 2 hexadecimal digits:
NN-NN-NN-DD-DD-DD or NN:NN:NN:DD:DD:DD
The first 6 hex digits identify the device manufacturer.
The second 6 hex digits identify the serial number of the device.

Question 24

Binary addition

Answer 24

If we add 0 + 0 we get 0.
If we add 1 + 0 (or 0 + 1) we get 1.
If we add 1 + 1, then we cannot use the symbol 2. So we need to carry the 1 and put 0 in the current place.

It might be the case that we have 1 + 1 and also a 1 carried over from the previous column.
If this is the case, then we carry the 1 and have 1 left over.
So we carry 1 and put 1 in the current place.

Question 25

Binary shifts

Answer 25

A binary shift is how a computer system performs basic multiplication and division.
Binary digits are moved left or right a set number of times.
A left shift multiplies a binary number by 2 (x2).
A right shift divides a binary number by 2 (/2).
A shift can move more than one place at a time, the principle remains the same.
A left shift of 2 places would multiply the original binary number by 4 (x4).
Binary shifts can cause a loss of precision by discarding bits, which can lead to changes in the numerical value.

Question 26

Left binary shift

Answer 26

In a left binary shift, each digit is moved one place to the left.
This has the effect of multiplying the number by two.
You must take care, when performing a left shift, that there is no overflow error (where we run out of space to store the last digit of the number).

Question 27

Right binary shift

Answer 27

In a right binary shift, each digit is moved one place to the right.
This has the effect of dividing the number by two.
You must take care when performing a right shift that no data is shifted off the right hand side. This can cause a loss of accuracy.

Question 28

Overflow error

Answer 28

Binary numbers are stored as a fixed length.
If a number is carried past the last place column, then this is called an overflow error.
Overflow errors can lead to inaccurate results and software crashes.

Question 29

Character sets

Answer 29

A character set is a defined list of characters that can be understood by a computer .
Each character is given a unique binary code.
Character sets are ordered logically, the code for ‘B’ is one more than the code for ‘A’.
A character set provides a standard for computers to communicate and send/receive information.
Without a character set, one system might interpret 01000001 differently from another.
The number of characters that can be represented is determined by the number of bits used by the character set.
Two common character sets are:
American Standard Code for Information Interchange (ASCII)
Universal Character Encoding (UNICODE)

Question 30

ASCII

Answer 30

The American Standard Code for Information Interchange (ASCII) character set is the most common character set.
Each character in ASCII is represented by a seven-bit binary code.
That means there is a maximum of 128 characters.
ASCII includes all commonly used letters and symbols in the English language.
Each letter is represented by seven bits.
This is useful because when used in an 8-bit system, the extra bit can be used as a check digit.

Question 31

Limitations of ASCII

Answer 31

128 characters is perfectly fine for the English language. But it does not leave space for characters from other languages.
An extended ASCII set was released which used all eight bits, but it was still not enough.
This led to the release of Unicode.

Question 32

Unicode

Answer 32

Unicode is a character set which was released because of the need to standardise character sets internationally.
Unicode aims to represent every possible character in the world.
The most common form of Unicode is UTF-8 and uses between eight and 32 bit binary codes to represent each character.
The first 256 characters in Unicode are identical to extended ASCII, which makes it backwards compatible with documents encoded using older character sets.
Unicode represents characters from all major alphabets of the world.
Unicode is also used to represent emojis!

Question 33

Bitmap

Answer 33

A bitmap image is made up of squares called pixels.
A pixel is the smallest element of a bitmap image.
Each pixel is stored as a binary code.
Binary codes are unique to the colour in each pixel.

Question 34

Colour depth

Answer 34

Colour depth is the number of bits stored per pixel in a bitmap image.
The colour depth is dependent on the number of colours needed in the image.
In general, the higher the colour depth the more detail in the image (higher quality).
In a black & white image the colour depth would be 1, meaning 1 bit is enough to create a unique binary code for each colour in the image (1=white, 0=black).
Common colour depths are 1-bit, 8-bit, 16-bit, and 24-bit.

Question 35

Resolution

Answer 35

Resolution represents the number of pixels in an image.
The number of pixels is found by multiplying the width by the height of the image.
An example resolution is 1080p which is 1920x1080.

Question 36

Metadata

Answer 36

Metadata is extra information that is added to an image file such as:
The resolution.
The colour-depth.
The encoding format.
The time and date of taking the photo.

Question 37

File size

Answer 37

The size (in bits) of an image file is calculated as follows:
File size (in bits) = image width x image height x colour depth (in bits)
The size of the image file in bytes is equal to:
File size (in bytes) = file size (in bits) ÷ 8

Question 38

Converting Binary to image

Answer 38

In a black and white image, each pixel is represented by 1 bit:
A 0 will represent a black area.
A 1 will represent a white area.
The image will be represented by a binary string. Use the value of each bit to colour each pixel in the right colour.
The binary string starts at the top-left of the image, and represents the first row, followed by the second row, and continues until the end of the image.

Question 39

Converting image to binary

Answer 39

Each pixel of the image will be represented by one bit of the binary string.
Starting at the top left, and working across the first row:
Write a 0 if the pixel is black.
Write a 1 if the pixel is white.
Continue this process until the end of the image.

Question 40

Sampling

Answer 40

When sound is recorded by a computer its amplitude is recorded at regular intervals.
The value of the amplitude at each sample is stored as a binary value.
The number of bits used to store each sample is known as the sample size.
The number of samples taken per second is known as the sampling rate.

Question 41

Quality of audio

Answer 41

Increasing the sampling rate will increase the quality of the audio.
Increasing the sample size will also increase the quality of the audio.
Unfortunately, increasing these make the file size larger.

Question 42

Bit rate

Answer 42

The bit rate is the amount of data stored per second of audio.
The bit rate is calculated as bitrate = sample rate x sample size.

Question 43

Compression

Answer 43

Representing audio, images, and especially video take up a lot of secondary storage space. Compression helps to reduce the size of these files so that we can store more data.

Question 44

Lossy compression

Answer 44

An algorithm is applied to remove unnecessary detail from the original file.
Some data is permanently lost, but enough remains so that the file is still useful and there is barely a noticeable difference.
Lossy compression results in dramatic file size reduction.

Question 45

Lossless compression

Answer 45

None of the original data is lost.
An algorithm can be used to perfectly restore the original file when needed.
This is especially useful for executable files, where all of the data is necessary.
Lossless compression causes file size to reduce moderately.

Question 46

Extended ASCII

Answer 46

Extended ASCII uses 8 bits, providing 256 unique codes (28 = 256) or a maximum of 256 characters it can represent.
Extended ASCII provides essential characters such as mathematical operators and more recent symbols such as ©.

Question 47

Vector

Answer 47

A vector image is created from mathematical equations and points.
Only the mathematics used to create the image are stored.
For example, to create a circle the data stored would be:
Centre point (x, y coordinates).
Radius.
Vector images are infinitely scalable.
Ideal for situations where the same image will be made bigger and smaller and a loss of quality is unacceptable.