Memory and Storage (2)

What is primary storage and why is it needed?

Primary storage connects directly with the CPU.

It is needed because the CPU cannot interact with secondary storage.

Is primary storage faster or slower than secondary?

Faster

Give 2 examples of primary storage.

RAM, ROM, Cache, Registers

What does volatile mean?

Loses data when power is lost

What does RAM stand for and what does it do?

Stands for Random Access Memory.

It stores currently running programs and is volatile.

It is slower than cache.

What does ROM stand for and what does it do?

Stands for Read Only Memory.

It stores the BIOS and is non-volatile.

It cannot be written to and stores data which shouldn't be changed.

What is virtual memory and when is it used?

Virtual memory is a part of the secondary storage that is used as temporary primary memory.

It is used when the RAM is full.

Give the process of virtual memory.

When the RAM is full, data is moved the virtual memory.

New programs can now be loaded into RAM.

When the data is needed again, it is moved back to the RAM.

Give one advantage of using virtual memory.

Improves performance, cheap

Give one disadvantage of using virtual memory.

Causes disk thrashing, slower than RAM

What is secondary storage and why is it needed?

Stores data permanently as it is non-volatile.

It stores software, files, programs etc.

It can be used to transfer files between devices.

What are the Qualities to assess secondary storage on?

Capacity

Speed
Portability

Durability

Reliability

Cost

What are the three types of secondary storage?

magnetic, optical, solid state

Give an example of optical storage.

CD, DVD, Blu-ray

Give 2 advantages of optical storage.

Very cheap, portable, durable/robust

Give a disadvantage of optical storage.

Very slow, small capacity

Give an example of magnetic storage

Hard drive, magnetic tape, floppy disk

Give 2 advantages of magnetic storage.

Large capacity, quite cheap

Give a disadvantage of magnetic storage.

Not durable (has moving parts), not portable (heavy)

Give an example of solid state storage.

USB flash drive, SD card, SSD

Give 2 advantages of solid state storage.

Very fast access speed, very portable, durable, doesn't get hot

Give a disadvantage of solid state storage.

Very expensive

Give the 6 properties of secondary storage.

Capacity; Speed; Cost; Portability; Durability; Reliability

What base do computers use?

Base 2 (binary)

Why do computers use binary?

Switches can only be on or off (1 or 0)

What base do people use?

Base 10 (decimal)

Why do people use decimal?

We have 10 fingers

What are the first 8 powers of 2?

1,2,4,8,16,32,64,128,256

What is a bit and values can it store?

Smallest unit of storage. Either 1 or 0 (on or off)

What is a byte and how many values can it store?

8 bits - can store 0 to 255

What is a nibble and how many values can it store?

4 bits (half a byte) - can store 0 to 16

What are the higher derivatives of byte?

Kilobyte, Megabyte, Gigabyte, Terabyte

How many bytes are in a kilobyte?

1024 (1000 in calculations)

Order from smallest to largest: GB, bit, PB, byte, nibble, MB

bit, nibble, byte, MB, GB, PB

Add 00100111 to 01001010

01110001

Add 01101111 to 10011010

10011010

Add 10001010 to 11000111

01010001 (Overflow error)

How do you find the file size of a sound file?

Sample rate (Hz) x duration (s) x bit depth (bit/sample)

What is the file size of a 10 sec sound file with sample rate of 100 Hz and bit depth of 4?

100 x 10 x 4 = 4000 bits = 500 bytes

How do you find the file size of an image file?

Image height (px) x image width (px) x colour depth (bit/px)

What is the file size of a 10 by 20 image with 8 bit colour depth?

10 x 20 x 8 = 1600 bits = 200 bytes

How do you find the file size of a text file?

Bits per character x number of characters

What is the file size of a 30 character text file with 8 bits per character?

30 x 8 = 240 bits = 30 bytes

Convert 1100 to decimal.

8 + 4 = 12

Convert 10011011 to decimal.

128 + 16 + 8 + 2 + 1 = 155

Convert 9 to 4-bit binary.

1001

Convert 100 to 8-bit binary.

00110100

Give the 4 golden rules of binary addition.

0 + 0 = 0; 1 + 0 = 1; 1 + 1 = 10; 1 + 1 + 1 = 11

What is hexidecimal?

Base 16

What digits does hex use?

0-9, A-F

Convert 01111001 to hex.

79

Convert 11010011 to hex.

D3

Convert A2 to binary.

10100010

Convert 39 (hex) to binary.

00111001

Convert 29 (decimal) to hex.

1D

Convert 127 (decimal) to hex.

7F

Convert A3 to decimal.

10*16 + 3 = 163

Convert 1C to decimal.

1*16 + 12 = 28

What does a binary shift do?

Multiply/divide the number by a power of 2.

What does a left binary shift of 2 do?

Multiplies number by 4

What does a right binary shift of 3 do?

Divides number by 8.

Perform a left shift of 3 on 00010110

10110000

Perform a right shift of 1 on 10100011

01010001

Define the most significant bit.

The largest non-zero bit in a binary number.

What is a character set?

A collection of all characters that a computer can use. Each character is represented by a unique binary number.

What does ASCII stand for?

American Standard Code for Information Interchange

What can ASCII represent, and how many bits does it use per character?

Can only represent English. It has 7 bits for 255 characters in total.

Give an advantage of ASCII.

Smaller than Unicode

Give a disadvantage of ASCII.

Can only represent English characters.

What is extended ASCII?

A character set which uses 8 bits and can represent common European symbols.

If 'R' in ASCII is 1010010, what is 'r'?

1110010

If 'b' in ASCII is 98, what is 'e'?

103

What is Unicode?

A character set which uses 32 bits and can represent characters in all languages, including emojis.

Give an advantage of Unicode.

Can represent all languages

Give a disadvantage of Unicode.

A lot more bits per character

How are images represented?

A bitmap made of pixels (picture elements). Each pixel has a binary number which represents its colour.

How are colours represented?

Each colour has a unique binary code, usually expressed with hex values (e.g. FF7F00 is orange)

What is metadata?

Data about data - gives information about the properties of a file.

Give 3 examples of metadata.

Resolution (height/width); Colour depth; Geolocation; Date/time created/edited; File type; Authorship

What is colour depth?

The number of bits used for each pixel. A higher colour depth means better quality but larger file size.

What is resolution?

The number of pixels in an image. A higher resolution means better quality but larger file size.

How is sound represented?

Amplitude of the sound wave is sampled at regular intervals. This amplitude is converted into a binary number.

What is sample rate?

The number of samples taken each second. Measured in Hertz, usually Kilohertz. A higher sample rate means better quality but larger file size.

What is duration?

The length of a sound file. Measured in seconds. A longer duration means larger file size.

What is bit depth?

The number of bits per sample. A larger bit depth means better quality but larger file size.

What is compression and why do we need it?

Compression reduces file sizes. This speeds up upload/download times and means the file takes up less space on secondary storage/server.

What is lossy compression?

Data is permanently lost to reduce file size. An algorithm is used to remove unneeded data.

What is lossless compression?

Data is temporarily lost to reduce file size. The data comes back when the file is decompressed.

How is an image file compressed?

Reduce resolution or colour depth (lossy)

How is a sound file compressed?

Reduce sample rate or bit depth (lossy)

How is a text file or code compressed and why?

Lossless - if any code is lost it will not run.