memory and storage

why does computer need primary storage

• 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 

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

where is primary storage used

• 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

disadvantage of primary storage

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

what is RAM

• 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

State 2 items that will be stored in the RAM (2)

-OS
-Other programs that are running
-Data in current use

A smart television allows the user to search the Internet and watch videos online.

The smart television uses RAM

Give two examples of data that the smart television could store in RAM [2]

How to answer this question

• Current channel being watched

• Current volume

• Current video/file/tv program being watched

• Web browser/applications that are running

• Data being downloaded/buffered

what is ROM

• ROM (Read Only Memory) is primary storage that stores bootstrap loader which is used to start the computer

• 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

what is 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

disadvantage of virtual memory

• Virtual memory is much slower than RAM and it's use will impact negatively on system performance

what should you do to avoid using virtual memory

• avoid the use of virtual memory, increase the size of the RAM

A computer only has 4GB of RAM, Fynn says that virtual memory can be used instead of adding more RAM.

1. Explain how virtual memory can compensate for the lack of RAM in Fynn's computer [3]

2. Explain why it would be beneficial for Fynn to get more RAM instead of relying on virtual memory [2]

How to answer these questions

1. What is the definition of virtual memory? how does it work?

2. What is the downside of using virtual memory? turn this into an advantage of adding more RAM

Answers

• How can Virtual Memory compensate

  • Virtual Memory is used when RAM is full

  • ...part of the secondary storage used as (temporary) RAM

  • Data from RAM is moved to the secondary storage/Virtual Memory (to make space in RAM)

  • RAM can then be filled with new data

  • When data in Virtual Memory is needed it is moved back to RAM 

• Benefit of more RAM

  • More RAM will improve the performance of the computer // More RAM will speed up the access to data

  • Virtual Memory is slower to access than RAM direct (because it has to go back to RAM first)

  • Moving data between RAM and VM takes processor time

what is cache

To store instructions / data that is frequently used / previously used / next to be used

· Data does not need to be fetched from RAM · Speeds up access

why is secondary storage needed

• 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)

compare performance and capacity of secondary storage compared to primary storage

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

A games console has secondary storage.

State, using an example, why the games console needs secondary storage [2]

How to answer this question

• They keyword is 'why', why does a games console need secondary storage? give an example, do not just describe what secondary storage is!

Answer

• To store data once the power is turned off / permanently // for non-volatile storage

• Examples could include:

  • Storing games

  • Save games

  • User data / profiles

  • Downloaded content / applications / updates

what some characteristics for secondary storage

• 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?

give examples of secondary storage devices

• Hard Disk Drives (HDD)

• Solid State Drives (SSD)

• Optical Discs (CDs, DVDs)

• USB Flash Drives

• Magnetic Tapes

what are the 3 types of secondary storage

• Magnetic

• Solid State

• Optical

what is magnetic storage

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

advantages of magnetic storage

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

disadvantages of magnetic storage

Durability - Moving parts can get damaged if dropped

Portability - Heavy & bulky making them less convenient for transport

Reliability - Prone to mechanical failure

 

Noise - Loud (spinning disks)

what is solid state storage

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

advantages of solid state storage

Capacity - Medium/high storage

Speed - Very fast read/write access

Durability - No moving parts

Portability - Small and no moving parts

Noise - Silent

disadvantages of solid state storag e

	Cost - Very high per gigabyte
	Reliability - Limited read/write cycles

what is optical storage

• 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

advanatges of optical

Advantages Disadvantages
Cost - Very low per gigabyte
Durability - No moving parts
Portability - Small and no moving parts
Noise - Silent

disadvanatges of optical

	Capacity - Very low
	Speed - Very slow read/write access
	Reliability - Prone to scratches

Zarmeen has purchased a new tablet computer. The tablet has an internal secondary storage device.

The storage device is a solid state device.

1. Give three benefits of the tablet having a solid state device instead of a magnetic device [3]

2. Give two drawbacks of the tablet having a solid state device instead of a magnetic device [2]

Answers

• Benefits

  • Faster access / read/write speeds

  • Smaller in physical size

  • More durable // no moving parts

• Drawbacks

  • More expensive (per gigabyte)

  • Smaller capacity (usually)

  • Limited number of read/write cycles

Guidance

• Portable is not enough on it's own

• No moving parts is not enough on it's own

examples of optical storages

CD, DVD, Blue-ray

examples of magnetic storages

Internal hard drive,

USB hard drive

Magnetic tape

examples of solid state storages

camera read/write card

USB memory stick

solid state drive (SSD)

give examples of what secondary storage might store

-images

-music

-applications (eg wordprocessors)

-the operating system

-programs

state the 4 devices commonly used for storage with the type of storage, storage capacity and cost

Name of Device	Type of Storage	Storage Capacity	Cost
Hard Disk Drive (HDD)	Magnetic	500GB - 8TB (consumer-grade) (high storage)	Low cost per GB
Solid-State Drive (SSD)	Solid Stae	128GB - 2TB (consumer-grade)	High cost per GB
USB Flash Drive	Solid State	8GB - 256GB (common sizes)	Moderate cost per GB
CD/DVD/Blu-ray Disc	Optical	CD: 700MB, DVD: 4.7GB - 9GB, Blu-ray: 25GB - 50GB	Low cost per disc

scenario 1- 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. What would be the most suitable storage device

• n 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

scenario 2-A school wants to backup all students work twice a day and keep it safe in case of any emergencies. The cost of the device is very important as the school budget is tight and they want a device that can hold terabytes of data in one go to minimise the amount of devices they would need to buy. what would be the most suitable storage device

• In this scenario a hard disk drive (HDD) would be most suitable

• A hard disk drive has the highest capacity and would limit the amount of devices they would need to buy, it is also relatively cheap per gigabyte compared to solid state. Reliability could be an issue but as this is being used for backing up data it will not be used constantly and would be less of a concern

scenario3-An international game studio wants to distribute it's new release for the latest games consoles. This could potential involve many millions of copies being sold so the device would have to extremely portable and cheap enough to produce so that the company do not make a loss. The device needs to be durable enough to withstand being handled regularly. what would be the most suitable storage device

• In this scenario a Blu-ray (optical) would be most suitable

• A Blu-ray disc is highly portable due to its size and weight and durable enough because it has no moving parts. The cost is low which is perfect in this scenario as the company could potentially be selling millions of copies

what do computers use binary numbers for

to represent data

why data must be stored in binary format

all information that is processed by a computer is in the form of a sequence of 1s and 0s. Therefore, all data that we want a computer to process needs to be converted into binary and also combining bits it is possible to represent any type of data- texts, images, sounds

with just two states, 0 and 1 electronic components are

-easier to manufacture

-cheaper

-more reliable

what is 1 bit

1 or 0 in binary

what is 1 nibble

4 bits

what is 1 byte

8 bits

what is 1 kilobyte

1000 bytes or 1KB

what is 1 megabyte

1000KB

what is 1 gigabyte

1000MB

what is 1 terabyte

1000GB

what is 1 petabyte

1000TB

Why does data have to be converted to binary to be processed by a computer?

• A computer is built using switches that can either be on or off, this fits the binary number system which only has two digits (1/0), which means off can be represented by a 0 and on can be represented by a 1

• This means all data must be converted to binary before a computer can understand and process it

• Converting data to binary allows computers to process it at an incredible speed, perform complex calculations and store vast amounts of data efficiently

Explain why computers process data in binary format [2]

• Computers consist of switches/transistors [1]

• 1 is represented as switch/transistor being on/open // 0 is represented as switch/transistor being off/closed [1]

What is data capacity?

• Data capacity is the maximum amount of information that a storage device can hold

• If you know the capacity of a storage device, you can calculate how much of different data types can be stored

• Examples of data that could be stored include text, images and sound files

sound file size =

= sample rate x duration (s) x bit depth

image file size = c

colour depth x image height (px) x image width (px)

text file size =

bits per character x number of characters

Lyla is a social media influencer. She creates images to be shared on her social media accounts.

Each image has a fixed size of 3 MB. She is storing the images on a USB flash drive which has a capacity of 6 GB.
Calculate how many images can be saved on the storage device. Show your working [2]

How to answer this question:

• Convert 6 GB to MB

• Divide the capacity in MB by the files size in MB

Answer

• 6 GB  = 6 * 1000 = 6000 MB

• 6000 / 3 = 2000 images

-convert denary number 89 into binary

-convert the binary 01100110 into denary

-1001101

-102

The rules of binary additions

0+0=0

1+0=1

1+1=0 carry 1

1+1+1=1 carry 1

00101011+01001010

01110101(117)

what is overflow error

when the data type used to store data was not large enough to hold the data

what is the hexadecimal

a base 16 number system

• from 0-9 in denary will be the same in hexadecimal

• from 10-15 in denary will be A-F in hexadecimal

Convert denary number 12 to heaxdecimal

-Convert denary number 24 to heaxdecimal

-Convert denary number 230 to heaxdecimal

-first convert into binary 00001100

-group it into nibble 0000 1100

-find hexa decimal equivalent for each nibble 0C

• 1 8

-E6

what is the most significant bit

the left-most bit in any representation

what is the least siginificant bit

the right -most bit in any representation

what happens when you perform 1-bit left shift

multiply original number by 2

what happens when you perform 1-bit right shift

divide the original number 2

what is a character set

a defined list of characters recognised by the computer hardware and software. With each character being represented by a single number

Why is it important that character sets are agreed standards(agreed way of numbering all the characters a computer uses)

if one device recognises the binary sequence 01000001 as A then we need other devices to recognise this same sequence as A

What is ASCII

American Standard Code for Information Interchange and was a 7-bit character set set meaning that could have 128 different combinations

The Extended-ASCII 8 bit character set

-256 different combinations and so provided characters for some foreign languages and other useful graphical symbols

why is the character set unicode needed

it is a fully international and multilingual character set, which includes all the characters from every written language and plus more modern languages such as emojis

-16 bit character set but recently extended to 24bits

how is a bitmap image stored

-images are made up of different coloured squares called pixels Each pixel has a specific colour, which can be represented by a specific code (binary value)

How many bits used to store image with 2 colours

a single bit which will give two combinations 0=white 1=black

examples of metadata about an image file

-height, width and colour depth

what does greater a color depth and resolution

-the larger the color depth and resolution, the larger the file size of the image

what is colour depth

The amount of bits used to store the colour of each pixel is known as the colour depth.

How is sound stored?

convert the analogue signals into a binary ones. Samples are taken per second. At each sample, the analogue wave is stored in binary to the closest value possible depending on the bit depth

what affects the quality of a digital converted sound wave

-sample rate-the greater the samples taken per second the higher the quality but also the larger the sound file will be

-bit depth-the greater the bit depth the more bits available and so the closer to actual value but increases file size

what is sample rate

how often(frequency) you record the amplitude of a sound wave. The more often you record a sample the smoother the playback will sound

what is sample rate measured

Hertz (Hz)

bit depth

number of bits available to store each sample

Duration

how many seconds of audio the sound file contains

size of sound sample =

durationxsample ratexbit depth

what is compression

Compression is reducing the the size of a file so that it takes up less space on secondary storage

reasons for compression

-maximise the amount that you can store in a device

-smaller files are quicker when transferred over the Internet

What is lossy compression?

• Lossy compression is when data is lost in order to reduce the size on secondary storage

• Lossy compression is irreversible

• Lossy can greatly reduce the size of a file but at the expense of losing quality

• Lossy is only suitable for data where reducing quality is acceptable, for example images, video and sound

• In photographs, lossy compression will try to group similar colours together, reducing the amount of colours in the image without compromising the overall quality of the image

what is lossless compression

• Lossless compression is when data is encoded in order to reduce the size on secondary storage

• Lossless compression is reversible, the file can be returned to its original state

• Lossless can reduce the size of a file but not as dramatically as lossy

• Lossless can be used on all data but is more suitable for data where a loss in quality is unacceptable, for example documents

• In a document, lossless compression uses algorithms to analyse the contents looking for patterns and repetition. For example, repeating characters are replaced with a single character and the number of occurrences in the document (“EEEEE” becomes “E5”)

When you open a lossless compressed document the decompression process reverses the algorithms and returns the data back to its original state

• Lossless compressed documents take up less storage space which means you can store more and they are quicker to share across a network

lossy vs lossless

lossy:

-some of the data is lost and cannot be recovered

-greatly reduces the file size

-reduces quality of image/sound

-suitable for images,sounds,videos

-cannot be used on texts and executable

lossless:

-none of the data is lost, it it encoded differently

-can be turned back into original form

-can be used on all type of data

-usually less effective than lossy compression at reducing file size

-most suitable for documents and and executable files