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

Hard disk drive

-capacity

-portability

-durability

-reliability

-cost