3.4b Memory - excluding cache and register - in 3.4a

Question 1

Define memory

Answer 1

The part of a computer that stores data.

Question 2

What is main memory:

• where?
• adv?
• practically?

Answer 2

Main memory is built inside the computer.
As a result, data can be read from and written to main memory extremely quickly.
This gives the processor fast access to the data and instructions that the main memory holds.

Question 3

2 types of main memory

Answer 3

There are two types of main memory:

• read-only memory (ROM)
• random access memory (RAM)

Question 4

What is ROM?

Contents retained/lost when turned off?

Answer 4

Read only memory. This is non-volatile memory or storage containing data that cannot be changed.

Its contents are not lost when the computer is turned off.

Question 5

Quality of ROM - and what this makes ROM ideal for?

Answer 5

ROM can be read from, but not written to, hence the term “read-only”.
This makes ROM ideal for storing instructions and data that are needed for the computer to run.
These instructions and data are usually programmed by the computer’s manufacturer and cannot be overwritten.

Question 6

Example of a program stored in ROM

• also when does it run
• what does it do

Answer 6

The Basic Input Output System (BIOS) is an example of a program that is stored in ROM.
The BIOS runs as soon as the computer is switched on.
It checks that the hardware is functioning correctly, then runs a second program known as the bootup or bootstrap program that loads the computer’s operating system from the hard drive into the RAM.

Question 7

RAM

• what is it?
• when computer switched off?

Answer 7

Random access memory (RAM) is volatile main memory.

It does not retain its contents without a constant supply of power. When a computer is switched off, the data and instructions held in RAM are lost.

Question 8

Why is RAM given the term ‘random access’

Answer 8

RAM is given the term “random access” because data can be stored and accessed from any location within the memory.

Question 9

What is RAM used to store?

So, for example?

Answer 9

RAM is used to hold data and programs that are currently in use.

In a modern PC, RAM is used to hold the operating system and any open documents and programs that are running.

Question 10

True/false?

RAM can be read from and written to, and is volatile.

Answer 10

True

Question 11

How can contents of RAM be changed - and when

- give 2 examples

Answer 11

The contents of RAM can be changed at any time, simply by overwriting them with other data and instructions.
For example, a user might close one document and open a second, or run a different program.

Question 12

More RAM = ?

Answer 12

The more RAM a computer has, the more data and programs it can hold simultaneously

Question 13

Upgradability of RAM?

Answer 13

RAM can also be upgraded fairly easily, unlike other types of main memory.

Question 14

2 marks - How does ROM differ from RAM?

Not in adv info

Answer 14

ROM is read only and non-volatile. RAM can be read from and written to and is volatile.

Question 15

The need for secondary storage - explain nicely

Has been removed

Answer 15

Computers use main memory such as random access memory (RAM) and cache to hold data that is being processed.
However, this type of memory is volatile - it loses its contents when the computer is switched off.
General purpose computers, such as personal computers and tablets, need to be able to store programs and data for later use.

Question 16

Therefore simply, secondary storage is needed to?

Answer 16

Secondary storage is needed to keep programs and data long term.

Question 17

What would happen without secondary storage + why

Answer 17

Secondary storage is non-volatile, long-term storage. Without secondary storage all programs and data would be lost the moment the computer is switched off.

Question 18

There are three main types of secondary storage in a computer system:
(Examples as well)

Answer 18

• solid state storage devices, such as USB memory sticks
• optical storage devices, such as CD, DVD and Blu-ray discs
• magnetic storage devices, such as hard disk drives

Question 19

What doesnt need secondary storage and why?

Answer 19

However, not all computers require secondary storage. Embedded computers, such as those found in a washing machine or central heating system, do not need to store data when the power is turned off. The instructions needed to run them are stored in read-only memory (ROM) and any user data is held in RAM.

Question 20

Solid state storage:

• what’s is it made of?
• features (2)

Answer 20

• Solid state storage is a special type of storage made from silicon microchips.
• It can be written to and overwritten like RAM.
• However, unlike RAM, it is non-volatile, which means that when the computer’s power is switched off, solid state storage will retain its contents.

Question 21

Where is solid state also used - example (2)

Answer 21

Solid state is also used as external secondary storage, for example in USB memory sticks and solid state drives.

Question 22

2 benefits of solid state storage - EXPLAINED

Answer 22

One of the major benefits of solid state storage is that is has no moving parts. Because of this, it is more portable, and produces less heat compared to traditional magnetic storage devices. Less heat means that components last longer.

Solid state storage is also faster than traditional hard disk drives because the data is stored electrically in silicon chips called cells. (Explanation next card)

Question 23

How solid state ACTUALLY works

Answer 23

Within the cells, the binary data is stored by holding an electrical current in a transistor with an on / off mode.
Unlike RAM which uses a similar technique, solid state storage retains this even when the power is switched off by using a technology known as flash memory.

Question 24

Flash memory ?

Answer 24

Non-volatile memory that can be read from and written to. It is suitable for secondary storage

• it is the medium for solid state storage

Question 25

Solid state storage is ideal for (3 examples)

Answer 25

Solid state is an ideal storage medium for many modern devices such as tablets, smartphones and digital cameras.

Question 26

Magnetic storage - example

Answer 26

Hard disk drives

Question 27

Magnetic storage - what it uses?

• what sections represent?
• how much data can be contained + why?

Answer 27

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 28

How to read/write data on magnetic devices?

Answer 28

As the disk is spinning, a read/write head moves across its surface.
To write data, the head magnetises or demagnetises a section of the disk that is spinning under it.
To read data, the head makes a note of whether the section is magnetised or not.

Question 29

Adv + disadvantages of magnetic devices

Answer 29

Magnetic devices are fairly cheap, high in capacity and durable.

However, they are susceptible to damage if dropped. They are also vulnerable to magnetic fields - a strong magnet might possibly erase the data the device holds.

Question 30

Optical devices

• how they work (what they use, to do what)
• describe its composition

Answer 30

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.

Question 31

What happens avec optical devices? HOW IT ACTUALLY WORKS

- what does what represent and how?

Answer 31

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 - land - represents a binary ‘1’, and no reflection - pits - represents a binary ‘0’.

Question 32

3 different types of optical media???

- explain each one w/ examples

Answer 32

• ROM media have data pre-written on them. The data cannot be overwritten. Music, films, software and games are often distributed this way.
• Read (R) media are blank. An optical device writes data to them by shining a laser onto the disc. The laser burns pits to represent ‘0’s. The media can only be written to once, but read many times. Copies of data are often made using these media.
• Read/write RW works in a similar way to R, except that the disc can be written to more than once.

Question 33

3 examples of optical devices

Answer 33

CD, DVD and Blu-ray discs are forms of optical storage.

Question 34

For adv and dis of solid state, magnetic, optical — see other deck

Answer 34

Ok

Question 35

In the exam you might be given a scenario and then be asked to recommend the most suitable storage media to use.
When choosing an appropriate storage media to use you need to consider the following things : (6)

Answer 35

Capacity The amount of data that can be stored, and the maximum size of the files.

Speed How quickly can the data be accessed from or written to the media

Portability Can the media be easily moved about? This depends on both the size and weight of the media.

Durability How resistant the media is to damage. Whether it is rugged enough to survive knocks, scratches, etc.

Reliability The shelf life of the media. How long it will retain data so that it can be accessed reliably and without error in the format in which it was originally saved.

Cost How expensive the media is in terms of cost per gigabyte of storage.

Question 36

Define cloud storage:

• what
• where
• how

Answer 36

Storing data at a remote location online is known as cloud storage. When files and data are sent to the cloud, they are actually being sent to a server that is connected to the internet. Files can be uploaded to a folder system and downloaded as required.

Question 37

What does the spec say to understand about cloud storage

Answer 37

Students should understand that cloud storage uses magnetic and/or solid state storage at a remote location

Question 38

In recent years, the cloud has also become a term for internet-based software facilities.

Cloud storage has many advantages:
(3)

Answer 38

• data can easily be accessed from anywhere with an internet connection.
• the business running the cloud storage service manages backups and security.
• additional storage can be added easily without having to invest in additional hardware.

Question 39

However, cloud storage also has a number of disadvantages associated with it: (4)

Answer 39

• if you can access your data from anywhere with an internet connection, then a hacker can potentially do the same.
• if your internet connection fails, then you won’t be able to access your files.
• you are relying on other people to correctly secure your data and keep backups.
• you don’t know if employees of the cloud service will have access to your data.

Question 40

What does a business that is considering using a cloud computing service have to think about
- big detailed chunk
— - what does it depend upon

Answer 40

A business that is considering using a cloud computing service will have to think about whether the advantages outweigh the risks. This is a complex decision and will depend on many factors, including the type of data to be stored in the cloud system.

Technology is always changing and it is important to think about the risks involved when using any new technology. This is especially important when that technology is used to store information that could be private and confidential. Do the risks outweigh the disadvantages? Is the technology likely to suffer from some kind of cyberattack?

Question 41

Q. Explain how a solid state disk drive (SDD) operates (4 marks):

Answer 41

• use electrical circuits to persistently store data;
• non-mechanical – nothing spins;
• contain a controller circuit board and lots of electrical circuits wired
together into a grid. The grid is organised into “pages”;
• hold data using microscopic electronic switches (floating gate
transistors) - these can be charged as + or –turned in to 1s and 0s;
• the transistors create NAND gates that trap electron flow within them. This continues when the power in the system is turned off;
• SSD are random access – so data transfer is quicker;
• if data is updated, the section of the SSD can’t just be over-written.
Data must be copied to main memory, written to a new area and the original section then erased.