1.2 Memory and Storage Flashcards
What are the two types of storage?
Properties of Primary Storage?
Consists of RAM, ROM, Cache and registers
- With Exception of ROM they are all volatile
- Relatively small storage capacity compared to secondary storage
- Very Fast access times compared to secondary storage
Properties of Secondary Storage
- Non-volatile
- Very slow access times compared to primary storage
It is needed as:
- Larger capacity compared to primary storage.
What is ROM?
What is it’s purpose?
Small piece of read-only, non-volatile memory which contains the bootstrap and BIOS which is located on the motherboard. It is smaller than RAM
The BIOS (Basic Input Output System) 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. The BIOS is always needed so it is stored in ROM.
What is RAM?
What is the purpose of RAM?
Larger than ROM, Smaller than secondary storage
RAM is fast, volatile, read-write memory which is used for the temporary storage of instructions and data.
When the computer Boots up, the OS is copied from secondary storage into RAM.
What happens when there is not enough storage in RAM?
What is Virtual Memory?
When programs and data are fetched and executed they are stored in RAM but this assumes that the RAM is big enough to hold the programs. However, there is significantly more room available on the hard disk.
So when you run out of RAM instruction & data that are not being used are transferred to the virtual memory on a hard disk.
If a different program is needed the program swapped out from RAM to Virtual Memory that are now needed
Why do we need secondary storage?
Secondary storage is needed because ROM is read only and RAM is volatile. IT is also needed for:
- Storage of programs and data when power is turned off
- Semi-permanent storage of data that can change
- backup of data files
- Archive of data files
What is a drive?
What is a media?
What are the three types of secondary storage?
What is a Magnetic Device and how does it work?
What is their advantages and Disadvantages?
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.
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.
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.
What is a Optical Device and how does it work?
What is their advantages and Disadvantages?
What are their types?
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’.
Optical media also come in different types:
- **ROMmedia** have data pre-written on them. The data cannot be overwritten. Music, films, software and games are often distributed this way.
- **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.
- **RW** works in a similar way to R, except that the disc can be written to more than once.
What is a Solid State Device and how does it work?
What is their advantages and Disadvantages?
Solid state devices use **non-volatile** random access memory **(RAM)** to store data indefinitely. They tend to have much faster access times than other types of device and, because they have no moving parts, are more durable.
Since this type of memory is expensive, solid state devices tend to be smaller in capacity than other types. For example, a solid-state drive that holds 256 **GB** might be of a similar cost to a hard disk with several terabytes capacity.
Solid state devices require little power, making them ideal for portable devices where battery life is a big consideration. They are also portable due to their small size and durability.
What are the characteristics of a Hard disk and what is it used for?
What are the characteristics of a CD-ROM/R and what is it used for?
What are the characteristics of a CD-RW and what is it used for?
What are the characteristics of a DVD RW and what is it used for?
What are the characteristics of a Blue-Ray and what is it used for?
What are the characteristics of a Solid State Drive and what is it used for?
What are the characteristics of a USB memory stick and what is it used for?
What are characteristics you should consider when buying secondary storage?
CSPDRC
Capacity
Speed
Portability
Durability
Reliability
Cost
What is Optical secondary suitable for?
What is Magnetic Storage Suitable for?
High Capacity
Fast Access
Low Cast
Cloud storage
What is solid state storage suitable for?
SSD,Memory sticks, Flash memory cards
Low power embedded systems
Portable devices
Silent Operation
Very Fast access
Small and Lightweight
How do you calculate the file size of text files?
How do you calculate the file size of sound files?
Sample Rate * Bit depth * Duration
How do you calculate the file sizes of image files?
Colour depth * Image Height * Image width
What is the different types of data measurement and their sizes?
REMEMBER FOR EVERY BYTE THERE ARE 8 BITS
Why do we use two states in electrical components?
What is Denary?
Convert the Denary Number 89 into binary
Convert the Binary number 01100110
What is Hexadecimal and what is it used for?
Convert 230 to Hexadecimal
What is the rules for binary addition?
What is overflow?
Overflow is when the 1 has gone beyond the capacity of our storage line. It cannot fit in the 8-bit binary line. It exceeds the maximum
What happens during a left binary shift?
What happens during a right binary shift?
Left shift Multiplies by 2
Right shift divides by 2
In both they lose precision
What are the two ways to store images in binary?
Bitmap Example
What is the number of bits required for each pixel dependent on?
How do you calculate the number of coulours
The number of colours required
The number of colours can be calculate using 2^n where n is the number of bits per pixel.
Number of bits per pixel is known as colour depth.
What is Metadata?
What happens if the colour depth and resolution increases?
What is the colour depth of photograph?
Metadata is additional data stored with the image to define the width, depth, height and colour packet.
The size of the file will increase
The colour depth is the number of colours per pixel.
What is a character set?
How many characters can we store if we only have 7 binary digits?
A defined list of characters recognised by the computer
There are loads of different characters we needed to store and for this we need a minimum of 7 bits per character.
2^7 = 128 charachters
It is important that all computers use the same binary code so computers are able to recognise each other. They have agreed standard.
What is ASCII?
What is Extended ASCII
What is UNICODE?
ASCII is American Standard Code for Information interchange is a seven bit character set(128 different combinations)
This was extended and called extended ASCII which is 8-bit.
Unicode wass made because there are thousands of international and multilingual characters and special symbol, We want to store and use all of these.
These need to conform to this standard.
It was originally 16-bit charachter set but it is now a 24-bit charachter set but this is slow so we use Hexadecimal as an alternative.
How do we visualise sound?
We can visualise sound as an analogue wave but to store an analogue wave in binary you have to convert it to digital signal.
What are the factors that affect the quality of a digitally converted sound wave?
Sample rate is how often you measure the amplitude of a wave
Bit depth represents how many different gradiations of amplitude can be represented in a digital wave form.
What is sound file size?
What is Bit Depth?
What is Sample Rate?
Sound file size is the total number of bits in a sound
Bit depth is the number of bits stored per sample
Sample Rate is the number of samples stored per second
What is Compression?
- Compression reduces the size of file by reducing the number of bits so it takes up less space.
- Maximize how much you can store on a device
- Smaller files are quicker when transferred over the internet.
What is lossy compression?
What are its advantages and Disadvantages?
With lossy compression, some data is removed and discarded, thereby reducing the overall amount of data and the size of the file.
However
- It takes up less bandwidth
- It cannot be used on Text and executable files.
- Suitable for image sound and video.
- Reduces quality.
- cannot be reversed.
What is lossless Compression?
What are its advantages and disadvantages?
Compression technique where None of the data is lost instead it is encoded differently
It can be used on all data file types
It can be reversed
It is suitable for text and executable files
However, It is less effective at reducing file size
Compare SSD and HDD
HDD is cheaper, higher in capacity and has a longer read/write life before it deteriorates while SSD is faster, more durable, silent and does not require defragmenting
What is Cache Memory?
Cache memory
Cache memory is a type of high-speed random access memory (RAM) which is built into the processor.
Data can be transferred to and from cache memory more quickly than from RAM. As a result, cache memory is used to temporarily hold data and instructions that the processor is likely to reuse. This allows for faster processing as the processor does not have to wait for the data and instructions to be fetched from RAM.
The more cache memory a computer has, the faster it runs. However, because of its high-speed performance, cache memory is more expensive to build than RAM. Therefore, cache memory tends to be very small in size.
To get around this issue, different types of cache exist:
L1 cache has extremely fast transfer rates, but is very small in size. The processor uses L1 cache to hold the most frequently used instructions and data.
L2 cache is bigger in capacity than L1 cache, but slower in speed. It is used to hold data and instructions that are needed less frequently.
Why do we need secondary storage?
What is Seconadary storage?
Secondary storage
General purpose computers, such as personal computers and tablets, need to be able to store programs and data for later use.Secondary storage is needed to keep programs and data indefinitely.
Secondary storage is non-volatile, long-term storage. It is used to keep programs and data indefinitely. Without secondary storage all programs and data would be lost the moment the computer is switched off.
Not all computers require secondary storage.Embedded computers, such as those found in a digital watch 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 ROM and any user data is held in RAM.
What is Analogue and Digital data?
Analogue data and digital data
Analogue data is a real-life signal that can vary greatly in value. Examples include:
- sound waves
- pressure
- temperature
Digital data is binary data which represents analogue data. Computers work with digital data. Analogue data must be converted to digital before a computer can use it. A device known as an analogue-to-digital convertor (ADC) is used to generate digital data from analogue signals. In the same way, a digital signal can be converted back to an analogue signal using a digital-to-analogue convertor (DAC).
Why do computers use binary?
What would these hex numbers be in denary?
- 11
- 2B
- FA
- 17
- 43
- 250
How do you multiply and divide numbers in binary?
Shift 4 places to the left means it would be doubled 4 times
Shift 3 Places to the right means it would be halved 3 times
Benifits of using Hexadecimal
- Easier to convert between binary and hex
They are simpler to remember - They are short so Less chance of input errors
What is Metadata?
Metadata
Files contain extra data called metadata. Metadata includes data about the file itself, such as:
- file type
- date created
- author
An image file also includes metadata about the image data itself, such as:
- the height and width of the image - this defines how many rows and columns the pixels are to be arranged in
- the resolution
- the colour depth
Without this metadata, the image data would not be correctly interpreted, meaning the image could not be correctly displayed.
Metadata is data about data!
Why must sound be converted into a digital signal?
Computers work in binary. All data must be converted into binary in order for a computer to process it. Sound is no exception. To do this, sound is captured - usually by a microphone - and then converted into a digital signal.
What are the factors which affect the size and quality of sound files?
Increasing sample rate(Measured in Hz) means better quality
Increasing bit depth means it will pick up quieter sounds
Compare both types of compression
What are Check digits?
Check digits
When transmitting data, errors may occur and some data may be incorrectly received. To overcome this, an extra value is transmitted to help determine if the data received is correct or incorrect. This value is known as a check digit.
The value of the check digit is usually calculated from the other data being sent. For example, the EAN8 barcode number system creates the check digit from the other seven numbers in the bar code:
- The first, third, fifth and seventh numbers are each multiplied by three, and then added together.
- The remaining numbers are added to the total.
- The total is divided by ten.
- The check digit is determined by subtracting the remainder from ten.
the code for ‘B’ will be one more than the code for ‘A’
so if A = 4, B = 5
This is for the exam. REmember this
