1.4 Secondary Storage Flashcards
What is secondary storage?
Secondary storage is storage that is non volatile and can usually be removed and put into another computer system
Can secondary storage be accessed by the CPU?
No
What are the uses of secondary storage?
- Programs and data are stored here
- Blu-rays may be used to distribute films
- Memory sticks may be used to transport data from one place to another
- Magnetic tape or external hard drives may be used for backup
- SD cards can be used for additional storage on cameras and smartphones; this is used for music, video and photos
Secondary storage devices:
- Hard Disk Drive (HDD)
- Solid State Drive (SDD)
- Offline secondary storage
Offline secondary storage devices:
- Compact Disk (CD)
- Digital Versatile Disk(DVD)
- Blu-ray
- Flash Memory
- SD cards
- Removable HDD or SDD
- Magnetic Tape
Storage methods
- Magnetic:
Mechanical parts move over the disks surface to read and write data magnetically, or a drive head reads a magnetic tape - Optical:
Lasers read and write data using light - Solid State:
Data is recorded onto solid memory chips without any moving parts
Magnetic disk basic features
- Disk contains concentric circles called tracks
- Each track is divided into sectors
- Disk heads mounted on mechanical arms read and write data
- A disk with a solid platter is a ‘hard’ disk
- Soft plastic disks are known as ‘floppy’ disks
Hard disks components
- Magnetic platter contains data
- Drive read / write head reads data on the drive
- Actuator moves the read / write arm
- Drive spindle rotates
Magnetic storage features:
- Fixed magnetic hard disks are still used in many PCs and laptops
- Very large capacity (up to 6gb or more)
- Very cheap form of storage
- Portable hard disks can be connected to a computer via a USB port
- They are used for backing up or transporting data-
Magnetic advantages:
Cheap, large storage capacities, relatively fast read and write speed
Magnetic disadvantages:
Lots of mechanical parts, durability issue, sealed unit due to disk head and platter precision and not very portable
Magnetic uses:
Personal computers, storage of large quantities of data
Magnetic capacities:
500GB - 12TB or greater
Optical storage basic features:
- Data is stored as pits and lands burnt or pressed into a spiral track circulating outwards from the centre
- A laser beam passes over the pits and lands the level of reflection is measured
From the signal, 0s and 1s can be derived
Optical advantages:
Cheap, very easily portable, takes up little space physically
Optical disadvantages:
Less storage capacity compared to other types
Easily damaged / scratched, requires a CD reader
Slow write speeds
Optical uses:
Songs, videos and other multi-media storage, backup and archiving of data
Optical capacities:
- CD ROM; up to 720MB
- DVD; up to 8.4GB (dual layered disk)
- Blu-Ray; up to 50GB (dual layered disk
CD vs Blu Ray
Blu ray can hold more space because it has a smaller pits and lands which allow it to store more data compared to CD which has bigger pits and lands. Also the wave length is larger
SSD basic features:
- SSD disks use non-volatile flash memory to store information
- Very fast read / write speeds as it doesn’t need to wait for a disk to spin to the correct location and an arm to move
- No mechanical or moving parts meaning these disks are very durable
How flash memory works:
- Large electric current used to force electrons through a barrier and trap them on the other side
- They remain on the other side until ‘flashed’ with a new current
e.g
Trapped (charged) or not trapped = 0 or 1
SSD advantages:
Highly durable, no moving parts, very fast read and write speeds, no noisy fan or drive arm, faster start up times
SSD disadvantages:
More expensive than magnetic hard disks, similar storage capacity as magnetic hard disks
SSD uses:
Higher end computers, laptops, smartphones and tablets
SSD capacitites:
100GB to 16TB
Flash memory:
Low cost, portable, no moving parts, durable
Can be used on offline devices such as cameras, mobile phones and USB memory sticks
Capacity meaning:
How much data can be stored
Speed meaning:
The rate (usually in MB/s) at which data can be read or written
Portability meaning:
How easy is it to carry
Durability meaning:
How fragile is the device? How can it cope in different temperatures or scenraios?
Reliability meaning:
How likely is the data (or some of it) to be lost?
Cost meaining:
What is the cost of the device? How much is it to store 1 MB of data?
Do different storage devices have a range of storage capacities?
Yes, in general, a higher capacity will allow greater data storage
When you know how much data you need to store, you can decide which storage devices would be most appropriate?
Use the advantages and disadvantages to decide which storage device is the best to use and explain why
Calculating data capacity:
Knowing the capacity required will enable us to make an informed decision as to which device to use.
How much storage would we need if we had 5000 photos and each photo has a file size of 10MB?
5000 x 10 = 50000 MB which is 5GB
A suitable storage device to store this would be Blu Ray for portability or SSD for faster access times and write speeds
