Secondary Storage devices Flashcards
What are secondary storage devices?
Secondary storage devices are used in computer systems to avoid having to re-enter programs and data for processing by storing a non-volatile or permanent copy. Additionally, data can be stored more than once so there is a backup copy for restoring lost data from the secondary storage device.
What are Hard disks?
The most common form of secondary storage device is the internal hard disk drive, where:
* Drive consists of a number of metal disks which have
been coated with a special magnetic material
* The disks are mounted on a common spindle and rotate
at high speed
* A series of read/write heads move across the disk surface together to access or store the data on the disk
* The hard disk mounted in a sealed unit and is connected to a power supply inside the computer
What type of storage devices are hard disks?
a magnetic storage device
What does it mean if ‘some hard disk drives are not permanently fixed’ ?
Some hard disk drives are not permanently fixed inside the computer but are removable from a bay in the computer; other hard drives are even more portable as they are connected externally to the computer via a USB cable.
What are the advantages of Hard disks?
- Hard disks have a high data transfer rate.
- High storage capacity (typically 500 gigabytes to 10 terabytes)
What are the disadvantages of Hard disks?
- Where hard disk is fixed inside the computer it can be difficult to transfer data to another computer.
- Care has to be taken handling portable hard disks due to their fragility.
What are optical disks?
Optical disks are known as optical storage devices, where:
* The optical disk is a plastic disk with a mirrored surface
* Binary data is burned or pressed onto the surface of the disk as series of ‘pits’ and ‘lands’
* Whichever method is used to create the disk, the ‘pit’ has a
binary value of zero, whereas the ‘lands’ have a binary value of one
* Laser beams are used to read the data stored on the disk since the ‘pits’ and ‘lands’ reflect different amounts of light, which can then be decoded into the original binary data
What is the storage capacity of a CD?
650 Mb
What is the storage capacity of a DVD?
4.7 Gb
What is the storage capacity of a Blu-ray?
25 Gb
What are the advantages of optical disks?
- Portable device that is cheap to produce – typical blank disks cost between 10p–50p each.
- Reasonable storage capacity for home and faster access time than magnetic tape.
- Optical drives are compatible with CD and DVD disks so data can be read from either media.
What are the disadvantages of optical disks?
- Care needs to be taken handling as scratching the shiny data side renders it inoperative.
- Less storage capacity than a hard disk means it is unsuitable for large volumes of data.
- Access time is greater than for hard disks and SSD devices.
What are solid state disks?
Solid-state disks act in a similar way to a hard drive except they
are flash memory secondary storage devices where:
* They are based on non-volatile NAND flash memory with a controller to manage pages, blocks of data and the complexities of writing
* The flash memory cells are grouped into a grid that is
separated into sections called ‘pages’, into which the data is stored
* A block consists of many pages and pages cannot be overwritten individually; the whole block has to be erased before the page can be overwritten
What is the speed of a SSD compared to a hard disk?
SSDs perform faster than hard drives as there are no moving parts in these devices; consequently they can read, write and access data faster.
Latency is a feature of hard disks as they are slow to access data due to having to spin and position read/write heads over the disk to access data.
What is the cost of a SSD compared to a hard disk?
SSDs are significantly more expensive to purchase than hard disks; consequently they tend to be smaller capacity than hard disk drives.
