1.1.3 storage Flashcards
Input devices
one which can be used to put data and information into a computer.
Output devices
an output device is one which can be used to send information from the
computer
Optical storage
optical devices are read from and written to using lasers. Binary information is represented by portions of the disc which either reflect or scatter the incident laser light written in spiral tracks on the disc’s surface.
The portions which are recessed, called pits, scatter light whereas the flat portions, called lands, reflect light. Pits represent a 0 and lands represent a 1.
CD/DVD-ROMs were, and in some cases still are, used as a means of delivering application software. They are light and easily transported, and need little physical space. (have a higher storage capacity than CDs, making them
suited to storing digital videos which require more storage space than audio files or photos. )
Their disadvantages include being easily damaged by scratches, their limited
storage capacity and relatively slow transfer speeds. Varieties of CD include CD-R
which can only be written to once, CD-RW which can be written to more than once
and CD-ROM which is written to during production and can then only be read from.
Blu-Ray
An advancement over DVDs, blu-ray discs have more than five times as much
storage than traditional DVDs, making them useful for storing high-resolution films.
Magnetic storage
Devices which store information magnetically represent binary information using two magnetic states:
polarised and unpolarised. If a portion of magnetic material is polarised, all magnetic poles align and can be read by a read/write head passing over the region. If an area is not polarised, magnetic poles are randomly scattered and produce a different reading on a read/write head. These two states can represent 1 and 0, allowing any
information to be represented in binary form. The most common type of magnetic storage is hard disk drives. However, magnetic tape also stores information magnetically.
Hard Disk Drives
Sometimes abbreviated to HDD, hard disk drives typically have high capacities of
between 500GB and 5TB. They work by rotating magnetic platters at high speeds
under a read/write head on an actuating arm.
An HDD is a hard disk drive. The drive is a mechanical device with many moving parts. In theory, this means that it is more likely to fail. However, HDDs are sold as sealed units, so the disk medium and drive mechanism are well protected from contamination and wear and tear. Data is represented on the disk surface (a metal platter) by magnetised dots. Binary data is represented through the two states of ‘magnetised’ and ‘not-magnetised’.
Fragmentation occurs when there is insufficient contiguous space to store the file. If a file is fragmented, then each part of the file will be in a separate location with a link to the next location; the file will be read by following the links until an end-of-file marker is reached. If a disk is nearly full, it will take longer to find space to write file segments, and it will take longer to access a file that is spread across several locations.
The main advantages of a magnetic hard disk are its capacity and cost. This traditional format still offers greater capacity at a much lower unit cost than SSDs. However, the gap between the technologies is narrowing fast.
Magnetic hard disks are best suited to desktop and laptop devices where low purchase cost is the most important selection criterion.
Flash/Solid state drive storage
An SSD is an electronic device that uses flash memory, and has no moving parts.
Compared to magnetic hard disks, SSDs offer many advantages. The main advantage is speed of access. Read-write access speeds for a standard SSD are in the range of 200–500 MB/s. Despite the fact that some operations will take longer than others, these timings are relative, and SSDs will always outperform magnetic or optical drives. The lack of moving parts also reduces the amount of energy consumed, which, in turn, reduces the amount of heat generated in a computer system.
However, while an SSD is robust, it does have a limited lifespan. The number of times that an SSD can be written to is finite, and memory cell ‘leakage’ can be a problem if devices are not powered up from time to time. As a result, they are not suitable for the long-term archiving of data.
At the time of writing (2020), SSD storage is still more expensive per GB than magnetic storage. High-end computer systems will sometimes have large-capacity solid-state disks, but this will add significantly to the overall cost of the device.
SSDs are particularly suitable for storing files that are read or changed frequently. Having your operating system on an SSD will likely dramatically improve the time that it takes for your system to go through its boot sequence
Flash memory can be erased and reprogrammed electronically, and is non-volatile,
meaning it stores its data even when power is lost. These features make SSDs a good
replacement for HDDs as they have the same functionality but improved performance.
virtual storage
Virtual storage is the name given to storing information remotely so that it can be accessed
by any computer with access to the same system, for example over the Internet. Examples
of virtual storage include cloud storage services like Google Drive and Microsoft OneDrive
as well as networked storage used in offices and schools.
As internet speeds increase, virtual storage is becoming a more popular method of storage
thanks to the convenience of files being available “in the cloud” on any device connected
to the Internet.
Virtual storage is often an abstraction of multiple drives acting like one. Information stored
in the cloud is actually stored on 100s of hard drives or SSDs formatted to act as a single
piece of storage.
While virtual storage is convenient to access and share, its disadvantages include
limitations of a user’s network speed and high costs.
