Storage devices and media

What is backing up of data? It’s the copying of files/data to a different medium (disk, tape, flash drive, etc) in case of a problem with the main secondary storage device. Backups are often stored in a different place to the main storage.

Reasons why backups are made? To safeguard against loss of data due to the failure of the original secondary storage device, hardware failure or possible corruption of files To safeguard against damage caused by hackers In case the files need to be used elsewhere Don’t necessary guard against the effect of a virus

Types of access Serial access Field: a single piece of info Record :one complete set of fields File: a collection of records Where data records are stored one after the other with no regard to the order; are read by starting at the beginning and reading through every record until you find the one that you want. When the original magnetic tape(master file) needs updating, an additional tape(transaction file) is required. The transaction file contains all the new data to allow the master file to be updated.

Direct access Is used with magnetic disks, optical media and solid state media. The computer uses the key field to calculate where data should be stored. It is then able to access the data directly from the calculated position. Faster than serial access.

Secondary storage media All systems have come equipped with some form of secondary storage. Ensure that data is stored permanently so that it can be used again later on. Storage/file sizes are measured in kilobytes, megabytes, gigabytes and terabytes.

Magnetic storage media

Magnetic storage media Depend on the magnetic properties of certain materials. Magnetic materials is coated on the surface of a disk or tape Many hard disk drive are made up of more than one disk and these disks are known as platters. Each platter is made from glass, ceramic or aluminium coated in a nickel alloy that can be magnetised

Fixed/internal hard disk drive (HDD) The main method used for data storage Uses: to store the operating system, systems software and working data; storing applications software that needs fast retrieval and storage of data Advantages: fast data transfer rate, fast access times to data Disadvantages: can be easily damaged, many moving parts when compared to solid state drives, can be quite noisy

Portable hard disk drives Work in much the same as fixed hard disk drive but are usually connected to computers via the USB port; can be disconnected and used on different computers Uses: used as backup systems to prevent loss of data, to transfer data/files/software between computers Advantages: fast data access time and data transfer rate, large memory capacity, used as method of transferring info between computers Disadvantages: can be easily damaged if dropped or subjected to a strong magnetic field

Magnetic tapes Uses: in applications where batch processing is used, backup media since all the data needs to be stored, used in long-term archiving of data Advantages: less expensive than hard disk, huge data, data transfer rate is fast Disadvantages: slow data access time, when updating another tape is needed to store the final updated version, are affected by magnetic fields.

Optical storage media

CD/DVD disks Laser light is used to red data and to write data on the disk’s surface. Uses a thin layer of metal alloy or light-sensitive organic dye to store data Data is stored in pits and bumps on the spiral track Can be designed as: -R: write once only -ROM: can only be read -RW: can be written/read from many times

CD-ROM and DVD-ROM Are ROM Data is stored as a series of pits and lands in the metallic optical layer Uses: store music files, software, games and reference software Advantages: hold far more data than floppy disks, less expensive than hard disk drive Disadvantages: data transfer rate and data access time is slower than hard disks

CD-R and DVD-R The letter R means the disk is recordable once only. A thin layer of an organic dye is used as the recording media Uses: home recording music and films, store data to be kept for later use or to be transferred to computers Advantages: cheaper than RW disks, once burned and finalized they are like a ROM Disadvantages: Not all CD/DVD players can read it, if finalized, it can only be recorded on once

CD-RW and DVD-RW RW means these disks are a rewritable media and can be written over several times. They don’t become ROM’s Uses: record television shows, not as wasteful as R format as more data can be added, used in CCTV systems Advantages: can be written over times, can use different file formats each time it’s used Disadvantages: can be expensive, possible to accidentally overwrite data

DVD-RAM Allow numerous read and write operations Can be read from and written to many times Uses: recording devices such as satellite receivers to allow simultaneous recording and playback Advantages: long life, possible to rewrite operation over 100000 times, fast access, large capacity Disadvantages: many systems won’t recognise it, expensive, have been superseded by newer technologies

Blu-ray discs Uses: home video consoles, storing and playing back movies, PCs can use it for data storage or backing up hard drives Advantages: large storage capacity, fast data transfer rate, fast data access speed Disadvantages: expensive, encryption problems

The future of optical media Many computer systems now come with USB connectors only and no CD/DVD drives The main method of transferring files has become flash memory Many people now store their music in: -hard disk drive systems -in MP3 format on: computers, tablets, phone, portable music player -using the cloud so they can access from anywhere -by streaming their music from internet

Solid State Storage Media

Solid state drives (SSD) SSDs are rapidly taking over HDDs Have no moving parts and all data is retrieved at the same rate no matter where it is stored The most common type of SSD devices store data by controlling the movement of electrons within NAND chips Advantages: light, lower power consumption, thin because of no moving parts, fast data access

Memory stick/pen drives Can store several gigabytes of data Usually connected to a computer through USB port Power to operate them is drawn from the host computer Uses: transporting files between computers, backup store, used as a security device to prevent software piracy Advantages: small, portable, doesn’t need additional software to work, not affected by magnetic fields Disadvantages: can’t write-protect data/files, easy to lose

Flash memory cards Uses: store photos on digital cameras, mobile phone memory cards, used in MP3 players, backup store in hand-held computer devices Advantages: compact, easy to remove and used in another device, robust Disadvantages: expensive, have a finite life regarding the number of times they can be read from or write to, lower storage capacity than hard disks