Secondary Storage Devices W. Overton

Hard Drive Information: Data is stored by magnetising the surface of flat, circular plates called platters. These rotate at very high speed and a read/write head moves from side to side to load and save data. The drive is inside a sealed unit because even a speck of dust could cause the heads to crash. Data is stored on the disc in blocks arranged in tracks and sectors. These are created when the hard disc is first formatted and this must take place before the disc can be used. For a drive to read data from a disc, the read/write head must move in or out to align with the correct track (the time to do this is called the seek time). It must wait then until the correct sector rotates round until it underneath the the read/write head. Applications: The hard drive is usually the main backing storage media for a typical computer or server. It is used to store: –The operating system (e.g. Microsoft® Windows) –Applications software (e.g. word-processor, database, spreadsheet, etc.) –Files such as documents, music, video etc. A normal home/school microcomputer would have a hard drive with a capacity of over 300 gigabytes. Advantages: Very fast access to data. Data can be read directly from any part of the hard disc (random access). The access speed is over 1000 KB per second. Disadvantages: Non really! It can however be a real disaster when they eventually fail because few home users have the data on their home computer hard drive backed up.

Magnetic Tape Information: Just like the tape in a tape-recorder, the data is written to or read from the tape as it passes the magnetic heads. It is necessary to start at the beginning of the tape and search for the data as the tape goes past the heads (serial access). Typical applications: Magnetic tapes are often used to make a copy of hard discs for back-up reasons. This is automatically done overnight on the KLB network and the tapes are kept in a safe place away from the server. Advantages: Magnetic tape is relatively cheap and tape cassettes can store very large quantities of data (typically 26 GB). Disadvantages: Accessing data is very slow because of the serial access because you cannot go directly to an item of data on the tape as you can with a disc.

CD-ROM Information: CD-ROM - means Compact Disc - Read Only Memory. This means you can only read from the media, not write or store data onto it. Like a floppy disc, a CD-ROM is removable media and it only starts spinning when requested so has to spin up to the correct speed each time it is accessed. It is much faster to access than a floppy but it is a lot slower than a hard disc. Typical applications: Most software programs are now sold on CD-Rom. Advantages: CD-ROM's hold large quantities of data (650 MB) and CD drives are common in all modern PCs. They are relatively tough as long as the surface does not get too scratched. Disadvantages: You cannot save files to a CD-Rom (although CD-R and CD- RW discs now exist which can be written to)

CD-R / CD-RW Description: CD-R:A blank compact disk which can be recorded only once. CD-RW: a blank compact disc that can be recorded, erased, and rerecorded many times. Typical Applications: Advantages: you can erase the disc, the info will always be there, it can be used over and over again which is good for updating files. Disadvantages: When you burn the disc the read speed is slower than a non- rewriteable disc. Cd-rw is less reliable

DVD-R / DVD-RW / Dual Layer DVD Description: DVD-R: a DVD which can be recorded on once only. DVD-RW: a DVD on which recordings can be made and erased a number of times. Dual layer DVD: Discs employ two recordable dye layers, each capable of storing nearly the 4.7 GB capacity of a single-layer disc, almost doubling the total disc capacity to 8.5 GB Typical Applications: Advantages: most compatible format and can be read by practically all DVD players. They can be read by DVD drives in computers, portable DVDs and home DVD players. They cost a little less than DVD+R, and are significantly cheaper than RW DVDs. Disadvantages: The major drawback to DVD-Rs is that they can only be written to once. Most people prefer to put routine system backups and temporary files onto a rewritable disc, which can be rewritten up to about 1,000 times.

Blu-ray Description: is a digital optical disc data storage format designed to supersede the DVD format. Typical Applications: To watch films, Blu-ray player. Advantages: Blu-Ray discs hold up to 50 GB of data, which is 5 times more than DVDs. They only work on HDTVs and they have special abilities that DVDs can never have. They are much more resistant to scratches due to a hard-layer coating and are even harder to break than a DVD. Disadvantages: The only disadvantage is that it can take a while for the disc to fully load.

Flash Memory/USB Storage Description: is a data storage device that includes flash memory with an integrated Universal Serial Bus (USB) interface. USB flash drives are typically removable and rewritable, and physically much smaller than an optical disc. Typical Applications: Store memory and carry it any where. Advantages: Data stored on flash drives is impervious to mechanical shock, magnetic fields, scratches and dust. These properties make them suitable for transporting data from place to place and keeping the data readily at hand. Disadvantages: Like all flash memory devices, flash drives can sustain only a limited number of write and erase cycles before the drive fails. This should be a consideration when using a flash drive to run application software or an operating system.

SSD (Solid State) Disk Description: These hard drives are faster, more reliable and much more efficient than normal hard drives (HDD). Very reliable and durable SSD hard drives are able to withstand knocks and shocks which makes them ideal for using in laptops. Typical Applications: Advantages: The speed of a Solid State Hard disk is not constrained by its parts, because there are no moving parts to a Solid State Drive. Solid State Disk Drive can start up over 25 times faster than the standard hard drive. Disadvantages: The Solid State Disk price per gigabyte is much higher than hard drives, so an upgrade to the same GB capacity can incur some considerable costs.

Network Storage Description :You can connect multiple PCs and servers into a local area network (LAN) or a wide area network (WAN). Typical Applications: Advantages: People can find and share information and data because of networking. This is beneficial for large organizations to maintain their data in an organized manner and facilitate access for desired people. Disadvantages: Security threats are always problems with large networks. There are hackers who are trying to steal valuable data of large companies for their own benefit. So it is necessary to take utmost care to facilitate the required security measures.

On-Line Storage Description: Online Storage is a browser-based application that allows you to store and access your important files, safely and securely online Typical Applications: Advantages: By storing your data online you are reducing the burden of your hard disk, which means you are eventually saving disk space. This is the main advantage of online data storage. You can access your data anywhere in the world. You don’t have to carry your hard disk, pen drive or any other storage device. Disadvantages: None of the thing in this world doesn’t have disadvantage. There are few disadvantages there while using online data storage but if you handle things with care then you can surely avoid them. Some of them are as follows.