Secondary Storage Methods

Storage Medium	Capacity	Information
CD	700MB	A disk format that works by using a laser to read and write data on/to   disks.  A CD can be a CD-ROM (read-only), CD-R (write once only) or CD-RW (rewritable).  Although data can be copied off of a CD-ROM it cannot have data written to it, and as such is described as ROM because it is read-only memory.  A CD-R can be written to by a CD writer, using a laser to change some of the 0s to 1s, though this process can only be done once because of the nature the disk.  On the other hand a CD-RW can be wiped an infinite amount of times by using a laser to set all binary digits to 0, then by writing in the same fashion to a CD-R.   CD-ROMs have been used for many years for distributing software and music, whilst CD-Rs and CD-RWs may be used for backups or archiving data.
DVD	4.7 GB (single layer) 9.4 GB (dual layer)	A similar technology to CDs although much more can be stored.  As such they can also be DVD-ROM, DVD-R or DVD-RW, and the writable and rewritable forms are written in the same manner as CD-Rs and CD-RWs.   This disk format in the ROM form is most commonly used now for non-HD films and software for both computers and games consoles, whilst the R and RW forms are also used for backups and archiving.
HD-DVD	15 GB (one layer) 30 GB (two layers)	A now abandoned format that once competed with Blu-Ray, and was a type of DVD that could store much more data.  They are too suitable for storing HD film though can store less of it.
Blu-Ray	25 GB (one layer) 50 GB (two layers)	A superior disc format that can store large quantities of data.  They can store 6x the amount that a conventional DVD can store, and like HD-DVD are read by a blue laser.  This is because it is higher frequency than the red laser found in CD and DVD drives.  Nowadays these are the universal format for watching HD films, and are also used as a storage medium for PS3 games.
Hard Drive Disk	Up to 2TB	The hard drive disk is the ultimate form of storage.  It is a physical medium that is used to store very large amounts of data, and may store a variety of things such as programs, games, documents and much more.    Hard drives contain a magnetic disk and a reading head, which acquires the data needed in a particular order, reading this data from sectors which are in tracks that are the concentric circles around the disk.  As the disk rotates the head also moves to read sectors off of different tracks and to not read any sectors which aren’t the right ones.  The head switches to the required track, waits until the required sector is reached, reads the data and moves onto to the next required sector in the same fashion.  It does this in order until all the required data is read.  A fragmented file may be stored in up to six different sectors.
Magnetic Tape	Up to 800GB	Magnetic tapes contain a magnetic ribbon-like tape that can store binary digits that is also read by a head.  This means that data can be stored, although every time a different piece of data needs to be accessed the tape has to be wound to the right place which is time consuming.  These tapes are often used for archiving and backing up files.
Floppy Disk	Up to 1.4MB	Floppy disks are a now defunct format which was once used to transfer small files and act as boot-up disks for when a computer is first used.  Each one contained a magnetic disk which was read by a head in the computer’s disk drive.  As such they worked in a way similar to the way that hard drives work.
USB Flash	64 GB and it is only a matter of time before it is more….	Both USB flash sticks and memory cards are flash memory storage mediums.  Whilst USB sticks are connected to USB ports on a computer, memory cards are plugged into unique slots.  Memory cards may also be used in small devices such as mobile phones or digital cameras.  Flash memory refers to a rewritable chip which is considered to be non-volatile, due to the way that it does not need to be powered to retain data.  Because of their portability and ever-growing capacity these devices are now often used instead of floppy disks for the purpose of file transfer.
Memory Card