Secondary Storage

Secondary storage is non-volatile, usually has large capacities and is relatively slower than primary storage.  The most notable secondary storage device is the hard disk drive.  It includes CDs, DVDs, BDs etc. 

Memory Cards

Memory for use in mobile devices that makes use of flash memory technology.  Most frequently used in cameras / PDA’s, etc. There are many different standards (the cards have different physical sizes and connections) including, amongst others, Compact Flash, Secure Digital, Multi-Media card, Memory stick, etc.

See http://www.wisegeek.com/what-is-a-flash-card.htm

Flash Memory

Flash memory is a type of EEPROM (electronically erasable programmable ROM). Used in memory cards, USB memory-sticks, music players, cell phones and solid-state drives. Unlike older versions of flash memory, small parts can be erased instead of having to clear the entire chip first.

Optical Media

Optical media are storage media that hold content in digital form and that are written and read by a laser; these media include CDs, DVDs and Blu-ray disks.

CD

The Compact Disc (also known as a CD) is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage (CD-ROM), write-once audio and data storage (CD-R), rewritable media (CD-RW), Video Compact Discs (VCD), Super Video Compact Discs (SVCD), PhotoCD, PictureCD, CD-i, and Enhanced CD. Audio CDs and audio CD players have been commercially available since October 1982.  A CD held up to 700MB of data.

DVD

Digital Versatile Disc or Digital Video Disc is a type of optical disk technology similar to the CD-ROM. A DVD holds a minimum of 4.7GB of data. DVDs are commonly used to store large files such as movies and sound files which require a large amount of storage space.   A DVD+R (Recordable) can only record data once and then the data becomes permanent on the disc.

DVD-RW (Re-Writable) can be erased and recorded over numerous times without damaging the medium.

Blu-ray

Blu-ray disks can hold up to 25GB of data per layer with the largest capacity multilayer disks holding about 128GB. The name Blu-ray Disc refers to the blue laser used to read the disc, which allows information to be stored at a greater density than is possible with the longer-wavelength red laser used for DVDs. Unfortunately this is still a very expensive technology.