Optical Storage Devices and Flash Memory

Optical storage is the storage of data on an optically readable medium. Data is recorded by making marks in a pattern that can be read back with the aid of light, usually a beam of laser light precisely focused on a spinning disc. An older example, that does not require the use of computers, is microform. There are other means of optically storing data and new methods are in development. Optical storage differs from other data storage techniques that make use of other technologies such as magnetism or semiconductors.Optical storage can range from a single drive reading a single CD-ROM to multiple drives reading multiple discs such as an optical jukebox. Single CDs (compact discs) can hold around 700MB (megabytes) and optical jukeboxes can hold much more.An optical drive is a device in a computer that can read CD-ROMs or other optical discs.It is estimated that in the year 2007, optical storage represents 27% of the world's technological capacity to store information.

Flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed.Introduced by Toshiba in 1984, flash memory was developed from EEPROM (electrically erasable programmable read-only memory). There are two main types of flash memory, which are named after the NAND and NOR logic gates. The internal characteristics of the individual flash memory cells exhibit characteristics similar to those of the corresponding gates.Whereas EPROMs had to be completely erased before being rewritten, NAND type flash memory may be written and read in blocks (or pages) which are generally much smaller than the entire device. NOR type flash allows a single machine word (byte) to be written—​to an erased location—​or read independently.The NAND type is primarily used in main memory, memory cards, USB flash drives, solid-state drives, and similar products, for general storage and transfer of data. NAND or NOR flash memory is also often used to store configuration data in numerous digital products, a task previously made possible by EEPROM or battery-powered static RAM. One significant disadvantage of flash memory is the finite amount of read/write cycles in a specific block.