strand3:IT systems


secondary storage
external image 200px-PersonalStorageDevices.agr.jpg

What is a secondary storage?
Secondary storage devices can be defined as devices which are newly created or made to replace the old and outdated ways of communication which existed before. We shall be looking at three main ways of secondary storage, they are;
A. Magnetic
B. Optical
C. Flash

A. Magnetic devices;

Magnetic devices and magnetic recording

Magnetic devices
This is the storage of data on a magnetized medium useing different patterns of magnetization in a magnetically material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads. As of 2009, magnetic storage media, primarily hard disks, are widely used to store computer data as well as audio and video signals. In the field of computing, the term magnetic storage is preferred and in the field of audio and video production, the term magnetic recording is more commonly used. The distinction is less technical and more a matter of preference. Other examples of magnetic storage media include floppy disks, magnetic recording tape, and magnetic stripes on credit cards.
. external image 200px-Reel-to-reel_recorder_tc-630.jpg
Figure 1.0
A reel-to-reel tape recorder (Sony TC-630). The magnetic tape is data storage medium. The recorder is data storage equipment using a portable medium (tape reel) to store the data.

b. Magnetic recording
Magnetic wire recording, and its successor, magnetic tape recording, involve the use of a magnetizable medium which moves with a constant speed past a recording head. An electrical signal, which is analogous to the sound that is to be recorded, is fed to the recording head, inducing a pattern of magnetization similar to the signal. A playback head can then pick up the changes in magnetic field from the tape and convert it into an electrical signal.

Optical devices;
Optical storage is a term referring to 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. A common modern technique used by computers involves a tiny 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 semi conductors.
a. Optical tape
Optical tape is a medium for optical storage generally consisting of a long and narrow strip of plastic on to which patterns can be written and from which the patterns can be read back. It shares some technologies with cinema film stock and optical disc, but is compatible with neither. In the 1990s, it was projected that optical tape would be a commonly used, high-capacity, high-speed computer data storage format. At least one working system and several prototypes were developed, but as of 2007, none of these technologies is widely used. The main similarity between the a magnetic and optical device is the magnetic-optical drive
external image 250px-35mm_film_audio_macro.jpg

The picture above shows a cinema film stock showing two digital audio formats (Blue: SDDS, Grey: DD) plus the traditional analogy audio tracks. While not strictly an optical tape format, it is very similar.
magneto-optical drive

Digital recording

Magneto-optical drive is a kind of optical disc drive capable of writing and rewriting data upon a magneto-optical disc. Although optical, they appear as hard disc drive to the operating system and do not require a special files system (they can be formatted as FAT, HPFS, NTFS, etc.). Magneto optical drives are common in some countries such as Japan but have fallen into disuse in other countries like the United States.

Flash devices;

Flash memory is a non-volatile computer storage that can be electrically erased and reprogrammed. It is a technology that is primarily used in memory cards and USB flash drives for general storage and transfer of data between computers and other digital products. It is a specific type of EEPROM (Electrically Erasable Programmable Read-Only Memory) that is erased and programmed in large blocks; in early flash the entire chip had to be erased at once. Flash memory costs far less than byte-programmable EEPROM and therefore has become the dominant technology wherever a significant amount of non-volatile, solid state storage is needed. Example applications include PDAs (personal digital assistants), laptop computers, digital audio players, digital cameras and mobile phones. It has also gained popularity in console video game hardware; where it is often used instead of EEPROMs or battery-powered static RAM (SRAM) for game saves data.
Since flash memory is non-volatile, no power is needed to maintain the information stored in the chip. In addition, flash memory offers fast read access times (although not as fast as volatile DRAM memory used for main memory in PCs) and better kinetic shock resistance than HARDDISK. These characteristics explain the popularity of flash memory in portable devices.

external image sdp_adata_flash_drive.jpgexternal image figure1.gif
external image iriver.jpg
Flash memory as a replacement for hard drives
An obvious extension of flash memory would be as a replacement for hard disks. Flash memory does not have the mechanical limitations and latencies of hard drives, so the idea of a solid-state drive, or SSD, is attractive when considering speed, noise, power consumption, and reliability. There is also some concern that the finite number of erase/write cycles of flash memory would render flash memory unable to support an operating system. This seems to be a decreasing issue as warranties on flash-based SSDs is approaching those of current hard drives.
Rather than entirely replacing the hard drive, hybrid techniques such as hybrid drive and Ready Boost attempt to combine the advantages of both technologies, using flash as a high-speed cache for files on the disk that are often referenced, but rarely modified, such as application and operating system executable files. Also, Adonis has a PCI adapter for 4 CF cards, creating a RAID-able array of solid-state storage that is much cheaper than the hardwired-chips PCI card kind.

XD-Picture Card

XD-Picture Card is a type of flash memory card, used mainly in digital cameras. XD originally stood for Extreme Digital. The cards were developed by Olympus and Fujifilm, and introduced into the market in July 2002. Toshiba Corporation and Samsung Electronics manufacture the cards for Olympus and Fujifilm. XD cards are now sold under other brands, including Kodak, SanDisk, PNY, and Laxer, but are not branded with the respective companies' logos, except for Kodak.
XD cards are used in Olympus and Fujifilm digital cameras and Olympus digital voice recorders; Fujifilm also made an MP3 player (xD-MP3) that used the cards. As of 2008, XD cards are available in capacities of 16 MB up to 2 GB.