Data Processing Systems includes how information is stored as well as how information is retrieved from those secondary storage units. All of these secondary storage devices are all types of a archives. Archives is to copy files to a long term storage medium for backup. Ususally two layers of backup: A disk drive and periodically files are stored on a disk, or secondary storage device.

This is a list of the physical storage devices you can use!

1. Magnetic Tapes - Cartriges, Tapes
2. Magnetic Disk - Flexible & Hard disks
3. Optical Disks - Compact Disks, Video disks
4. Microfiche
5. On line vs. batch processing

Magnetic Tapes

There are two types of Magnetic Tapes one is reels and the other is cartriges. This medium is a flexible mylar tape coated with magnetic oxide. They both require a tape drive, which is also called a sequential access device, to be able to access these two types of storage devices. They are able to store a tremendous amount of data and they are rather inexpensive. The disadvantages of the magnetic tapes is that it reads sequentially which means that it must look at each file that proceeds the file that you are looking for. By using sequentially access the retrieval time is much slower. Magnetic tapes are usually used for backing up files but the cartriges are much faster than the reals. For more information check out Magnetic Tapes.

Magnetic Disks

Magnetic Disks are commonly called Floppy disks, or hard disks. The hard disks size is 3.5" and it is now capable of being removed, but the floppy disks size is 5.25". Magnetic disks are used for storing large amounts of data data. Disks have a circular plate mounted on a central spindle and coated in a magnetic material. They use a direct access which means that they don't have to read all the proceeding files all it has to do is find the file by using an index. They have a read/write head in order to transfer data. The capacity of the disk is the number off bytes it can store. Some magnetic disks come in air tight packaging with more than one disk contained in the package at a time. The disks have magnetic zones which are aligned with the head which then writes data by altering the alignment. Information is retrieved by detecting the current pulses induced in a coil as the zones with different magnetic alignment pass under it. Data may be stored on either or both surfaces of the disks in concentric rings. The data is written and read by disk drives by rotating the disks and positioning them over the desired tracks.

A Floppy disk is made from a thin sheet of plastic, very inexpensive and very portable. Hard disks are made from rigid platters of aluminum, they are faster and they hold more information than floppies. The advantages of the Magnetic Disks is that they are easy to use, direct access, and they are compact. Some disadvantages of Magnetic tapes is that if they are set by any other electronical device the disks will be totally erased, and volnerable to power surges.

A Magnetic Disk is like a phonograph record except that the data is encoded as microscopic magnetized needles on to the disk's surface rather than as grooves in the vinyl. Also you are capable of recording and erasing many times. For more information check out Magnetic Tapes.

Optical Disk

Optical disks use laser technology to store information by burning holes into the recording surface. To read the disk, another laser shines on the disk and detects the holes by changes in the reflection pattern. A disk drive spins the disk and a read/write head actually reads and writes the data. One kind of an Optical disk is the Compact disk. The CD is what is considered to be a WORM, which means write once and read many. This means that it can only be written once but you can read it many times but you can never resave anything on it again. The Compact Disk can hold as much information as can 70 diskettes (maxiumum capacity is 600 megabytes) and the compact disk is less suseptible to data loss or disk crashes due to energy surges. The disadvantages of the Compact Disk is that they are more costley and they do have slower access time than do magnetic disks. If you want more information check Compact Discs.

Another type of Optical disk is the Video disk. The Video disk stores audio, video, and textual information. The information can be viewed as one frame at a time or it can be seen in motion like a movie. This is most often used by people in marketing and in advertising.

Microfiche

Microfiche is a miniature copies of documents or images. Microfiche is a 4 inch by 6 inch transparent plastic which can store 270 pages each, this is at 48 times reduction. These methods are frequently employed by libraries to store back issues of publications like reports, periodicals, newspapers, and journals. The images are retrieved by using a specialized machine called a microfiche reader/printer. The computer generated titles and indexes allow for the fast retrieval from the microfiche on to the readers/printers. The advantages of Microfiche is that there is a cost benefit, independent technology, and easy to implament. Microfish seems to be very old but it will never really be out dated because you will always beable to read old information with it. If you want some more information check Microfiche.

Batch Processing vs. On-line Processing

Batch Processing you begin with capturing your information on a well designed source document. Then you combine the documents into groups and generate control totals. Now enter that into the system and perform a edit check. Now save the input and reconcile the input to control totals before beinning processing. For example, the preparation of monthly customer bills by a utility company. This is batch processing because they don't need this immediatley they only have to be ready when it is time to send the bill to the customer so they have a whole month to prepare them.

On-line Batch is when you just enter the data into the sytem. You need a well designed input scrren rather than the source documents. Next the system will perform edit checks and then save the input. Then you process the input from the storage device.

On-line Real Time you enter data into the system using a well designed input screen just like On-line Batch. Then the system performs the edit check and then you continue with the processign once input phase is complete. On-line Real Time updates information immediatley. For example, hotels use this processing device because it updates reservations and cancellations immediatley so they know what rooms are taken and which one's are vacant.