LASER HOLOGRAPHIC, STORAGE DEVICES

LASER HOLOGRAPHIC STORAGE

With recent advances in holography and laser beam technology, computer developers are studying optical memories with capacity greater than 100 megabits of data and random access time may be as short as one microsecond. Hologrammes make use of high-energy laser beam to store or display three dimensional images. The image produced by a hologram can easily be read by a photodetector, and information can be stored.

A holographic memory is made on a special recording medium similar to photographic film. Information is retrieved from the memory by projecting the data recorded on the hologram onto a light sensitive detector. The detector converts the optical information into electronic signals that computer can process.

STOREAGE DEVICES

Computer storage also referred as computer memory is actually an electronic file in which instructions and data are placed until needed. Computer storage is divided into two classes:

1. Main Storage or Main Memory
2. Secondary Storage or Secondary Memrory

MEMORY UNITS

The capacity of a storage device is expressed as number of byties, characters or bits. One byte is a group of eight bits that one character. Thus if the memory of a computer is 32000 bytes, it means that it can store 32000 characters.

BITS AND BYTES

The basic unit of a digital computer is a bit, which stands for binary digit. A bit is binary number and has value1 or 0 representing ON or OFF state. In microprocessor, bits are grouped into set of eight, called a byte, a four-bit sequence is called a nibble. The memory of a computer can be thought of cells. Each of these cells contains one bit of information. Each cell will have either 0 or 1 state. The combination of eight such cells forms one byte. Each byte contains one character sucl, as A, B,......etc. A group of bits representing data or instruction that form the basic information unit of the computer is called a "word". A word may have a length of 8 bits, 16 bits, 32 bits or more. Thus a word of 16 bits size can be called as 2-byte word. Generally computers that handle larger words are considered to be more powerful than the computer that use smaller word sizes because greater amount of information can be processed in a single cycle. The storing capacity of a computer is measured in bytes. The basic unit of information in digital computers is a bit, which stands for binary digit. A bit is binary number and has value1 or 0 representing ON or OFF state.

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