Concept of Bit,Byte,Word and Nibble:
Storage Capacity is the amount of data that can be stored in the storage unit. The storage capacity can be expressed in terms of Bytes. Storage units are
(a) Bit (Binary Digit):
A binary digit is logical 0 or 1 representing a passive or an active state of a component in an electric circuit.
(b) Nibble:
A group of four bits is called nibble.
(c) Byte:
A group of 8 bits is called byte. A byte is the smallest unit which can represent a data item or a character.
(d) Computer word (or word):
A computer word like a byte, is a group of fixed number of bits processed as a unit which varies from computer to computer but is fixed for each computer.
The length of a computer word is called word-size or word length and be as small as 8 bits or may be as long as 96 bits. (i.e. 8. 16.32.64.96 A computer stores the information in the from of computer words.
•Measuring Unit of Storage Capacity
The storage capacity can be expressed in terms of Bytes. Measuring unit of storage capacity are:
(i) Kilobyte (KB)
1KB = 1024 Bytes
(ii) Megabyte (MB)
1 MB = 1024 KB
(iii) Giga Byte (GB)
1 GB 1024 MB
(iv) Tera Byte (TB)
1 TB 1024 GB
(v) Peta Byte (PB)
1 PB=1024 TB
• Performance Parameters of Computer Memory
There are three performance parameters.
(a) Access Time:
Access time is defined as time required to locate and retrieve a record.
(b) Memory-Cycle Time:
Memory-Cycle Time is defined as time passed between initiation of two successive memory operations. (e.g. two read operations) Hence, Memory-Cycle time consists of the access time plus any additional time required before a second access can start.
(c) Access Rate:
Access Rate is defined as number of Read/Write operations carried out per second.
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