The Word
A word is a group of 16 bits. But traditionally the boundary for a Word is defined as either 16-bits or the size of the data bus for the processor and a Double Word is Two Words. Therefore a Word and a Double Word is not a fixed size but varies from system to system depending on the processor. However for conceptual reading, we will define a word as two bytes.
When we see a word on bit level, it will be numbered as the bits in a word starting from bit zero (b0) through fifteen (b15). The bit level representation will be as follows:
b15 |
b14 |
b13 |
b12 |
b11 |
b10 |
b9 |
b8 |
b7 |
b6 |
b5 |
b4 |
b3 |
b2 |
b1 |
b0 |
Where bit 0 is the LSB (Least Significant Bit) and bit 15 is the MSB (Most Significant Bit). When there is need to refer the other bits in a word, their bit position number is used to refer them.
In this way a word contains exactly two bytes such that from Bit b0 to Bit b7 form the low order byte and bits b8 through b15 form the high order byte. With a word of 16-bits, we can represent 216 (65536) different values. These values may be of following:
- The unsigned numeric values in the range of 0 to 65,535.
- The Signed numeric values in the range of -32,768 to +32,767
- Any data type with no more than 65,536 values. In this way words are mostly used for:
- 16-bit integer data values
- 16-bit memory addresses
- Any number system requiring 16 bits or less
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