Re: not gates
mabauti,
Functionally there is no difference. The two different symbols are used for clarity. For example, if the input is an active low signal, it is clearer to use the symbol on the left to indicate that when the input is active, a logic "1" will appear on the output. The same reasoning is used for alternate symbols for other gates. For example, the standard symbol for a NAND gate is an AND gate with a bubble on the output. An equivalent symbol is an OR gate with bubbles on the inputs. If the output is active high, then it makes sense to use the alternate symbol to indicate that the output is active when a "0" is applied to either input. On the other hand, if the ouptut is active low, then it makes sense to use the standard sysmbol to indicate that the output is active when a 1 is applied to all the inputs (input a AND input b AND input c ...). There are times when these rules do not apply, in which case, the standard symbol is usually used.
Regards,
Kral