# NON-INVERTING GATES

We started with NAND and NOR gates because they're easier to build than the logically more fundamental AND and OR gates.
A non-inverting gate can be made in the obvious way by putting an inverter after an inverting gate. If all you want is a single gate, you can't really do any better than that. However, you'll see later that when a number of gates are put together into a larger circuit, sometimes you can find a more efficient way of implementing the circuit as a whole.

## Alternative Logic Symbols

While we're on the subject of equivalent logic, it's worth noting that there are a variety of ways of drawing logic symbols for all the basic gates, depending on where we choose to put the inversion circles. Sometimes using these alternative forms can make a logic diagram clearer, particularly when so-called "active low" signals are involved.
An active-low signal is one that does something when it goes low rather than high. For example, if we had two conditions represented by active-low signals, and we wanted to produce an active-high signal when both of them are true, we might choose to use the AND symbol with inverted inputs, which is equivalent to a NOR gate (4th row). Similarly, the inverter symbol with the circle on the input is often used when the intention is to convert an active-low signal into an active-high one.