Hallo Diane,

in the early days of digital electronics 'wired-and' circuitry was widely used. If you have a look at classical 7400-series, you will see that many devices are fabricated with two different output options: Totem-pole or open-collector. E.g. 7400 has totem-pole outputs, while 7401 has open-collector outputs, but both consist of quadruple 2-input positive-nand gates.
If you connect several open-collector outputs together, and from this point a pull-up resistor to Vcc, then this arrangement works like a 'wired-and' gate, means, connection point has high level only when all open-collector outputs are turned-off, representing high level. Only one open-collector output turned-on, representing low level, gives low level at connection point.
By this methode 'and' gating can be implemented without the use of any additional circuitry. In early days of digital electronics the saving of additional circuitry by the help of this 'wired-and' scheme was widely used. But 'wired-and' circuitry has an important disadvantage: In order to avoid too much current through turned-on output transistor pull-up resistor must be rather high. So, something much bigger than 100 Ohm was often used. As impedance of turned-on transistor is much smaller than this pull-up (about 30 Ohm), source impedance of 'wired-and' circuitry is very different for low level output and high level output. This has important consequences on noise immunity and rise-time of signal: If output impedance (source impedance) is low, then coupling of noise into output via stray capacitance is decreased. Also, output signal change is faster, because any load capacitance is faster charged or discharged. So, if 'wired-and' circuitry switches from low to high, load capacitance must be charged by rather high pull-up resistor, resulting in increased rise-time and increased susceptibility to load capacitance variations. Also noise can easier coupled into signal via stray capacitance. If, on the other hand 'wired-and' circuitry switches from high to low, then load capacitance is discharged very fast, susceptibility of slew rate to load capacitance variations is drastically decreased and noise coupling into signal via stray capacitance is also drastically decreased.

So, when you use 'wired-and' circuitry negativ logic is highly advantegous.

Now, you might ask, why there is open-collector output used and not open-emitter. Well, this has to do with realization of nand-gate by the help of transistor circuitry (TTL).

Bye,
Kai