designdigital-logic
In my career I've often encountered signals that are active low (Reset being the most common). I've even seen interfaces where all control signals are actively low.
To me, this is very unintuitive and confusing.
Why is there ever a need to use actively low?
Is it merely historic or is there actual gate count / power concerns that explains it?
Look at what happens during power-up: Vcc rises to a point where it's high enough to make everything work properly. However, that point isn't clearly defined and may vary from device to device. It makes sense not to use this voltage to reset the controller.
It's easy, however, to keep a level low regardless of Vcc. After all, Reset is already active the instant you switch power on, since at that moment everything is at a low level.
edit
The graph below illustrates how the output voltage of the reset controller (i.c. an MC34064) remains low until Vcc is high enough to have the complete microcontroller stable.
Essentially, either works; A is probably better, B is more flexible.
A will drive the reset line to '1' faster, which could be an issue on a very large board.
B allows the option of adding other means of driving reset - hidden switch + paperclip, brownout monitor, watchdog timer, etc. It probably doesn't even cost the board space for a resistor, because a lot of microcontrollers have software configurable pullup resistors on each pin.
Best Answer
In historical digital designs, active low signals would be used whenever their use would allow reducing the number of gates in a design, and thus reduce the cost of the circuit. I can imagine it was even more common in IC designs than in discrete logic, because all logic was essentially built from inverting (NAND) gates, but I'm not personally experienced in that area.
That level of optimization is rarely needed today, or at least it's done automatically by synthesis tools so that it's transparent to the designer. Like you noticed, there's only a few cases where active low signals are still very commonly seen.
One advantage of an active low signal for functions like reset and interrupts, is it's very easy to create "wired OR" logic for an active low signal simply by using open collector outputs.
That is, if there's several different circuits that need to be able cause a reset or an interrupt, each of them can simply have an open-collector output tied to the ~RESET or ~INT wire. Then, any one of them can pull the line low and cause the appropriate response without the need for any additional logic to combine the signals.