hot spot

n.

1. [primarily used by C/Unix programmers, but spreading] It is received wisdom that in most programs, less than 10% of the code eats 90% of the execution time; if one were to graph instruction visits versus code addresses, one would typically see a few huge spikes amidst a lot of low-level noise. Such spikes are called hot spots and are good candidates for heavy optimization or hand-hacking. The term is especially used of tight loops and recursions in the code’s central algorithm, as opposed to (say) initial set-up costs or large but infrequent I/O operations. See tune, hand-hacking.

2. The active location of a cursor on a bit-map display. “Put the mouse’s hot spot on the ‘ON’ widget and click the left button.”

3. A screen region that is sensitive to mouse gestures, which trigger some action. World Wide Web pages now provide the canonical examples; WWW browsers present hypertext links as hot spots which, when clicked on, point the browser at another document (these are specifically called hotlinks).

4. In a massively parallel computer with shared memory, the one location that all 10,000 processors are trying to read or write at once (perhaps because they are all doing a busy-wait on the same lock).

5. More generally, any place in a hardware design that turns into a performance bottleneck due to resource contention.