[popularized by Eugene Brooks c.1990] A microprocessor-based machine that infringes on mini, mainframe, or supercomputer performance turf. Often heard in “No one will survive the attack of the killer micros!”, the battle cry of the downsizers.
The popularity of the phrase ‘attack of the killer micros’ is doubtless reinforced by the title of the movie Attack Of The Killer Tomatoes (one of the canonical examples of so-bad-it's-wonderful among hackers). This has even more flavor now that killer micros have gone on the offensive not just individually (in workstations) but in hordes (within massively parallel computers).
[2002 update: Eugene Brooks was right. Since this term first entered the Jargon File in 1990, the minicomputer has effectively vanished, the mainframe sector is in deep and apparently terminal decline, and even the supercomputer business has contracted into a smaller niche. It's networked killer micros as far as the eye can see. —ESR]