:hash bucket: /n./ A notional receptacle, a set of which might be used to apportion data items for sorting or lookup purposes. When you look up a name in the phone book (for example), you typically hash it by extracting its first letter; the hash buckets are the alphabetically ordered letter sections. This term is used as techspeak with respect to code that uses actual hash functions; in jargon, it is used for human associative memory as well. Thus, two things `in the same hash bucket' are more difficult to discriminate, and may be confused. "If you hash English words only by length, you get too many common grammar words in the first couple of hash buckets." Compare {hash collision}.
:hash collision: /n./ [from the techspeak] (var. `hash clash') When used of people, signifies a confusion in associative memory or imagination, especially a persistent one (see {thinko}). True story: One of us [ESR] was once on the phone with a friend about to move out to Berkeley. When asked what he expected Berkeley to be like, the friend replied: "Well, I have this mental picture of naked women throwing Molotov cocktails, but I think that's just a collision in my hash tables." Compare {hash bucket}.
:hat: /n./ Common (spoken) name for the circumflex (`^', ASCII 1011110) character. See {ASCII} for other synonyms.
:HCF: /H-C-F/ /n./ Mnemonic for `Halt and Catch Fire', any of several undocumented and semi-mythical machine instructions with destructive side-effects, supposedly included for test purposes on several well-known architectures going as far back as the IBM 360. The MC6800 microprocessor was the first for which an HCF opcode became widely known. This instruction caused the processor to {toggle} a subset of the bus lines as rapidly as it could; in some configurations this could actually cause lines to burn up.
:heads down: [Sun] /adj./ Concentrating, usually so heavily and for so long that everything outside the focus area is missed. See also {hack mode} and {larval stage}, although this mode is hardly confined to fledgling hackers.
:heartbeat: /n./ 1. The signal emitted by a Level 2 Ethernet transceiver at the end of every packet to show that the collision-detection circuit is still connected. 2. A periodic synchronization signal used by software or hardware, such as a bus clock or a periodic interrupt. 3. The `natural' oscillation frequency of a computer's clock crystal, before frequency division down to the machine's clock rate. 4. A signal emitted at regular intervals by software to demonstrate that it is still alive. Sometimes hardware is designed to reboot the machine if it stops hearing a heartbeat. See also {breath-of-life packet}.
:heatseeker: /n./ [IBM] A customer who can be relied upon to buy, without fail, the latest version of an existing product (not quite the same as a member of the {lunatic fringe}). A 1993 example of a heatseeker is someone who, owning a 286 PC and Windows 3.0, goes out and buys Windows 3.1 (which offers no worthwhile benefits unless you have a 386). If all customers were heatseekers, vast amounts of money could be made by just fixing the bugs in each release (n) and selling it to them as release (n+1).
:heavy metal: /n./ [Cambridge] Syn. {big iron}.
:heavy wizardry: /n./ Code or designs that trade on a particularly intimate knowledge or experience of a particular operating system or language or complex application interface. Distinguished from {deep magic}, which trades more on arcane *theoretical* knowledge. Writing device drivers is heavy wizardry; so is interfacing to {X} (sense 2) without a toolkit. Esp. found in source-code comments of the form "Heavy wizardry begins here". Compare {voodoo programming}.
:heavyweight: /adj./ High-overhead; {baroque}; code-intensive; featureful, but costly. Esp. used of communication protocols, language designs, and any sort of implementation in which maximum generality and/or ease of implementation has been pushed at the expense of mundane considerations such as speed, memory utilization, and startup time. {EMACS} is a heavyweight editor; {X} is an *extremely* heavyweight window system. This term isn't pejorative, but one hacker's heavyweight is another's {elephantine} and a third's {monstrosity}. Oppose `lightweight'. Usage: now borders on techspeak, especially in the compound `heavyweight process'.