The New Hacker's Dictionary

141

much." Compare [1349]weenie, [1350]Amiga Persecution Complex.

---

Node:bit, Next:[1351]bit bang, Previous:[1352]bigot, Up:[1353]= B =

bit n.

[from the mainstream meaning and `Binary digIT'] 1. [techspeak] The unit of information; the amount of information obtained by asking a yes-or-no question for which the two outcomes are equally probable. 2. [techspeak] A computational quantity that can take on one of two values, such as true and false or 0 and 1. 3. A mental flag: a reminder that something should be done eventually. "I have a bit set for you." (I haven't seen you for a while, and I'm supposed to tell or ask you something.) 4. More generally, a (possibly incorrect) mental state of belief. "I have a bit set that says that you were the last guy to hack on EMACS." (Meaning "I think you were the last guy to hack on EMACS, and what I am about to say is predicated on this, so please stop me if this isn't true.")

"I just need one bit from you" is a polite way of indicating that you intend only a short interruption for a question that can presumably be answered yes or no.

A bit is said to be `set' if its value is true or 1, and `reset' or `clear' if its value is false or 0. One speaks of setting and clearing bits. To [1354]toggle or `invert' a bit is to change it, either from 0 to 1 or from 1 to 0. See also [1355]flag, [1356]trit, [1357]mode bit.

The term `bit' first appeared in print in the computer-science sense in a 1948 paper by information theorist Claude Shannon, and was there credited to the early computer scientist John Tukey (who also seems to have coined the term `software'). Tukey records that `bit' evolved over a lunch table as a handier alternative to `bigit' or `binit', at a conference in the winter of 1943-44.

142

---

Node:bit bang, Next:[1358]bit bashing, Previous:[1359]bit, Up:[1360]= B

=

bit bang n.

Transmission of data on a serial line, when accomplished by rapidly tweaking a single output bit, in software, at the appropriate times. The technique is a simple loop with eight OUT and SHIFT instruction pairs for each byte. Input is more interesting. And full duplex (doing input and output at the same time) is one way to separate the real hackers from the [1361]wannabees.

Bit bang was used on certain early models of Prime computers, presumably when UARTs were too expensive, and on archaic Z80 micros with a Zilog PIO but no SIO. In an interesting instance of the [1362]cycle of reincarnation, this technique returned to use in the early 1990s on some RISC architectures because it consumes such an infinitesimal part of the processor that it actually makes sense not to have a UART. Compare [1363]cycle of reincarnation.

---

Node:bit bashing, Next:[1364]bit bucket, Previous:[1365]bit bang, Up:[1366]= B =

bit bashing n.

(alt. `bit diddling' or [1367]bit twiddling) Term used to describe any of several kinds of low-level programming characterized by manipulation of [1368]bit, [1369]flag, [1370]nybble, and other smaller-than-character-sized pieces of data; these include low-level device control, encryption algorithms, checksum and error-correcting codes, hash functions, some flavors of graphics programming (see [1371]bitblt), and assembler/compiler code generation. May connote either tedium or a real

143

technical challenge (more usually the former). "The command decoding for the new tape driver looks pretty solid but the bit-bashing for the control registers still has bugs." See also [1372]bit bang, [1373]mode bit.

---

Node:bit bucket, Next:[1374]bit decay, Previous:[1375]bit bashing, Up:[1376]= B =

bit bucket n.

[very common] 1. The universal data sink (originally, the mythical receptacle used to catch bits when they fall off the end of a register during a shift instruction). Discarded, lost, or destroyed data is said to have `gone to the bit bucket'. On [1377]Unix, often used for [1378]/dev/null. Sometimes amplified as `the Great Bit Bucket in the Sky'. 2. The place where all lost mail and news messages eventually go. The selection is performed according to [1379]Finagle's Law; important mail is much more likely to end up in the bit bucket than junk mail, which has an almost 100% probability of getting delivered. Routing to the bit bucket is automatically performed by mail-transfer agents, news systems, and the lower layers of the network. 3. The ideal location for all unwanted mail responses: "Flames about this article to the bit bucket." Such a request is guaranteed to overflow one's mailbox with flames. 4. Excuse for all mail that has not been sent. "I mailed you those figures last week; they must have landed in the bit bucket." Compare [1380]black hole.

This term is used purely in jest. It is based on the fanciful notion that bits are objects that are not destroyed but only misplaced. This appears to have been a mutation of an earlier term `bit box', about which the same legend was current; old-time hackers also report that trainees used to be told that when the CPU stored bits into memory it was actually pulling them `out of the bit box'. See also [1381]chad box.

Another variant of this legend has it that, as a consequence of the `parity preservation law', the number of 1 bits that go to the bit bucket must equal

144

the number of 0 bits. Any imbalance results in bits filling up the bit bucket. A qualified computer technician can empty a full bit bucket as part of scheduled maintenance.

---

Node:bit decay, Next:[1382]bit rot, Previous:[1383]bit bucket, Up:[1384]= B =

bit decay n.

See [1385]bit rot. People with a physics background tend to prefer this variant for the analogy with particle decay. See also [1386]computron, [1387]quantum bogodynamics.

---

Node:bit rot, Next:[1388]bit twiddling, Previous:[1389]bit decay, Up:[1390]= B =

bit rot n.

[common] Also [1391]bit decay. Hypothetical disease the existence of which has been deduced from the observation that unused programs or features will often stop working after sufficient time has passed, even if `nothing has changed'. The theory explains that bits decay as if they were radioactive. As time passes, the contents of a file or the code in a program will become increasingly garbled.

There actually are physical processes that produce such effects (alpha particles generated by trace radionuclides in ceramic chip packages, for example, can change the contents of a computer memory unpredictably, and various kinds of subtle media failures can corrupt files in mass storage), but they are quite rare (and computers are built with error-detecting circuitry to compensate for them). The notion long favored among hackers that cosmic rays are among the causes of such events turns

145

out to be a myth; see the [1392]cosmic rays entry for details.

The term [1393]software rot is almost synonymous. Software rot is the effect, bit rot the notional cause.

---

Node:bit twiddling, Next:[1394]bit-paired keyboard, Previous:[1395]bit rot, Up:[1396]= B =

bit twiddling n.

[very common] 1. (pejorative) An exercise in tuning (see [1397]tune) in which incredible amounts of time and effort go to produce little noticeable improvement, often with the result that the code becomes incomprehensible. 2. Aimless small modification to a program, esp. for some pointless goal. 3. Approx. syn. for [1398]bit bashing; esp. used for the act of frobbing the device control register of a peripheral in an attempt to get it back to a known state.

---

Node:bit-paired keyboard, Next:[1399]bitblt, Previous:[1400]bit twiddling, Up:[1401]= B =

bit-paired keyboard n.,obs.

(alt. `bit-shift keyboard') A non-standard keyboard layout that seems to have originated with the Teletype ASR-33 and remained common for several years on early computer equipment. The ASR-33 was a mechanical device (see [1402]EOU), so the only way to generate the character codes from keystrokes was by some physical linkage. The design of the ASR-33 assigned each character key a basic pattern that could be modified by flipping bits if the SHIFT or the CTRL key was pressed. In order to avoid making the thing even more of a kluge than it already was, the design had to group characters that shared the same basic bit pattern on one key.

146

Looking at the ASCII chart, we find: high low bits bits 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 010 ! " # $ % & ' ( ) 011 0 1 2 3 4 5 6 7 8 9

This is why the characters !"#$%&'() appear where they do on a Teletype (thankfully, they didn't use shift-0 for space). The Teletype Model 33 was actually designed before ASCII existed, and was originally intended to use a code that contained these two rows: low bits high 0000 0010 0100 0110 1000 1010 1100 1110 bits 0001 0011 0101 0111 1001 1011 1101 1111 10 ) ! bel # $ % wru & * ( " : ? --- , . 11 0 1 2 3 4 5 6 7 8 9 ' ; / - esc del

The result would have been something closer to a normal keyboard. But as it happened, Teletype had to use a lot of persuasion just to keep ASCII, and the Model 33 keyboard, from looking like this instead: ! " ? $ ' & - ( ) ; : * / , . 0 1 2 3 4 5 6 7 8 9 + ~ < > x |

Teletype's was not the weirdest variant of the [1403]QWERTY layout widely seen, by the way; that prize should probably go to one of several (differing) arrangements on IBM's even clunkier 026 and 029 card punches.

When electronic terminals became popular, in the early 1970s, there was no agreement in the industry over how the keyboards should be laid out. Some vendors opted to emulate the Teletype keyboard, while others used the flexibility of electronic circuitry to make their product look like an office typewriter. Either choice was supported by the ANSI computer keyboard standard, X4.14-1971, which referred to the alternatives as `logical bit pairing' and `typewriter pairing'. These alternatives became known as `bit-paired' and `typewriter-paired' keyboards. To a hacker, the bit-paired keyboard seemed far more logical -- and because most hackers in those days had never learned to touch-type, there was little pressure from the pioneering users to adapt keyboards to the typewriter standard.

The doom of the bit-paired keyboard was the large-scale introduction of the computer terminal into the normal office environment, where out-and-out technophobes were expected to use the equipment. The `typewriter-paired' standard became universal, X4.14 was superseded by X4.23-1982,

147

`bit-paired' hardware was quickly junked or relegated to dusty corners, and both terms passed into disuse.

However, in countries without a long history of touch typing, the argument against the bit-paired keyboard layout was weak or nonexistent. As a result, the standard Japanese keyboard, used on PCs, Unix boxen etc. still has all of the !"#$%&'() characters above the numbers in the ASR-33 layout.

---

Node:bitblt, Next:[1404]BITNET, Previous:[1405]bit-paired keyboard, Up:[1406]= B =

bitblt /bit'blit/ n.

[from [1407]BLT, q.v.] 1. [common] Any of a family of closely related algorithms for moving and copying rectangles of bits between main and display memory on a bit-mapped device, or between two areas of either main or display memory (the requirement to do the [1408]Right Thing in the case of overlapping source and destination rectangles is what makes BitBlt tricky). 2. Synonym for [1409]blit or [1410]BLT. Both uses are borderline techspeak.

---

Node:BITNET, Next:[1411]bits, Previous:[1412]bitblt, Up:[1413]= B =

BITNET /bit'net/ n., obs.

[acronym: Because It's Time NETwork] Everybody's least favorite piece of the network (see [1414]the network) - until AOL happened. The BITNET hosts were a collection of IBM dinosaurs and VAXen (the latter with lobotomized comm hardware) that communicate using 80-character [1415]EBCDIC card images (see [1416]eighty-column mind); thus, they tend to mangle the headers and text of third-party traffic from the rest of the ASCII/[1417]RFC-822 world with annoying regularity. BITNET was also

150

Node:black hole, Next:[1449]black magic, Previous:[1450]black art, Up:[1451]= B =

black hole n.,vt.

[common] What data (a piece of email or netnews, or a stream of TCP/IP packets) has fallen into if it disappears mysteriously between its origin and destination sites (that is, without returning a [1452]bounce message). "I think there's a black hole at foovax!" conveys suspicion that site foovax has been dropping a lot of stuff on the floor lately (see [1453]drop on the floor). The implied metaphor of email as interstellar travel is interesting in itself. Readily verbed as `blackhole': "That router is blackholing IDP packets." Compare [1454]bit bucket and see [1455]RBL.

---

Node:black magic, Next:[1456]Black Screen of Death,

Previous:[1457]black hole, Up:[1458]= B =

black magic n.

[common] A technique that works, though nobody really understands why. More obscure than [1459]voodoo programming, which may be done by cookbook. Compare also [1460]black art, [1461]deep magic, and [1462]magic number (sense 2).

---

Node:Black Screen of Death, Next:[1463]Black Thursday, Previous:[1464]black magic, Up:[1465]= B =

Black Screen of Death n.

[prob. related to the Floating Head of Death in a famous "Far Side" cartoon.] A failure mode of [1466]Microsloth Windows. On an attempt to launch a DOS box, a networked Windows system not uncommonly blanks