diff definition
/dif/ 1. A change listing, especially giving differences
between (and additions to) different versions of a piece of
source code or documentation (the term is often used in the
plural "diffs"). "Send me your diffs for the Jargon File!"
Compare vdiff.
2. Specifically, such a listing produced by the diff Unix
command, especially when used as input to the patch utility
(which actually performs the modifications). This is a common
method of distributing patches and source updates.
3. To compare (whether or not by use of automated tools on
machine-readable files).
See also vdiff, mod.
[Jargon File]
(1995-02-10)
Nearby terms:
Didot point « die « die horribly « diff » Difference Engine » difference equation » differential backup
Difference Engine definition
<computer, history> Charles Babbage's design for the first
automatic mechanical calculator. The Difference Engine was a
special purpose device intended for the production of
mathematical tables. Babbage started work on the Difference
Engine in 1823 with funding from the British Government. Only
one-seventh of the complete engine, about 2000 parts, was
built in 1832 by Babbage's engineer, Joseph Clement. This was
demonstrated successfully by Babbage and still works
perfectly. The engine was never completed and most of the
12,000 parts manufactured were later melted for scrap.
It was left to Georg and Edvard Schuetz to construct the first
working devices to the same design which were successful in
limited applications. The Difference Engine No. 2 was finally
completed in 1991 at the Science Museum, London, UK and is on
display there.
The engine used gears to compute cumulative sums in a series
of registers: r[i] := r[i] + r[i+1]. However, the addition
had the side effect of zeroing r[i+1]. Babbage overcame
this by simultaneously copying r[i+1] to a temporary register
during the addition and then copying it back to r[i+1] at the
end of each cycle (each turn of a handle).
Difference Engine at the Science Museum.
(1997-09-29)
Nearby terms:
die « die horribly « diff « Difference Engine » difference equation » differential backup » differential driver
difference equation definition
A relation between consecutive elements of a sequence. The
first difference is
D u(n) = u(n+1) - u(n)
where u(n) is the nth element of sequence u. The second
difference is
D2 u(n) = D (D u(n))
= (u(n+2) - u(n+1)) - (u(n+1) - u(n))
= u(n+2) - 2u(n+1) + u(n)
And so on. A recurrence relation such as
u(n+2) + a u(n+1) + b u(n) = 0
can be converted to a difference equation (in this case, a
second order linear difference equation):
D2 u(n) + p D u(n) + q u(n) = 0
and vice versa. a, b, p, q are constants.
(1995-02-10)
Nearby terms:
die horribly « diff « Difference Engine « difference equation » differential backup » differential driver » differential line
differential backup definition
<operating system> A kind of backup that copies all files
that have changed since the last full backup. Each
differential backup will include all files in previous
differential backups since the full backup so to restore a
version of a file, you only need to search the full backup and
the relevant differential backup.
Some systems support differential backup by associating an
"Archive" flag with each file and setting this flag whenever
the file is modified to indicate that it should be included in
the next backup. A differential backup does not change this
flag, whereas an incremental backup resets it.
(2004-03-05)
Nearby terms:
diff « Difference Engine « difference equation « differential backup » differential driver » differential line » Diffie-Hellman
differential driver definition
<hardware> An electronic device (commonly an integrated
circuit), containing two amplifiers, used to drive a
differential line.
(1995-03-14)
Nearby terms:
Difference Engine « difference equation « differential backup « differential driver » differential line » Diffie-Hellman » digerati
differential line definition
<hardware> A kind of electrical connection using two wires,
one of which carries the normal signal (V) and the other
carries an inverted version the signal (-V). A differential
amplifier at the receiver subtracts the inverted signal from
the normal signal to yield a signal proportional to V. This
subtraction is intended to cancel out any noise induced in the
wires, on the assmption that the same level of noise will have
been induced in both wires. Twisted pair wiring is often
used to try to ensure that this is the case.
The two wires might be connected at the receiver to separate
analogue to digital converters and the subtraction performed
digitally.
The RS-422 serial line standard specifies differential
drivers and receivers, whereas the earlier RS-232 standard
does not.
Opposite: single ended.
(1995-03-08)
Nearby terms:
difference equation « differential backup « differential driver « differential line » Diffie-Hellman » digerati » digest
Diffie-Hellman definition
<cryptography> A public-key encryption key exchange
algorithm.
FAQ.
(1999-03-15)
Nearby terms:
differential backup « differential driver « differential line « Diffie-Hellman » digerati » digest » Digex
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