Swap

Swap (pronounced swop)

(1) To exchange, barter, or trade, as one thing for another.

(2) To substitute (one thing) for another (sometimes used in the forms swap-out & swap-in).

(3) To make an exchange.

(4) In finance, the verbal shorthand for a number of transactions (credit default swaps, currency swaps etc).

(5) In computer programming, exchanging two variables in the memory of a computer

(6) In computer operating systems, as swap partition, a partition of the physical data storage media used for paging to augment random access memory (RAM).

(7) In instrumentation as the acronym SWAP (Sun Watcher using Active Pixel System Detector and Image Processing), a space instrument used on solar satellites.

(8) In instrumentation as the acronym SWAP (Solar Wind At Pluto), a space instrument used in the observation of Pluto (which should still be a planet).

(9) In international development as the acronym SWAp (Sector-Wide Approach), a paradigm in the sector.

(10) In Cambridge University slang, a social meal at a restaurant between two university societies, usually involving drinking and banter; commonly associated with fining and pennying; the crewdate is the Oxford University equivalent.

Circa 1200: From the Middle English swappen (to swap (the original meeting was “to hurl, to strike, strike hands (in bargaining)”) and cognate with the dialectal German schwappen (to slosh, slop, to clap, box (the ears)).  Swap is a noun or verb, swapper a noun, swapped & swapping are adjectives or verbs (used with or without objects).  The alternative spelling, restricted mostly to the UK is swop.  The plural is swaps,

The seemingly strange etymological path from Middle English swappen ("to hurl" or "to strike") to the modern meaning of “swap” is thought to be an allusion to striking hands together when making an exchange, the handshake sealing the deal (ie the swap) as it were; the evolution of the word thus imitative of the sound of hitting or slapping.  The origin of swappen was the Middle English swippen (to strike, hit), from the Old English swipian (to scourge, strike, beat, lash), from the Old English swappian, a secondary form of the Old English swāpan (to swoop), from the Old Norse svipa (to swoop, flash, whip, look after, look around) which begat also swipe.  The verb (circa 1200) was the first form in the sense of "to strike, strike the hands together.  The sense of "to exchange, barter, trade" dates from the 1590s, the noun in this sense first recorded in the 1620s. Although swap-meets are an ancient institution of the barter economy known to many cultures and pre-dating antiquity, the term “swap-meet” seems not to have existed prior to 1968 when added to American English.

Bill Clinton walks the dogs.

Swap files and operating systems

A swap file (known also as virtual memory) is a file (with special attributes) stored on a hard disk (or SSD) where data is written if the physical random access memory (RAM) available becomes insufficient for the stable functioning of the operating system.  RAM is preferable for operations because, being essentially static electricity, it is so much faster than even the fastest forms of hard disk or SSD.  

Older versions of Windows used pagefile.sys as a page file but since Windows 10, the function has been split into pagefile.sys and swapfile.sys which by default reside in the root of the system (c:\) drive and, for good reason, are hidden from the user.  Pagefile.sys stores data from installed (third-party) applications while swapfile.sys handles data from Windows and applications installed from the Microsoft Store.  In years gone by, there were advantages to be had in terms of speed and storage by tweaking swapfile settings (the size and the volume on which it sat) and some disabled it entirely if they had a surfeit of RAM.  Those with long memories will recall even a time when Windows permitted a choice between a temporary and permanent swap file and there were reasons why one could be preferable to the other.  However, with modern versions of Windows, it shouldn’t be disabled because many applications require it to exist and without one, simply won’t start.  For what most people do most of the time, it’s best to ignore the settings and just allow the operating system to set the configuration, even though on a machine with much RAM, the swap file is used seldom.

However, for nerds and megalomaniacs, it remains possible to tinker although, unless simulating one’s own thermonuclear explosions or modelling the global climate, few are likely to notice much difference.  It needs to be done with caution because if the swap file is too big then system will slow because RAM is often ignored whereas if it is too small, there comes a point at which that becomes functionally the same as disabling feature.  Computer magazines used to publish ways to calculate the ideal size, either by (1) a calculation based on the size of the hard drive and installed RAM and (2), a calculation which involved assessing a typical use of physical RAM but most now concede that on modern PCs (ie 8 or more GB RAM), it’s best to allow the operating system handle the allocation.  Users can still experiment but Microsoft cautions the swap file size should never be set to more than twice the size of physical RAM; instability is assured.  There are different rules and parameters for Windows Server; because of the way Windows is written, there are special settings and system administrators have to make allowances so in event of system crashes, there’s sufficient space for dump files which can reveal much.  For those who don’t, in another context, wish anything to be revealed, page files can be encrypted although, while secure, that does impose some overhead on disk input/output.

Under Linux, the golden rule long was that a swap size should be double the installed RAM but that hardly applies to modern machines, indeed, on some boxes, that may no longer even be possible.  Many Linux distributors are actually silent on the matter, perhaps reflecting the not improbable assumption their users are nerdier than the Windows crowd and will likely work things out themselves but some do provide guidance.

(1) Red Hat suggest a swap size of 20% of RAM for modern systems (which they define as 4GB or more RAM).

(2) CentOS suggests (2a) twice the size of RAM if RAM is less than 2 GB or (2b) size of RAM + 2 GB if RAM size is greater than 2 GB.

(3) Ubuntu notes (3a) if hibernation is used, a swap of the size of RAM plus the square root of the RAM size is necessary, (3b), if RAM is less than 1 GB, swap size should be at least the size of RAM and at most double the size of RAM & (3c) if RAM is more than 1 GB, swap size should be at least equal to the square root of the RAM size and at most double the size of RAM.

In their hearts, all Unix guys really long for the world of the mainframes where the distinctions between ram and disk space really didn’t exist and for most users, the same thing applies under Linux: it’s usually best just to let the system decide.

Swap Films

“Swap” films are a common trope in commercial cinema, done so often one wonders if the screen-writers might not be ungrateful were the scripts for such things handed to AI (artificial intelligence) bots; it must be a thankless task to try to come up with some original take on the concept.  Probably, every twenty-odd years, scripts could be recycled and few except pedantic critics would notice.  Swap films with the Freaky Friday title have appeared four times since 1976 (another is threatened) and at least two others have been made which follow variations of the plotline.  The Parent Trap franchise is built around a different sort of swap, one which doesn’t depend on any aspect of the supernatural.  Using the title there have been two feature-length films and three made television features with Disney said to have another release in the pipeline.  This swap theme (two characters changing places for some purpose) has been used in fiction (in print and on screen) literally dozens of times in genres as varied as rom-coms (romantic comedy), fantasy and horror.

Swap Movie DVD twin-packs: The Parent Trap and Freaky Friday.