Glob (programming) and spool (/var/spool)

Http://en.wikipedia.org/wiki/Glob_ (programming)

 

In computer programming, in particle in a Unix-like environment, the termGlobbingIs sometimes used to refer to pattern matching based on wildcard characters.^{[Citation needed] The noun "glob" is used to refer to a participant pattern, e.g ."Use the glob*. LogTo match all those log files".[Citation needed] Its notation is simpler than regular expressions, and without their expressive power.}

 

 

Http://en.wikipedia.org/wiki/Spooling

In computing,SpoolIs an acronymSimultaneous peripheral operations on-line. It is a type of buffering. The most common spooling application is print spooling, which places a task (or 'print job') into a queue for extended or later processing.

 

Contents [hide]

• 1 origin of the term
• 2 History
• 3 Process
  • 3.1 banner page
• 4 uses and advantages
• 5 types
• 6 See also
• 7 References

 

Origin of the term [edit]

According to Tanenbaum, "Spool" is an acronymSimultaneous peripheral operations on-line;^{[1] for printers:Simultaneous peripheral output on line. Possibly the term is influenced by the reel (orSpool) Of a magnetic tape, the part on which tape is wound for later use. A more modern interpretation of spool comes from the flowchart drawing icon of a spool of thread, which, in IBM-ese, represents the (perhaps) temporary storage of data on a magnetic disk drive, under the control of an operating system task.}

History [edit]

In a computer system peripheral equipment such as printers and punched card readers and punches are very slow relative to the performance of the rest of the system. getting input into and output from the system was quickly seen to be a bottleneck. for example a job which read punched cards or generated printed output directly was forced to run at the speed of the slow mechanical devices.

In the late 1950 s and early 1960 s, computers used spool software, e.g ., IBM "Spool System", 7070-io-076, to copy files from one medium to another: punch card to tape, tape to punch card and tape to printer, with occasional use for card-to-card copying.^{[1] The introduction of the relatively inexpensive IBM 1401 led to a temporary ction in the use of spool software, since implements large computer installations used a stand-alone 1401 to drive printers and card equipment and process tapes for a larger computer system.}

Early mainframe computers had no disk drives and slightly more recent ones had, by current standards, small and expensive hard disks; in later systems offline tape handling and spool use of tape disappeared in favor of disks. software such as IBM's attached support processor allowed a smaller system/360 to process spool files on disk for one or more larger systems.

Process [edit]

The most common spooling application is print spooling: specified ents formatted for printing are usually stored into an area on a disk and retrieved and printed by a printer at its own rate. printers typically can print only a single document at a time and require seconds to minutes to do so. with spooling, multiple processes can write documents to a print queue without waiting. as soon as a process has written its document to the spool device, the process can perform other tasks, while a separate printing process operates the printer.

For example, when a city prepares payroll checks, the actual computation may take a matter of minutes or even seconds, but the printing process might take hours. if the program printed directly, computing resources (CPU, memory, peripherals) wocould be tied up until the program was able to finish. the same is true of personal computers. without spooling, a word processor wocould be unable to continue until printing finished. without spooling, most programs wocould be relegated to patterns of fast processing and long waits, an inefficient paradigm.^[2]

Spooler or print management software allow priorities to be assigned to jobs, running y users when their output has been printed, distribute jobs among several printers, allow forms or paper to be changed, or select it automatically, generate banner pages to identify and separate print jobs, etc.

A batch processing system uses spooling to maintain a queue of ready-to-run jobs which can be started as soon as the system has the resources to process them.

Banner page [edit]

A banner page (also calledBurst page,Job Sheet, OrPrinter Separator), Is used in computerized printing in order to separate documents (or "print jobs") from each other and to identify, e.g ., the originator of the print request by username, an account number, a bin for pickup. these pages are typically used in office environments where users share a small number of printers. in some cases, print jobs are sent to a central processing area where messengers take the printouts back to the owner, but the usual practice in modern office environments is for the user to retrieve his or her own documents. the banner page makes it clear who printed each job.

Depending upon the configuration, the banner page may be generated by the print spooler-software running on a computer which buffers and prioritizes print jobs-by a print server-a computer or device that is connected to one or more printers and to client computers over a network-or by the printer itself.

Uses and advantages [edit]

The temporary storage area to which e-mail is delivered by a mail transfer agent and in which it waits to be picked up by a Mail User Agent is sometimes calledMail Spool. Likewise, a storage area for Usenet articles may be referred to asNews Spool. (On Unix-like systems, these areas are usually located in/Var/spoolDirectory.) mail and news spools usually allow random access to individual messages.

In the later 1960 s and early 1970 s, computers handled punch cards, and spooling systems such as hasp, Fido, patches,^{[3] shadow & shadow II (primarily teleprocessing, but control program same as patches), power, grasp, and the Spooler found they cocould benefit batch programs by spooling card input and output. (some centers directed punch card and printed output to tape for later processing. the term 'spooling' may derive from these reels or 'spools' of tape, although the terms normally used for tape wereReelOrTape Volume; This etymology has not been sourced .)[2]}

 

Http://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard

/var/spool	Spool for tasks waiting to be processed,E.g., Print queues and outgoing mail queue.
/var/spool/mail	Deprecated location for users 'mailboxes.[8]