EPFO EO/AO 2023 General Ability Test · Question 48 of 120

Correct — C, (c) Simultaneous peripheral operation on-line. Spool is an acronym, and the two words that decide this item are the first and the last. SIMULTANEOUS is the whole idea. A processor works in millionths of a second and a printer works in seconds; if the processor waited for the printer, it would spend nearly all its time idle. Spooling breaks the dependency by interposing a temporary store — the buffer in memory or on disk that the stem refers to. Output destined for the slow device is written into that store at processor speed and the program moves on, while a separate system process drains the store to the device at the device's own speed. The two operations therefore proceed simultaneously, which is the property the name records. Because the store is a disc file rather than a small area of memory, it can hold many complete jobs, so a queue forms and several users can share one printer without any of them waiting for the others to finish. ON-LINE is the half candidates get wrong, and it is a historical point. In the early batch era, the slow work really was done off-line: a job's output was written to magnetic tape by the main computer, the tape was carried across the machine room to a small separate machine, and that machine drove the printer. Spooling replaced that arrangement by doing the same overlap without a second machine and without human carriage — the peripheral operation now happened on-line, under the control of the same system, while the processor got on with other jobs. The word in the acronym is the claim being made about the technique. Print spooling is the survival of this in everyday work: a document sent to print appears in a queue, the application returns control immediately, and jobs can be reordered or deleted while they wait, because none of them has reached the printer yet.

• (a)Simple peripheral operation on-line — The second half is right and the first word is wrong, which makes this the most attractive of the three. Nothing about the technique is described by the word 'simple' — it involves a spool file, a queue, a scheduler and a system process draining the queue, and it exists precisely because the naive simple arrangement of making the processor wait for the device is unacceptable. The word that belongs there is the one that names the benefit: the processor's work and the device's work go on at the same time.
• (b)Simple peripheral operation off-line — Wrong in both of the words that carry meaning. It gets the middle two right, which is no help, because all four options share them. Read as a description it says the opposite of the technique on both counts: the arrangement is not simple, and the peripheral is not driven off-line by some separate machine but by the running system itself.
• (d)Simultaneous peripheral operation off-line — The trap set for a candidate who knows the first word and guesses the last. Off-line operation is the OLDER practice that spooling superseded — output taken away on tape and printed by a separate small computer, achieving the overlap at the cost of a second machine and a human carrying the reel. Naming the technique after the thing it replaced would be an odd choice, and the standard expansion does not do it.

Spooling is an operating-system technique for managing devices that are far slower than the processor, and it belongs to the same family of ideas as buffering and caching. Buffering places a small area of main memory between a program and a device so that the transfer of one block can overlap the processing of another; the overlap is within a single job. Spooling goes further by using a disc file as an arbitrarily large buffer, which allows the overlap to run ACROSS jobs and creates a queue that can be managed — reordered, held, prioritised or deleted. It also solves a sharing problem: a printer cannot be interleaved between two programs a line at a time without producing nonsense, so it is a dedicated device; spooling makes it behave like a shared one by letting the system, not the programs, decide when each complete job is fed to it. Input spooling once did the same in reverse, reading punched cards to disc so that jobs could start without waiting for the card reader. The daemon or service that drains the queue and the spool directory in which the files sit are the parts an administrator actually deals with when a print queue jams.

The computers block of the EO/AO paper regularly asks for the expansion of an acronym, and it chooses acronyms whose wrong expansions are individually plausible — every option here is a grammatical phrase about peripherals. The examiner is testing recall, but the recall is anchored if the candidate knows what problem the technique solves, because the two decisive words then follow from the explanation rather than from memory. The habit rewarded is turning an acronym question into a question about purpose.

• Spool stands for Simultaneous Peripheral Operation On-Line.
• It places output for a slow device in a temporary store — a spool file on disc — so the processor need not wait for the device.
• The processor's work and the device's work therefore proceed simultaneously, which is what the first word records.
• The store is large enough to hold complete jobs, so a queue forms and one printer can serve many users.
• Off-line operation, in which output was written to tape and printed by a separate machine, is the older practice spooling replaced.
• Print spooling is the everyday survival of the technique: the application returns control at once and the job waits in a queue.
• Buffering overlaps transfer with processing inside one job using main memory; spooling uses disc and overlaps across jobs.
• A printer is a dedicated device that cannot be interleaved between programs; spooling is what makes it shareable.

• Remembering the first word and guessing the last, which lands on the off-line option.
• Reading 'simple' as a reasonable description of a technique whose whole purpose is to avoid the simple arrangement.
• Treating spooling and buffering as the same thing; the difference is the medium and whether the overlap crosses jobs.
• Assuming a document has reached the printer once the application says it has been sent — until the queue drains, it has not.

Operating-system items in EO/AO papers are usually acronym expansions or one-line definitions — spooling, thrashing, deadlock, virtual memory, kernel, booting. Expect all four options to be well-formed phrases differing in one or two words, so learn the expansions exactly and attach each to the problem it solves, which is what makes the exact words recoverable under time pressure.

No directly related past PYQ was found.

• practice — not a real PYQ

  Spooling is used mainly to :

  • (a)Increase the clock speed of the processor
  • (b)Allow the processor to continue working without waiting for a slow input or output device
  • (c)Protect files against unauthorised access
  • (d)Convert a program written in a high level language into machine code

  Answer(b) Allow the processor to continue working without waiting for a slow input or output device

• practice — not a real PYQ

  The main difference between buffering and spooling is that spooling :

  • (a)Uses main memory while buffering uses secondary storage
  • (b)Uses secondary storage and can overlap the input or output of one job with the computation of another
  • (c)Works only with input devices
  • (d)Requires a separate off-line computer

  Answer(b) Uses secondary storage and can overlap the input or output of one job with the computation of another