EPFO APFC 2023 General Studies · Question 85 of 120

Correct — C, (c) CHKDSK. The command is the contraction of the two words 'check disk', and the contraction was made by deleting the vowels from each word rather than by shortening the phrase: check becomes CHK and disk becomes DSK, giving CHKDSK. It is a command-line utility of MS-DOS and of every version of Windows since, and it does exactly what the stem describes. Run against a volume, it examines the file system's metadata — the directory entries, the file allocation structures, the security descriptors and the index — reports inconsistencies such as lost clusters, cross-linked files and orphaned records, and prints a summary of the volume's status. Given the appropriate switch it also repairs what it finds: /F fixes errors on the disk, /R goes further and locates bad sectors and recovers whatever information in them is still readable, and /X forces the volume to dismount first so that the repair can proceed. Because a repair needs exclusive access, running it against the system volume ordinarily results in the check being scheduled for the next restart rather than performed immediately. The reason the other three options exist is that all of them are things a candidate might reasonably expect the command to be called. One is the phrase as it is spoken and as the graphical tool labels itself, one drops a different letter from the same contraction, and one has the two halves the wrong way round. None of them is a command that any version of DOS or Windows recognises. The way to hold the right one is to remember the rule that generated it — take 'check disk', delete the vowels, keep the order — because that rule produces CHKDSK and none of the other three.

• (a)CHKDK — This is not a command. It is the correct answer with one letter missing: CHKDSK contracts 'check disk' to CHK and DSK, and CHKDK has lost the S from the second half, leaving a contraction of nothing in particular. It is the hardest of the three wrong options to reject on sight, because it has the right length, the right shape and the right first three letters, and a candidate who recognises the answer by its silhouette rather than by its derivation will accept it. That is precisely why the derivation is worth learning rather than the string. Both halves of the command name keep all three of their consonants: check gives C, H and K; disk gives D, S and K. Any string that has only two consonants in its second half cannot be the contraction, whatever else it looks like.
• (b)CHECKDISK — This is the name of the operation, not the name of the command. Users and documentation both speak of running check disk, and the graphical equivalent in Windows presents itself under an error-checking label rather than as a string to be typed, so the full spelling feels right. It has never been the command, and there is a historical reason it could not have been. The MS-DOS file system limited a name to eight characters followed by a three-character extension, and every command of that era was an executable file subject to that limit. CHECKDISK is nine characters, so it could not have been an executable name when the utility was written, and the name has been carried forward unchanged ever since for compatibility. The general lesson is worth more than this one item: the vowel-less names of the early command set — CHKDSK, DISKPART, DEFRAG, FORMAT, XCOPY — are artefacts of that eight-character limit.
• (d)DSKCHK — This is the right pair of syllables in the wrong order. CHKDSK reads as check-disk, the verb before the object, which is the ordinary word order of the phrase and of most commands in this family; DSKCHK reverses it to disk-check. Nothing in DOS or Windows answers to it. The option is aimed at the candidate who has memorised that the answer consists of CHK and DSK joined together but has not fixed which comes first, and it is the reason the derivation matters: the command is the two spoken words with their vowels removed, so the order of the words is the order of the letters. A useful cross-check is that the utility's own output and its documentation both refer to it as check disk, never as disk check.

A file system is the structure an operating system imposes on a storage volume so that a stream of sectors can be read and written as named files. Alongside the data itself it keeps metadata: the directory tree, a record of which clusters belong to which file, free-space information, and on modern systems a journal of pending changes. That metadata can become inconsistent — through a power failure or a crash during a write, through a program that terminates without closing files, or through the physical failure of the sectors on which it is stored — and the characteristic symptoms are lost clusters marked as used but belonging to no file, cross-linked files whose records claim the same cluster, orphaned directory entries and unreadable sectors. Every operating system therefore ships a consistency checker. On MS-DOS and Windows it is CHKDSK, run from the command line, which examines the file system's structures, reports what it finds and, with the /F, /R or /X switches, repairs errors, recovers what is readable from bad sectors, or dismounts the volume so that repairs can be made. The Unix and Linux equivalent is fsck. It is important to keep this apart from two neighbouring operations that are often confused with it. Defragmentation rearranges the physical layout of files so that each occupies contiguous clusters, which is a performance measure and not a repair. And a system file checker verifies the integrity of the operating system's own files, which is a different object of attention from the file system that holds them.

This is a recall item, and it belongs to a class that this paper's computers block returns to repeatedly: the answer is a named thing, the option set is built from near-misses of that name, and no amount of reasoning about disks will produce it if the name has not been learnt. What makes the item fair rather than arbitrary is that the name was generated by a rule, and the rule is recoverable. Early command names were constrained to eight characters by the file system of the time and were formed by stripping vowels out of ordinary English words, which is why the command set of that era reads the way it does. A candidate who knows that rule can reconstruct CHKDSK from 'check disk' under examination conditions; a candidate who has only seen the string will be at the mercy of an option set specifically designed to blur it, with one letter dropped in one option, the words spelled out in another and their order reversed in a third. The wider habit this rewards is the one that pays across the whole computers block of this exam: learn the handful of named commands, protocols and utilities exactly, and learn one sentence about what each does, because the questions ask for identification rather than for use. Half a minute is the right budget for an item of this kind, and there is nothing in it to work out.

• CHKDSK is the command-line utility of MS-DOS and Windows that checks the file system and the file system metadata of a volume for logical and physical errors and reports the volume's status. The name is the phrase 'check disk' with the vowels removed from both words, in that order.
• Its switches decide whether it merely reports or also repairs: /F fixes errors found on the disk, /R locates bad sectors and recovers readable information from them, and /X forces the volume to dismount before the check. A repair needs exclusive access, so a check of the system volume is usually scheduled for the next restart.
• The typical faults it addresses are lost clusters that are marked as in use but belong to no file, cross-linked files whose records claim the same cluster, orphaned directory entries and sectors that can no longer be read reliably.
• The equivalent utility on Unix and Linux systems is fsck. Keeping the two names paired is worth doing, because the exam asks for the counterpart as readily as it asks for the command itself.
• Disk checking is not defragmentation and not system file checking. Defragmentation rearranges files into contiguous clusters for performance, and a system file checker verifies the operating system's own files; neither repairs the file system's structures.
• Command names of the MS-DOS era were limited to eight characters by the file system of the time, which is why the command set is full of vowel-less abbreviations. A nine-character name such as the fully spelled-out phrase could not have been an executable name then, and the shortened form has been carried forward unchanged.

• Recognising the answer by its silhouette. Three of these options have roughly the same shape as the command, and the closest of them differs by a single missing letter, so shape alone does not separate them.
• Choosing the fully spelled-out phrase because it is what people say and what the graphical tool is labelled. The spoken name of an operation and the string that has to be typed are different things.
• Getting the two halves the right way round. The command reads check-disk, verb before object, and the reversed form is a printed option in this very question.
• Confusing disk checking with defragmentation or with a system file check. All three are maintenance operations invoked from the same place, but only one of them examines the file system for errors.
• Assuming the check can always be run at once. Repairing a mounted volume requires exclusive access, so a check of the system volume is normally deferred to the next restart.

The computers block asks about commands and utilities in three ways. The commonest is this one: a one-line description of what a utility does, with four spellings of a single name among which only one is real. The second gives the command and asks what it does, or asks which switch produces a particular behaviour, which is why the small set of switches is worth knowing alongside the name. The third asks for the counterpart on another operating system — the Unix utility that corresponds to a Windows one, or the reverse — and rewards learning the two names as a pair. Across all three, what is being tested is precise recall of a name and a single sentence of function, not any deeper understanding of storage. The efficient preparation is a short list of the utilities this exam actually mentions, each with its purpose, its two or three important switches and its equivalent in the other family, and a note of the naming convention that generated the abbreviations, since that convention makes the strings reconstructible rather than merely memorable.

No directly related past PYQ was found.

• practice — not a real PYQ

  Which one of the following command-line utilities performs, on a Unix or Linux system, the role that CHKDSK performs on Windows — checking a file system for inconsistencies and repairing them?

  • (a)grep
  • (b)fsck
  • (c)chmod
  • (d)mount

  Answer(b) fsck — the file system consistency check, which examines a Unix or Linux file system's metadata for errors and can repair them, and is the direct counterpart of CHKDSK. The others do unrelated work: grep searches text for a pattern, chmod changes file permissions, and mount attaches a file system to the directory tree, which is a precondition for using a volume rather than a check on it.

• practice — not a real PYQ

  Which switch instructs CHKDSK not merely to fix file system errors but also to locate bad sectors on the volume and recover whatever information in them is still readable?

  • (a)/F
  • (b)/R
  • (c)/X
  • (d)/V

  Answer(b) /R — it locates bad sectors and recovers readable information from them, and it carries out the error fixing of /F as well, which is why it takes considerably longer to run. /F fixes errors in the file system's structures without scanning the medium for bad sectors, /X forces the volume to dismount before the check so that exclusive access is available, and /V lists the files as it goes.