S6 ICT: System Maintenance and Documentation (four maintenance types, MTBF and availability, 3-2-1 backup) Tutor Prep Guide with a 45-minute plan, teaching script and common errors

2026-11-15

Tutor lesson-prep guides · Secondary ICT

Students assume the job ends at go-live, and stop when asked what five years of maintenance costs or what availability means. This lesson splits life after launch into four maintenance types, two time measures and three documents.

Objectives — By the end of the lesson students can: (1) split 200 tickets into corrective 40 per cent, adaptive 30 per cent, perfective 20 per cent and preventive 10 per cent, that is 80, 60, 40 and 20, with an example of each; (2) turn 40,000 a year for five years into 200,000 and state it as 133.3 per cent of the 150,000 development cost; (3) turn 8,760 hours and 4 failures into an MTBF of 2,190 hours, an MTTR of 3 hours and 99.86 per cent availability; (4) state who reads the user manual, the system documentation and the operations runbook, and explain 3-2-1 as three copies, two media and one off-site.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Percentages	What is 40 per cent of 200 tickets	80 tickets
Division	8,760 hours with 4 failures: the average gap	2,190 hours
Ratios	150,000 development and 200,000 maintenance: the multiple	1.333 times, 133.3 per cent
Averages	12 hours of downtime across 4 failures: the average repair	3 hours

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-6 min	Entry check	Ask 40 per cent of the tickets, 8,760 over 4, 200,000 against 150,000, and 12 over 4; keep the answers on the board	Spoken answers, working on paper
6-16 min	Act one: four maintenance types, four kinds of ticket	Four columns for corrective, adaptive, perfective and preventive, each with a real example and a share	Students classify a database upgrade as adaptive
16-26 min	Act two: MTBF, MTTR and availability	8,760 over 4 gives 2,190; 12 over 4 gives 3; 2,190 over 2,193 gives 99.86 per cent	Students compute all three with units (hours, per cent)
26-36 min	Act three: three documents and 3-2-1 backup	A 40-page manual and a 120-page system document, three times longer; three copies, two media, one off-site	Students say which document a new engineer reads
36-42 min	Question types with changed numbers	Switch to 300 tickets, 6 failures and 18 hours of downtime, then run the four question types	Students do one and write the unit
42-45 min	Exit check	Three spoken questions; note which act each error comes from	All three correct

03 Teaching script (read it out)

Scene 1: Act one: four maintenance types, ranked by share

Go-live is not the finish line. Corrective maintenance fixes faults, such as a monthly report rounding the wrong way, and takes 40 per cent, that is 80 of the 200 tickets. Adaptive maintenance follows a changing environment, such as upgrading the database version or changing a formula when the tax rate moves, at 30 per cent or 60 tickets. Perfective maintenance improves something that already works, such as adding an export to Excel button or cutting a report from 3 seconds to 1, at 20 per cent or 40 tickets. Preventive maintenance acts before anything breaks, such as refactoring an unmaintainable block or renewing a certificate, at 10 per cent or 20 tickets. The four shares add to exactly 200. One test classifies any ticket: broken and being fixed is corrective, an outside change forces the edit and it is adaptive, a user wants it better and it is perfective, and nobody asked but you did it anyway and it is preventive.

After a database upgrade an old program can no longer connect: which maintenance type is that ticket, and why not corrective?

Scene 2: Act two: MTBF is how often it breaks, MTTR is how long it stays broken

Two time measures. MTBF is the mean time between failures: 365 days times 24 hours is 8,760 hours a year, with 4 failures, so 8,760 over 4 gives 2,190 hours, one failure per 2,190 hours on average. MTTR is the mean time to repair: 4 failures cost 12 hours of downtime in total, so 12 over 4 gives 3 hours. Availability puts the two together as uptime over total time, that is 2,190 over 2,190 plus 3, which is 0.99863 or 99.86 per cent. Be careful not to subtract MTTR from 100: its unit is hours. Take 3 over 2,193 for 0.137 per cent of downtime, then 100 minus 0.137 gives 99.86 per cent, and both routes must agree. Pushing 99.86 to 99.99 can be done by lengthening MTBF or shortening MTTR, and the two routes cost very differently.

If failures drop from 4 to 2 a year but each repair takes 4 hours, does availability rise or fall?

Scene 3: Act three: documentation has readers, and backup has three numbers

Documentation is not one book but three, each with its own reader. The 40-page user manual is for end users: how to use it, what each button does, no technical detail. The 120-page system documentation is for the engineer who inherits the system: architecture, table structures, interface specifications, three times the pages of the manual because it must allow changes without asking the original author. The operations runbook is for whoever runs it: backup, restart, and the first step when something fails. Backup follows 3-2-1: at least three copies, on two different media, with one off-site. Three copies beat an accidental deletion and a ransomware encryption at once; two media avoid one bad batch of drives failing together; off-site avoids fire or flood taking the whole room. A backup that is never restored is not a backup, so restore drills belong in the runbook.

A company backs up daily but keeps every copy in another folder on the same server: does that meet 3-2-1?

04 Question types and worked steps

Type	Example	Steps	Answer
Classify maintenance tickets	200 tickets across four types	Ask whether it is broken, forced by the environment, wanted better, or preventive, then apply the share	Corrective 80, adaptive 60, perfective 40, preventive 20
Compute MTBF and MTTR	8,760 hours, 4 failures, 12 hours of downtime	MTBF is total hours over failure count; MTTR is downtime over failure count	MTBF 2,190 hours, MTTR 3 hours
Compute availability	MTBF 2,190 and MTTR 3	Uptime over total time, or 100 minus the downtime share	99.86 per cent
Explain documentation and backup	A 40-page manual and a 120-page system document	Name the reader of each, then the three 3-2-1 numbers and the incident each prevents	The system document is three times the manual; three copies, two media, one off-site

Sanity check (teach this): Four checks: (1) the four maintenance shares must total 100 per cent, and 110 means an arithmetic slip; (2) MTBF must exceed MTTR, since the reverse would mean a machine spends longer broken than working; (3) availability lies between 0 and 100 per cent, so 100.4 per cent means the denominator is wrong; (4) the three numbers in 3-2-1 are copies, media types and off-site copies, never three computers, two departments and one password.

05 Independent practice (3 questions)

Question	Answer	What to watch
200 tickets with 40 per cent corrective: how many	80	Check 200 times 0.4, not times 4
8,760 hours a year with 4 failures: the MTBF	2,190 hours	Total hours over failures, not over downtime
MTBF 2,190 and MTTR 3: the availability	99.86 per cent	Uptime over total time, or 100 minus 3 over 2,193

06 Common mistakes and what to say

Mistake	Student writes	Say this
Treating the four types as four stages	Answering that corrective comes first, then adaptive, then preventive	The four types coexist; one month can hold a bug fix, a version upgrade, a new feature and a refactor. The classifier is why the work was done, not when.
Using downtime as the MTBF numerator	Answering 12 over 4 as the MTBF	That is the MTTR, how long repair takes. The MTBF is uptime over failures, 8,760 over 4, giving 2,190.
Subtracting MTTR from 100	Answering 100 minus 3 as 97 per cent	MTTR is measured in hours and cannot be subtracted from a percentage. Divide 3 by 2,193 for 0.137 per cent, then subtract from 100 for 99.86.
Calling three folders a backup strategy	Answering that three copies already exist in three folders on the server	Three copies on one machine die in one incident. 3-2-1 requires two media, one off-site copy, and a restore drill to prove it works.

07 Homework (paper, section and question numbers)

Secondary ICT prep guide: system maintenance and documentation chapter (question types and chapter exercises) — Chapter exercises, questions 1 to 4

08 Exit check (last 5 minutes)

Question	Answer	Decision
200 tickets with 30 per cent adaptive: how many	60	Wrong: reteach act one, four columns and shares
8,760 hours, 4 failures and 12 hours of downtime: MTBF and MTTR	MTBF 2,190 hours, MTTR 3 hours	Wrong: reteach act two, the two numerators differ
Three copies all on the same server: does that meet 3-2-1?	No, two media and one off-site copy are missing	Wrong: reteach act three, what each number prevents

09 Tutor FAQ

How does this relate to the S5 system development life cycle?

The life cycle runs requirements, design, implementation, testing and maintenance, and this chapter magnifies the last box. Most of the money and risk after launch sit in maintenance, which is why it is examined.

Is 45 minutes enough for four maintenance types and availability?

Yes, if act one takes ten minutes. One example per column settles the types, and the time belongs to the three computations in act two, which are the examined arithmetic.

Are 8,760, 2,190 and 99.86 per cent real figures?

No, they are teaching numbers chosen to divide cleanly. Real failure rates and downtime vary widely, and the definitions and conversions are the point.

Find a tutor — free Tutor Registration →

A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.