← Years 9–10 Digital Systems

Availability

Authorised users can reach data and systems when they need them, such as a school network that stays up. Attacks and hardware failure can reduce it.

Part of: 9-10 Digital Technologies Vic Curric - Digital Systems and Security — Module 15, VCE Software Development - U4O2 - Cyber Security: secure software development practices — Module 17, VCE Data Analytics - U4O2 - Cyber Security: Data Security — Module 34, IGCSE Computer Science 0478 — 5.3 Cyber Security — Module 5, ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control — Module 97, ACARA Digital Technologies Years 9–10 — Cyber Security Threats and Vulnerabilities — Module 5

Understanding Availability in Years 9–10 Digital Systems

What it does: When authorised students cannot reach the network or their files, availability has been lost. Availability is about access when needed. Keeping data secret is confidentiality, not availability. Hardware failure can stop authorised users reaching data and systems. Locking a classroom door does not stop access to a digital system. This is the definition of availability: the right people can get to the system or data whenever they need it. Uptime measures how much of the time a system can be used, so a high percentage means strong availability.

Common mistakes: A single = assigns a value. An if statement needs == to compare. It should be if server_up == True:. The system meets its availability goal when uptime is at least the target, so the operator should be >=, not <=.

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This module's key terms are also in a printable crossword (Modules 13–24) and word search (Modules 13–40).

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Learning

Duo

Which statement best describes availability?

Only the data owner can ever open a fileAuthorised users can reach data and systems when they need them

Matches

Availability = keeping data secret from outsiders

↓

This describes confidentiality, not availability. Availability is about authorised users being able to reach data and systems when needed.

Applying

Meanings

Term

Availability

Meaning

Authorised users can reach data and systems when they need them, such as a school network that stays up. Attacks and hardware failure can reduce it.

Practice

IF school_network = "down" THEN

Testing

Gaps

availability ← uptime total * 100

Check Answer

Spots

1server_up = True

2if server_up = True:

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Quick Questions

1. Which statement best describes availability?

A. Authorised users can reach data and systems when they need them ✓

B. Only the data owner can ever open a file

Availability is about access when needed. Keeping data secret is confidentiality, not availability.

2. A school network is down during a Year 10 exam and students cannot log in. Which part of security is affected?

A. Confidentiality

B. Availability ✓

The system is not reachable when students need it, so availability has been reduced. Nobody necessarily saw secret data.

3. Which event can reduce availability?

A. A hard drive failure that takes a file server offline ✓

B. Locking a classroom door at night

Hardware failure can stop authorised users reaching data and systems. Locking a classroom door does not stop access to a digital system.

4. A denial of service attack floods a school website with traffic. What does it mainly target?

A. Authentication, so the attacker can guess passwords

B. Availability, so real users cannot reach the site ✓

A denial of service attack overloads a system so authorised users cannot get in. That reduces availability.

5. True or false: A system that is secure but offline all day still has good availability.

A. False ✓

B. True

If authorised users cannot reach the system when they need it, availability is poor, no matter how secure it is.

Match the Pairs

Availability → Authorised users can reach data and systems when they need them

Uptime: 99.9% → The system is working and reachable almost all of the time, which shows high availability

A school network goes down during a lesson, so students cannot open their work → Availability lost: network offline

A denial of service attack floods a server so real users cannot get in → Attack: DoS -> Availability reduced

Availability = keeping data secret from outsiders → This describes confidentiality, not availability. Availability is about authorised users being able to reach data and systems when needed.

Hardware failure cannot affect availability → Hardware failure can reduce availability. If a server or disk breaks, users may not be able to reach the system or data.

Key Term

Availability

Authorised users can reach data and systems when they need them, such as a school network that stays up. Attacks and hardware failure can reduce it.

Fill in the Blanks

1. uptime ← 9900 total ← 10000 availability ← uptime / total * 100

Hint: Type the arithmetic operator that divides the time the system was up by the total time to work out availability as a percentage.

2. IF serverStatus = "down" THEN DISPLAY "Network is down" ENDIF

Hint: Type the command that shows a message to students when the school network is unavailable.

3. IF diskFailed THEN useBackup() ENDIF

Hint: Type the keyword that starts a decision, so a backup is used when hardware fails and keeps the system available.

4. IF requests > 100 THEN blockTraffic() ENDIF

Hint: Type the comparison operator that checks whether there are more requests than the limit, as in a flood attack.

5. IF isAuthorised AND systemUp THEN grantAccess() ENDIF

Hint: Type the logical operator that needs both conditions to be true before access is given.

Spot the Error

Question 1

A server_up = True

B if server_up = True:

C print('Log in OK')

D else:

E print('Network down')

Line B — A single = assigns a value. An if statement needs == to compare. It should be if server_up == True:

Question 2

A uptime = 99

B target = 95

C if uptime <= target:

D print('Available')

Line C — The system meets its availability goal when uptime is at least the target, so the operator should be >=, not <=.

Question 3

A disks = 2

B failed = 1

C working = disks - failed

D if working > 0

E print('Data reachable')

Line D — An if statement must end with a colon. It should be if working > 0: so the data stays reachable on the working disk.

Question 4

A requests = 5000

B limit = 1000

C overloaded = requests < limit

D print(overloaded)

Line C — A denial of service flood overloads a server when requests are greater than its limit, so the operator should be >.

Question 5

A servers = ['A', 'B']

B for s in servers:

C print('Check', server)

D print('Backup ready')

Line C — The loop variable is s, so server is not defined and causes an error. It should be print('Check', s).

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