ITPEC FE Morning April 2023 Question 16

System Availability Comparison — rank three system configurations by availability.

Given identical components with availability A:

• •Dual system — both computers run simultaneously; system fails only if both fail
• •Availability = 1 - (1 - A)²
• •Cold standby system — one active, one powered off as backup; switchover on failure
• •Availability > A but < dual (switchover delay, backup may fail to start)
• •Simplex system — single computer, no redundancy
• •Availability = A

Order (highest → lowest): Dual system → Cold standby system → Simplex system

Why not others:
- (a) Cold standby first — wrong; dual has higher availability than cold standby
- (b) Cold standby first, simplex second — wrong on both positions
- (d) Simplex first — wrong; single system has the lowest availability

Key rule: More active redundancy = higher availability. Dual (both active) > Cold standby (passive backup) > Simplex (no backup).

AI-generated — may contain errors