ITPEC IP April 2025 Question 14

Two systems perform the same processing and compare the results; a failed one is isolated and the other continues — that is a dual system.

In a dual system both systems run the same job at the same time and collate their outputs, so an error shows up as a mismatch. If one system fails, it is cut off and the other simply carries on, with almost no interruption. This gives very high reliability, but both systems do the same work, so capacity is not increased.

Answer (a)

Why not others:

• •(b) — using two devices to double the processing capacity is load sharing, a multiprocessor configuration; a dual system gains reliability, not capacity
• •(c) — describes a duplex system: an active system for online processing and a standby system (here busy with batch work) that takes over when the active one fails
• •(d) — describes a tandem configuration, devices in series each taking a share of the functions; it is fast, but any single failure stops the service

Key rule: Dual system = two systems doing the same work and comparing results; duplex system = one active system plus a standby that takes over after a failure.

System Component · AI-written, may contain errors