Operating Systems and Data Communication
Operating Systems and Data Communication tests what an OS manages, how processes move between states, and how data travels between devices over a network.
Core rules
- An OS is system software that manages processes, memory, files, devices and security, and provides a user interface (CLI or GUI).
- OS types include batch, multiprogramming, time-sharing, real-time, distributed and mobile. Real-time systems must meet deadlines.
- Process states: new, ready, running, waiting and terminated. Only one process per CPU core is running at a time.
- Data communication needs a sender, a receiver, a transmission medium, a message and a protocol.
- Transmission modes: simplex (one direction only), half-duplex (both directions but not simultaneously) and full-duplex (both directions simultaneously).
- Media are guided (twisted pair, coaxial cable, fibre optic) or unguided (radio, microwave, infrared).
- Networks are classified as LAN, MAN and WAN; topologies include star, bus, ring and mesh.
- Bandwidth is capacity, usually in bits per second; latency is delay.
Worked example
How long does a 10 MB file take over an 8 Mbps link, ignoring overhead? Convert megabytes to megabits: 10 × 8 = 80 megabits. Time = 80 Mb ÷ 8 Mbps = 10 seconds. Notice that MB (megabytes) and Mb (megabits) differ by a factor of 8; treating 10 MB as 10 Mb would wrongly give 1.25 seconds.
Traps that cost marks
- Confusing MB with Mb in speed calculations.
- Saying a half-duplex link allows simultaneous two-way traffic; that is full-duplex.
- Describing an OS as application software such as a word processor.
- Confusing bandwidth (capacity) with latency (delay).
- Assuming a real-time OS is simply a fast OS; the key requirement is meeting deadlines.