Digital systems
Digital systems
This domain tests whether you can explain how digital systems work and how design choices shape performance, security and usability. Expect questions that ask you to identify components, trace a data flow, or justify a design trade-off rather than name hardware.
Core rules and concepts
- A system is components, relationships, a boundary and a purpose, with inputs, processes, outputs and feedback. Behaviour emerges at system level: an app can be perfectly coded and still misroute drivers through a faulty feedback loop.
- Abstraction and layers. Hardware, operating system, application, network and user each hide detail from the layer above. Standardised interfaces - protocols, APIs, file formats - are what make interoperability possible.
- Data, information, knowledge. Bits are raw symbols; information is data processed into meaning; knowledge is information placed in context and acted on.
- Networks. Packet switching routes independent packets; bandwidth is capacity, latency is delay. TCP/IP, HTTP and DNS are conventions that let heterogeneous devices exchange data.
- Security. Confidentiality, integrity and availability; authentication (who you are) is not authorisation (what you may do); hashing checks integrity while encryption protects confidentiality.
Worked example
A 4000 × 3000-pixel photo at 24-bit colour, uncompressed, is 4000 × 3000 × 3 bytes = 36,000,000 bytes, about 36 MB. Over a perfect 8 Mbps link (1 MB/s) that uploads in roughly 36 seconds. JPEG at about 10:1 compression gives 3.6 MB, so about 3.6 seconds - but it is lossy and discards detail. The reasoning to show is the trade-off: compression buys speed and storage at the cost of fidelity, and the right balance depends on purpose.
Traps that cost marks
- Confusing bandwidth with latency.
- Writing that the system decides, instead of locating the algorithm, data or human behind the decision.
- Assuming all compression is lossless, or that digital means accurate.
- Confusing authentication with authorisation.
- Listing components without explaining how they interact.