BIG IDEA 4: COMPUTER SYSTEMS AND NETWORKS · CHEAT SHEET
Computer Systems and Networks — the one-page version
Every key term and every exam tip from the 3 topics in this big idea. Print it, fold it, read it on the bus.
4.1The Internet
- Computer network
- interconnected devices that can send and receive data
- Internet
- a global network of networks using open protocols
- Packet
- a small unit of data with metadata for routing and reassembly
- Router
- a device that forwards packets toward their destination
- IP address
- a unique numeric address for a device on a network
- Protocol
- an agreed set of rules for formatting and transmitting data
- TCP
- a protocol that ensures reliable, ordered delivery of packets
- DNS
- the system that translates domain names into IP addresses
- Bandwidth
- the maximum rate of data transfer, in bits per second
- World Wide Web
- a system of linked resources accessed over the internet via HTTP
Tip: Two distinctions the exam loves: internet vs. World Wide Web (network vs. a service on it), and TCP vs. UDP (reliable/ordered vs. fast/unguaranteed). And if an option says packets must travel the same route or arrive in order, it's wrong — they don't, and reassembly handles it.
4.2Fault Tolerance
- Fault tolerance
- the ability of a system to keep working when components fail
- Redundancy
- having multiple copies or paths so a single failure isn't fatal
- Single point of failure
- a component whose failure would bring down the system
Tip: For network-diagram questions, count paths. Ask: for each connection, if I delete it, can every device still reach every other? A connection whose removal isolates a device is the vulnerability. The answer to "how do we improve fault tolerance" is always "add another path."
4.3Parallel and Distributed Computing
- Sequential computing
- operations executed one after another on a single processor
- Parallel computing
- splitting a task across multiple processors running at the same time
- Distributed computing
- multiple networked computers cooperating on one problem
- Speedup
- sequential time divided by parallel time
Tip: For the timing calculation: (1) list tasks that must be sequential — they add up; (2) for parallel tasks, distribute them to balance the processors and take the longest processor's total; (3) add the two. The answer is never the average of parallel tasks — it's the maximum.