Computer Systems, Networks, and Security
This domain tests computer organization, operating-system roles, network layering and addressing, and security principles. Expect questions that connect a protocol or security control to its purpose.
Systems fundamentals
- The CPU repeats fetch, decode, and execute. Registers are fastest, then cache, RAM, and secondary storage.
- Virtual memory maps logical addresses to physical frames and can use disk when RAM is full.
- An operating system schedules processes, manages memory and files, and enforces permissions.
Networks
- The TCP/IP model includes application, transport, internet, and link layers. TCP is connection-oriented and reliable; UDP is connectionless and does not guarantee delivery.
- IP addresses identify interfaces; MAC addresses identify link-layer hardware. Private ranges include 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.
- DNS resolves names to addresses; DHCP assigns addresses; HTTP carries web requests.
Security
- The CIA triad is confidentiality, integrity, and availability. Authentication proves identity; authorization grants permissions.
- Symmetric encryption uses one shared key; asymmetric encryption uses a public/private key pair. Hashing verifies integrity but is not encryption.
- Firewalls filter traffic; TLS protects data in transit. Common attacks include phishing, malware, denial of service, and SQL injection.
Worked example
For 192.168.10.0/26, how many usable host addresses exist? The prefix is 26 bits, so host bits are 32 - 26 = 6. Total addresses are 2^6 = 64. Subtract the network and broadcast addresses to get 62 usable hosts. The subnet mask is 255.255.255.192 because the last octet has two high bits set: 128 + 64 = 192.
Traps that cost marks
- Confusing MAC addresses with IP addresses.
- Treating UDP as reliable or connection-oriented.
- Counting all addresses in a subnet as usable hosts.
- Calling a hash an encryption method.
- Mixing authentication with authorization.