Operating Systems

What an operating system is for, how it is organised and how programs talk to it.

• Goals and functions of an operating system
• Kernel mode and user mode
• System calls and the API
• Monolithic, layered, microkernel and modular structures
• Interrupts and the boot process
• Types of systems: batch, time-sharing, real-time, distributed

Covered in 1:1 mentoring sessions

The process abstraction, its life cycle and how threads share work inside it.

• Process, program and process control block
• Process states and transitions
• Context switching
• Process creation and termination (fork, exec, wait)
• Threads, user and kernel threads, multithreading models
• Inter-process communication: pipes, shared memory, message passing

• Processes, threads, process states and context switching

How the operating system chooses which process runs next.

• Scheduling criteria: utilisation, throughput, turnaround, waiting, response
• First-come first-served and shortest job first
• Shortest remaining time and priority scheduling
• Round Robin and time quantum
• Multilevel queue and multilevel feedback queue
• Gantt charts and average time calculations
• Introduction to real-time and multiprocessor scheduling

• CPU scheduling: FCFS and SJF
• CPU scheduling: Round Robin, priority and multilevel queues

Keeping shared data correct when many processes or threads run together.

• Race conditions
• The critical-section problem and its three requirements
• Peterson's solution and hardware support (test-and-set, compare-and-swap)
• Mutex locks and semaphores
• Producer-consumer, readers-writers and dining philosophers
• Monitors and condition variables

• Synchronisation, critical sections and semaphores

When processes wait forever, and what the system can do about it.

• System model and resource-allocation graphs
• Four necessary conditions for deadlock
• Deadlock prevention
• Deadlock avoidance and safe states
• The banker's algorithm
• Deadlock detection and recovery

• Deadlock: conditions, prevention and avoidance

How memory is divided and mapped for many processes at once.

• Address binding, logical and physical addresses
• Contiguous allocation, fragmentation and compaction
• First fit, best fit and worst fit
• Paging, page tables and the TLB
• Multi-level and inverted page tables
• Segmentation and segmentation with paging

• Memory management: paging and segmentation

Running programs larger than physical memory by loading pages only when needed.

• Demand paging and page faults
• Page replacement: FIFO, optimal and LRU
• Belady's anomaly and the clock algorithm
• Frame allocation
• Thrashing and the working-set model
• Copy-on-write and memory-mapped files

• Virtual memory and page replacement algorithms

How the operating system manages disks and devices.

• I/O hardware, polling, interrupts and DMA
• Disk structure and access time
• Disk scheduling: FCFS, SSTF, SCAN, C-SCAN, LOOK
• RAID levels
• Buffering, caching and spooling
• Device drivers

Covered in 1:1 mentoring sessions

How files and directories are named, stored and protected.

• File concepts, attributes and operations
• Directory structures
• Allocation: contiguous, linked, indexed, inodes
• Free-space management
• File system mounting and access methods
• Journaling and crash consistency (overview)

• File systems and basic Linux concepts

Access control basics, and exam-style practice across the whole syllabus.

• Goals of protection and the access matrix
• Authentication and common threats
• Virtualisation and containers (overview)
• Mixed numerical practice
• Short-answer and concept questions
• Past-paper style revision plan

• Practice: OS rapid-fire and numericals