What are some common algorithms used in operating system development?

1 Scheduling algorithms

Scheduling algorithms are used by the operating system to determine how CPU time is allocated to processes that are ready to run. Different algorithms have different objectives, such as maximizing throughput or minimizing response time. Some of the most common scheduling algorithms are First-come, first-served (FCFS), Shortest job first (SJF), Round-robin (RR), Priority-based, and Multilevel feedback queue. FCFS assigns the CPU to the process that arrives first and runs until completion or interruption. SJF assigns the CPU to the process with the shortest estimated run time and runs until completion or interruption. RR assigns the CPU for a fixed time slice or quantum and rotates them in a circular queue. Priority-based assigns the CPU to the process with the highest priority and runs until completion, interruption, or preemption by a higher-priority process. Lastly, Multilevel feedback queue uses multiple queues with different priorities and time slices and moves processes between them based on their behavior and feedback.

2 Memory management algorithms

Memory management algorithms are used by operating systems to allocate physical and virtual memory to processes. These algorithms strive to maximize memory utilization, reduce fragmentation, and prevent swapping or paging. Common memory management algorithms include fixed partitioning, variable partitioning, paging, segmentation, and virtual memory. Fixed partitioning divides physical memory into fixed-sized partitions and assigns one partition to one process at a time. Variable partitioning divides the physical memory into variable-sized partitions based on the size of the processes and uses best fit, worst fit, or first fit to allocate them. Paging divides the physical memory and the virtual memory into equal-sized pages and frames and maps them using a page table. Segmentation divides the virtual memory into variable-sized segments that correspond to logical units of a process and maps them to the physical memory using a segment table. Virtual memory uses a combination of paging and segmentation to allow the processes to use more memory than the available physical memory by swapping or paging the pages or segments to the disk.

3 File system algorithms

File system algorithms are used to optimize disk space, reduce access time, and ensure data reliability and security. Common algorithms include file allocation, which determines how disk blocks are allocated to files; directory structure, which determines how files and directories are arranged and named; free space management, which keeps track of free disk blocks; and disk scheduling, which determines the order in which the operating system services disk requests. File allocation methods include contiguous, linked, indexed, or combined allocation. Directory structure structures include single-level, two-level, tree-structured, acyclic graph, or general graph. Free space management techniques include bit vector, linked list, grouping, or counting. Disk scheduling strategies include first-come, first-served, shortest seek time first, scan, c-scan, or look.

4 Synchronization algorithms

Synchronization algorithms are used by the operating system to coordinate the concurrent execution of multiple processes or threads that share resources or data. Their goal is to prevent race conditions, deadlocks, starvation, or inconsistency. Mutual exclusion, for example, ensures that only one process or thread can access a critical section or a shared resource at a time by using locks, semaphores, monitors, or message passing. Deadlock detection and avoidance resolves the situation where a set of processes or threads are waiting for each other to release the resources they hold through methods such as resource allocation graph, banker's algorithm, or wait-for graph. The dining philosophers problem illustrates the problem of synchronization and deadlock in a scenario where five philosophers share five forks and need two forks to eat with solutions such as resource hierarchy, odd-even rule, or arbitrator. Lastly, the producer-consumer problem illustrates the problem of synchronization and buffering in a scenario where one or more producers produce items and one or more consumers consume them with solutions such as bounded buffer, semaphore, or monitor.

5 Security algorithms

Security algorithms are used to protect the system and data from unauthorized access, modification, or damage. They aim to ensure the confidentiality, integrity, and availability of resources and information. Authentication algorithms verify the identity of users or processes using passwords, tokens, biometrics, or certificates. Authorization algorithms determine the permissions and privileges of users or processes using access control lists, role-based access control, or mandatory access control. Encryption algorithms transform data into an unreadable form with symmetric-key encryption, asymmetric-key encryption, or hashing. Auditing algorithms record and monitor activities and events on the system with logs, alerts, or reports.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?