Persistent Storage: Understanding Magnetic Disks and Their Performance

This lecture discusses the concept of persistence in computer science, emphasizing its importance in maintaining state beyond the lifespan of a process. It begins by defining persistence and contrasting it with non-persistent states. The instructor highlights various storage media, focusing on magnetic disks, which have been crucial in computing history. The lecture explains the mechanics of magnetic disks, including their structure, operation, and performance characteristics. Key concepts such as seek time, rotational latency, and transfer time are introduced, illustrating how they affect disk performance. The instructor provides examples of disk throughput and emphasizes the significance of scheduling I/O operations to optimize performance. Different disk scheduling algorithms, including FIFO, shortest seek time first, and the elevator algorithm, are discussed, showcasing their impact on minimizing seek time and preventing starvation. The lecture concludes with a summary of the essential role magnetic disks play in modern computer systems, particularly in data centers and operating systems.