This is a revision document with the notes from lessons. All of the content included in this booklet is what you need to know about Unit 1.2.1 from OCR’s A Level Computer Science specification. Perfect to use for revision, or as a handout. Includes the following sub-topics: The need for, function and purpose of Operating Systems Memory management (Paging, segmentation & virtual memory) Interrupts (the role of interrupts and Interrupt Service Routines (ISR), role within the fetch decode execute cycle) Scheduling (round robin, first come first served, multi-level feedback queues, shortest job first, remaining time) Distributed, embedded, multi-tasking, multi-user, and real time operating systems BIOS Device Drivers