Operating System Functions

Lecturer: Dr S.M. Hand (smh22@cl.cam.ac.uk)

No. of lectures: 8

Prerequisite course: Operating Systems or Operating System Foundations

This course is a prerequisite for Distributed Systems (Part II and Diploma).

Aims

This course hopes to impart a detailed understanding of the algorithms and techniques used within operating systems. It aims to consolidate the knowledge learned in earlier courses, and to encourage students to develop an appreciation for the trade-offs involved in designing and implementing an operating system.

Lectures

• Introduction and Review. OS functions. Structures: kernel, microkernel, vertical. Multiprocessor schemes. Execution: processes and threads. User versus kernel threads. Combined scheme: scheduler activations.

• CPU Scheduling. Preemptive/non-preemptive. Static and dynamic priority schemes. Multiprocessor issues. Problems with priority. Real-time scheduling: static versus dynamic algorithms. Examples (RM, EDF, etc.). Priority inversion. SRT scheduling.

• Memory management. Logical versus physical addresses. Address binding. Single and multi-VAS models. Review: segmented/paged memory. Translation schemes. Demand paging/segmentation. Replacement strategies: OPT, FIFO, LRU (and approximations), NRU, LFU/MFU, MRU. Working set schemes. Application hooks. Prepaging and page daemons. Case studies. Other VM techniques. [2 lectures]

• Storage Systems. Basic I/O revisited. Disks. Logical volumes. RAID. Disk scheduling: FCFS, SSTF, SCAN, C-SCAN, etc. SRT disk scheduling. Disk caching; motivation, Unix buffer cache, NT cache manager, extensibility. Filing systems: overview, requirements. Data and metadata. Directory implementation. Query-based retrieval. Examples: FAT, FFS/EXT2, NTFS. Other schemes. [2 lectures]

• Protection. Requirements. Subjects and objects. Design principles. Authentication schemes. Access matrix: ACLs and capabilities. Combined scheme. Covert channels. Hardware capability systems. Software capability systems.

• Extensibility. Motivation. Low-level techniques: VM, etc. OS-level techniques: linux, NT, SPIN, Vino. User-level techniques: microkernels, Exokernel, Nemesis. Future directions.

Objectives

At the end of the course students should be able to

• differentiate threads and processes

• argue for and against dynamic priority-based scheduling

• write a simple program which implements any simple disk scheduling algorithm

• define the ``working set'' of a process

• sketch the design of a log-structured file system

• compare and contrast user- and kernel-level threads

• describe the advantages/disadvantages of the various page-replacement strategies

• understand the differences between ACLs and capabilities

• explain the operation of the RM and EDF scheduling algorithms

• discuss the benefits of disk caching

• describe three techniques for supporting extensibility

Recommended books

Bacon, J. (1997). Concurrent Systems. Addison-Wesley (2nd ed.).
Silberschatz, A., Peterson, J.L. & Galvin, P.B. (1998). Operating Systems Concepts. Addison-Wesley (5th ed.).
Tanenbaum, A.S. (1992). Modern Operating Systems. Prentice-Hall.
Leffler, S. (1989). The Design and Implementation of the 4.3BSD Unix Operating System. Addison-Wesley.
Solomon, D. (1998). Inside Windows NT. Microsoft Press (2nd ed.).
Singal, M. & Shivaratri, N. (1994). Advanced Concepts in Operating Systems: Distributed, Database, and Multiprocessor Operating Systems. McGraw-Hill.