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Comp.os.research: Frequently answered questions [1/3: l/m 13 Aug 1996]

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Archive-name: os-research/part1
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Last-Modified: Tue Aug 13 21:03:39 1996
URL: http://www.serpentine.com/~bos/os-faq/

See reader questions & answers on this topic! - Help others by sharing your knowledge
		Answers to frequently asked questions
		  for comp.os.research: part 1 of 3

		       Copyright (C) 1993--1996
			   Bryan O'Sullivan



			  TABLE OF CONTENTS


1.     Introduction
1.1.   How to read this article
1.2.   Reader contributions and comments
1.3.   Acknowledgments and caveats

2.     Recurrent discussions
2.1.   Microkernels, macrokernels, and the in-betweenies
2.2.   Threads
2.2.1. Distinguishing features
2.2.2. Characterising implementations of multithreading
2.2.3. The history of threads

3.     File systems
3.1.   Extent-based versus log-structured file systems

4.     Mobile and disconnected computing
4.1.   Constraints on software
4.2.   Communications protocols
4.3.   Access to files
4.4.   Power management
4.5.   Other issues
4.6.   An introductory mobile computing bibliography

5.     Operating systems teaching
5.1.   What good undergraduate-level texts are available?
5.2.   Graduate-level texts
5.3.   Do any texts cover the implementation of specific operating systems?
5.4.   What instructional operating systems can I use?
5.5.   Where can I find the canonical list of OS papers for grad courses?




Subject: [1] Introduction From: Introduction This posting consists of answers to many of the questions most frequently asked and summaries of the topics most frequently covered on comp.os.research, the Usenet operating systems research discussion group. The purpose of this posting is to circulate existing information, and to avoid rehashing old topics of discussion and questions. Please read all parts of this document before posting to this newsgroup. This newsgroup is moderated; the moderator is Darrell Long <darrell@cse.ucsc.edu>. A companion posting to the FAQs, `Welcome to comp.os.research', briefly covers the moderation policy and guidelines for posting to comp.os.research. It can be found in either comp.os.research or news.answers, and is posted regularly. Due to its size, the FAQ is split up into three parts; each is posted once a month. The welcome posting is posted fortnightly. The FAQ is also available in hypertext form on the World-Wide Web, at <URL:http://www.serpentine.com/~bos/os-faq>. You may prefer to browse the FAQ on the Web rather than on Usenet, as it contains many useful hyperlinks. Note: chunks of text of the form [92-02-12-21-20.29] indicate the original posting from which a section of this article was inspired, snarfed, or just plain copied wholesale. The FAQ as available on the Web has hyperlinks to the relevant articles. Other chunks in square brackets are comments and reminders to myself. These latter sections of text will be removed as appropriate material is added, but the attributions will remain.
Subject: [1.1] How to read this article From: Introduction This article is posted in digest format; using the `G%' command from within the `nn' newsreader should split it up into separate sub-articles which you can browse through. To skip to a particular question numbered n.m, use `/: \[n\.m\]' from most pagers. From within GNU Emacs, you can use `C-s [n.m]'. This article is treated as an outline when edited by GNU Emacs.
Subject: [1.2] Reader contributions and comments From: Introduction Your contributions, comments, and corrections are welcomed; mail sent to <os-faq@cse.ucsc.edu> will be dealt with as quickly as I can manage. Generally, performing a reply or followup to this article from within your newsreader should do the Right Thing. While I am more than happy to include submissions of material for the FAQ if they seem appropriate, it would make my life a lot easier if such text were proof-read in advance, and kept concise. I don't have as much time as I would like to digest 15K text files and summarise them in three paragraphs for inclusion here. If you are interested in contributing material, please see the to-do list at the end of part 3 of the FAQ.
Subject: [1.3] Acknowledgments and caveats From: Introduction Although this FAQ has been the result of a co-operative effort, any blame for inaccuracies and errors lies entirely with my edits. I would like to thank the following people for their part in contributing to this article: Arindam Banerji <axb@cse.nd.edu> Surendar Chandra <surendar@cs.duke.edu> Steve Chapin <sjc@cs.purdue.edu> Crispin Cowan <crispin@csd.uwo.ca> Dan Hildebrand <danh@qnx.com> Gordon Irlam <gordoni@home.base.com> Alan Judge <amjudge@dsg.cs.tcd.ie> Darrell Long <darrell@cse.ucsc.edu> Chris Maeda <cmaeda@cs.washington.edu> Peter Magnusson <psm@sics.se> Craig Partridge <craig@bbn.com> Tom Van Vleck <tom_van_vleck@taligent.com> Robert Walsh <rjwalsh@maths.tcd.ie>
Subject: [2] Recurrent discussions From: Recurrent discussions A number of topics tend to appear with regularity in comp.os.research. This section attempts to go over some of the most commonly-covered ground. I haven't made the list of topics covered exhaustive by any means.
Subject: [2.1] Microkernels, macrokernels, and the in-betweenies From: Recurrent discussions A recurrent topic of discussion in this newsgroup has been the comparison between microkernel (for example Mach and QNX) and `macrokernel' (traditional Unix) operating systems. The basic notion of a microkernel consists of devolving as much functionality as possible into processes rather than the kernel itself; different systems take different approaches to implementing this. For example, some systems (such as Mach) leave device drivers in the kernel, and place higher-level services (such as file systems) outside; others (such as QNX) move device drivers outside of the kernel. However, anecdotal evidence [93-03-03-07-56.52] suggests that the distinction between microkernel and monolithic architectures is becoming more blurred as time goes on, as the two advance. For example, most modern monolithic kernels now implement multiple threads of execution and fine-grained parallelism. Architecturally, this approach begins to appear similar to a microkernel with several kernel-space processes working from shared memory. As an aside, people often complain that the Mach system can't be a `real' microkernel, because it is so large (at least, this is the argument most frequently cited). However, I have been told that automatically-generated code stubs contribute very significantly to the size of the kernel, and that some size reduction would be likely if MIG (the stub generator) produced better code. [Can someone from CMU comment on this?] As mentioned above, the leaving of device drivers in the kernel also contributes to Mach's size. Debating microkernels versus monolithic kernels on the basis of kernel size misses the central, architectural point. In the same way as the point of a RISC processor is not to minimise the instruction count, but rather to make a different tradeoff between what is implemented in the processor instruction set and what is implemented in other ways, the microkernel architectural issue is to determine which services are implemented in the microkernel, and which services are implemented external to that microkernel. By making appropriate choices here, the goal is to enhance various OS attributes in a manner that might not be addressable with a monolithic kernel OS. System attributes such as performance, flexibility, realtime, etc. are all variables which are taken into account. Some history: Ira Goldstein and Paul Dale were the coiners of the term `microkernel' back around 1989.
Subject: [2.2] Threads From: Recurrent discussions The exact meaning of the term `thread' is not generally agreed upon. One of the more common usages denotes a `lightweight' process (sequential flow of control) which shares an address space and some other resources with others, and for which context switching time is lower than for `heavyweight' (i.e. kernel-supported) processes. Throughout the following material, when we refer to `processes', this can be taken as meaning heavyweight processes.
Subject: [2.2.1] Distinguishing features From: Recurrent discussions Some of the features which distinguish different approaches to threading are listed below: - Number of *concurrent* flows of control: generally, threads may potentially make use of multiple processors in order to allow several to execute concurrently. That is, the model usually takes into consideration the possibility that there may be more than one flow of control active at any time. - Scheduling policy: a thread scheduler may be pre-emptive, in which case a thread is put to sleep either when it waits upon some resource or runs for the full duration of its time quantum, or non-pre-emptive, in which case individual threads continue to run until they relinquish the processor themselves (either through waiting on a resource or calling the analogue of a sleep() function). Systems which are non-pre-emptive and may only ever have a single active flow of control (regardless of the number of processors available) are referred to as coroutine systems. Coroutine programming requires quite a different approach from threads-based programming, as many of the synchronisation and resource-sharing problems which occur in threaded environments need never trouble the coroutines programmer.
Subject: [2.2.2] Characterising implementations of multithreading From: Recurrent discussions An important distinction may be made between user-level threads and kernel-supported threads. A user-level thread maintains all its state in user space. A consequence of this is that no kernel resources need to be allocated per thread, and switching between threads can be done without changing address space. A disadvantage is that user level threads cannot execute while the kernel is busy, for instance, with paging or I/O. This would require some knowledge and participation on the part of the kernel. It is possible to combine both methods, as is done in SunOS 5.x (aka Solaris 2.x). Here, one or more light weight processes (LWPs) multitask one or more user-level threads, which in turn are implemented using user-space libraries. Some issues which characterise thread implementations, and which determine the uses to which a threads package may be put, include: - How much by way of kernel resources does a thread require? This will typically limit the number of threads that can be started by a process. - Under what circumstances will the entire process hang? For instance, if some thread gets a page fault, may another thread in that process be dispatched? - Does switching threads require a full system call (as on the SPARC), or may context switches between threads be performed entirely at user level? - How are signals handled? Can signals be masked individually per thread? Is there a `broadcast' signal? - How are stacks handled? Will the stacks shrink/grow dynamically on a per thread basis? Several systems today (QNX and Plan 9, for instance) take the stance that threads `fix the symptom, but not the problem'. Rather than using threads because the OS context switch time is too slow, a better approach, according to the architects of these systems, is to fix the OS. It's ironic, now that even PC-hosted desktop OSes provide MMU-protected multitasking, the fashionable programming model has become multiple threads running in a common address space, making debugging difficult, and also making it more difficult to generate reliable code. With fast context switching, existing OS services like explicitly allocated shared memory between a team of cooperating processes can create a `threaded' environment, without opening the Pandora's box of problems that a fully shared memory space entails.
Subject: [2.2.3] The history of threads From: Recurrent discussions [93-04-21-13-32.11] [92-01-27-17-05.54] The notion of a thread, as a sequential flow of control, dates back to 1965, at least, with the Berkeley Timesharing System. Only they weren't called threads at that time, but processes [Dijkstra, 65]. Processes interacted through shared variables, semaphores, and similar means. Max Smith did a prototype threads implementation on Multics around 1970; it used multiple stacks in a single heavyweight process to support background compilations. Perhaps the most important progenitor of threads is the programming language PL/I, from about the 1965 time frame. The language as defined by IBM provided a `CALL XXX (A, B) TASK;' construct, which forked a thread for XXX. It is not clear whether any IBM compiler ever implemented this feature, but it was examined closely while Multics was being designed; it was decided that the TASK call as defined didn't map onto processes, since there was no protection between the threads of control. So Multics took a different direction, and the TASK feature was removed from PL/I by IBM in any case, along with the ABNORMAL attribute and lots of other weird stuff. Then came Unix, in the early 1970s. The Unix notion of a `process' became a sequential thread of control *plus* a virtual address space (incidentally, the Unix notion of a process derived directly from the Multics process design [Saltzer, 66]). So `processes', in the Unix sense, are quite heavyweight machines. Since they cannot share memory (each has its own address space), they interact through pipes, signals, etc). Shared memory (also a rather ponderous mechanism) was added much later. After some time, Unix users started to miss the old processes that could share memory. This led to the `invention' of threads: old-style processes that shared the address space of a single Unix process. They also were called `lightweight', by way of contrast with `heavyweight' Unix processes. This distinction dates back to the very late 70s or early 80s, i.e. to the first `microkernels' (Thoth (precursor of the V-kernel and QNX), Amoeba, Chorus, the RIG-Accent-Mach family, etc). On a side note, threads have been in continuous use in telecommunications applications for quite a long time. See also: [Cheriton, 79] Cheriton, D. R., `Multi-process structuring and the Thoth operating system', Ph.D. Thesis, University of Waterloo, 1979. [Daley & Dennis, 68] Daley, R. C., Dennis, J. B., `Virtual memory, processes, and sharing in Multics', Comm, ACM 11, 306-312, May 1968. [Dennis & van Horn, 66] Dennis, J. B., van Horn, E. C., `Programming semantics for multiprogrammed computations', MAC-TR-21, 1966. [Dijkstra, 65] Dijkstra, E. W., `Cooperating sequential processes', in `Programming Languages', Genuys, F. (ed.), Academic Press, 1965. [Saltzer, 66] Saltzer, J. H., `Traffic control in a multiplexed computer system', MAC-TR-30 (Sc.D. Thesis), July, 1966.
Subject: [3] File systems From: File systems This field is discussed both here and in the comp.arch.storage newsgroup. This section needs fleshing out at the moment; it will grow over time (hopefully!).
Subject: [3.1] Extent-based versus log-structured file systems From: File systems [92-11-18-10-57.53] [92-11-22-10-16.26] A general definition for a log-structured storage system might be the following: logging is an append-only storage semantics. The unit of logging is the record. Write accesses append records to the end of the log. A log record may become obsolete. Useless records are compacted out of the log when possible. Other write accesses are forbidden. An extent-based file system is another candicate for better filesystem performance. The approach used under QNX, for example, is to have files exist as an array of extents on disk, where each is extent is as many contiguous blocks as could be allocated at that location. By using a bitmap for space allocation, files can also grow `in-place', if adjacent free space on disk exists. This approach allows the unit of disk space allocation to remain 512 bytes, which is also the smallest unit of physical I/O. The potential performance bottleneck of this approach does not happen because the filesystem code passes I/O requests to the disk drivers in units of extents, not 512 byte blocks. The filesystem also heuristically modifies the size of the pre-read requests based on the historical access pattern to the file. This approach provides the performance advantages of larger physical disk block sizes, without the wasted disk space that results from unused portions of large blocks, or the complexity of trying to allocate space from partially unused blocks.
Subject: [4] Mobile and disconnected computing From: Mobile and disconnected computing The subject of operating systems for mobile and frequently-disconnected computers has become a recurrent topic in this newsgroup. This section attempts to give an overview of issues in this area. [Text by Arindam Banerji.]
Subject: [4.1] Constraints on software From: Mobile and disconnected computing System software for mobile computing is impeded by four distinct constraints: - Compared to stationary computers, mobile computers will always be resource poor [Satyanarayan, 93]. Although currently available PDAs (Personal Digital Assistants) compare favourably with the stand-alone workstations of a few years ago [Marsh, 93], they'll most probably lag behind in compute capabilities, available power, storage availability and communication bandwidth, for some time to come. - Mobility entails computation amid fluctuating resource availability and constraints [Banerji, 93]. Communication bandwidth may be available at discrete intervals, an available resource may suddenly become unreachable or an otherwise in-expensive communication link may be randomly replaced by an expensive alternate in transit. - Security threats to both mobile computational elements as well as the data accessed by them are greatly increased [Satyanarayan, 93]. Not only is it easier to lose, damage or be robbed of a carry-along PDA, but it is often easier to tap into the data transferred (as is well-known to much of the cellular communication industry). Very little work, except for that undertaken by the cellular communication industry, has been done in the area of addressing the specific security needs of mobile computing (as far as I know). - User needs and their application requirements may not be the same as those in stationary systems [Weiser, 91]. As mobile computers become ubiquitous (this phrase coined by Mark Weiser), the number of computer users will most probably increase exponentially. Most or many of these users will be far less computer literate than the average computer user of today. In addition, shopping, information browsing and entertainment may be the typical use of such mobile units, as opposed to traditional scientific computing, database support or word processing. - With the presence of PCMCIA slots in a PDA, it also becomes necessary for an OS to be able to mount and dismount entire OS subsystems on the fly [Hildebrand, 94]. Operating systems need to be able to treat networking, filesystems, and other services as facilities which may be loaded and unloaded on demand. Based upon an amalgam of these criteria, the next few sections discuss some of the main areas of ongoing research in mobile computing.
Subject: [4.2] Communications protocols From: Mobile and disconnected computing Mobile-IP [Myles & Perkins, 93] `allows packets between mobile hosts or networks and other hosts (including fixed hosts) to be delivered along close to optimal routes'. Compatibility with existing IP implementations is one of the key problems in Mobile-IP. For example, [Perkins et. al, 93], have suggested a scheme based upon the loose source routing option of IP packets, but most existing IP implementations do not implement this option. Scalability is yet another important issue. The Columbia scheme [Ioannidis et al., 91] uses IP-in-IP encapsulation, thus avoiding problems with non-conforming implementations; but it achieves only sub-optimal routing for mobility across widely distributed locations [Aziz, 94]. Some efficient implementations of IP-in-IP encapsulation capable of supporting near-optimal wide area mobile routing have been suggested [Aziz, 94], but more experimentation is required. For resource-constrained mobile computers, hosting a full IP protocol suite may be an unacceptable resource burden. Being able to gateway with a lightweight protocol to a network node which is hosting a `heavyweight' protocol suite is a valuable capability [Hildebrand, 94]. Lightweight protocols can also make better use of the bandwidth limitations of wireless communications. Apart from this, architectures and implementations that handle the impact of mobility at higher layers have also been proposed -- such as the connection-oriented services discussed by Katz [Keeton et. al., 93], and the mobile socket interface discussed by Casey [Casey, 93]. Current trends would appear to suggest that some form of Mobile-IP will soon become standard, whereas connection maintenance and caching in higher-level protocols still needs to be resolved.
Subject: [4.3] Access to files From: Mobile and disconnected computing File access in a mobile computing environment, where the communication link to a file server is not guaranteed, has been a major area of study. Coda [Satyanarayan, 90], a descendant of the Andrew File system (AFS), pioneered support for disconnected operations in file-systems. Coda increases file availability by replicating a single volume at multiple server locations. Disconnected operations occur when the set of accessible servers for a particular volume becomes null. Coda supports disconnected operations by pre-caching the files a user is most likely to need and then allowing all operations on cached copies of these files, while disconnected. Upon reconnection, reintegration occurs through reconciliation of the cached copy with the now-reachable server's copy, through the use of a replay log maintained during the disconnection. Disconnected operations have also been implemented for AFS [Huston, 93]. The highly available peer-to-peer based Ficus [Page, 91] file system achieves similar results, although mobile computing was not one its initial applications. Caching issues are beginning to predominate the open research topics in this area. In between connected and disconnected states, there are many states of expensive, intermittent and unreliable connections. Adapting caching to these varying situations is a necessity. More importantly, as introduced by the Hoarding scheme of Coda, user control over some caching behavior is extremely beneficial, and this need for user input becomes even more important when the server connection is weak.
Subject: [4.4] Power management From: Mobile and disconnected computing Current battery technology limits PDA use to only a few hours. The conservation of power through system software is thus becoming a major area of research in mobile computing. Two specific approaches to this problem exist. - Some researchers [Greenawalt, 93] are attempting to analyse the effects of application type, user input and operating system implementations on device power consumption. Based upon simulation data, several power consumption models have been proposed for disks [Greenawalt, 93] [Douglis & Marsh, 93]. Work in characterising and analysing the power consumption problem is still ongoing. - Several industry-led efforts, on the other hand, have focussed on building system support for dynamic power-saving mechanisms. The Advanced Power Management standard presents an interface and structure for manipulating power consumption. The Nomadic System Group at Sun Microsystems has integrated similar support into SVR4 [Bender et. al, 93]; these facilities are also available in QNX. Complete analysis of peripheral device power usage and experimentation with different strategies for implementing power management will certainly be useful.
Subject: [4.5] Other issues From: Mobile and disconnected computing Two significant aspects of mobile computing give applications in this environment a very different flavour. - The dynamic nature of the environment forces applications to handle changes in the availability and allocation of software resources. Dynamic changes to environment variables [Schilit, 93], change in the available version of a library [Goldstein, 94] and the ability to lookup and retrieve objects from remote locations [Theimer, 93] are all required to solve this problem. For the very same reasons, user interfaces add on an extra dimension, an issue which very few have addressed so far [Landay & Kaufmann, 93]. All this has caused certain vendors to move towards interpreted environments, based on scripting(??) languages as such as Script-X (Kaleida) and Open Scripting Architecture (Apple). - Money will be a constituent of many of the transactions and applications that mobile computers will typically be used for. Hence, many pieces of system software will be required to handle, understand and optimise the use of money [Kulkarni, 94]. As mentioned by Ed Frank at the ICDCS '93 panel discussion on mobile computing, transaction involving `money and sex' may well become the biggest uses of the mobile computer. Some initial forays into reviewing policies for pricing Internet services [Shenker, 93] may prove to be very useful and so will the experience of current consumer service providers such as CompuServe and America Online. This area will perhaps show the biggest divergence in the years to come, since applications will be far more customer-needs driven than technology-driven, as they have been in the past. Finally, aspects of hardware support are critical to positioning any discussion on mobile computing. The most ambitious system is perhaps the ParcTab system [Schilit, 93] under development at Xerox PARC. The ParcTab is a PDA that communicates via infrared data packets to a network of infrared transceivers. The network, designed for use within a building, designates each room as a communication cell. This infrastructure has the responsibility for providing reliable service as the ParcTab user moves from room to room. More general purpose but less ambitious PDAs are currently available from AT&T (EO), Apple (Newton), IBM (Simon) etc. Almost all recognise some alternate form of input, such as handwriting. The capabilities of these PDAs are sure to increase in the coming years, and hopefully their prices will not follow a similar trend.
Subject: [4.6] An introductory mobile computing bibliography From: Mobile and disconnected computing [Marsh, 93] Marsh, B., Douglis, F. & Caceres, R., `System issues in mobile computing', Technical Report, Matsushita Information Technology Laboratory, ITL-TR-50-93 [Satyanarayanan, 93] Satyanarayanan et. al, `Experience with disconnected operation in a mobile computing environment', Proceedings of Mobile and Location-Independent Computing Symposium, August 93, pp. 11-28 [Banerji, 93] Banerji, A., Cohn, D. & Kulkarni, D., `Mobile computing personae', Proceedings of Fourth Workshop on Workstation Operating Systems, October 93, pp. 14-20 [Weiser, 91] Weiser, M., `The computer for the 21st century', Scientific American, September 91, pp. 94-104 [Myles & Perkins, 94] Myles, A. & Perkins, C., Internet Draft, September, 93 [Perkins et. al, 93] Bhagwat, P. & Perkins, C., `A mobile networking system based on IP', Proceedings of Mobile and Location-Independent Computing Symposium, August 93, pp. 69-82 [Ioannidis et. al, 91] `IP based protocols for mobile internetworking', Proceedings of the SIGCOMM-91 conference: Communications, Architectures and Protocols, September 91, pp. 235-245 [Aziz, 94] Aziz, A., `A scalable and efficient intra-domain tunneling mobile-IP scheme', ACM SIGCOMM-Computer Communications Review, Vol 24., No. 1, January 94, pp. 12-20 [Keeton et al., 93] Keeton, K. et al., `Providing connection oriented network services to mobile hosts', Proceedings of Mobile and Location-Independent Computing Symposium, August 93, pp. 83-102 [Casey, 94] Casey, M., `Application and communication support for mobile computing', Dissertation Proposal, University of Notre Dame, January 94 [Satyanarayanan, 90] Satyanarayanan, M., et al., `Coda: A highly available File-system for a distributed workstation environment', IEEE Transactions on Computers 39(4), April 90 [Huston, 93] Huston, L. & Honeyman, P., `Disconnected operation for AFS', Proceedings of Mobile and Location- Independent Computing Symposium, August 93, pp. 1-10 [Page, 91] Page, T. et al., `Architecture of the Ficus replicated file system', Tech Report CSD-910005, University of California, Los Angeles, March 91 [Greenawalt, 93] Greenawalt, P., `Modelling power management for hard disks', Intl. Workshop on Modelling, Analysis & Simulation of Computer and Telecommunication Systems, January 94 [Douglis & Marsh, 93] Douglis, F. & Marsh, B., `Low power disk management for mobile computers', Technical Report, Matsushita Information Technology Laboratory, MITL-TR-53-93 [Bender et. al, 93] Nomadic Systems Group, Sun Microsystems, `UNIX for Nomads: Making UNIX support mobile computing', Proceedings of Mobile and Location-Independent Computing Symposium, August 93, pp. 53-68 [Schilit, 93] Schilit, B., Theimer, M. & Welch, B., `Customizing mobile applications', Proceedings of Mobile and Location-Independent Computing Symposium, August 93, pp. 129-138 [Hildebrand, 94] Hildebrand, D., `QNX: microkernel technology for open systems handheld computing', Proceedings of Pen and Portable Computing Conference Exposition, May 1994. Available via ftp from <URL:ftp://ftp.qnx.com/pub/papers/>. [Goldstein, 94] Goldstein, T. & Sloane, A., `The object binary interface -- C++ objects for evolvable shared class libraries', Proceedings of the USENIX C++ Conference, April 94 [Theimer, 93] Theimer, M., Demers, A. & Welch, B., `Operating system issues for PDAs', Proceedings of Fourth Workshop on Workstation Operating Systems, October 93, pp. 14-20 [Landay & Kaufmann, 93] Landay, J. & Kaufmann, T., `User-interface issues in mobile computing', Proceedings of Fourth Workshop on Workstation Operating Systems, October 93, pp. 40-47 [Kulkarni, 94] Kulkarni, D., Banerji, A., Cohn, D., `Operating systems and cost management', Operating Systems Review, January 94. [Shenker, 93] Shenker, S., `Service models and pricing policies for an integrated services Internet', Proceedings on Conference on Public Access to the Internet, JFK School of Government, Harvard University, May 93 [Schlitt, 93] Schlitt et al., `The ParcTab mobile computing system', Proceedings of Fourth Workshop on Workstation Operating Systems, October 93, pp. 34-39
Subject: [5] Operating systems teaching From: Operating systems teaching This section attempts to give some useful pointers to people who teach operating systems, both at undergraduate and postgraduate level.
Subject: [5.1] What good undergraduate-level texts are available? From: Operating systems teaching The comments below have been provided by a variety of people, so any `me's or `I's you encounter are not necessarily those of the maintainer! - `Operating Systems Concepts', fourth edition, by Abraham Silberschatz and Peter Galvin is the latest version of this popular text. Addison-Wesley, 1994, ISBN 0-201-50480. This book has been revised to include new and updated information, examples, diagrams, and an expanded bibliography. I think this is the `standard' OS text, although I have a couple of others that I also think are good, and that I draw from when I teach OS. Previous editions of the dinosaur book don't have the greatest organisation, and sometimes wander when describing things. Its strong point lies in the copious examples. Speaking of the third edition (I haven't seen a copy of the fourth edition yet): The first 84 pages cover operating system basics, the next 120 pages cover process management including 30 pages on deadlocks. 130 pages on storage management: memory, virtual memory, secondary storage. 70 pages on file systems and protection. Then 100 pages on distributed systems. The last part of the book has case studies on Unix and Mach: 50 pages on Unix and 30 pages on Mach. The last chapter gives a short 10 page historical perspective. Mail a message with contents `send help' to <os4e@aw.com> for further details of the new edition. The book gives a good (but slightly theoretical) overview of operating system concepts. A good complement would be the books covering Minix or BSD, which are more implementation-oriented. - `Operating Systems', Harvey Deitel, Addison-Wesley, 1990, ISBN 0-201-18038-3. Not a bad book; gives the same sort of theoretical treatment of operating systems as the dinosaur book. Includes case studies on Unix, MS DOS, MVS, VM, the Macintosh OS, and OS/2. - `An Operating Systems Vade Mecum', second edition, by Raphael Finkel, 1988, Prentice Hall, ISBN 0-13-637950-8. I really like this book; it is a bit more theoretical than the dinosaur book, but is well-written and clear. I would accompany it with labs based on one of the educational experimental OS's (NachOS, OSP) for hands-on experience. The edition mentioned above is now out of print. However, it may be obtained via anonymous ftp from <URL:ftp://ftp.ms.uky.edu/pub/tech-reports/UK/cs/>. Here is the associated chunk of README: This textbook is out of print. It was published by Prentice Hall. The author now owns the copyright. Permission is granted to copy this text for any noncommercial purpose. Feel free to generate copies of the text for your students. You may also photocopy the original book without restriction. Kindly send suggested upgrades to the author: <raphael@ms.uky.edu>. He is planning a new edition sometime. [It's been a few years since I've looked at this book, so I can't remember what it contains. Can anyone help?] - `The Logical Design of Operating Systems', second edition, Lubomir Bic, Alan Shaw, 1988, Prentice Hall, ISBN 0-13-540139-9. This one isn't as theoretical as Finkel's book, nor is it as long as the dinosaur book. I haven't tried to use it in a course yet, but it looks like a fairly well-rounded text. [Can anyone write a paragraph on the various topics covered ... ?] - `Operating Systems', second edition, William Stallings <ws@shore.net>, Prentice-Hall, 1995, ISBN 0-02-415493-8. I received very positive feedback from students about the first edition of this book; I have not yet seen the second edition. The explanations of topics were easy to understand and complete. An especially nice feature was that at the end of each chapter OS/2, Unix and MVS were used to demonstrate real life implementations of the theory talked about. I found this tying together of theory and practice much nicer than having the practice lumped at the end of the book. - `Modern Operating Systems,' Andrew Tanenbaum <ast@cs.vu.nl>, 1992, Prentice Hall, ISBN 0-13-588187-0. This started out as a rewrite of the Minix book, but he pulled the Minix-specific material and added seven chapters on distributed systems. It's a bit heavy for undergrads, depending on how far into the distributed systems you go, but I like Tanenbaum as an author. He'll be bringing out a second edition of the Minix book sometime soon; as he says, one is for `hands-on' (Minix) and one is for `hands-off' (Modern OS). The book is divided into two parts: `traditional' introductory material, taken more or less verbatim from the Minix book, and an introduction to distributed systems. Each parts concludes with a case study and comparison of two well-known systems (Unix and MS-DOS, and Mach and Amoeba). The bibliography at the end is organised well for more advanced coverage of the topics encountered throughout the book. Topics covered in the first part include process concepts, memory management, file system organisation and I/O, and deadlock detection and avoidance. The second part addresses issues such as distributed communication, synchronisation (the section on clock synchronisation is well put together), processes in distributed environments (nothing on process migration), and distributed file systems (using AFS as an example). The second part seems more suitable for advanced undergraduate level or introductory graduate level studies. This book has been translated into German; it is available from Carl Hanser Verlag as `Moderne Betriebssysteme', ISBN 3-446-17472-9. - `Operating System Design: the Xinu Approach', Douglas Comer, Timothy Fossum, 1984, Prentice Hall, ISBNs 0-13-638180-4 (PC edition) and 0-13-638529-X (Macintosh edition). A walk-through of the principles behind, and implementation of, the Xinu operating system, a small instructional OS similar to Unix. While this text is aging somewhat, it presents its material in a clear fashion, and does a good job of covering the "standard" fundamentals of operating systems. - `Operating Systems: Design and Implementation', Andrew S. Tanenbaum, 1986 (?), Prentice Hall, ISBN 0-13-637406-9. This, along with Comer's Xinu books, is the classic text which `teaches by doing', covering the design and implementation of Minix, a microkernel operating system which has a programming and user interface similar to Unix. As with Comer's books, this text is showing its age somewhat (the source is very much out of date with the current Minix distribution), but it still does a good job of presenting the basics of operating system implementation. - `Operating Systems Programming: The SR Programming Language', Stephen J. Hartley <shartley@mcs.drexel.edu>, Oxford University Press, 1995, ISBN 0-19-5095790. SR is a language for concurrent programming; this book presents the language, presents some example programs in the context of operating systems or concurrent programming, and provides exercises in the form of Open Student Laboratories. The book is designed to be used in conjunction with one of the standard operating systems texts to provide concurrent programming experience, or can be used alone as an introductory concurrent programming book. I have not seen a copy of it yet, and so cannot comment on its quality. The example programs in the book are intended for running in a Unix environment; they are available via anonymous ftp from <URL:ftp://mcs.drexel.edu/pub/>, and the SR language itself is available from <URL:ftp://cs.arizona.edu/>.
Subject: [5.2] Graduate-level texts From: Operating systems teaching This section is still under construction. - `Distributed Systems', second edition, by Sape Mullender, Addison-Wesley, 1994, ISBN 0-201-62427-3. A review is forthcoming. - `Distributed Operating Systems -- the Logical Design', Andrzej Goscinski, Addison-Wesley, 1991, ISBN 0-201-41704-9. A thorough desk reference, but reads a little too much like an encyclopedia for use as a textbook. - `Modern Operating Systems,' Andrew Tanenbaum <ast@cs.vu.nl>, 1992, Prentice Hall, ISBN 0-13-588187-0. The section of this book which covers distributed systems is suitable for use at introductory graduate level. See above for further details. - `Concurrent Systems', Jean Bacon, 1992, Addison-Wesley, ISBN 0-201-41677-8. This covers much the same material as `Modern Operating Systems', but goes into rather more detail on databases and languages. The book is divided into four parts, and comes with a separate instructor's manual (ISBN 0-201-62406-0). The first covers basic material, such as OS functions, and system and language support for concurrent processes. Part 2 deals with simple concurrent actions, covering topics such as shared-memory IPC, message passing, persistent data, crashes, and distributed data. The third part of the book covers transactions, concurrency control, and failure recovery. The final section presents a set of case studies, with Unix, Mach and Chorus being covered, along with some of the work done at Cambridge over the past decade. An interesting emphasis is placed on language-level support for concurrency throughout the book, and the focus on database issues is also a good thing. I haven't read the book in as much detail as I would like, but it seems to be well put together. The cramming of so many topics under one cover means that there is probably too much material for a single undergraduate course, and the book perforce does not go into as much detail as I would like on some topics (a problem I also find with Tanenbaum's book). Well worth a look, however. - `Distributed Systems: Concepts and Design', second edition, George Coulouris <George.Coulouris@dcs.qmw.ac.uk>, Jean Dollimore, and Tim Kindberg, Addison-Wesley 1994, ISBN 0-201-62433-8. This text treats a wide variety of issues at a level suitable for advanced undergraduate and postgraduate teaching. Basic topics covered include IPC, networking and RPC, upon which notions of distributed operation and provision of services are built. Coverage of distributed synchronisation leads on to a treatment of replication, simple transactions and concurrency control. The final chapters include material on distributed transactions, fault tolerance, security, and distributed shared memory. Illustrative examples taken from modern `real world' systems such as Sun RPC, the Andrew File System, and PGP are provided throughout the book, and case studies of the Amoeba, Mach, Chorus, and Clouds systems appear towards the end. Exercises are presented at the end of each chapter. The prose is clear, and the layout pleasant. This is, by a narrow margin, the best distributed systems textbook I have come across. - `Advanced Concepts in Operating Systems -- Distributed, Multiprocessor, and Database Operating Systems', Mukesh Singhal, Niranjan G. Shivaratri, McGraw-Hill, 1994, ISBN 0-07-057572-X. A solid work on advanced operating systems, with some emphasis on theoretical aspects. Well over 2/3 of the book focuses on distributed operating systems. It does a good job of covering all the bases, but at times omits vital information or obfuscates what should be simple issues.
Subject: [5.3] Do any texts cover the implementation of specific operating systems? From: Operating systems teaching Some books commonly used in conjunction with the texts listed above are: - `The Design and Implementation of the 4.3BSD Unix Operating System', Samuel Leffler, Kirk McKusick, Michael Karels, John Quarterman, 1989, Addison-Wesley, ISBN 0-201-06196-1. This book describes the kernel of 4.3BSD Unix in some detail, covering process and memory management (the latter being heavily VAX-oriented), file system organisation, device driver internals, terminal handling, IPC, network communications, some details of the Internet protocols, and system operation. I found this book to be well-written and concise. Accompanying the above is the `4.3BSD Answer Book', Samuel Leffler, Kirk McKusick, 1991, Addison-Wesley, ISBN 0-201-54629-9. This short book provides answers to all of the exercises found at the end of each chapter in the daemon book. - `The Design of the Unix Operating System', Maurice Bach, 1986, Prentice Hall, ISBN 0-13-201757-1. This is the authoritative description of the internals of System V Release 2 Unix. Due to copyright restrictions, it contains no actual code, but rather pseudo-code (I didn't find this to be a problem). Topics covered include file system internals, process control and scheduling, memory management, IPC, and device driver architecture. Coverage of mutliprocessor and distributed Unix systems is dated, but this remains a classic operating systems text. - `The Magic Garden Explained: The Internals of Unix System V Release 4', Berny Goodheart, James Cox, 1994, Prentice Hall, ISBN 0-13-098138-9. This books covers the workings of SVR4 in substantial detail; it is more detailed than either of the above texts, and appears to be of very high quality. While the authors recommend the book be read in parallel with study of the original Unix source code, sufficient pseudocode representation of the key algorithms has been included to permit a more or less detailed study without restricted access to the original source code. - `Unix Internals: The New Frontiers', Uresh Vahalia, 1995, Prentice Hall, ISBN 0-13-101908-2. This is quite simply a wonderful book. The broad issues it covers include threads and lightweight processes, and how they interact; signal implementations, process group and session management; process scheduling; IPC; kernel synchronisation and multiprocessor architectures; local and distributed filesystems; kernel memory management; and device driver architectures. Each topic is accompanied by details of its implementation under modern Unix variants such as Solaris 2.x, SVR4.2, and 4.4BSD, and its treatment by the Mach kernel. The writing style is concise and pleasant, and the treatment of each topic is satisfyingly thorough and clear. If you are interested in the implementation of Unix or other operating systems, this book is a "must have". - `Unix Systems for Modern Architectures: Caching and Symmetric Multiprocessing for Kernel Programmers', Curt Schimmel, 1995, Addison-Wesley, ISBN 0-201-63338-8. Covers in extensive detail the operation of caches and symmetric multiprocessors, how they interact, and the issues operating systems must address in order to make effective use of them. Issues addressed include the management of virtually- and physically-tagged caches on uniprocessors, synchronisation and mutual exclusion techniques for multiprocessors, standard multiprocessor kernel architectures, and multiprocessor cache coherency. This book is written in a clear manner, and illustrated effectively. Each chapter ends with lists of exercises and references. My copy contains a number of typographical errors, but I am told that later printings have addressed this issue. I am not aware of any similar book which covers the implementation of a distributed system.
Subject: [5.4] What instructional operating systems can I use? From: Operating systems teaching - Minix, from Amsterdam's Vrije Universiteit, was developed by Andy Tanenbaum <ast@cs.vu.nl>, and is a mostly-Unix lookalike based on a message-passing microkernel-similar architecture. The system is used in Tanenbaum's `Modern Operating Systems' and its predecessor, `Operating Systems: Design and Implementation'. See the Minix Information Sheet, posted regularly to comp.os.minix, for ordering information; Minix is copyrighted and is not in the public domain, but is available from <URL:ftp://ftp.cs.vu.nl/pub/minix>. For further information, see Andy's Web page at <URL:http://www.cs.vu.nl/~ast>. - NachOS is an instructional OS developed at Berkeley by Tom Anderson <tea@cs.berkeley.edu>, Wayne Christopher, Stephen Procter (and others?). It currently runs on DEC MIPS and Sun SPARC workstations, HP PA-RISC, and 386BSD machines. The NachOS system, along with sample assignments and an overview paper which was presented at Usenix, is available via anonymous ftp from <URL:ftp://ftp.cs.berkeley.edu/ucb/nachos>. - OSP (current version is 1.7) is an operating systems simulator, available via ftp from <URL:ftp://sblapis1.cs.sunysb.edu>, with username ospftp, and password as in the instructor's guide. Used in `OSP---an Environment for Operating Systems', Michael Kifer, Scott Smolka, Addison-Wesley. - RCOS (Ron Chernich's Operating System) is a simulated operating system that is intended to demonstrate graphically the concepts behind operating systems. Students can investigate and modify the algorithms it uses, and write programs in a Pascal-like language (extended with semaphores and shared memory) which it will execute. RCOS has a windowing interface, and currently runs under MS-DOS; an alpha-quality Unix/X11 port is also available. For further details, check out the Web page at <URL:http://cq-pan.cqu.edu.au/david-jones/projects/rcos>. - SunOS Minix consists of a set of patches for Minix which allows the Minix system to run in a single monolithic Unix process on top of SunOS 4.x on Sun 3 and Sun 4 machines. SunOS Minix is produced by applying a set of patches to Mac Minix 1.5 (both 1.5.10.0 and 1.5.10.1 can be used) or PC Minix 1.5. Also, Atari Minix has been used as the base version by at least one person. The latest version (2.0) includes a preliminary attempt at a port to Solaris 2.x. SunOS Minix is available via anonymous ftp from <URL:ftp://csc.canterbury.ac.nz/UNIX/>. - VSTa is not intended as an instructional operating system, but it is certainly small and concise enough to be tractable, and the code is clean and provides modern microkernel features. See part 2 of the FAQ for further details. - Xinu was developed at Purdue by Doug Comer and some others. It was designed to be small and layered, so that the code is succinct and easily understandable. It is intended for education, and is a `conventional' operating system. Xinu runs on the IBM PC, Sun-3, SPARC, LSI, MIPS, Macintosh, and VAX architectures. The system is used in Comer's `Operating System Design: the Xinu Approach'. See <URL:http://www.cs.purdue.edu/homes/dec/xlicense.html> for licensing information.
Subject: [5.5] Where can I find the canonical list of OS papers for grad courses? From: Operating systems teaching [93-03-14-17-09.47] Darrell Long <darrell@cse.ucsc.edu> maintains a bibliography which provides a good starting point for graduate OS course reading lists. This may be imported using refdbms as ucsc.grad.os, from refdbms.cse.ucsc.edu 4117 or refdbms.cs.vu.nl 4117.

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