Meeting Pearls 1/Meeting Pearls Vol 1 (1994).iso/installed_progs/text/faqs/os-research.part1

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Subject: Comp.os.research: Frequently answered questions [1/2]
Newsgroups: comp.os.research,comp.answers,news.answers
From: [e-mail] (Bryan O'Sullivan)
Date: 1 May 1994 08:58:56 GMT

Archive-name: os-research/part1
Version: $Revision: 1.13 $
Last-Modified: $Date: 1994/04/29 22:00:19 $

        Answers to frequently asked questions
          for comp.os.research: part 1 of 2

              Copyright (C) 1994
               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.     Distributed systems
4.1.   What is the current status of the (insert name) project?
4.2.   How do approaches to load balancing differ?
4.3.   Fault tolerance in distributed systems
4.4.   Naming in distributed systems
4.5.   Distributed shared memory
4.6.   What have we learned?

5.     Mobile and disconnected computing
5.1.   Constraints on software
5.2.   Communications protocols
5.3.   Access to files
5.4.   Power management
5.5.   Other issues
5.6.   An introductory mobile computing bibliography

6.     Operating systems teaching
6.1.   What good undergraduate-level texts are available?
6.2.   What instructional operating systems can I use?
6.3.   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 both parts of this document before posting to
this newsgroup.

This newsgroup is moderated; the moderator is Darrell Long
<[e-mail]>.  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 two 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
http://www.maths.tcd.ie/scrg/os-faq.html.  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 <[e-mail]> 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.

------------------------------
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        <[e-mail]>
Surendar Chandra    <[e-mail]>
Steve Chapin        <[e-mail]>
Crispin Cowan        <[e-mail]>
Dan Hildebrand        <[e-mail]>
Gordon Irlam        <[e-mail]>
Darrell Long        <[e-mail]>
Chris Maeda        <[e-mail]>
Peter Magnusson        <[e-mail]>
Craig Partridge        <[e-mail]>
Tom Van Vleck        <[e-mail]>
Robert Walsh        <[e-mail]>

------------------------------
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.

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?]

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] Distributed systems
From: Distributed systems

A great deal of the high-profile research carried out in operating
systems these days deals with distributed computing.  Not
surprisingly, discussions of distributed systems make up a large
amount of the traffic on comp.os.research.

------------------------------
Subject: [4.1] What is the current status of the (insert name) project?
From: Distributed systems

See the section on `available software' for information on
distributions of some of the systems mentioned here.

- The Amoeba project is still going.  There are roughly 20 people
  working on it, but most of these are no longer kernel hackers.  They
  are working on using it for parallel programming, wide-area
  distributed systems, and other things.  Amoeba is used in over 100
  universities at the moment, and is also used at commercial
  institutions.

- Cronus is still under development at BBN.  The current public
  release is 3.0.  The project currently has two thrusts---as the base
  for advanced distributed system R&D, and as a platform for
  constructing and deploying sophisticated distributed applications.

  Ongoing research topics include the integration of Cronus and Mach
  technology, the exploration of techniques for the construction of
  WAN-based and multi-organisational applications, investigation into
  the integration of distributed systems and network management
  systems, and work in high-performance distributed computing.

- Horus is being developed by the same group that worked on Isis; the
  head of this group is Robbert van Renesse.

- Isis is no longer being developed at Cornell; it is now managed as a
  commercial product.

- Mach: awaiting response from rfr

- Plan 9 is currently being restructured to make good use of a 300MBPS
  fibre-optic network.  A general release of the system is under
  consideration at the moment.

- QNX is a commercial realtime OS with an installed base of over
  250,000 systems.  It is used extensively in process control, factory
  automation, medical instrumentation, communications and
  point-of-sale.  A number of universities are also doing research
  with QNX.

- The Sprite network operating system project is winding down.  The
  user community is shrinking, and only three people are currently
  using the system as a basis for graduate research.  Sprite is
  continuing to be used as the testbed for the Berkeley RAID project.

------------------------------
Subject: [4.2] How do approaches to load balancing differ?
From: Distributed systems

Load-balancing policy falls into two broad groups: static and dynamic.
Static policies use algorithms which operate without regard to
run-time loads across a system, while dynamic policies use the
run-time performance of various parts of a system in order to make
more `informed' decisions about balancing.

[92-11-06-12-53.57] A dynamic load-balancing policy is one which uses
run-time state information in making scheduling decisions.

There are two kinds of dynamic policies: adaptive and non-adaptive.
The latter always use the same (fixed, load-dependent) policy; the
former may adjust policy parameters in order to gradually improve
their performance.

The key point is that while non-adaptive policies use only the
information about the run-time state, adaptive policies use, in
addition to this, information about current performance.

In adaptive policies, the rules for adjusting policy parameters may be
static or dynamic.  An example of the former might be: `shift to a
conservative migration rule when system-wide load patterns are varying
too rapidly'.  An example of the latter could be: `increase
sender-side threshold when migrated jobs cause slowdown rather than
speedup'.  Some researchers refer to the performance-driven adaptation
exhibited by the second policy as `learning'.

Since both non-adaptive policies and adaptive policies with static
rules really use only load information, it is confusing to distinguish
between them.  One way to avoid such confusion is to restrict the use
of the word `adaptive' to policies that use performance feedback in
order to drive their adjustment of policy parameters.

------------------------------
Subject: [4.3] Fault tolerance in distributed systems
From: Distributed systems

[There has been a lot of traffic on this.  Material sought.]

------------------------------
Subject: [4.4] Naming in distributed systems
From: Distributed systems

[Material on naming and/or global naming sought.]

------------------------------
Subject: [4.5] Distributed shared memory
From: Distributed systems

[As for naming.]

------------------------------
Subject: [4.6] What have we learned?
From: Distributed systems

Andy Tanenbaum started a (very long) thread on this topic in
comp.os.research in April of 1992 [92-04-03-17-10.05].  The interested
reader is directed to the comp.os.research archives, since this thread
proved rather divisive (i.e. nobody really agreed on any issue).


------------------------------
Subject: [5] 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: [5.1] 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.

Based upon an amalgam of these criteria, the next few sections discuss
some of the main areas of ongoing research in mobile computing.

------------------------------
Subject: [5.2] 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.

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: [5.3] 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: [5.4] 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].

Complete analysis of peripheral device power usage and experimentation
with different strategies for implementing power management will certainly
be useful.

------------------------------
Subject: [5.5] 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 [Schlitt, 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 [Schlitt, 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: [5.6] 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
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[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',
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[Ioannidis et. al, 91]
  `IP based protocols for mobile internetworking', Proceedings of the
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[Aziz, 94]
  Aziz, A., `A scalable and efficient intra-domain tunneling mobile-IP
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[Keeton et al., 93]
  Keeton, K. et al., `Providing connection oriented network services
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[Casey, 94]
  Casey, M., `Application and communication support for mobile
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[Satyanarayanan, 90]
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    for a distributed workstation environment', IEEE Transactions on
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[Huston, 93]
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[Page, 91]
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[Greenawalt, 93]
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[Douglis & Marsh, 93]
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[Bender et. al, 93]
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[Schlitt, 93]
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[Goldstein, 94]
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[Theimer, 93]
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[Shenker, 93]
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    pp. 34-39



------------------------------
Subject: [6] 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: [6.1] 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.

  New to the current edition (mail a message with contents `send help'
  to <[e-mail]> for further details):

  - New, early coverage of light-weight processes and threads.

  - Expanded coverage of Memory Management, including modern computer
    architectures.

  - Enhanced realistic discussion of File System design,
    implementation, And secondary storage management.

  - Improved coverage of real time and multiprocessor systems.

  - New coverage of networking as it relates to operating systems.

  - Expanded and up-to-date coverage of UNIX and the Mach operating
    system.

  - Common operating systems, including Sun Solaris 2, MS-DOS, OS/2,
    Macintosh, in each chapter to illustrate concepts and show
    performance examples.

  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.

- `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
  ftp.ms.uky.edu:pub/tech-reports/UK/cs/vade.mecum.2.ps.Z.  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: [e-mail].  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 ... ?]

- `Modern Operating Systems,' Andrew Tanenbaum, 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).

  This book has been translated into German; it is available from
  Carl Hanser Verlag as `Moderne Betriebssysteme', ISBN 3-446-17472-9.

- `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.

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 not to hand right now.  This is the
  authoritative description of the internals of System V Unix.  Due to
  copyright restrictions, it contains no actual code, but rather
  pseudo-code (I didn't find this to be a problem).  I haven't read
  this book in a few years, so I can't remember what it covers.

- `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.

I am not aware of any similar book which covers the implementation of
a distributed system.

------------------------------
Subject: [6.2] What instructional operating systems can I use?
From: Operating systems teaching

- Minix, from Amsterdam's Vrije Universiteit, was developed by Andy
  Tanenbaum, 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.

- NachOS is an instructional OS developed at Berkeley by Tom Anderson
  <[e-mail]>, 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
  ftp.cs.berkeley.edu:ucb/nachos.

- OSP (current version is 1.7) is an operating systems simulator,
  available via ftp from 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.

- 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
  csc.canterbury.ac.nz:UNIX/SMX_2_00.TAR_Z.

- 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'.
  Contact <[e-mail]> or Prentice Hall for ordering
  information; Xinu is copyrighted and is not in the public domain.

------------------------------
Subject: [6.3] 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 <[e-mail]> 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.