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%%EndProlog
%%Page: 0 1
BS
0 SI
12 /Times-Bold AF
20549 8004 MT
(Mach: A Foundation for Open Systems)SH
11 SS 
26628 10314 MT
(A Position Paper)SH
9 /Times-Roman AF
19137 11905 MT
(Richard Rashid, Robert Baron, Alessandro Forin, David Golub,)SH
20375 12919 MT
(Michael Jones, Daniel Julin, Douglas Orr, Richard Sanzi)SH
/Times-Italic SF
25512 14947 MT
(School of Computer Science)SH
25550 15961 MT
(Carnegie Mellon University)SH
24812 16975 MT
(Pittsburgh, Pennsylvania 15213)SH
/Times-Roman SF
33300 24017 MT
(for proprietary systems -- each at considerable expense.  Bal-)50 W
11 /Times-Bold AF
7200 24137 MT
(1. Introduction)SH
9 /Times-Roman AF
33300 25115 MT
(looning software development)
166 W( costs translate into increased)167 W
7700 25235 MT
(Operating systems have become one of the most hotly con-)75 W
33300 26213 MT
(cost for the user)
3 W( and delays in the introduction of new features)2 W
7200 26333 MT
(tested battlegrounds for)
203 W( "open system standards".  Various)202 W
33300 27311 MT
(and new applications.)SH
7200 27431 MT
(national, international and industry)
128 W( groups are attempting to)129 W
7200 28529 MT
(define, implement and ultimately convince users to buy)
97 W( new)96 W
7200 29627 MT
("open" computing environments. Most of these efforts have)138 W
11 /Times-Bold AF
33300 29848 MT
(2. An Alternative Approach to OS)SH
7 /Times-Roman AF
21350 30398 MT
(1)SH
9 SS 
7200 30725 MT
(centered around versions of the UNIX)75 W
21925 XM
([9] operating system,)75 W
11 /Times-Bold AF
34400 30946 MT
(Organization)SH
9 /Times-Roman AF
7200 31823 MT
(but there is no consensus among industrial groups as to which)20 W
33800 32044 MT
(An alternative approach)
68 W( to building an entire operating sys-)69 W
7200 32921 MT
("version" of UNIX is ultimately the correct)
102 W( basis for a open)101 W
33300 33142 MT
(tem is to separate those parts of the operating system which)105 W
7200 34019 MT
(system standard.  Already two)
46 W( major industrial organizations,)47 W
33300 34240 MT
(control the basic)
343 W( hardware resources -- often called the)344 W
7200 35117 MT
(the Open Software)
65 W( Foundation and UNIX International, have)64 W
33300 35338 MT
(operating system "kernel" -- from those parts of the)
38 W( operating)37 W
7200 36215 MT
(endorsed two rather different UNIX)
83 W( implementations: IBM's)84 W
33300 36436 MT
(system which determine the unique characteristics of)
332 W( an)333 W
7200 37313 MT
(AIX and AT&T's System V.4. Non-UNIX systems)
144 W( such as)143 W
33300 37534 MT
(operating system)
158 W( environment, for example a particular file)157 W
7200 38411 MT
(the Macintosh OS, MS-DOS and)
305 W( OS/2 are also seen as)306 W
33300 38632 MT
(system interface. The advantage of this)
87 W( scheme is that it can)88 W
7200 39509 MT
("standards" by various hardware and software developers.)SH
33300 39730 MT
(allow more than one operating system environment to be)250 W
7700 40734 MT
(This divergence of systems and)
4 W( standards raises fundamental)3 W
33300 40828 MT
(implemented on the same hardware/software base so that)275 W
7200 41832 MT
(issues about the strategy which should be employed in the)175 W
33300 41926 MT
(machine dependent software need be written only once for)175 W
7200 42930 MT
(development of open operating systems. It)
191 W( has become in-)190 W
33300 43024 MT
(each new architecture.)SH
7200 44028 MT
(creasingly important to provide support within a)
81 W( single com-)82 W
33800 44249 MT
(The Carnegie)
121 W( Mellon University Mach kernel)
122 W( [1])
SH( is an ex-)122 W
7200 45126 MT
(puting environment for "multiple)
299 W( standards", i.e. multiple)298 W
33300 45347 MT
(ample of this layered approach to)
166 W( operating system design.)165 W
7200 46224 MT
(operating system environments)
68 W( which may be tailored to dif-)69 W
33300 46445 MT
(Mach is)
63 W( a multiprocessor kernel that incorporates in one sys-)64 W
7200 47322 MT
(ferent vendor or user needs.  Moreover,)
169 W( manufacturers fre-)168 W
33300 47543 MT
(tem a number of key facilities that allow the efficient im-)190 W
7200 48420 MT
(quently need to)
93 W( provide customers with continuing access to)94 W
33300 48641 MT
(plementation of those functions necessary)
146 W( to support binary)147 W
7200 49518 MT
(proprietary operating systems developed during)
217 W( the 1960's)216 W
33300 49739 MT
(compatibility with existing operating system environments.)220 W
7200 50616 MT
(and 1970's \050e.g. VMS, MVS and MS-DOS\051.)SH
33300 50837 MT
(These mechanisms are intended not simply as)
131 W( extensions to)132 W
7700 51841 MT
(Traditional systems such as UNIX or VMS are implemented)25 W
33300 51935 MT
(normal operating system facilities but as a)
144 W( foundation upon)143 W
7200 52939 MT
("all in one piece" with knowledge about)
216 W( the basic system)215 W
33300 53033 MT
(which UNIX and other operating system facilities can be)250 W
7200 54037 MT
(structure spread)
221 W( throughout. They are poorly suited to the)222 W
33300 54131 MT
(built.)SH
7200 55135 MT
(compatible support of multiple operating)
292 W( system environ-)291 W
33800 55356 MT
(We believe that such)
203 W( a design is very well suited to the)202 W
7200 56233 MT
(ments. As)
485 W( a result,)
130 W( large computer manufacturers are com-)131 W
33300 56454 MT
(implementation of modern)
77 W( systems, and that it can yield sig-)78 W
7200 57331 MT
(monly forced to support)
47 W( several completely distinct operating)46 W
33300 57552 MT
(nificant improvements in terms)
72 W( of structure, without sacrific-)71 W
7200 58429 MT
(system groups: one for OS/2, one)
54 W( for UNIX and one or more)55 W
33300 58650 MT
(ing performance.)
77 W( Furthermore,)
380 W( it also allows, at least poten-)78 W
10800 50 7200 59734 UL
33300 59748 MT
(tially, for more)
73 W( than one operating system environment to be)72 W
33300 60846 MT
(supported in "native)
348 W( mode" simultaneously on the same)349 W
5 SS 
7900 60909 MT
(1)SH
7 SS 
8150 61200 MT
(UNIX is a trademark of AT&T Bell Laboratories)SH
9 SS 
33300 61944 MT
(hardware. To)
469 W( demonstrate the practical applicability of)
122 W( this)121 W
22500 50 7200 63042 UL
33300 63042 MT
(concept, and to)
52 W( evaluate its strengths and weaknesses, we are)53 W
33300 64140 MT
(currently working on three separate approaches to)
18 W( implement-)17 W
7 SS 
7200 64155 MT
(This research was sponsored by)
212 W( the Defense Advanced Research Projects)213 W
7200 64988 MT
(Agency \050DOD\051, ARPA Order No. 4864, monitored by)
123 W( the Space and Naval)122 W
9 SS 
33300 65238 MT
(ing a 4.3 BSD [3] environment within the Mach framework.)SH
7 SS 
7200 65821 MT
(Warfare Systems Command under contract N00039-85-C-1034.)SH
11 /Times-Bold AF
33300 67775 MT
(3. Mach Features Supporting OS Emulation)SH
9 /Times-Roman AF
33800 68873 MT
(Mach provides an unusually flexible)
58 W( execution environment)59 W
33300 69971 MT
(for both system and user applications. It exposes the)
39 W( manage-)38 W
33300 71069 MT
(ment of CPU, communication, virtual memory)
39 W( and secondary)40 W
ES
%%Page: 1 2
BS
0 SI
9 /Times-Roman AF
7200 7817 MT
(storage resources in a way that allows)
194 W( system applications)193 W
33300 XM
(processes using Mach's)
59 W( flexible virtual memory management)58 W
7200 8915 MT
(such as database management facilities)
37 W( to use those resources)38 W
33300 XM
(facilities. The)
731 W( parent process that established this)
253 W( shared)254 W
7200 10013 MT
(efficiently.)SH
33300 XM
(library can then tell the Mach kernel to redirect system call)125 W
33300 11111 MT
(traps from the child into the shared library in the address)210 W
7700 11238 MT
(The key)
135 W( features of Mach in its role as a system software)134 W
33300 12209 MT
(space of that child.  This)
138 W( allows any embedded system call)137 W
7200 12336 MT
(kernel are:)SH
33300 13307 MT
(traps in a program binary to be interpreted outside the kernel)65 W
/Symbol SF
8811 13663 MT
(\267)SH
/Times-Roman SF
9450 XM
(support for multiple threads)
153 W( of control within a)154 W
33300 14405 MT
(and either handled directly or converted into a message to be)60 W
9450 14761 MT
(single address space,)SH
33300 15503 MT
(sent to)
190 W( a system server.  There is an override facility that)191 W
/Symbol SF
8811 16466 MT
(\267)SH
/Times-Roman SF
9450 XM
(an extensible and secure interprocess com-)515 W
33300 16601 MT
(allows the transparent library code to redirect a call to the)175 W
9450 17564 MT
(munication facility \050IPC\051 [10],)SH
33300 17699 MT
(kernel if necessary,)
135 W( to simplify development and debugging)136 W
33300 18797 MT
(of the transparent library itself.)
37 W( This facility can be used for a)36 W
/Symbol SF
8811 19269 MT
(\267)SH
/Times-Roman SF
9450 XM
(architecture independent virtual memory manage-)SH
33300 19895 MT
(variety of purposes, such as:)SH
9450 20367 MT
(ment \050VM\051 [7],)SH
/Symbol SF
34911 21222 MT
(\267)SH
/Times-Roman SF
35550 XM
(binary compatibility with non-Mach OS environ-)55 W
/Symbol SF
8811 22072 MT
(\267)SH
/Times-Roman SF
9450 XM
(integrated IPC/VM support, including:)
144 W( copy-on-)143 W
35550 22320 MT
(ments,)SH
9450 23170 MT
(write message)
318 W( passing, copy-on-reference net-)319 W
/Symbol SF
34911 24025 MT
(\267)SH
/Times-Roman SF
35550 XM
(support for multiple OS environments \050e.g. UNIX)SH
9450 24268 MT
(work communication and extensible memory ob-)55 W
35550 25123 MT
(4.3 BSD, UNIX V.4\051,)SH
9450 25366 MT
(jects,)SH
/Symbol SF
34911 26828 MT
(\267)SH
/Times-Roman SF
35550 XM
(debugging and monitoring and)SH
/Symbol SF
8811 27071 MT
(\267)SH
/Times-Roman SF
9450 XM
(hooks for transparent shared libraries, to)
79 W( provide)80 W
9450 28169 MT
(binary compatibility with existing operating sys-)95 W
/Symbol SF
34911 28533 MT
(\267)SH
/Times-Roman SF
35550 XM
(network redirection of OS traps.)SH
9450 29267 MT
(tem environments.)SH
7700 30492 MT
(The Mach kernel provides software equivalents of)
131 W( the key)132 W
11 /Times-Bold AF
33300 31070 MT
(4. In-kernel OS Emulation)SH
9 /Times-Roman AF
7200 31590 MT
(elements of uniprocessor and multiprocessor architectures.)270 W
33800 32168 MT
(In the first implementation of)
13 W( a 4.3 BSD emulation on top of)14 W
7200 32688 MT
(The Mach thread mechanism, for example, is)
308 W( a kind of)309 W
33300 33266 MT
(Mach, the Mach kernel is used as the)
15 W( lower layer of a two-tier)14 W
7200 33786 MT
(software processor.)
279 W( By)
781 W( allowing multiple threads to run)278 W
33300 34364 MT
(operating system implementation. In such a)
34 W( scheme the Mach)35 W
7200 34884 MT
(within the same program, Mach permits a system)
72 W( or applica-)73 W
33300 35462 MT
(kernel provides support for key functions such as virtual)275 W
7200 35982 MT
(tion programmer to directly manage multiple CPUs in)
53 W( a mul-)52 W
33300 36560 MT
(memory, scheduling, interprocess communication and device)85 W
7200 37080 MT
(tiprocessor. Mach's)
1025 W( interprocess communication facility)400 W
33300 37658 MT
(access. The target operating)
60 W( system can then be implemented)59 W
7200 38178 MT
(\050IPC\051 provides the kind)
109 W( of I/O channel between threads that)108 W
33300 38756 MT
(using these functions.  In this approach)
208 W( the entire system,)209 W
7200 39276 MT
(may exist in a multiprocessor)
80 W( with a message-passing bus or)81 W
33300 39854 MT
(kernel and OS environment, is packaged as a)
15 W( unit and run in a)14 W
7200 40374 MT
(between workstations on a network.)SH
33300 40952 MT
(privileged state just as in a)
162 W( traditional OS design. In many)163 W
7700 41599 MT
(Interprocess communication and memory management in)255 W
33300 42050 MT
(respects it continues to resemble)
88 W( the more traditional operat-)87 W
7200 42697 MT
(Mach are)
45 W( tightly integrated. Memory management techniques)46 W
33300 43148 MT
(ing systems it)
293 W( replaces. One advantage to this approach,)294 W
7200 43795 MT
(\050such as the use of memory re-mapping to avoid data)375 W
33300 44246 MT
(however, is that more than one)
123 W( OS environment can be im-)122 W
7200 44893 MT
(copying\051 are employed)
143 W( whenever large amounts of data are)144 W
33300 45344 MT
(plemented using the same kernel interface -- reducing the)225 W
7200 45991 MT
(sent in a message from one)
98 W( program to another. This allows)97 W
33300 46442 MT
(software effort required)
48 W( to bring a new architecture to market)47 W
7200 47089 MT
(the transmission of megabytes of data at very low cost.)SH
33300 47540 MT
(with several supported operating systems.)
21 W( Another)
269 W( advantage)22 W
7700 48314 MT
(One of the)
293 W( most unusual and important facilities Mach)294 W
33300 48638 MT
(is that the basic)
103 W( kernel could be made freely available to all)102 W
7200 49412 MT
(provides is the notion of a memory object which an applica-)85 W
33300 49736 MT
(without compromising the proprietary added value of)
31 W( the par-)32 W
7200 50510 MT
(tion program)
88 W( may create and manage. The memory object is)89 W
33300 50834 MT
(ticular operating)
104 W( system environment layered above it.  This)103 W
7200 51608 MT
(like a file or data container which can be mapped into)
166 W( the)165 W
33300 51932 MT
(approach would allow companies to share the costs of porting)25 W
7200 52706 MT
(address space of a program. Unlike)
234 W( traditional systems in)235 W
33300 53030 MT
(the kernel to a new architecture.)SH
7200 53804 MT
(which the operating system has)
65 W( complete control of "paging")64 W
33800 54255 MT
(Commercial versions of Mach available)
138 W( today are, in fact,)137 W
7200 54902 MT
(data to and from such a data object,)
36 W( Mach allows the applica-)37 W
33300 55353 MT
(examples of 4.3 BSD)
290 W( UNIX layered above Mach kernel)291 W
7200 56000 MT
(tion which)
35 W( creates the memory object to act as though it were)34 W
33300 56451 MT
(primitives and packaged together with)
145 W( the Mach code.  Al-)144 W
7200 57098 MT
(the disk storage or "pager" for that object.  Mach)
234 W( virtual)235 W
33300 57549 MT
(though one might assume)
41 W( that this layered approach to UNIX)42 W
7200 58196 MT
(memory objects)
105 W( are represented as communication channels.)104 W
33300 58647 MT
(implementation would be a performance disadvantage,)550 W
7200 59294 MT
(On a page fault, the kernel sends a)
136 W( message to the backing)137 W
33300 59745 MT
(measurements of Mach versus traditional UNIX implemen-)175 W
7200 60392 MT
(storage communication channel of a memory object to get the)25 W
33300 60843 MT
(tations indicate otherwise.)
163 W( Simple)
550 W( compilation benchmarks)162 W
7200 61490 MT
(data contained in the faulted page.)
383 W( This)
992 W( provides the)384 W
33300 61941 MT
(on SUN 3/60)
268 W( workstations, for example, run nearly 40%)269 W
7200 62588 MT
(flexibility necessary to implement)
47 W( efficiently such system ap-)46 W
33300 63039 MT
(faster under)
37 W( Mach than they do under Sun Microsystems own)36 W
7200 63686 MT
(plications as file systems, databases,)
146 W( dynamic encryption or)147 W
33300 64137 MT
(SunOS 4.0 version of UNIX.)
161 W( Times)
549 W( for UNIX "fork" and)162 W
7200 64784 MT
(compression of data on access or even)
369 W( network shared)368 W
33300 65235 MT
("exec" operations are also nearly a factor)
67 W( of two faster under)66 W
7200 65882 MT
(memory.)SH
33300 66333 MT
(Mach than SunOS.)SH
7700 67107 MT
(Finally, the Mach transparent library facility)
109 W( allows a code)110 W
7200 68205 MT
(library to be loaded into the address space of a program)250 W
7200 69303 MT
(without its knowledge, which can intercept system calls)
28 W( made)29 W
7200 70401 MT
(by that program.  Transparent shared)
33 W( libraries are loaded by a)32 W
7200 71499 MT
(parent process and)
460 W( transparently inherited by its child)461 W
ES
%%Page: 2 3
BS
0 SI
9 /Times-Roman AF
35550 7817 MT
(could allow vendors with proprietary OS environ-)SH
11 /Times-Bold AF
7200 7937 MT
(5. Out-of-kernel OS Emulation: Two)SH
9 /Times-Roman AF
35550 8915 MT
(ments to more quickly take)
12 W( advantage of Mach as)13 W
11 /Times-Bold AF
8300 9035 MT
(Approaches)SH
9 /Times-Roman AF
35550 10013 MT
(a basis for their systems.)SH
7700 10133 MT
(A second approach to building)
137 W( a layered operating system)138 W
7200 11231 MT
(environment has even greater potential for)
361 W( open system)360 W
33800 11238 MT
(In practice, this single task)
245 W( Unix server works well and)244 W
7200 12329 MT
(development. The kernel can be packaged by itself as a)
4 W( "pure")5 W
33300 12336 MT
(demonstrates the feasibility of)
290 W( such an approach. Its im-)291 W
7200 13427 MT
(kernel with no operating)
260 W( system environment. In this ap-)259 W
33300 13434 MT
(plementation was completed in less than)
166 W( sixth months, and)165 W
7200 14525 MT
(proach, only the)
6 W( kernel runs in privileged state. The rest of the)7 W
33300 14532 MT
(can already be used for self-development.)
7 W( It)
241 W( currently runs on)8 W
7200 15623 MT
(operating system environment runs, in)
70 W( effect, as one or more)69 W
33300 15630 MT
(VAX and Sun 3 platforms and is functionally interchangeable)25 W
7200 16721 MT
(programs \050or, more precisely, one or more)
106 W( server processes\051)107 W
33300 16728 MT
(with existing versions of 4.3)
112 W( BSD/Mach on those machines.)113 W
7200 17819 MT
(on top of the kernel. User applications run as before, but)220 W
33300 17826 MT
(We expect to extend this implementation to the other)425 W
7200 18917 MT
(instead of making direct calls on the operating)
197 W( system via)198 W
33300 18924 MT
(hardware platforms which run Mach and to put this version)125 W
7200 20015 MT
(system calls traps, the kernel's)
129 W( communication and memory)128 W
33300 20022 MT
(into production use within CMU over the next)
128 W( few months.)127 W
7200 21113 MT
(management facilities are employed to communicate infor-)200 W
33300 21120 MT
(Initial performance measurements are encouraging.)
114 W( A)
454 W( com-)115 W
7200 22211 MT
(mation between the)
559 W( application and operating system)558 W
33300 22218 MT
(pilation benchmark which takes takes)
38 W( 29 seconds to complete)37 W
7200 23309 MT
(processes. The reason this)
140 W( implementation strategy is so at-)141 W
33300 23316 MT
(on a Sun 3/60 running in-kernel 4.3BSD/Mach takes)
303 W( 34)304 W
7200 24407 MT
(tractive for open systems, is that)
96 W( it can allow more than one)95 W
33300 24414 MT
(seconds with out-of-kernel BSD support)
63 W( and 49 seconds run-)62 W
7200 25505 MT
(operating system environment to be)
162 W( supported on the same)163 W
33300 25512 MT
(ning under SunOS 4.0.)SH
7200 26603 MT
(machine, on the same kernel, at)
58 W( the same time. Systems such)57 W
7200 27701 MT
(as UNIX or OS/2 could)
180 W( potentially co-exist in their native)181 W
11 /Times-Bold AF
33300 28049 MT
(7. Multiserver UNIX)SH
9 /Times-Roman AF
7200 28799 MT
(form. The)
424 W( kernel becomes a kind of universal "socket" into)99 W
33800 29147 MT
(This system divides responsibility)
53 W( for UNIX support among)54 W
7200 29897 MT
(which more than one operating system environment)
156 W( can be)157 W
33300 30245 MT
(a collection of libraries and servers responsible for particular)75 W
7200 30995 MT
(plugged, insulating that software)
35 W( from the hardware itself and)34 W
33300 31343 MT
(OS functions)
221 W( such as naming, authentication and file data)222 W
7200 32093 MT
(greatly simplifying its design and maintenance.)SH
33300 32441 MT
(access. Wherever)
251 W( possible, the)
13 W( interfaces between the various)12 W
7700 33318 MT
(This approach is currently being put to the test at Carnegie)90 W
33300 33539 MT
(system components, and those components themselves, are)200 W
7200 34416 MT
(Mellon in the development of)
113 W( two rather different user-state)112 W
33300 34637 MT
(designed to be independent)
160 W( of the target environment. This)159 W
7200 35514 MT
(implementations of Berkeley UNIX 4.3 BSD:)
779 W( the)780 W
33300 35735 MT
(approach presents two major advantages:)SH
/Times-Italic SF
7200 36612 MT
(Multithreaded System)136 W
/Times-Roman SF
15572 XM
(and the)136 W
/Times-Italic SF
18694 XM
(Multiserver System)136 W
/Times-Roman SF
(. Both im-)135 W
/Symbol SF
34911 37062 MT
(\267)SH
/Times-Roman SF
35550 XM
(access to various)
60 W( system resources can be shared)61 W
7200 37710 MT
(plementations run unmodified 4.3 BSD binaries.)SH
35550 38160 MT
(by multiple independent operating system en-)305 W
35550 39258 MT
(vironments, communicating over a network or)260 W
11 /Times-Bold AF
7200 40247 MT
(6. The Multithreaded UNIX Server)SH
9 /Times-Roman AF
35550 40356 MT
(concurrently executing on the same machine.)SH
7700 41345 MT
(This system consists of transparent library)
289 W( support aug-)290 W
/Symbol SF
34911 42061 MT
(\267)SH
/Times-Roman SF
35550 XM
(individual components can easily be reused for)175 W
7200 42443 MT
(mented by)
137 W( a multithreaded UNIX server.  This server, con-)136 W
35550 43159 MT
(the implementation of different operating system)75 W
7200 43541 MT
(tained in a single task, is typically invoked)
86 W( via a Mach mes-)87 W
35550 44257 MT
(environments.)SH
7200 44639 MT
(sage exchange for)
257 W( each system call issued by application)256 W
33800 45482 MT
(On the negative side, this approach)
186 W( requires sophisticated)185 W
7200 45737 MT
(processes. In)
313 W( addition to managing)
44 W( system call emulation for)45 W
33300 46580 MT
(synchronization between servers)
266 W( to achieve precise UNIX)267 W
7200 46835 MT
(Unix processes, the Unix server acts)
73 W( as an external pager for)72 W
33300 47678 MT
(semantics, and)
104 W( very careful design of the standardized inter-)103 W
7200 47933 MT
(Unix inodes.  It is implemented using Mach's)
253 W( C-Threads)254 W
33300 48776 MT
(faces. The)
313 W( major interfaces defined)
44 W( for that system organiza-)45 W
7200 49031 MT
(package with each incoming request)
213 W( handled by a cthread)212 W
33300 49874 MT
(tion are:)SH
7200 50129 MT
(allocated from a pool of waiting threads.)SH
/Symbol SF
34911 51201 MT
(\267)SH
/Times-Roman SF
35550 XM
(a standard access)
184 W( protocol defining the authen-)183 W
7700 51354 MT
(A single task operating system emulation)
219 W( of this kind is)220 W
35550 52299 MT
(tication, access control and naming procedures)230 W
7200 52452 MT
(attractive for several reasons:)SH
35550 53397 MT
(used for access to all system objects)
17 W( such as files,)16 W
/Symbol SF
8811 53779 MT
(\267)SH
/Times-Roman SF
9450 XM
(The server is)
184 W( solely responsible for performing)183 W
35550 54495 MT
(devices, processes, etc.)SH
9450 54877 MT
(the emulation of all)
137 W( OS environment semantics.)138 W
9450 55975 MT
(The structure of the server)
120 W( is, in fact, similar to)119 W
/Symbol SF
34911 56200 MT
(\267)SH
/Times-Roman SF
35550 XM
(a standard I/O protocol for the transfer of data)175 W
9450 57073 MT
(that of an in-kernel)
53 W( implementation; it has global)54 W
35550 57298 MT
(between the producers and consumers)
292 W( of that)291 W
9450 58171 MT
(knowledge of all the information needed)
111 W( for the)110 W
35550 58396 MT
(data.)SH
9450 59269 MT
(emulation. Internal)
665 W( context switching between)220 W
/Symbol SF
34911 60101 MT
(\267)SH
/Times-Roman SF
35550 XM
(a standard exception protocol to handle excep-)200 W
9450 60367 MT
(threads can be extremely fast.)SH
35550 61199 MT
(tions happening)
82 W( during client-server interactions,)81 W
/Symbol SF
8811 62072 MT
(\267)SH
/Times-Roman SF
9450 XM
(The OS server is completely pageable and can in)50 W
35550 62297 MT
(and to report asynchronous events to clients.)SH
9450 63170 MT
(fact make more efficient use)
12 W( of memory \050by shar-)13 W
33800 63522 MT
(The following sections describe the major)
189 W( components of)190 W
9450 64268 MT
(ing data structures and stack space\051 than can a)175 W
33300 64620 MT
(this system.)SH
9450 65366 MT
(multiple server implementation.)SH
10 /Times-Bold AF
33300 66370 MT
(7.1. Mach Object Programming Facility)SH
9 /Symbol AF
8811 67071 MT
(\267)SH
/Times-Roman SF
9450 XM
(It can be)
141 W( relatively straightforward to transform)142 W
33800 67468 MT
(The development of the multiserver)
113 W( UNIX system is aided)112 W
9450 68169 MT
(an existing in-kernel OS implementation into)345 W
33300 68566 MT
(by a C-based)
241 W( object-oriented programming package called)242 W
9450 69267 MT
(such a)
138 W( server, because most of the code can be)139 W
/Times-Italic SF
33300 69664 MT
(MachObjects)SH
/Times-Roman SF
(, which has been)
35 W( integrated with the Mach inter-)34 W
9450 70365 MT
(simply carried)
229 W( over. This can make it easy to)228 W
33300 70762 MT
(process communication facility.  This package allows:)SH
9450 71463 MT
(preserve both existing code and semantics.)
129 W( This)130 W
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9 /Times-Roman AF
35550 7817 MT
(protocols used for network access \050TCP/IP, OSI,)75 W
/Symbol SF
8811 7920 MT
(\267)SH
/Times-Roman SF
9450 XM
(dynamic class/method specification,)SH
35550 8915 MT
(etc\051,)SH
/Symbol SF
8811 9625 MT
(\267)SH
/Times-Roman SF
9450 XM
(class/superclass hierarchy,)SH
/Symbol SF
34911 10620 MT
(\267)SH
/Times-Roman SF
35550 XM
(the UNIX)
42 W( File Server, which manages UNIX file)43 W
/Symbol SF
8811 11330 MT
(\267)SH
/Times-Roman SF
9450 XM
(multiple inheritance through delegation,)SH
35550 11718 MT
(systems on permanent storage,)
72 W( but uses the stan-)71 W
35550 12816 MT
(dard naming and I/O protocols, so that it is)
11 W( acces-)12 W
/Symbol SF
8811 13035 MT
(\267)SH
/Times-Roman SF
9450 XM
(automatic remote delegation \050through IPC\051,)SH
35550 13914 MT
(sible from all environments,)SH
/Symbol SF
8811 14740 MT
(\267)SH
/Times-Roman SF
9450 XM
(user-specifiable method lookup)
412 W( to implement)413 W
/Symbol SF
34911 15619 MT
(\267)SH
/Times-Roman SF
35550 XM
(the NFS Server, which translates requests)
171 W( from)170 W
9450 15838 MT
(other forms of inheritance,)SH
35550 16717 MT
(the standard access)
260 W( and I/O interface into the)261 W
/Symbol SF
8811 17543 MT
(\267)SH
/Times-Roman SF
9450 XM
(automatic dispatching of method invocations to)175 W
35550 17815 MT
(NFS protocol,)
8 W( allowing access to remote NFS file)7 W
9450 18641 MT
(multiple threads of control,)SH
35550 18913 MT
(systems,)SH
/Symbol SF
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(\267)SH
/Times-Roman SF
9450 XM
(reference count garbage collection of objects and)SH
/Symbol SF
34911 20618 MT
(\267)SH
/Times-Roman SF
35550 XM
(the UNIX TTY Server,)
90 W( a front-end for access to)91 W
35550 21716 MT
(terminal lines and pseudo terminals, implement-)120 W
/Symbol SF
8811 22051 MT
(\267)SH
/Times-Roman SF
9450 XM
(automatic object locking.)SH
35550 22814 MT
(ing the line disciplines and)SH
7700 23276 MT
(To simplify the organization of the various components,)250 W
7200 24374 MT
(libraries of standard MachObjects)
135 W( classes are used, that im-)134 W
/Symbol SF
34911 24519 MT
(\267)SH
/Times-Roman SF
35550 XM
(the UNIX Pipe Server, implementing traditional)130 W
7200 25472 MT
(plement the standard)
268 W( system interfaces. In many cases, a)269 W
35550 25617 MT
(UNIX pipes, using FIFO)
463 W( buffers in shared)462 W
7200 26570 MT
(special MachObject mechanism is used to)
131 W( allow a server to)130 W
35550 26715 MT
(memory.)SH
7200 27668 MT
(dynamically select the class of an object to be instantiated in)70 W
7200 28766 MT
(its client's)
137 W( address space. When this approach is used, only)136 W
11 /Times-Bold AF
33300 29252 MT
(8. Related Work)SH
9 /Times-Roman AF
7200 29864 MT
(the client-side object must implement the standard)
57 W( interfaces.)58 W
33800 30350 MT
(Several other research groups)
303 W( are also investigating the)304 W
7200 30962 MT
(Each server may use a different, specialized protocol to com-)50 W
33300 31448 MT
(issues involved)
108 W( with OS emulation, particularly with respect)107 W
7200 32060 MT
(municate with the client-side objects that it returns.)SH
33300 32546 MT
(to the UNIX environment.)
612 W( CMU's Accent operating)613 W
33300 33644 MT
(system [6])
SH( was used as the base for a System III Unix)
41 W( emula-)40 W
10 /Times-Bold AF
7200 33810 MT
(7.2. Transparent Library)SH
9 /Times-Roman AF
33300 34742 MT
(tion called)462 W
/Times-Italic SF
38224 XM
(QNIX)SH
/Times-Roman SF
(. The)1149 W
/Times-Italic SF
44011 XM
(Amoeba)SH
/Times-Roman SF
47649 XM
(system [8])
SH( uses port)463 W
7700 34908 MT
(The transparent library is responsible for translating)
282 W( the)283 W
33300 35840 MT
(capabilities in a manner very similar to that of Mach to)270 W
7200 36006 MT
(UNIX 4.3 BSD system calls from)
56 W( an application process into)55 W
33300 36938 MT
(implement a)
92 W( fast server-based system. The)93 W
/Times-Italic SF
49432 XM
(CHORUS)SH
/Times-Roman SF
53300 XM
(system)SH
7200 37104 MT
(invocations on the appropriate)
190 W( system servers, via the cor-)191 W
33525 38036 MT
([2] has adopted an)
84 W( object-oriented approach to build a com-)83 W
7200 38202 MT
(responding MachObjects elements.)SH
33300 39134 MT
(plete UNIX emulation; its use of memory protection is)350 W
7700 39427 MT
(An important)
37 W( aspect of the system organization is that many)36 W
33300 40232 MT
(however rather different)
98 W( from that adopted for the Mach OS)97 W
7200 40525 MT
(emulated system calls, for example)175 W
/Times-Italic SF
20975 XM
(read)SH
/Times-Roman SF
23025 XM
(and)SH
/Times-Italic SF
24725 XM
(write)SH
/Times-Roman SF
(, can be)175 W
33300 41330 MT
(emulators. The)275 W
/Times-Italic SF
39475 XM
(Taos)SH
/Times-Roman SF
41725 XM
(system [4])
SH( provides an emulation of)275 W
7200 41623 MT
(implemented within the transparent library with no messages)75 W
33300 42428 MT
(Ultrix in the Topaz environment. Several of)
17 W( the concepts used)16 W
7200 42721 MT
(exchanged with servers.  This is possible)
83 W( because many data)84 W
33300 43526 MT
(for the Mach OS emulators are inspired)
58 W( from ideas presented)59 W
7200 43819 MT
(objects can be)
282 W( represented as Mach memory objects and)281 W
33300 44624 MT
(with the)SH
/Times-Italic SF
36450 XM
(Sprite)SH
/Times-Roman SF
38825 XM
(and)SH
/Times-Italic SF
40350 XM
(V)SH
/Times-Roman SF
41125 XM
(systems [5] [11].)SH
7200 44917 MT
(mapped into the address space of the)
58 W( transparent library after)59 W
7200 46015 MT
(a)SH
/Times-Italic SF
7953 XM
(open)SH
/Times-Roman SF
10056 XM
(call is)
128 W( made. The)127 W
/Times-Italic SF
16940 XM
(read)SH
/Times-Roman SF
18942 XM
(and)SH
/Times-Italic SF
20594 XM
(write)SH
/Times-Roman SF
22796 XM
(calls thus translate)127 W
7200 47113 MT
(into simple memory references into this mapped area.)SH
11 /Times-Bold AF
33300 47161 MT
(9. Mach availability)SH
9 /Times-Roman AF
33800 48259 MT
(The portability of Mach has been)
31 W( demonstrated by the range)30 W
10 /Times-Bold AF
7200 48863 MT
(7.3. System Servers)SH
9 /Times-Roman AF
33300 49357 MT
(of uniprocessor and multiprocessor systems on which)
206 W( it is)207 W
7700 49961 MT
(The various system servers cooperate to implement)
6 W( the func-)7 W
33300 50455 MT
(available. Mach)
615 W( has been)
195 W( ported to the VAX architecture)194 W
7200 51059 MT
(tions needed for the emulation.)
120 W( As indicated, many of these)119 W
33300 51553 MT
(uniprocessors and multiprocessors, the SUN)
246 W( 3 family, the)247 W
7200 52157 MT
(servers are in fact independent of the specific)
47 W( UNIX environ-)48 W
33300 52651 MT
(IBM RT PC family, the)
163 W( DecStation 3100, the 64-processor)162 W
7200 53255 MT
(ment, and only the fact)
162 W( that they are invoked from the 4.3)161 W
33300 53749 MT
(IBM RP3, the 8-processor IBM)
21 W( ACE multiprocessor worksta-)22 W
7200 54353 MT
(BSD transparent library produces 4.3 BSD semantics from)
3 W( the)4 W
33300 54847 MT
(tion, the Sequent Balance, the Macintosh II, the IBM 370, the)30 W
7200 55451 MT
(point of view of the application)
33 W( processes.  The major servers)32 W
33300 55945 MT
(SUN 4, the Intel 386 and the Intel i860.)
43 W( Implementations)
312 W( for)44 W
7200 56549 MT
(are or will be:)SH
33300 57043 MT
(other MIPS R2000 and R3000)
63 W( machines are nearing comple-)62 W
/Symbol SF
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(\267)SH
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9450 XM
(the Name Server, implementing a hierarchical)280 W
33300 58141 MT
(tion and several implementations for the Motorola 88000 are)75 W
9450 58974 MT
(name space with only directories, symbolic)
71 W( links)70 W
33300 59239 MT
(underway. Commercial versions)
115 W( of Mach are available from)114 W
9450 60072 MT
(and mount points, which can be used to)
328 W( tie)329 W
33300 60337 MT
(BBN Advanced Computers, Evans and Sutherland)
79 W( Computer)80 W
9450 61170 MT
(together several other name spaces)
67 W( and represent)66 W
33300 61435 MT
(Division, Encore Computers and NeXT.)
70 W( In)
363 W( addition to these)69 W
9450 62268 MT
(the "root" of the UNIX name space,)SH
33300 62533 MT
(vendor releases of Mach, Mt Xinu,)
47 W( Inc. has announced that it)48 W
33300 63631 MT
(will develop commercial end-user releases of Mach for a)250 W
/Symbol SF
8811 63973 MT
(\267)SH
/Times-Roman SF
9450 XM
(the Task)
95 W( Manager, responsible for keeping track)96 W
33300 64729 MT
(variety of machine architectures.)
396 W( Finally,)
1018 W( Prime, Intel,)397 W
9450 65071 MT
(of all the application processes participating in)
18 W( an)17 W
33300 65827 MT
(Olivetti, Convergent)
158 W( and AT&T have recently announced a)157 W
9450 66169 MT
(operating system environment,)SH
33300 66925 MT
(joint research project to build a multiprocessor)
231 W( version of)232 W
/Symbol SF
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(\267)SH
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9450 XM
(the Authentication Server, used)
337 W( to verify the)338 W
33300 68023 MT
(System V.4 using the Mach kernel.)SH
9450 68972 MT
(credentials of processes performing operations on)15 W
33800 69248 MT
(All software implemented by the Mach project)
144 W( is licensed)143 W
9450 70070 MT
(behalf of the authorized users of the system,)SH
33300 70346 MT
(and distributed to universities, research laboratories and cor-)100 W
33300 71444 MT
(porations at no cost by Carnegie Mellon.)SH
/Symbol SF
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(\267)SH
/Times-Roman SF
9450 XM
(the Network Server, implementing the transport)150 W
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(References)SH
8 SS 
7200 9944 MT
(1.)SH
/Times-Roman SF
8200 XM
(Accetta, M.J., Baron, R.V., Bolosky, W., Golub, D.B., Rashid,)SH
7200 10868 MT
(R.F., Tevanian, A., and Young, M.W.  Mach: A New Kernel Foun-)SH
7200 11792 MT
(dation for UNIX Development.  Proceedings of Summer Usenix,)SH
7200 12716 MT
(July, 1986.)SH
/Times-Bold SF
7200 14189 MT
(2.)SH
/Times-Roman SF
8200 XM
(Francois Armand and Michel Gien and Marc Guillemont and)SH
7200 15113 MT
(Pierre Leonard.  Towards a Distributed UNIX System - The)SH
7200 16037 MT
(CHORUS Approach.  Proceedings of the European UNIX Systems)SH
7200 16961 MT
(User Group Conference, September, 1986.)SH
/Times-Bold SF
7200 18434 MT
(3.)SH
/Times-Roman SF
8200 XM
(Joy, W., et. al.  4.2BSD System Manual.  Technical report ,)SH
7200 19358 MT
(Computer Systems Research Group, Computer Science Division,)SH
7200 20282 MT
(University of California, Berkeley, July, 1983.)SH
/Times-Bold SF
7200 21755 MT
(4.)SH
/Times-Roman SF
8200 XM
(Paul R. McJones and Garret F. Swart.  Evolving the UNIX System)SH
7200 22679 MT
(Interface to Support Multithreaded Programs.  Research Report 21,)SH
7200 23603 MT
(DEC Systems Research Center, September, 1987.)SH
/Times-Bold SF
7200 25076 MT
(5.)SH
/Times-Roman SF
8200 XM
(John K. Ousterhout and Andrew R. Cherenson and Frederick)SH
7200 26000 MT
(Douglis and Michael N. Nelson and Brent B. Welch.  "The Sprite)SH
7200 26924 MT
(Network Operating System".)SH
/Times-Italic SF
16878 XM
(IEEE Computer 21)SH
/Times-Roman SF
(, 2 \050February 1988\051,)SH
7200 27848 MT
(23-36.)SH
/Times-Bold SF
7200 29321 MT
(6.)SH
/Times-Roman SF
8200 XM
(Rashid, R. F. and Robertson, G.  Accent: A Communication)SH
7200 30245 MT
(Oriented Network Operating System Kernel.  Proc. 8th Symposium)SH
7200 31169 MT
(on Operating Systems Principles, December, 1981, pp. 64-75.)SH
/Times-Bold SF
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(7.)SH
/Times-Roman SF
8200 XM
(Rashid, R.F., Tevanian, A., Young, M.W., Golub, D.B., Baron,)SH
7200 33566 MT
(R.V., Black, D.L., Bolosky, W., and Chew, J.J.  Machine-)SH
7200 34490 MT
(Independent Virtual Memory Management for Paged Uniprocessor)SH
7200 35414 MT
(and Multiprocessor Architectures.  Proceedings of the 2nd Sym-)SH
7200 36338 MT
(posium on Architectural Support for Programming Languages and)SH
7200 37262 MT
(Operating Systems, ACM, October, 1987.)SH
/Times-Bold SF
7200 38735 MT
(8.)SH
/Times-Roman SF
8200 XM
(Robbert van Renesse and Hans van Staveren and Andrew)SH
7200 39659 MT
(S. Tanenbaum.  "Performance of the World's Fastest Distributed)SH
7200 40583 MT
(Operating System".)SH
/Times-Italic SF
13879 XM
(ACM Operating Systems Review 22)SH
/Times-Roman SF
(, 4 \050October)SH
7200 41507 MT
(1988\051, 23-34.)SH
/Times-Bold SF
7200 42980 MT
(9.)SH
/Times-Roman SF
8200 XM
(D.M. Ritchie and K. Thompson.  "The UNIX time-sharing)SH
7200 43904 MT
(system".)SH
/Times-Italic SF
10347 XM
(Bell System Technical Journal)SH
/Times-Roman SF
20498 XM
(\050July 1978\051.)SH
/Times-Bold SF
7200 45377 MT
(10.)SH
/Times-Roman SF
8600 XM
(Sansom, R.D., Julin, D.P. and Rashid R.F.  Extending a)SH
7200 46301 MT
(Capability Based System into a Network Environment.  Proceedings)SH
7200 47225 MT
(of the ACM SIGCOMM 86 Symposium on Communications Ar-)SH
7200 48149 MT
(chitectures and Protocols, August, 86, pp. 265-274. Also available as)SH
7200 49073 MT
(Technical Report CMU-CS-86-115.)SH
/Times-Bold SF
7200 50546 MT
(11.)SH
/Times-Roman SF
8600 XM
(Willy Zwaenepoel.  "Implementation and Performance of Pipes)SH
7200 51470 MT
(in the V-System".)SH
/Times-Italic SF
13324 XM
(IEEE Trans. on Comput. C-34)SH
/Times-Roman SF
(, 12 \050December)SH
7200 52394 MT
(1985\051, 99-106.)SH
ES
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(Table of Contents)SH
10 SS 
8700 9017 MT
(1. Introduction)SH
53500 XM
(0)SH
8700 10097 MT
(2. An Alternative Approach to OS Organization)SH
53500 XM
(0)SH
8700 11177 MT
(3. Mach Features Supporting OS Emulation)SH
53500 XM
(0)SH
8700 12257 MT
(4. In-kernel OS Emulation)SH
53500 XM
(1)SH
8700 13337 MT
(5. Out-of-kernel OS Emulation: Two Approaches)SH
53500 XM
(2)SH
8700 14417 MT
(6. The Multithreaded UNIX Server)SH
53500 XM
(2)SH
8700 15497 MT
(7. Multiserver UNIX)SH
53500 XM
(2)SH
9 SS 
10350 16489 MT
(7.1. Mach Object Programming Facility)SH
53550 XM
(2)SH
10350 17481 MT
(7.2. Transparent Library)SH
53550 XM
(3)SH
10350 18473 MT
(7.3. System Servers)SH
53550 XM
(3)SH
10 SS 
8700 19553 MT
(8. Related Work)SH
53500 XM
(3)SH
8700 20633 MT
(9. Mach availability)SH
53500 XM
(3)SH
ES
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