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A MO E B AThe Study of a Distributed Operating System

Compiled & Prepared By:

Patel Nupur ([email protected])

Shah Palak ([email protected])

VI th Semester - Computer Engg.

U.V.Patel College of Engg, Mehasana.
http://var/www/apps/conversion/current/tmp/scratch7889/[email protected]://var/www/apps/conversion/current/tmp/scratch7889/[email protected]://var/www/apps/conversion/current/tmp/scratch7889/[email protected]://var/www/apps/conversion/current/tmp/scratch7889/[email protected]

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Fields Of Application ........15

Conclusion ............15

Bibliography.........16

ABSTRACT

For my physical studies like Measurement of velocity gradients in high viscose liquids I

use Amoeba as a compact and powerful lab measurement system with many reducedpc systems for only data recording together with high speed Pentium PC's for data

analysis connected through a standard 10 Mbps Ethernet network. Putting all machines

together to one large coupled system is very simple and flexible. Only less

administration work must be done.

Amoeba doesn't make any usage of the BIOS. All needed hardware driversare delivered within the Amoeba kernel. But the first bootstrap stage (Amoebastandalone boot program on floppy or hard disks) needs the BIOS to load the first

Amoeba kernel.Amoeba builds upon a traditional micro kernel. It supports true

multithreading (kernel controlled), segment based memory management.Currently, it's the fastest distributed operating system.

Here I m giving u concise and informal introduction to distributed operatingsystem-AMOEBA

Compiled & Prepared By Patel Nupur & Shah Palak 3

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WHAT IS AMOEBA?

Amoeba is a distributed operating

system. It collects a huge variety of single

machines connected over a (fast) network to

one, huge computer. It was originally

developed at the Vrije Universiteit in

Amsterdam by Andrew Tanenbaum and

many more. Amoeba was always designed to

be used, so it was deemed essential toachieve extremely high performance.

Amoeba system will connect the multiple

Amoeba system in different sites into a single

coherent system. This goal is obtained by

using the object and capabilities in a uniform

way. Currently, it's the fastest distributed

operating system. The original Amoeba

sources are handled under a public license -

similar the BSD license.Amoeba builds upon a traditional

micro kernel. It supports true multithreading

(kernel controlled), segment based memory

management. All Amoeba components

communicate with each other over a

standardized RPC (Remote Procedure Call)


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interface - simple but very powerful. No

matter if a client or server thread is running

in kernel or user mode - it uses the same RPC

interface. Always. Everywhere. This leads to

a very clean and simple OS design, very wellsuited for beginners.

Because Amoeba was designed from

scratch with new concepts, never seen

before, it suffered from a lack of application

programs. Therefore a POSIX-compliant

UNIX emulation was added. It makes porting

UNIX programs much easier! Now, with

additional changes, a huge variety of

application programs from the UNIX-world

work under Amoeba: X11 with applications,

various compilers (gcc, ocaml, tcl/tk), bash

shell, editors and many, many more. Amoeba

is ready to use! Of course not without (little)

problems.

It's still in a slightly experimental

state, but ready to use. FSD-Amoeba is

intended to use for dedicatedprogrammers only, and not for end users!

HISTORY

Developed at the Vrije UniversiteitAmsterdam, Netherlands. Chief designer:

Andrew S. Tanenbaum Other developers were Frans Kaashock,

Sape J. Mullender, Robbert van Renesse,

Leendert van Doorn, Kees Verstoep and

many, many more. First proto release in 1983 (V1.0), last

official release 1996 (V5.3) Supports

multiple architectures: 68k, i80386,

SPARC

DESIGN GOALS

Transparency:

One of the main goals of the Amoebadevelopment was to design a transparent

distributed system that allows users to log

into system as a whole: Transparency. Thatmeans: Hiding the comlexities of a

distributed system from the users. Amoeba

users should not be concerned about thenumber of processors in the system, nor must

they know the location of the other machines

or servers (like the Filesystem server...).

Distribution:

Several machines connected over a networkoperate as a single system: Distribution.

Amoeba gives its users the illusion ofinteracting with a single, powerful system.

Parallelism:

On an Amoeba system, a single program orcommand can use multiple processors to

increase performance. The user simply

requests an operation, and the Amoeba OS

decides the best way to execute the request.Amoeba will decide which processor (or

processors) is appropriate for the request,based on the current state of the system.Additionally, special development tools have

been made for an Amoeba environment that

takes advantage of the inherent parallelism.For example, Amoeba supports a parallel

'make' program.

Small Kernel approach:

To enhance flexibility and to minimize kernel

size its design was based on micro kernel

approach. That is, in Amoeba several of the

standard services, such as file service, arebuilt outside kernel in user space. This helps

in enhancing flexibility because these

services can be easily modified and multipleversions of service can be simultaneously run

on the same system to suit the needs of

different users.


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Performance:

Much effort was given to meet this goal!!!

This is accomplished with a newly developed

High Performance network protocol called

FLIP (Fast Local Internet Protocol). WhenFLIP was developed, none of the current

protocols provided adequate support for

distributed systems. FLIP performs clean,simple and efficient communication between

distributed nodes. Development from the scratch;

Amoeba doesnt based on anyexisting operating system

Amoeba interact with the user as a

UNIX-like Timesharing System

High performance IPC message

passing for local, privileged user processes;

transfer of several data buffers with one

transaction; shared segment support with VM

address translation by the IPC module:

Implemented, shared segment support now

available

User process interrupt handler:

working

User process I/O port access: done

fast context switch (both thread and

process): currently not achieved

Clean and simple virtual memory

(but without page swapping): exists

already

SYSTEM ARCHITECTURE

Amoeba implements a universaldistributed Client-Server-Model. In fact,basically the whole system needs only three

Functions to do all the work: The transaction

call from the Client, and the GetRequest andPutReply functions on the Server side.

Amoeba Many different Processor

architectures are supported: i80386

(Pentium), 68k, SPARC. Today, only the

i80386 architecture is significant for building

an Amoeba system (cheap!!!).System consists of four principle

components:

Workstations Pool Processors Specialized Servers (File server...) Gateways

File Servers

The file server distributed with

Amoeba is called the Bullet Server. It uses a

large buffer cache to provide very high

performance. Thus the file server should berun on a machine with a large amount of

RAM, and, of course, a disk. There is a

modified version of the bullet server, calledbulletb, using a different cache method, and

needing less memory.

For the file server, the more memory

present, the better the performance. Thefollowing table shows the minimum amount

of memory needed for an isolated file server

host, a boot host, the installation, and theworkstation kernel. It also shows the largest

main memory support by the kernel. In most

cases this will not be supported by thephysical machine.

On the various 80x86 machines it

may be possible to insert up to 512 MB**,

depending on the machine. You need at least


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4 MB RAM to run the bare kernel and

perhaps a login shell, for example a text only

console or a special I/O Hardware Server, aprinter spooler or something else.

Kernel Minimum

MemoryRequirement

Software

Limit onMemory

Workstation 4 MB 512 MB

Fileserver 16 MB 512 MB

Installation 32 MB 512 MB

Boot (withFS)

64 MB 512MB

Fig. 1. Minimum memory requirements forfile server machines and maximum memory

configurations supported by Amoeba.

At heart of the Amoeba system are

several specialized servers that carry out andsynchronize the fundamental operations of

the kernel. Amoeba has a directory server(called SOAP) that is the naming service forall objects used in the system. SOAP

provides a way to assign ASCII names to an

object so it's easier to manipulate(by

humans). The directory server can replicate

files without fearing their change. Amoebahas of course a file server (called the Bullet

Server) that implements a stable high speedfile service. High speed is achieved by using

a large buffer cache. Since the files are first

created in cache, and are only written to diskwhen they are closed, all the files can be

stored contigously. The underlying idea

behind immutable files is to prevent the

replication mechanism from undergoing raceconditions. And file server crashes normally

don't result in an inconsistent file system!The Bullet server uses the virtual disk serverto perform I/O to disk, so it's possible that the

file server run as a normal user program!

The Boot server control all global systemservers (outside the kernel): start, check and

poll, restart if crashed.

Workstations

Workstations allow the users to gain access to

the Amoeba system. There is typically oneworkstation per user, and the workstation are

mostly diskless; only a workstation kernel

must be booted (from floppy, via tftp, burnedin Flash-EEPROM). Amoeba supports X-

Windows and UNIX-emulation.

The primary function of workstationsis to run the user interface (for example the X

window system) and so they do not require

large amounts of memory. 8 MB is the lower

limit for color and monochrome X servers. 16MB and more is recommended. For a generic

text terminal, 4MB is still enough. It is also

possible to use an X terminal as a

workstation. (If the X terminal does notunderstand the Amoeba network protocol it

will be necessary to use a TCP/IP server toconvert network protocols which reduces

perceived performance.)If no bitmap display

is available a regular terminal can be used.Itwill not run X windows, of course.

Pool Processors

.The V8-SPARC processor pool at the VU

Amoeba is designed as a collection of micro

kernels. Thus the Amoeba system consists ofmany CPU's connected over a network. Each

CPU owns his own local Memory in therange from 2MB to several 100MB. A huge

number of Processors build the so calledProcessor pool. This group of CPUs can be

dynamically allocated as needed by the

system and the users. Specialized servers,called Run server, distribute processes in a

fair manner to these machines.


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performance on Ethernet networks - see the

performance page for details.

Interprocess Procedure Call (IPC): used byprocesses and the kernel (for example device

drivers in user space) to interchange

messages and data buffers on the localmachine; optimized for low latency and high

transfer rates

Kernel administration

Remote rebooting of kernels: with a simple

RPC boot request it's possible to boot new

kernels on machines already running with an

Amoeba kernel.

Remote status report: nearly all kernel

related informations and statistics can be

retrieved remotely using a simple RPC

request, including the kernel message buffer(the content you can see printed on the

terminal console).

Now it's possible to run device drivers,

network protocol stacks, file systemservers,..., in user mode as generic user

processes (with some more privileges). Local

modules now communicate with the newenhanced IPC interface.

Most device drivers and many other

parts (servers) currently inside the Amoeba

should move outside the kernel in usual userprocesses with privileged rights. Similar

concepts from Mach, VSTa, L3/4 and QNX

influenced the new design to create an

Operating System ready for the third

millenium!

MICRO KERNEL DESIGN

Clean and unified interaction betweenkernel modules and processes inside and

outside of the kernel device drivers can be

implemented as generic user processesoutside the kernel fast I/O response time

kernel and user thread support (both

controlled by the kernel) small set of system

callsA small piece of code, called the

microkernel, is present on all Amoeba

machines and they run nearly the samemicrokernel which handles Low level I/O management Communication between processes or

threads Low level Memory management Process and thread (kernel/user space)

managementServer processes (see above) supply

other operating system services and

generally run in user mode. This job

specialization allows the microkernel to besmall and efficient, increases reliability,

allows as much as possible of the operatingsystem to run as user processes, providing

flexibility and no extra burdens are added to

individual CPUs with facilities that it doesn'tneed.

Process concept:

Amoeba supports traditional processconcept

Processes consists of several threads (at

least one) Each thread has his own registers,

Instruction Pointer, stack; but all threads

of a process share the same memoryregion

Example: File server. Each request is

handled by one thread, but all threads use

the same cache; synchronization throughMutex and Semaphores

Memory management:


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Threads can allocate and deallocate

blocks of memory, called Segments . These segments can be read and written,

and cans be mapped into and out of the

address space of the process.

A process owns at leat one segment, butmay have many more of them. Segments can be used for text, data,

stack, or any other purpose the processdesires. The operating system doesnt

enforce any particular pattern on segment

usage.

I/O-Management:

For each I/O-Device attached to a

machine, there is a device driver in the

kernel. The driver manages all I/O for the

device. All drivers are static linked to the kernel;

no dynamic Module support Mostly the communication with Device-

Drivers are performed through the

standard message protocol (like the restof the system in user space)

Communication:

Two forms of communication are

provided: Point-to-Point communication Group communication

AMOEBAS OBJECT CONCEPT &

CAPABILITIES

The central point of the software

concept for a server implementation is the

Object concept. Each object consists of

Data and Operations on this data

Amoeba is organized as a collection

of objects (essentially abstract data types);

each with some number of operations thatprocesses can perform on it. Operations on

an object are performed by sending a

message to the object's server. Objects arecreated by processes and managed by the

corresponding server. There are many

different object classes:

Files Directories

Memory segments Processes I/O-Devices (Hard drive...) Terminals ...

Operations on objects are performedwith Stub-procedures. When an object is

created, the server returns a Capability. All

Amoeba objects (files, programs, memory

segments, servers) are protected and

described with so called Capabilities thecapability is used to address and protect the

object. A typically capability is shownbelow.

Figure 6. Capability [Tanenbaumet.al(1990, p

42)]

Service Port field identifies theserver.

Object field tells which object is

being referred to, since a servernormally will manage several

objects.

Rights field specifies whichoperations are allowed (e.g.

capability for a file may be read

only). Since capabilities are

managed in user space

Check field is needed to protectthem cryptographically, to preventusers from tampering with them.

PROCESS MANAGEMENT


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A process is an object in Amoeba.

Information about the processes in Amoeba

are contained in capabilities and in a datastructure called a process descriptor, which is

used for process creation and stunned

processes (and process migration). Theprocess descriptor consists of four

components:

The host descriptor provides the

requirements for the system where the

process must run, by describing whatmachine it can be run

The capabilities include the capability of

the process which every client needs, andthe capability of a handler, which deals

signals and process exit The segment component describes the

layout of the address space (see below) The thread component describes the state

of each of the threads (see below) in the

process and their state informations (IP,Stack,)

Amoeba supports a simple thread

model. When a process starts up, it has atleast one thread. The number of threads isdynamic. During execution, the process can

create additional threads. And existing

threads can terminate. All threads aremanaged by the kernel. The advantage of this

design is that when a thread does a RPC, the

kernel can block that thread and schedule

another one in the same process if one is

ready!

Three methods are provided for threadsynchronization: Mutexes

Semaphores Signals

Mutex is like a binary semaphore. It can be

in one of two states, locked or unlocked.Trying to lock an unlocked mutex causes it to

become locked. The calling thread continues.

Trying to lock a mutex that is already locked

causes the calling thread to block untilanother thread unlocks the mutex.

Semaphores is the second way threads can

synchronize is by counting These are slower

than mutexes, but there are times when theyare needed. A semaphore can't be negative.

Try down a zero semaphore causes thecalling thread to block until another thread

does an up operation on the semaphore.

Signals are asynchronous interrupts sentfrom one thread to another in the same

process. Signals can be raised, caught, or

ignored. Asynchronous interrupts between

processes use the stun mechanism.

MEMORY MANAGEMENT

Amoeba supplies a simple memory

management based on segments. Each

process owns at least three segments:

1. Text/Code segment

2. Stack segment for the mainthread/process

3. Data segment

Each further thread gets his own stack

segment, and the process can allocatedarbitrary additional data segments.

All segments are page protected by the

underlying MMU, the kernel segments, too.


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COMMUNICATION

All processes, the kernel too, communicate

with a standardized RPC (Remote procedurecall) interface. There are only three functions

to reach this goal:

trans(req_header, req_buf, req_size,

rep_header,rep_buf, rep_size)

do a transaction to anotherserver

getreq(req_header,req_buf,req_siz)

get a client request

putrep(rep_header,rep_buf,rep_siz)

send a reply to the client

The first function is used by client to

send a message to a server, and get a reply

from the server on this request. The reply andrequest buffers are generic memory buffers

(char). The reply and request headers are

simple data structures to describe the requestand the capability of the server. On the other

side, teh server calls within an infinite loop

the getreq function. Each time a client sendsthis server (determined by a server port - see

capabilities for details) a message, the getreqfunction returns with the client data filled in

the request buffer, if any. The request headercontains informations about the client

request.

Because the client expects a reply, the

server must send a reply (either with orwithout reply data) using the reply function.

THE VIRTUAL AMOEBA MACHINE (VAM)


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New operating systems mostly lack of

actual device drivers, especially on the i86-

pc platform. For specialized machines, for example

data acquisition systems, or device

minimized numeric cluster machines, thenative Amoeba kernel is the best choice,

featuring a modern and clean microkernel,

and exploring the power of the Amoebasystem.

GENERAL REQUIREMENTS

The Amoeba distributed operating

system can run on many different types andbrands of computers. It is intended that it

should run on a network with at least fivecomputers. Although it is today technicallypossible to run Amoeba with just a single

processor, it is not a satisfactory way to use

the system. For a standalone system (withperhaps additional secondary machines) the

main machine should be equipped with at

least 64 MB RAM (128 MB recommended)and at least with 500MB disk space. It is,after all, a distributed operating system. To

get good results from the system you should

have a separate machine for the file server,one workstation per user (to run the user

interface) and a group of pool processors to

perform the actual work and to run variousservers. In general, at least five hosts are

needed for pleasurable computing, although

it's not true today anymore because of todays

fast Pentium machines. All the Amoeba hostsmust be connected by a network so that they

can communicate with each other, although

they need not necessarily be all on the samenetwork, as long as all the networks are

connected via gateways.

Currently, Fireball Amoeba only supports

Ethernet. In special only the 10 MBit/s

connectivity with RJ45 or RG58 connectors,

and now 100 MBit/s Fast Ethernet, too.

IMPLEMENTATION

According to Tanenbaum (1990),AMOEBA system has been implemented to

five different CPU : 68010, NS 32016, 8088,

VAX, PDP-11. The idea is to provide auniversal single powerful time sharing

systems, which consists of a collection of

machines, potentially distributed amongseveral countries. Current configuration has

48 single board VME based computers using

68020 and 68030 CPU and also 10 VAX

CPU forming additional processor pool.

A library which supports to run UNIXprogram on AMOEBA had been written.

Current research includes connectingAMOEBA at 5 locations in 3 countries.

Using Wide Area Network facilities.

SECURITY

Amoeba has two level of protection:

Ports for protecting access to server

Capabilities for protecting access toindividual objects.

Since the kernel must be kept as small as

possible, to implement the security aspect

there is two solutions.

hardware solution: A small interface box

(F - box) are put between each processor

module and the network. It can be done byputting into the VLSI chip in interface card,

or on a small printed circuit board which

attach to network. This solution is currently

used.software solution: since ports for public

servers are known to all users it is easy for an

intruder to impersonate a server just by doinga get_rerequest on the servers port. So the F-

box is built as a cryptographic algorithms

which has the same function with the F-box.


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The F box is one way function mapping Get-

port to Put-port

Put-port = F(Get-port)

Thus that given G, P can be computed, but

that given P, calculating G is not practicallyfeasible.

Figure 7. Network security[Goscinski(1991,

p823)]

COMPARISION OF AMOEBA AND

V

There are some similarity between

Amoeba and V. Some of feature in Amoeba

are adapted from V. Some features ofAmoeba had been planed by the designer of

V to be implemented in the future, for

instance processor pool concept. [Cheriton

(988)].

Amoeba and V use the small kernel to

provide the infrastructure of the distributed

system. Kernel provides the communication,

process manager, memory manager and asmall server. Most of other facilities which

usually are in the Operating System run on

the top of the kernel at the user level. Thisapproach makes V and Amoeba more flexible

and more reliable, because if something goes

wrong in a server, the other server which is inthe other site (physically or logically) can

take over the process).

Amoeba and V are free-market model

service, Service such as the file system are inprinciple just an ordinary user process. Any

user who unsatisfied with the standard file

system will be able to write their own system.

Amoeba and V use client-server and

remote procedure call. The difference is the

transport protocol, V uses the VMTP butAmoeba does not. V and Amoeba allow the

process to migrate to another processor, if the

processor is busy or high loaded.V does not have the processor pool,

and there is no dynamic processor allocation.

Amoeba has a processor pool and does the

processor allocation. V had not beendeveloped to use the Wide Area Network, but

Amoeba has been implemented using WAN.

By using workstation as the processor, V cantake advantages of the modern and powerful

workstation, and the system will be more

reliable, because the responsibility of process

is distributed in each workstation.

Amoeba use only a single naming

mechanism (object with capability), It makes

the system will be more consistent and easier

to used. V uses 3 level of naming. At the toplevel of V naming mechanism, the

mechanism will works similar with object

and capability.

Amoeba is more fault tolerance thanV (Cheriton 1988), because V was designed

for interactive workstation, so if there aresomething goes wrong, user can re-execute.Amoeba is more secure than V, first Amoeba

using cryptography for naming, and secondly

Amoeba uses the hardware one wayscrambler.

Amoeba performance depends on the

processor pool, thus if there is a malfunction

it the processor pool all system will stop. Incontrast, V uses the processor in every

workstation, thus the responsibility of the

work is distributed to each workstation.

In the development process, V ismainly addressed to provide a fast

communication between work station, but

Amoeba is addressed to provide an objectoriented distributed operating system. And V

is designed to support parallel and real time


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application on shared memory multiprocessor

machine.

The performance comparison betweenAMOEBA and V

System Null

RPC

in

msec

Throughput

in KBps

Estimated

CPUMIPS

AMOEBA 1.1 820 3.0

V 2.5 546 2.0

Table 1. Comparison between V and Amoeba

[Tanenbaum(1990, p57)]

This measurement is done from user to user,

and using SUN 3/60 for AMOEBA and SUN3/75 for V system. From this table can be

shown that the throughput of Amoeba is

better than V. and the overall CPU MIPS isbetter as well.

FIELDS OF APPLICATION

The VAM system can be used in the

following applications fields: Distributed measuring and data

acquisition systems, for example remotedigital camera servers connected with

an Ethernet network. The native Amoeba kernel is very well

suited for embedded systems. Distributed control systems. High performance parallel computing

and other distributed numerical

computations.

Distributed file systems using raw disk

access on the top of standard operatingsystems.

An example for a processor pool: About

60-80 Sun motherboards were build into a

rack system at the Vrije Univerity. Of coursecheap and normal IBM-PC 's can be used as

CPU-Servers, too!!!

CONCLUSION

A distributed system potentially willbe more reliable and low cost than a time

sharing system. However some problem still

arises in the designing of a distributed system. Those problems are communication

primitives, naming , resource management,

fault tolerance and the protection issues. The

hardware configuration which will be used

will determine the model of the operatingsystem, for instance a processor poll model

will be difference with workstation poolmodel.

The kernel model provide definition

of each facility based on maximisingperformance, minimising complexity in the

kernel maximising the reliability and security

attribute of the system. By placing the other

service outside the kernel and keeping thekernel as small as possible, the system is

more flexible and reliable.The client-server model with remoteprocedure call have proved that using basic

primitive communication the overhead of

communication can be reduced. The speed ofcommunication between processor

determines the performance of the system.

By using the object and capabilitymodel, Amoeba is more flexible and more

easily be used. Amoeba is the only one

Distributed Operating System which

implements Wide Area Network.

BIBLIOGRAPHY

BOOK:

Distributed Operating Systems by Tanenbaum


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Distributed Operating Systems Concepts and Design by Pradeep K. Sinha

Web site:

http://www.cs.odu.edu/

http://images.google.co.in/images?

q=distributed+operating+system&hl=en&btnG=Google+Search

http://fsd-amoeba.sourceforge.net/amoeba.html

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