MOOSE project -- looking for a language

[Jean-Pierre Weber]

Hi!
I saw your post in comp.compilers about your ideas for a new OS.
Although it is not exactly the same, some of your ideas seemed to be
close to what has been done in the TAOS operating system.
(Among other things, they achieved machine independence by using
a virtual instruction set that gets translated to the real one
when the module gets loaded in memory)

I am joining a file about it I pulled off the net a few months ago.

Hope this helps,
J.-P.

============================================================================
| Jean-Pierre Weber                                               | We  do |
| Fibre Optics Research Centre | Phone:  +46 8 757 4513           |    \|/ |
| Ericsson Components AB       | Fax:    +46 8 757 4764           | ----O- |
| KI/EKA/S/RF                  | e-mail: ekajewe@hall.ericsson.se |    /|\ |
| S-164 81 KISTA , SWEDEN      | MEMO:   ERI.EKA.EKAJEWE          | lasers |
============================================================================


>From N.S.Spellings@uk.ac.bham ()
Newsgroups: comp.lang.misc
Subject: Taos Information (long)
Date: 01 Jun 94 11:33:01 BST

==============================================================================
Hi all, just thought this may be of interest to you folk....

For those who wish to obtain more information, Toa Systems Ltd may be
contacted at the following places :

Taos Global Distributors (Japan Office) Tel. +81 3 3223 1020
                                        Fax. +81 3 3223 1288

Internation Office (London) Tel. 081 905 5708
                            Fax. 081 905 5709

Taos Development Company (Toa Sytems Ltd) Tel. 081 905 5706
                                          Fax. 081 905 5709

or write to :  PO Box 2320
               London
               NW11 6PW
               England

Please note that I, nor Five Star Software do not have any connection wi
Systems Ltd.

Hope someone finds this useful....

Regards,

 .Neil Spellings.
 .Five Star Software.

                             ----BEGINS----


                          An Introduction To Taos
                          =======================

Audience
--------
This document, which has been designed to address a wide audience,
gives a brief introduction to the ideas behind Taos and its benefits. We have
attempted to keep the technological language to a minimum although the very
nature of the subject matter makes it necessary for explanations in some of
the sections to be quite technical.

Overview
--------
Computing has been getting steadily more restrictive. The move to so called
"open" systems has not helped improve portability, has not produced credible
support for parallel systems and has not stopped the further development of
increasingly complex interfaces between operating systems and applications.
All in all, it has done nothing to improve the lot of the developer or the
consumer.

The Taos operating system addresses these issues. Its existence and success
is good  news for technology from small embedded systems through to
supercomputers and large scale network applications.

Taos is not conventional as it has not evolved from an existing operating
system. Tao Systems developed Taos taking into account the commercial and
technological realities of the time whilst also removing the limitations
enforced upon the user market.

Key Features
------------
Taos, a compact, general purpose kernel for parallel processing systems
embodies a number of vital ideas.

* Hardware Independence - Taos applications run of different processor
  architectures without any re-compilation of programs.

* Load-Balancing - Taos provides an optimum distribution of processes over
  the network.

* TOTAL OPEN COMPUTING  : Heterogeneous Processing - Parallel applications
  are able to execute over networks of dissimilar processors.

* Dynamic Binding - Only those parts of an application which are needed at
  any time are loaded into memory.

* Multi-Threading - A piece of code loaded into memory, is available to all
  programs which need it.

* Parallelism -Taos uses a process-based program design model.

* Asynchronous-Messaging - Messaging does not halt the sending process

* Minimal Kernel - Taos has a very compact implementation, optimising
  performance and minimising memory requirements.

The Challenge of Parallel Systems
---------------------------------

Why has parallel processing remained on the property, given the obvious
potential this technique has to increase the power of computers way beyond
the possible from increasing the power of a single processor?

The answer is that, whilst it is comparatively easy to build massive parallel
computers, programming them has proven immensely difficult.

This has been due to a number of factors including :

  A lack of suitable general purpose programming methodology;

  Programs written to run a one machine tend to be tied to that one machine,
  possibly a single configuration;

  Uncertainty as to the which computation and communication model to use.

Parallel - Features & Benefits
------------------------------
Taos is a software response to the challenge of harnessing parallel hardware.
Parallel systems are complex, comprising thousands of processors with
different amounts of memory, link standards and so on. Taos exploits the
power of the hardware, whilst presenting the programmer with a clean, simple
and powerful programming environment.

Taos enables programmers to think about the design of their applications in
terms of parallel processes. They are completely free to build and structure
of processes and communications they need. It is the programmer's
responsibility to think about their applications and identify the appropriate
decomposition into parallel processes. But once this is determined, Taos will
manage the distribution of these processes on any target network. Programmers
need not concern themselves with the actual hardware and network architecture
upon which their applications will run, including adjustments to the network
size. Taos grows over all processors available on the network, and will
expand if more processors are added; whilst applications grow over the
available processors as they create objects during their execution.

This means that it is easier to write "shrink-wrapped" applications for
parallel computers using Taos than it is to write them for single processor
operating systems, as applications code will run on any processor supported
by Taos.

Taos uses a process and communications model of parallelism. Each process can
execute on a separate processor, and talk by sending messages to each other.
The processes are fast ad can only interact by passing messages. There is
deliberately no concept of shared memory, though Taos can be implemented on
shared memory machines.

Taos does not attempt to evolve from a sequential model; extracting
parallelism from sequential programs does not and will not work. So, Taos has
been designed as a perfect fir for parallel systems. Taos software exploits
parallelism; creating parallel applications using Taos is easy. By creating
objects and passing messages, the programmer generates the opportunity for
Taos to distribute the objects over processors and thus generate parallelism.

The final important point to re-emphasise is that it is up to the programmer
to write their programs so that the objects can execute in parallel.
parallelism is not automatically created, nor should it be. There are
instances where a program must be sequential to behave correctly.

Portable - Features & Benefits
------------------------------
Portability is normally taken to mean that programs written in a language
(such as C) to run on a particular processor, can be re-compiled to run on a
different processor without  the need to re-write any (or a small portion) of
the code. This approach has its limitations as a new compiler needs to be
written for every processor type introduced. This can consume a great deal of
effort to achieve.

Taos takes a different approach. By targeting all compiled code at the Taos
Virtual Processor, porting relates only to the VP itself and not to the
applications, whatever language they may be written in. In effect the
portability has been taken from the language level to the processor level.
Furthermore, this low level portability facilitates heterogeneous processing
support. See Heterogeneous Processing, below.

Taos can be ported with little effort to any processor or communications
hardware. The only part of Taos that needs to be re-coded to support a new
physical processor, the the Translator. The Translator is the program which
converts VP code into the native code for the processor. Once the translator
is written, all applications written for any processor, in any language which
compiles to VP, will become instantly executable on the new processor type.

So, to reiterate; programs written on any supported platform will run on all
other supported platforms without any changes; you dont event have to
re-compile.

Virtual Processor - Features & Benefits
---------------------------------------
The Taos virtual processor is an imaginary 64bit microprocessor which can be
extended to 128bit and beyond with no limitation but which also runs
effectively on 32bit processors.

All programs are compiled or assembled into virtual processor code and are
kept in this form on disk. The VP code is translated into native code of the
processor on which it is to run only when it is needed. The translation
occurs as the VP ode is loaded from disk, across the network and into memory
of the target processor.

This mechanism is at the heart of Taos' dynamic binding facilities. See
Dynamic Binding, below.

It would be wrong to think that this slows the system down. Most processors
are able to translate VP into native code faster than VP code can be loaded
from disk and sent across the network, so there is no visible overhead.
Indeed, VP code is often more compact than the native code; therefore less
disk space is used and code is loaded faster than if it were native for the
processor.

If there are particular advantages in using native version of the code, then
this can be stored on disc, and will be loaded in preference to the VP
system. This would be because the performance of the code would benefit from
specific instructions supported in hardware by a particular processor.

A VP version of the code will run on any processor for which a translator is
available. There is no need for re-compilation, see Portability, above.

Dynamic Binding - Features & Benefits
-------------------------------------
Some readers may be familiar with dynamic linking. Taos dynamic binding is
more than dynamic linking. code units are brought into memory only when
needed. This is how it works :

  As a process executes it will ask fr a named piece of code, a tool.

  This will be brought in from disk and translated into native code, before
  being executed.

  This tool may, in turn, call further tools, following the above procedure.

  Once a tool has finished being executed, it may be removed from memory if
  no other process is referencing it.

This implies that many processes may share code (tools), i.e. multi-threading
code. This is highly memory efficient. Once a tool has finished being
executed, it stays on the list of available tools. Should it be needed again,
this local copy will be used, thus avoiding a re-load from disk. ONly is
memory get filled up will the tool be flushed and subsequent calls require a
re-load from disk.

Taos' dynamic binding and VP code combine to enable Taos to exploit
heterogeneous parallel hardware.

Total Open Computing - Features & Benefits
------------------------------------------
Taos is able to run on any hardware which there is a translator. This
provides the basic facility which enables programmers to write code which can
be run on a wide range of hardware. This, together with Taos' dynamic
binding, enables programs to run over a network of differing processor and
communications types without changes to the code, or any re-compilation.

Heterogeneous processing is the exploitation of a range of different
processor memory and communications hardware to create a versatile parallel
computing machine.

Such machines may be built from a variety of hardware to support different
kinds of computation. For example, a vision system requires a front end to do
the initial work on the raw images being received, tom find edges, shapes,
etc. This stage of the problem is well suited to parallel hardware, whereas
the back end will need to extract meaning from the shapes, which is more
suited to implementation on hardware supporting list or network processing.
The ability of software to run a variety of hardware is essential for this
type of machine to be successfully exploited. Furthermore, Taos provides
access to information about the hardware available in the network. So,
programs can take advantage of special purpose hardware to run specific
objects. This means that sophisticated adaptive programs can be written
within the Taos model to get most from heterogeneous machines.

Heterogeneous processing is the complete Open System, in which all aspects of
the processing are distributed across dissimilar processors, networks and
architectures. It benefits consumers who can select processors on the basis
of current price; performance or whichever criteria they select as their
priority, without prejudicing future decisions. For manufactures, it gives
them the flexibility to improve hardware design and not become locked into
historical decisions for the sake of software compatibility. Therefore, we
call this aspect of Taos "Total Open Computing".

Minimal Kernel - Features & Benefits
------------------------------------
The key to Taos' applicability to so many areas lies in its compact kernel.
This is all that is needed for a processor to provide all of the Taos
services.

The Taos kernel provides all the facilities needed to support its simple
execution model, yet the whole kernel is only 12K.

The kernel executes on every processor in the network from boot, and its
facilities include memory management and cacheing, object creation,
distribution and execution, object message passing and tool calling. There
are also calls to provide global name management, local timer and scheduling,
and access to network hardware information.

The programmer is free to add objects to the system as appropriate. Examples
of these may be hardware drivers or file system objects.

Objects and Messages - Features & Benefits
------------------------------------------
Taos objects are also parallel processes. Each object which Taos creates is
given its own process to execute it. The difference between objects and
processes lies in what they are about; objects are about data and code, they
occupy memory space; processes are about processors, they consume processor
time. Put the two together and you have an object which is executing,
consuming memory space and processor time. A process brings an object to
life.

Objects can only interact with other objects by sending and receiving
messages. As objects can exist om separate processors, memory can not be
shared between objects. Taos provides a light-weight-mail system to
communicate between processors.

Messages are just like letters, you send them by posting them in a mailbox
with an address on it. You use letters to communicate with people to whom you
cannot talk directly. So it is also with Taos objects; you use messages to
communicate with other objects, as you cannot talk to them directly since
they can be on separate processors.

When you send a message you specify the mail address of the recipient. The
sending of mail is equivalent to popping a letter into a post-box.
Conversely, each process has a mail-box in which mail is placed by the
messaging system. Objects receive mail be checking their mail-boxes. Messages
are typed, so the object can distinguish between a variety of possible
incoming message types.

Messages conform to the basic bode format, plus extensions, to hold the
sender's address and the message's destinations address. When mail arrives it
is left on a list for the receiving process to look at.

Taos provides a simple mechanism to send messages, there being only two
facilities in its messaging system, to send and receive messages. Messages
are sent asyncronously; once a message has been sent on its way the sending
process is free to continue its execution. Synchronous communication can be
achieved by waiting for a returned acknowledge message. Taos' method of
communication ensures that parallel processes execute independently of one
another for as much of the time as possible. An object may need to wait for a
message before it continues processing, but a sending object will now wait
until the destination has received it.

The mailing system uses a distributed algorithm which finds multiple paths to
a destination and may use more than one route for each message sent, thus
making best use of all available communication paths. If one route is
bottlenecked then the message will get through via another.

Distributed processing - Features & Benefits
--------------------------------------------
The whole conceptual approach to the design, implementation and execution of
Taos is organic. A program evolves to fill the network during runtime. Other
systems introduce bottlenecks by requiring a system-wide time-stamp on all
messages, or by maintaining a central control over the distribution
algorithm.

Taos does not attempt to impose a central control over te execution of an
application. The kernel is small enough to exist on every processor,
providing local services to the objects on its processor and interacting with
adjacent processors' kernels to provide message passing and process
distribution.

Distribution is based on processes which pass messages. Load balancing (the
distribution of processes over the network to maximise the performance of the
system) is achieved via a simple algorithm based on the computation and
communication requirements of the objects. When on object is created, the
loading on the local processor is compared with the loading on neighbouring
processors and th object is allocated to the most suitable processor.

Each processor hold minimal routing information for each communications
channel eo enable messages to be forwarded towards their destinations.
Messages are routed to their destinations in much the same way as water flows
down through pipes under the effect of gravity.

During the execution of a program, processes distribute themselves over the
available processors as they are created. The net effect is that objects
spread out over the available processors in much the same way as liquid
spreads out over a surface.

Object Oriented Design - Features & Benefits
--------------------------------------------
Taos was conceived to take advantage of the re-usablility and robustness
provided by an object based approach to design.

Object ideas are exploited at all levels of Taos, from kernel data structures
to high level classes. Kernel objects are used to build higher level
messaging passing object.

The basic data node structure used bt Taos is inherited by all objects in the
system. This enables Taos to manipulate all entities which conform to this
very simple structure. Message passing objects, the messages which they pass
to each other and the tools which they use to process their data all conform
to this basic data structure. New types of objects may be introduced by the
programmer.

  Data nodes are the basic object in the system.

  Tool objects are bits of code, like formal object oriented programming's
  methods, but without and restrictions on their use.

  Control objects, as they are known, are objects which have a process
  associated with them. They communicate via messages and can be distributed
  over processors. Such a message passing object will typically contain several
  components which are references to tool objects. See Objects and Messages
  above.

  Classes provide higher functionality such as Window and Polygon World.
  These are formed of message passing objects bound together to form the
  class object. A class may make use of many objects working in parallel.
  These objects are made available to the user in the form of calls to the
  class, for example, create new windows and manipulate them using method
  calls. So the user just sees functionality such as "open window" and does
  not need to be concerned with underlying parallelism generated by the
  execution of the objects in the class.

Programmers are encouraged to use existing messages, tools, objects, and
classes, to create their own new ones.

There are presently over 3000 tools covering a wide range of basic
functionality from string and file handling to classes supporting 3D polygon
world. Re-use and relax! A program to fly-through a fractal landscape is
under 100 lines long, when written using the existing objects.

Object and Memory Management - Features & Benefits
--------------------------------------------------
Taos executes objects and manages memory in a very consistent manner.

The Taos software model use processes, messages and objects, whilst its
hardware model uses processors with local memory and communication channels
between processors. The way to view objects is that they consume memory
space, whereas processes consume processor time. An object need a process to
enable it to execute.

Upon creation of an object Taos allocates the object to a processor and then
allocates a process to enable the object. A typical Taos object is a few
hundred bytes in size. So, they lie between fine-grain Smalltalk-style
objects and course-grain UNIX-style objects.

The lowest level object in Taos is the 'node'. The is the simplest entity
with which Taos deals. It is a variable sized packet of data which can be
placed in a doubly linked list. All Taos entities conform to this basic
format.  From this basic building block, other structures have been grown,
such as tools, messages and other types of system object.

Nodes have a type field which identifies what type of Taos object the node
holds and hence how it should be processed. Pre-defined types include: Tools,
Control Objects, Bitmaps, Graphical Objects and Class Objects. The user can
define new types.

Nodes are in one of two forms. When the node is on disk or being communicated
across a network, it is held in 'template' form, as it is loaded into memory
and made ready to be executed it si converted to 'process-ready' form. As the
template is converted to process-ready, and translation from VP code to the
local processor's native code is performed, and the node is inserted into a
list of other process-ready objects (see Dynamic Binding and Portability).
Once a mode is in a process-ready list it can be processes. The node type
determines how it is to be processes. Two types to focus on are the Control
object and the Tool object.

When a Control object is created the object's template is distributed and
made process ready on a processor. A process is made available to the object
and it start to execute. A Control object is made up of one or more
components, which are all Taos nodes of one type or another. Each component
is executed in sequence until the last one is finished when the Control
object closes and its process finishes. The components may be other Control
objects, tools, graphic objects etc. Tools are bits of code which operate on
the data defined in a Control object. For example, they may perform
calculations and send and receive messages to and from other Control objects.
All Control objects are created by another Control object, and each has the
mail address of its parent, forming a tree. Tools, being nodes, can be
manipulated by the kernel. A control object may consist of some local memory
space and some constituent tools which operate on the data.

Whilst the Control object is the smallest entity which can execute in
parallel, it is not the finest granularity of memory management. Individual
tool can be loaded from disk, as they are also Taos objects (conforming to
the basic node format). A Control object template only holds the text names
of its constituent components, not the actual code. As a Control object is
created, the kernel checks to see is th tools which the components reference
are already available in memory, and if they are, simply points to them. Only
if an object is not present will it be loaded from disk and be made
process-ready. So all Taos objects can be multi-threaded. You will never have
two copies of the same object in the same memory space, unless you
specifically request it (see Dynamic Binding).

Another feature of the execution mechanism is that only those components
which are needed are loaded. If you design your application so that it is
built of hierarchically structured Control objects, then code will only every
be loaded if it is executed. If the path of execution does not pass the
particular component then it will not be loaded and thus occupy no space. So,
the amount of memory consumed is kept to and absolute minimum and is driven
by the execution of the program.

Conclusion
----------
Taos is the ground breaking revolution for which the electronics,
computing and communications worlds have been waiting. For years the
information world has been outgrowing its boots, becoming cumbersome and
sluggish. The push of new technologies and of parallel processing in
particular has forced a profound re-think of what an operating system should
be.

Taos provides what is needed, no more no less; it is simply the right product
at the right time. Elegant, compact and versatile, it provides the programmer
with simple yet powerful tools to exploit the emerging technologies.

Taos is not just another development, it is a Holy Grail, a complete product
with substance as strong as the claims made for it, and implications that can
not yet be realised. Exactly what it is that makes Taos so significant may be
argued for a long time given its many benefits.

For those of use who carry the torch of Open Computing, Taos provides the
ultimate open platform through distributed processes across dissimilar
processors to achieve HETEROGENEOUS PROCESSING or TOTAL OPEN COMPUTING. this
is achieved by having totally PORTABLE CODE. Taos-based applications are
written only once, so that software houses can now channel funding into the
development of new products rather than having to allocate vast sums towards
the porting of existing packages from one platform to another.

Taos' PARALLEL PROCESSING facilities generate a MASTERLESS NETWORK with no
practical limit on its size and providing LINEAR SCALABILITY of performance.
Developing products for a parallel environment has traditionally been a major
stumbling block. But writing parallel program for Taos is as easy as writing
programs for a single processor environment; and once a program is written it
will run on any processor supported by Taos without any changes.

The LOAD BALANCING techniques employed by Taos enable applications to exploit
additional processing power as it is added, without re-compilation, even
during the execution of the program.

Taos' OBJECT ORIENTED programming techniques have led to the creation of
thousands of reusable tools which will be used over an over again in future
software developments. Other Object Orientated techniques have so far failed
to live up to expectations, but Taos shows that this methodology can, if
employed wisely, yield massive benefits to the programmer and end user.

Taos' lack of protocol layers make is very reactive to stimuli and this
combined with its highly efficient DYNAMIC BINDING, provides the bases for
truly REAL TIME systems.

Taos' SCALABILITY enables it to underpin massive superscalable networks,
whilst its COMPACTNESS makes it an obvious choice for embedded applications.

This only provides a brief overview of just some of the features and benefits
of Taos; despite this document's limitations, what we hope it does emphasise
is the remarkable flexibility of Taos and the broad range of markets for
which it is ideally suited.

----ENDS----

----------------------------------------------------------------------
Neil Spellings                          Five Star Software
Five Star Software                      1 Dove Cottages
                                        Scropton
email : N.S.Spellings@uk.ac.bham        Derbyshire
tel   : (0374) 227802                   DE65 5PN
----------------------------------------------------------------------