and only such information can eventually and enrich the whole system. basis of any reliable information upon which new information can be built that will enrich the whole system; when this information eventually settles, it enriches in turn the OS, and can serve as a universal basis for even further enhancements. That is the utility of Operating Systems.
That's why the power and long-term utility of an OS mustn't be measured according to what the OS does currently allow to do, but according to how easily it can be extended so that more and more people share more and more complex software. That is, the power of an OS is not expressed in terms of services it statically provide, but in terms of services it can dynamically manage; intelligence is expressed not in terms of knowledge, but in terms of evolutivity toward more knowledge. A culture with a deep knowledge but that would prevent or considerably slowdown further innovations, like the ancient chinese civilization, would indeed be quite harmful. An OS providing lots of services, but not allowing its user to evolve would likewise be harmful. Utility lies in new, original information; a large body of acquired information is a sign of past utility, but quite independent from current utility.
Again, we find the obvious analogy with human culture for which the same stands; the analogy is not fallacious at all, as the primary goal of an operating system is allowing humans to communicate with computers more easily to achieve better software. So an operating system is a part of human culture, though a part that involves computers.
Multiplying the actual services provided by an operating system may be an expedient way to solve computer problems, in the same way that multiplying welfare institutions may be an expedient way to solve the everyday problems of a human system; the progress of the system ultimately means that those services will actually be multiplied in the long run. However, from the point of view of utility, what counts is not any the objective state of the system at any given moment, and its ephemeral advantages, but the dynamic project of the system across time, and its smaller, but growing, long-standing advantages.
the information in an OS is virtually (not forcibly physically) duplicated at each node. Hence growing the OS for ever more feature is harmful, as it would involve an ever increased waste of resources duplicated at each node, instead of letting each node develop original information in a way adapted to its immediate environment.
.....
The deepest flaw in computer design
is this idea that there is a fundamental difference
between system programming and usual programming,
between usual programming and "mere" using.
The previous point shows how false is this conception.
The truth is any computer user, whether a programming guru or a novice
user, is somehow trying to communicate with the machine. The easier
the communication, the quicker better larger the work is getting done.
Of course, there are different kinds of use;
actually, there are infinitely many.
You can often say that such kind of computer use is
much more advanced and technical than such other;
but you can never find a clear limit,
and that's the important point
(in mathematics, we'd say the space of kinds of computing is connected).
Of course also,
any given computer object has been created by some user(s),
who programmed it above a given system,
and is being used by other (or the same) user(s),
who program using it, above the thus enriched system.
That is, there are computer object providers and consumers.
But anyone can provide some objects and consume other objects;
providing objects without using some is unimaginable,
while using objects without providing any is pure useless waste.
The global opposition between users and programmers that roots
the computer industry is thus inadequate;
instead, there is a local complementarity between providers and consumers
of every kind of objects.
Some say that common users are too stupid to program;
that's only despising them;
most of them don't have time and mind
to learn all the subtleties of advanced programming;
Most of the time, such subtleties shouldn't be really needed,
and learning them is thus a waste of time
but they often do manually emulate macros,
and if shown once how to do it,
are very eager to use or even write their own macros or aliases.
Others fear that encouraging people to use a powerful programming
language is the door open to piracy and system crash,
and argue that programming languages are too complicated anyway.
Well, if the language library has such security holes and cryptic syntax,
then it is clearly misdesigned;
and if the language doesn't allow the design of a secure, understandable
library, then the language itself is misdesigned (e.g. "C").
Whatever was misdesigned, it should be redesigned, amended or replaced
(as should be "C").
If you don't want people to cross an invisible line, just do not draw roads
that cross the line, write understandable warning signs, then hire an army of
guards to shoot at people trying to trespass or walk out of the road.
If you're really paranoid, then just don't let people near the line:
don't have them use your computer. But if they have to use your computer,
then make the line appear, and abandon these ill-traced roads and fascist
behavior.
So as for those who despise higher-order and user-customizability, I shall repeat that there is NO frontier between using and programming. Programming is using the computer while using a computer is programming it. Which does not mean there is no difference between various users-programmers; but creating an arbitrary division in software between "languages" for "programmers" and "interfaces" for mere "users" is asking reality to comply to one's sentences instead of having one's sentences reflect reality: one ends with plenty of unadapted, inefficient, unpowerful tools, stupefies all computer users with a lot of unuseful ill-conceived, similar but different languages, and wastes a considerable lot of human and computer resources, writing the same elementary software again and again.
But this accounts only for centralized design; it appears that what system acknowledge as first-class objects are actually very coarse-grained information concepts, and that a meaningful study of information flow should take into account much finer-grained information, that such system just do no consider at all, hence being unadapted to the actual use that is done of them.
How does this design generalize to arbitrary OSes?
What do OS kernels provide that is essential to all OSes,
and what do they do that is costly noise?
To answer such questions, we must depart from the traditional
OS point of view that we know is flawed,
and see how are OSes doing, that we recognized as such,
that traditional design refuses to consider this way,
and what the analogy to human systems lead to.
Thus, we see that of course, centralization of the information flow through the kernel is not needed: hence, information most often is much more efficiently passed directly from object to object without any intermediate. Also,
To conclude, we'll say that the kernel is the central authority used to coordinate software components, and solve conflicts, in a computer system.
As a blatant example
of the lack of evolution of system software quality
is the fact that
the most popular system software in the world (MS-DOS)
is a fifteen-year old thing that does not allow the user
to do either simple tasks, or complicated ones,
thus being a no-operating system,
and forces programmers to rewrite low-level tasks
everytime they develop any non-trivial program,
while not even providing trivial programs.
This industry-standard has always been designed
as a least sub-system possible for the Unix system,
which itself is a least subsystem of Multics
made of features assembled in undue ways
on top of only two basic abstractions,
the raw sequence of bytes ("files"),
and the ASCII character string.
As these abstractions proved not enough to express adequately the semantics of new hardware and software that appeared, Unix has had a huge number of ad-hoc "system calls" added, to extend the operating system in special ways. Hence, what was an OS meant to fit the tiny memory of then available computers, has grown into a tentaculous monster with ever growing pseudopods, that wastes without counting the resources of the most powerful workstations. And this, renamed as POSIX, is the new industry standard OS to come, whose promoters crown as the traditional, if not natural, way to organize computations.
Following the same tendency, widespread OSes are
found upon a large number of human interface services,
video and sound.
This is known as the "multi-media" revolution,
which basically just means that your computer produces
high-quality graphics and sound.
All that is fine:
it means that your system software
grants you access to your actual hardware,
which is the least it can do!
But software design, a.k.a. programming,
is not made simpler for that;
it is even made quite harder:
while a lot of new primitives are made available,
no new combinatorials are provided
that could ease their manipulation;
worse, even the old reliable software is made obsolete
by the new interface conventions.
Thus you have computers with beautiful interfaces
that waste lots of resources,
but that cannot do anything new;
to actually do interesting things,
you must constantly rewrite everything from almost scratch,
which leads to very expensive low-quality slowly-evolving software.
[= most of the energy is wasted in a fight for supremacy
between monopolies]
The current computing world is anything but a failure.
So many things are now done by computers that relieve people
from stupid repetitive work, and so many things are done that
just could not be done without computers,
that nobody can deny the utility of today's computers
relatively to the implicit reference being the absence of computers.
But somehow, programming techniques are finding their limits
as programs reach the size beyond which
no human can fully understand the whole of one.
And the current OS trend, by generating code bloat,
makes those limits reached much faster than they should,
while wasting lots of human resources.
It is thus necessary to see
why current programming techniques lead to code bloat,
and how this trend can be slowed down, set back, or reversed.
Of course, we easily can diagnose about the "multimedia revolution" that it stems from the cult of external look, of the container, to the detriment of the internal being, the contents; such cult is inevitable whenever non-technical people have to choose without any objective guide among technical products, so that the most seductive wins. So this general phenomenon, which goes beyond the scope of this paper, though it does harm to the computing world, and must be fought there as well as elsewhere, is a sign that computing spreads and benefits to a large public; by its very nature, it may waste a lot of resources, but it won't compromise the general utility of operating systems. Hence, if there is some flaw to find in current OS design, it must be looked for deeper.
Computing is a recent art, and somehow, it left its Antiquity for its Ancien Régime. Its world is dominated by a few powerful companies, that wage a perpetual war to each other, where At the same time, there are heavens where computists can grow in art while freely benefitting ..... isn't the deeply rooted .....
Actually, the ..... the informational status of the computer world is quite remindful of the political status of .....
Well, firstly, we may like to find some underlying structure of mind in terms of which everything else would be expressed, and that we would call "kernel". Most existing OSes, at least, all those software that claim to be an OS, are conceived this way. Then, over this "kernel" that statically provides most basic services, "standard libraries" and "standard programs" are provided that should be able to do all that is needed in the system, that would contain all the system knowledge, while standard "device drivers" would provide complementary access to the external world.
We already see why such a conception may fail: it could perhaps be perfect for a finite unextensible static system, but we feel it may not be able to express a dynamically evolving system. However, a solid argument why it shouldn't be able to do so is not so obvious at first sight. The key is that like any complex enough systems, like human beings, computer have some self-knowledge. The fact becomes obvious when you see a computer being used as a development system for programs that will run on the same computer. And indeed the exceptions to that "kernel" concept are those kind of dynamic languages and systems that we call "reflective", that is, that allow dynamical manipulation of the language constructs themselves: FORTH and LISP (or Scheme) development systems, which can be at the same time editors, interpreters, debuggers and compilers, even if those functionalities are available separately, are such reflective systems. so there is no "kernel" design, but rather an integrated OS.
And then, we see that if the system is powerful enough (that is, reflective), any knowledge in the system can be applied to the system itself; any knowledge is also self-knowledge; so it can express system structure. As you discover more knowledge, you also discover more system structure, perhaps better structure than before, and certainly structure that is more efficiently represented directly than through stubborn translation to those static kernel constructs. So you can never statically settle once and for all the structure of the system without ampering the system's ability to evolve toward a better state; any structure that cannot adapt, even those you trust the most, may eventually (though slowly) become a burden as new meta-knowledge is available. Even if it actually won't, you can never be sure of it, and can expect only refutation, never confirmation of any such assumption.
The conclusion to this is that you cannot truly separate a "kernel" from a "standard library" or from "device drivers"; in a system that works properly, all have to be integrated into the single concept, the system itself as a whole. Any clear cut distinction inside the system is purely arbitrary, and harmful if not done due to strong reasons of necessity.
Well, we have seen that an OS' utility is not defined in terms
of static behavior, or standard library functionality; that it
should be optimally designed for dynamic extensibility, that it
shall provide a unified
interface to all users, without enforcing arbitrary layers
(or anything arbitrary at all). That is, an OS should be primarily
open and
rational.
But then, what kind of characteristics are these ? They are features
of a computing language. We defined an OS by its observational semantics,
and thus logically ended into a good OS being defined by a good way to
communicate with it and have it react.
People often boast about their OS being "language independent", but what
does it actually mean ?
Any powerful-enough (mathematicians say universal/Turing-equivalent)
computing system is able to emulate any language, so this is no valid argument.
Most of the time, this brag only means that they followed no structured plan
as for their OS semantics, which will lead to some horrible inconsistent
interface, or voluntarily limited their software to interface with the
least powerful language.
So before we can say how an OS should be, we must study computer languages, what they are meant to, how to compare them, how they should be or not.
Also see the disaster of State managing services.
Well, then
Seeing how existing human States and computer kernels fail to do their job is left as an exercise to the reader.
The point is that all this infrastructure is meant to help objects (people) communicate with each other in fair terms, so that the global communication is faster, safer, and more accurate, with less noise, while consuming less resources. It should make the objects nearer to each other.
The role of State id to allow people to communicate.
To stay politically as neutral as possible (after all, this is a technical paperr), the paper should try to not explicitly use a reference to State, if possible. Instead, it would conclude with a note according to which the very same argument would hold when applied to human societies as similar dynamical systems.
Those habits, it must be said, were especially encouraged by the way information could not spread and augment the common public background, since because of lack of theory and practice of what a freely communicating world could or should be, only big companies enforcing "proprietary" label could up to now broadcast their software; people who would develop original software thus had (and sadly still have) to rewrite everything from almost scratch, unless they could afford a very high price for every piece of software they may want to build upon, without having much control on the contents of such software.
But why stop there ? Everytime we have a set of level, we can define a new level by having objects that arbitrarily manipulate any lower object (that's ordinals); so we have objects that manipulate arbitrary objects of finite level, etc. There is an unbounded infinity of abstraction levels. To have the full power of abstraction, we must allow the use of any such level; but why not allow manipulating such full-powered systems ? Any logical limit you put on the system may be reached one day, and this day, the system would become completely obsolete; that's why any system to last must potentially contain (not in a subsystem) any single feature that may be needed one day.
The solution is not to offer any bounded level of abstraction, but unlimited abstracting mechanisms; instead of offering only terminal operators (BASIC), or first level operators (C), or even finite-order offer combinators of arbitrary order.
offer a grammar with an embedding of itself as an object. Of course, a simple logical theorem says that there is no consistent internal way of saying that the manipulated object is indeed the system itself, and the system state will always be much more complicated than it allows the system to understand about itself; but the system implementation may be such that the manipulated object indeed is the system. This is having a deep model of the system inside itself; and this is quite useful and powerful. This is what I call a higher-order grammar -- a grammar defining a language able to talk about something it believes be itself. And this way only can full genericity be achieved: allowing absolutely anything that can be done about the system, from inside, or from outside (after abstracting the system itself).
.....
First, we see that the same algorithm can apply to arbitrarily complex data
structures; but a piece of code can only handle a finitely complex data
structure; thus to write code with full genericity, we need use code as
parameters, that is, second order. In a low-level language (like "C"),
this is done using function pointers.
We soon see problems that arise from this method, and solutions for them. The first one is that whenever we use some structure, we have to explicitly give functions together with it to explain the various generic algorithm how to handle it. Worse even, a function that doesn't need some access method about an the structure may be asked to call other algorithms which will turn to need know this access method; and which exact method it needs may not be known in advance (because what algorithm will eventually be called is not known, for instance, in an interactive program). That's why explicitly passing the methods as parameters is slow, ugly, inefficient; moreover, that's code propagation (you propagate the list of methods associated to the structure -- if the list changes, all the using code changes). Thus, you mustn't pass explicitly those methods as parameters. You must pass them implicitly; when using a structure, the actual data and the methods to use it are embedded together. Such a structure including the data and methods to use it is commonly called an object; the constant data part and the methods, constitute the prototype of the object; objects are commonly grouped into classes made of objects with common prototype and sharing common data. This is the fundamental technique of Object-Oriented programming; Well, some call it that Abstract Data Types (ADTs) and say it's only part of the "OO" paradigm, while others don't see anything more in "OO". But that's only a question of dictionary convention. In this paper, I'll call it only ADT, while "OO" will also include more things. But know that words are not settled and that other authors may give the same names to different ideas and vice versa.
BTW, the same code-propagation argument explains why side-effects are an especially useful thing as opposed to strictly functional programs (see pure ML :); of course side effects complicate very much the semantics of programming, to a point that ill use of side-effects can make a program impossible to understand or debug -- that's what not to do, and such possibility is the price to pay to prevent code propagation. Sharing mutable data (data subject to side effects) between different embeddings (different users) for instance is something whose semantics still have to be clearly settled (see below about object sharing).
The second problem with second order is that if we are to provide functions
other functions as parameter, we should have tools to produce such functions.
Methods can be created dynamically as well as "mere" data, which is all the
more frequent as a program needs user interaction. Thus, we need a way to
have functions not only as parameters, but also as result of other functions.
This is Higher order, and a language which can achieve this has a
reflective semantics. Lisp and ML are such languages; FORTH also, whereas
standard FORTH memory management isn't conceived for a largely dynamic use of
such feature in a persistent environment. From "C" and such low-level
languages that don't allow a direct portable implementation of the
higher-order paradygm through the common function pointers (because low-level
code generation is not available as in FORTH), the only way to achieve
higher-order is to build an interpreter of a higher-order language such as
LISP or ML (usually much more restricted languages are actually interpreted,
because programmers don't have time to elaborate their own user customization
language, whereas users don't want to learn a new complicated language for
each different application and there is currently no standard user-friendly
small-scale higher-order language that everyone can adopt -- there are just
plenty of them, either very imperfect or too heavy to include in every
single application).
With respect to typing, Higher-Order means the target universe of the language is reflective -- it can talk about itself.
With respect to Objective terminology, Higher-Order consists in having classes as objects, in turn being groupable in meta-classes. And we then see that it _does_ prevent code duplication, even in cases where the code concerns just one user as the user may want to consider concurrently two -- or more -- different instanciations of a same class (i.e. two sub-users may need toe have distinct but mostly similar object classes). Higher-Order is somehow allowing to be more than one computing environment: each function has its own independant environment, which can in turn contain functions.
To end with genericity, here is some material to feed your thoughts about
the need of system-builtin genericity: let's consider multiplexing.
For instance, Unix (or worse, DOS) User/shell-level programs are ADTs,
but with only one exported operation, the "C" main() function per executable
file. As such "OS" are huge-grained, with ultra-heavy inter-executable-file
(even inter-same-executable-file-processes) communication semantics no one can
afford one executable per actual operation exported. Thus you'll group
operations into single executables whose main() function will multiplex those
functionalities.
Also, communication channels are heavy to open, use, and maintain, so you must explicitly pass all kind of different data & code into single channels by manually multiplexing them (the same for having heavy multiple files or a manually multiplexed huge file).
But the system cannot provide builtin multiplexing code for each single program that will need it. It does provide code for multiplexing the hardware, memory, disks, serial, parallel and network lines, screen, sound. POSIX requirements grow with things a compliant system oughta multiplex; new multiplexing programs ever appear. So the system grows, while it will never be enough for user demands as long as all possible multiplexing won't have been programmed, and meanwhile applications will spend most of their time manually multiplexing and demultiplexing objects not yet supported by the system.
Thus, any software development on common OSes is hugeware. Huge in hardware resource needed (=memory - RAM or HD, CPU power, time, etc), huge in resource spent, and what is the most important, huge in programming time.
The problem is current OSes provide no genericity of services. Thus they can never do the job for you. That why we really NEED generic system multiplexing, and more generally genericity as part of the system. If one generic multiplexer object was built, with two generic specializations for serial channels or flat arrays and some options for real-time behaviour and recovery strategy on failure, that would be enough for all the current multiplexing work done everywhere.
So this is for Full Genericity: Abstract Data Types and Higher Order.
Now, if this allows code reuse without code replication -- what we wanted --
it also raises new communication problems: if you reuse objects especially
objects designed far away in space or time (i.e. designed by other
people or an other, former, self), you must ensure that the reuse is
consistent, that an object can rely upon a used object's behaviour. This is
most dramatic if the used object (e.g. part of a library) comes to change
and a bug (that you could have been aware of -- a quirk -- and already have
modified your program accordingly) is removed or added. How to ensure object
combinations' consistency ?
Current common "OO" languages are not doing much consistency checks. At most, they include some more or less powerful kind of type checking (the most powerful ones being those of well-typed functional languages like CAML or SML), but you should know that even powerful, such type checking is not yet secure. For example you may well expect a more precise behavior from a comparison function on an ordered class 'a than just being 'a->'a->{LT,EQ,GT} i.e. telling that when you compare two elements the result can be "lesser than", "equal", or "greater than": you may want the comparison function to be compatible with the fact of the class to be actually ordered, that is x<y & y<z => x<z and such. Of course, a typechecking scheme, which is more than useful in any case, is a deterministic decision system, and as such cannot completely check arbitrary logical properties as expressed above (see your nearest lectures in Logic or Computation Theory). That's why to add such enhanced security, you must add non-deterministic behaviour to your consistency checker or ask for human help. That's the price for 100% secure object combining (but not 100% secure programming, as human error is still possible in misexpressing the requirements for using an object, and the non-deterministic behovior can require human-forced admission of unproved consistency checks by the computer).
This kind of consistency security by logical formal property of code is called a formal specification method. The future of secure programming lies in there (try enquire in the industry about the cost of testing or debugging software that can endanger the company or even human lives if ill written, and insurance funds spent to cover eventual failures - you'll understand). Life concerned industries already use such modular formal specification techniques.
In any cases, we see that even when such methods are not used automatically by the computer system, the programmer has to use them manually, by including the specification in comments or understanding the code, so he does computer work.
Now that you've settled the skeleton of your language's requirements, you can think about peripheral deduced problems.
.....
Moreover, it is very hard to anticipate one's future needs; whatever you do, there will always be new cases you won't have.
lastly, it doesn't replace combinators And finally, as of the combinatorials allowed allowing local server objects to be saved by the client is hard to implement eficiently without the server becoming useless, or creating a security hole;
..... At best, your centralized code will provide not only the primitives you need, but also the combinators necessary; but then, your centralized code is a computing environment by itself, so why need the original computing environment ? there is obviously a problem somewhere; if one of the two computing environment was good, the other wouldn't be needed !!!; All these are problems with servers as much as with libraries.
Actually, the same holds for any kind of static information that might have been gathered about programs: you can live without the computer checking it, by checking it yourself. But then you must do computer work, are not guaranteed to do it properly, and cannot offer the guarantee to your customers, as youuur proof is all inside your mind and not repeatable!!!
A structure A is interpreted in another structure B if you can map the symbols of A with combinations of symbols of B (with all the properties conserved). The simplest way to be interpreted is to be included.
A structure A is a specialization of a structure B if it has the same symbols, but you know more properties about the represented objects.
The simplest case is when the object is atomic, and can be read or modified atomically. At one time, the state is well defined, and what this state is what other sharers see.
When the object is a rigid structure of atomic objects, well, we assume that you can lock parts of the object that must be changed together -- in the meantime, the object is unaccessible or only readable -- and when the modification is done, everyone can access the object as before. That's transactions.
Now, what to do when the object is a very long file (say text), that each user sees a small part of it (say a full screen of text), and that someone somewhere adds or deletes some records (say a sentence) ? Will each user's screen scroll according to the number of records deleted ? Or will they stay at the same spot ? The later behaviour seem more natural. Thus, a file has this behaviour that whenever a modification is done, all pointers to the file must change. But consider a file shared by _all_ the users across a network. Now, a little modification by someone somewhere will affect everyone ! That's why both the semantics and implementation of shared objects should be thought about longly before they are settled.
Imagine that a real-time process is interrupted for imperative reasons (e.g. a cable was unplugged; a higher-priority process took over the cpu, etc): will it continue where it stopped ? or will it skip what was done during the interruption ? Imagine the system runs out of memory ? Whose memory are you to reclaim back ? To the biggest process ? The smallest ? The oldest ? The lowest real-time priority ? The first to ask for more ? Or will you "panic" like most existing OSes ? If objects spawn, thus filling memory (or CPU), how to detect "the one" responsible and destroy it ?
If an object locks a common resource, and then is itself blocked by a failure or other unwilling latency, should this transaction be cancelled, so others can access the resource, or should all the system wait for that single transaction to end ?
As for implementation methods, you should always be aware that
defining those abstraction as the abstractions they are,
rather than hand-coded emulation for these,
allows better optimizations by the compiler,
quicker write phase for the programmer,
neater semantics for the reader/reuser,
no implementation code propagation for the reimplementer,
etc.
Partial evaluation should also allow specialization of code that don't use all the language's powerful semantics, so that standalone code be produced without including the full range of heavy reflective tools.
To conclude, there are essentially two things we fight: lack of feature and power from software, and artificial barriers that misdesign of former software build between computer objects and others, computer objects and human beings, and human beings and other human beings.
Centralized code is also called "client-server architecture"; the central code is called the server, while those who use it are called clients. And we saw that a function server is definitely something that no sensible man would use directly; human users tend to write a library that will encapsulate calls to the server. But it's how most operating systems and net-aware programs are implemented, as it's the simplest implementation way. Many companies boast about providing client-server based programs, but we see there's nothing to boast about it; client-server architecture is the simplest and dumbest mechanism ever conceived; even a newbie is able to do that easy. What they could boast about would be not using client-server architecture, but truely distributed yet dependable software.
A server is nothing more than a bogus implementation for a library, and shares all the disadvantages and limits of a library, with enhanced extensibility problem, and additional overhead. It's only advantage is to have a uniform calling convention, which can be useful in a system with centralized security, or to pass the stream of arguments through a network to allow distant client and servers to communicate. This last use is particularly important, as it's the simplest trick ever found for accessing an object's multiple services through a single communication line. Translating software interface from library to server is called multiplexing the stream of library/server access, while the reverse translation is called demultiplexing it.
So we see that system designers are ill-advised when they provide such specific multiplexing, that may or may not be useful, whereas other kind of multiplexing is always needed (a proof of which being people always boasting about writing -- with real pain -- "client/server" "applications"). What they really should provide is generic ways to automatically multiplex lines, whenever such thing is needed.
More generally a useful operating system should provide a generic way to share resources; for that's what an operating system is all about: sharing disks, screens, keyboards, and various devices between multiple users and programs that may want to use those accross time. But genericity is not only for operating systems/sharing. Genericity is useful in any domain; for genericity is instant reuse: your code is generic -- works in all cases -- so you can use it in any circumstances where it may be needed, whereas specific code must be rewritten or readapted each new time it must be used. Specificity may be expedient; but only genericity is useful on the long run.
Let us recall that genericity is the property of writing things in their most generic forms, and having the system specialize them when needed, instead of hard-coding specific values (which is some kind of manual evaluation).
Now, How can genericity be achieved ?
This just has all the advantages and disadvantages of the client/server: surely this ensures consistency of data, but efficiency is the worst possible among systems that ensure it, because of centralization.
An efficient system would achieve consistency of installed software without sacrificing performance, and without requiring a modification of current hardware, by doing all the consistency enforcement in software. Memory that is local to network hosts is then used for data cacheing and replication; CPU resources can be used to do distributed computations, etc. A software solution could do things great. A hardware solution like NCs is just waste of resources.
All the more, NCs do not even have compatibility, and do not allow any particular leverage of existing software, so that they are really a big gratuitous waste of resources. For a fraction of the price of all the wasted hardware resources, a proven distributed OS could be developed and marketed!
response to human
Multiplexing means to split a single communication line or some other resource into multiple sub-lines or sub-resources, so that this resource can be shared between multiple uses. Demultiplexing is recreating a single line (or resources) from those multiple ones; but as dataflow is often bi-directional, this reverse step is most often unseparable from the first, and we'll only talk about multiplexing for these two things. Thus, multiplexing can be used to share a multiple functions with a single stream of calls, or convertly to have a function server be accessed by multiple clients.
Traditional computing systems often allow multiplexing of some physical resources, thus spliting them into a first (but potentially very large) level of equivalent logical resources. For example, a disk may be shared with a file-system; CPU time can be shared by task-switching; a network interface is shared with a packet-transmission protocol. Actually, what any operating system does can be considered multiplexing. But those same traditional computing systems do not provide the same multiplexing capability for arbitrary resource, and the user will eventually end-up with having to multiplex something himself (see the term user-level program to multiplex a serial line; or the screen program to share a terminal; or window systems, etc), and as the system does not support anything about it, he won't do it the best way, and not in synergy with other efforts.
What is wrong with those traditional systems is precisely that they only allow limited, predefined, multiplexing of physical resources into a small, predefined, number of logical resources; there they create a big difference between physical resources (that may be multiplexed), and logical ones (which cannot be multiplexed again by the system). This gap is completely arbitrary (programmed computer abstractions are never purely physical, neither are they ever purely logical); and user-implemented multiplexers must cope with the system's lacks and deficiencies.
whereas with the intelligent worker, you may have to invest in his formation, but will always have a proficient collaborator after a short adaptation period. After all, even the dumb worker had to learn one day, and an operating system was needed as a design platform for any program.
But why should you depend on dynamic guesses? A Good programming language would allow you
Open system means that people can contribute any kind of information
they want to the available cultural background,
without having to throw everything away and begin from scratch,
because the kind of information they want to contribute does not
fit the system.
Example: I can't have lexical scopes in some
wordprocessor spell-checker, only one "personalized dictionary"
personalized at once (and even then, I had to hack a lot
to have more than one dictionary,
by swapping a unique global dictionary). So bad.
I'll have to wait for next version of the software.
Because so few ask for my feature, it'll be twenty years until
it makes it to an official release. Just be patient.
Or if I've got lots of time/money, I can rewrite the whole
wordprocessor package to suit my needs. Wow!
On an open system, all software components must come in small grain,
with possibility of incremental change anywhere,
so that you can change the dictionary-lookup code to handle
multiple dictionaries merged by scope, instead of a unique global one,
without having to rewrite everything.
Current attempts to build an open system have not been fully successful. The only successful approach to offer fine-grained control on objects has been to let sources freely available, allowing independent hackers/developers to modify and recompile; but apart from the object grain problem, this doesn't solve the problems of open software. Other problems include the fact This offers no semantical control of seamless data conservation accross code modification; contributions are not really incremental in that the whole software must be integrally recompiled, stopped, relaunched; Changes that involve propagation of code among the whole program cannot be done incrementally with non because they
Example: with low-level languages like C, you can't define a generic function to work on any integer, then instanciate to the integer implementation that fits the further problem. If you define a function to work on some limited number type, then it won't work on longer numbers than the limit allows, while being wasteful when cheaper more limited types might have been used. Then if some 100000 lines after, you see that after all, you needed longer numbers, you must rewrite everything, while still using the previous version for existing code. Then you'll have two versions to co-debug and maintain, unless you let them diverge inconsistently, which you'll have to document. So bad. This is being required to say too much.
And of course, once the library is written, in a way generic enough so it can handle the biggest numbers you'll need (perhaps dynamically sized numbers), then it can't take advantage of any particular situation where the known constraints on numbers could save order of magnitudes in computations; of course, you could still rewrite yet another version of the library, adapted to that particular knowledge, but then you again have the same maintenance problems as above. This is being required to say too little.
Any "information" that you are required to give the system before you know it, without your possibly knowing it, without your caring about it, with your not being able to adjust it when you further know more, all that is *noise*.
Any information that you can't give the system, because it won't heed it, refuse it as illegal, implement in so inefficient a way that it's not usable, is *lack of expressiveness*.
Current languages are all very noisy and inexpressive. Well, some are even more than others.
The "best" available way to circumvent lack of expressiveness from available language is known as "literate programming", as developed, for example, by D.E.Knuth with his WEB and C/WEB packages. With those, you must still fully cope with the noise of a language like C, but can circumvent its lack of expressiveness, by documenting in informall human language what C can't express about the intended use for your objects.
Only there is no way accurately verify that objects are actually used consistently with the unformal documented requirements, which greatly limits the (nonetheless big) interest of such techniques; surely you can ask humans to check the program for validity with respect to informal documentation, but his not finding a bug could be evidence for his unability to find a real bug, as well as the possible absence of bug, or the inconsistency of the informal documentation. This can't be trusted remotely as reliably as a formal proof.
The Ariane V spacecraft software had been human-checked thousands of times against informal documentation, but still, a software error would have $10^9 disappear in fumes; from the spacecraft failure report, it can be concluded that the bug (due to the predictable overflow of an inappropriately undersized number variable) could have been *trivially* pin-pointed by formal methods! Please don't tell me that formal methods are more expensive/difficult to put in place than that the rubbish military-style red-tape-checking that was used in place.
As a french taxpayer, I'm asking immediate relegation of the responsible egg-heads to a life-long toilet-washing job (their status of french "civil servants" prevents their being fired). Of course my voice is unheard.
Of course, there are lots of other software catastrophes that more expressive languages would have avoided, but even this single 10 G$ crash would pay more than it would ever cost to develop formal methods and (re)write all critical software with!
It is as if mathematicians would have to learn a completely new language, a completely new formalism, a completely new notation, for every mathematical theory! As if every book couldn't actually assume results from other books, unless they were proven again from scratch.
It is as if manufacturers could not assemble parts unless they all came from the same factory.
Well, such phenomena happen in other place than computer software, too. Basically, it might be conceived as a question of lack of standards. But it's much worse with computer software, because computer software is pure information. When software is buggy, or unable to communicate, it's not worth a damn; it ain't even good as firewood, as metal to melt or anything to recycle.
Somehow, the physical world is a universal standard for the use of physical objects. There's no such thing in the computer world where all standards are conventional.
Worse, progress in hardware and software implementation techniques is incompatible with the advent of definitive computerware standards, so that either standards are made ephemeral, or implementational progress is throttled.
And the solution is Reflection.
Reflection does allow to refine implementations, to move between standards, to prove new meta-theorems and use them, to juggle between representations so as to pick up the most adequate for a given task without sacrificing consistency, to reuse (meta)theorems from other people, etc.
Well, that's a tough one. Here is what I told Yahoo: "TUNES is a project to replace existing Operating Systems, Languages, and User Interfaces by a completely rethough Computing System, based on a correctness-proof-secure higher-order reflective self-extensible fine-grained distributed persistent fault-tolerant version-aware decentralized (no-kernel) object system."
Now, there are lots of technical terms in that. Basically, TUNES is a project that strives to develop a system where computists would be much freer than they currently are: in existing systems, you must suffer the inefficiencies of
So to conclude, there is essentially one thing that we have to fight: the artificial informational barriers that lack of expressivity and misdesign of former software, due misknowledge, misunderstanding, and reject of the goals of computing, build between computer objects and others computer objects, computer objects and human beings, human beings and other human beings.
Faré -- fare@tunes.org