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Further reading

Overview
1989
123456
1990
7891011
1991
121314151617
1992
181920212223
1993
242526272829
1994
303132333435
1995
36373839
Index
Index

Issue 21: July 1992

Flagship Issue 21

Flagship Issue 21
Full image ⇗
© UKRI Science and Technology Facilities Council

The cover photograph shows a Cray Y-MP8I

New Cray Y-MP at the Atlas Centre

Most readers know that the ABRC's Supercomputing Sub-committee and the SERC's Supercomputing Management Committee have been considering options for increasing the vector-processing capacity available nationally for peer-reviewed research projects. This is a first stage of a longer term programme of upgrades to the national high performance computing facilities, about which the Chairman of the SMC, Professor P G Burke, writes in Future UK Supercomputing below. The outcome of the first stage considerations was a recommendation, which was accepted and approved by the Council of SERC on June 10, for a Cray Y-MP8I/8128 to be located at the Atlas Centre. The Cray X-MP/416, which has been in service for over five years, is to be closed down after the Y-MP has become fully operational.

The new supercomputer will have eight processors, 128 Mwords (1 Gbyte) of memory and 100 Gbytes of disk storage. Each Y-MP processor has about 1.4 times the peak performance of an X-MP processor and is architecturally similar, so the whole machine can be expected to have about 2.8 times the power of the four-processor Cray X-MP/416. The Y-MP is due to be delivered in August. There will then be an installation, commissioning and acceptance period which is expected to last a few weeks, after which the services can begin to be transferred from the X-MP to the Y-MP. More details on the timescale and transition arrangements are given in the article by John Gordon. Our intention is to make the transition as smooth as possible and to bring the new machine into service around the start of the new academic year.

Brian Davies, Associate Director Central Computing

Future UK Supercomputing

As Chairman of SERC's Supercomputing Management Committee, I am very pleased that we are now proceeding with the first stage of improving the national facilities for high performance computing.

With the installation of the Cray Y-MP8I/8128 at the Atlas Centre, the overall national capacity for conventional supercomputing will be doubled, and I am sure that this will enable substantial progress to be made by many projects which have had to be constrained by competition for limited resources.

The SMC, together with the ABRC Supercomputing Subcommittee which is chaired by Sir Eric Ash, is developing a policy for the provision of further new facilities. The SMC has requested updates of statements on the computational needs of all the Research Councils and it will draw heavily on these in shaping its ideas. Detailed consideration will be given in the next few months to the steps that should be taken on massively parallel computing; we must also ensure that the facilities we provide are adequately equipped with data storage and high performance communications facilities.

The Committee will be holding a Town Meeting in September in which current plans and future possibilities will be discussed with the user community; notice of this meeting can be found later in this newsletter. I hope that the event will provide an opportunity for a wide-ranging exploration of the issues, and I look forward to seeing many of you there.

Professor P G Burke, Chairman, SERC's Supercomputing Management Committee

The Hardware of the Y-MP

Early in August, the Atlas Centre will take delivery of a new Cray Y-MP supercomputer. This will have an aggregate peak performance of 2.7 Gflops, nearly three times that of our current X-MP.

The new machine (serial number 1712) is a Y-MP8I/8128

8I to show its eight processor chassis with integrated I/O sub-system,

8 because it has eight processors, and

128 for its 128 MWords of memory.

The architecture of the machine is very similar to the existing Cray X-MP. The clock cycle is reduced from 8.5 nsec to 6.0 nsec and each of the eight processors has a peak performance of 333 Mflops. Cray have designed the Y-MP to reduce memory contention and the performance improvement should be slightly better than the increase in clock speeds.

The new machine's memory size of 128 MWords is a great improvement on that of the X-MP, removing the constraints of memory usage for most users.

Compatibility with the X-MP is excellent and the Y-MP can even run X-MP binary-executable files (with, however, some overhead on memory management).

Another major improvement will be the much greater capacity of the on-line disk storage. The initial configuration will be 47 Gbyte of high speed DD60 disk drives (up to 24 Mbyte/sec) and 53 Gbyte of slower DD61 drives (up to 3 Mbyte/sec). For performance-critical areas like program swap space, the DD60 drives will be striped so that I/O across more than one drive can take place in parallel for a higher bandwidth. We expect most of the DD61 disk space to be used for users' permanent data, and most of the fast DD60 space to be used for important system files, swap space, and the more heavily used temporary files.

The networking of the Y-MP will be similar to that of the X-MP, but as the JANET IP service (JIPS) becomes more widely available, we expect to see a more widespread use of interactive working on the Y-MP. Its greater memory size will allow much more interactive use without an impact on overall system performance. The Y-MP will inherit all the "front-end" connections of the current machine: VM/CMS, VAX/VMS and the RS/6000 UNIX1 front-end.

Roger Evans, Head of Advanced Research Computing Unit

Software on the Y-MP

Compatibility with X-MP

We intend that the Y-MP service will support all the current user and application code from the X-MP. In order to make the changeover as transparent as possible, the X-MP service will move to UNICOS version 6.1.6 in late July and the Y-MP service will start in late September or early October with exactly the same release levels of operating system and compilers.

The Y-MP hardware can run existing X-MP binaries without any change, but with the restriction that they can only be loaded on 16 MWord boundaries in real memory and can only use four processors for multi-tasking. As memory at address zero is used by the operating system code, there can be only seven X-MP binaries loaded on a 128 MWord machine. Running existing binaries will be acceptable for the first month or two of the new service, but there will then be some pressure to recompile to produce true Y-MP binaries. No changes to program source code should be necessary, but now is a good time to start looking for your source so that you will be able to recompile when the time comes.

New Applications Software

As part of the new installation Cray are providing additional application software. Cray's Multi Purpose Graphics Software (primarily aimed at engineers with Silicon Graphics workstations, including the Indigo) which has recently been mounted on the X-MP will be included in the Y-MP package, as will Unichem, Cray's integrated chemistry package, also supporting Silicon Graphics workstations. Both MPGS and Unichem can run across the JIPS service to users' own workstations.

We have also ordered Gaussian 92 for installation on the Y-MP. Gaussian 92 claims to be far more efficient than previous versions and can make use of the multiple processors and large memory available on the Cray. If any of the other applications we support have Y-MP-specific versions we shall try to obtain them.

General graphics support will be easier on the Y-MP through the inclusion of CVT (Cray Visualisation Toolkit) which contains the OSF/Motif library so that Motif applications can now be built directly under UNICOS.

Front-end Stations

The existing front-end station software on VM/CMS and VAX/VMS will continue to be available, but for a transition period only. The station protocol is proprietary to Cray, does not run over wide area networks and has a syntax (CRSUBMIT etc.) which is unique to Cray. As part of the move to open and portable systems we intend to move to RQS (Remote Queuing System) and will run RQS and the existing station software alongside each other for a few months.

RQS has the same syntax as the NQS software used both to submit batch jobs from an interactive UNICOS session and in versions of NQS available on workstations and mini-supercomputers from other suppliers. Full guidance on moving to RQS will be given well in advance of the removal of the station software and after the start of the production Y-MP service.

John Gordon, Head of Applications & User Support

A UNIX Front-end for the Atlas Cray

Earlier this year an IBM RS/6000 model 550 was purchased to act as a UNIX front-end for the Atlas Centre Cray. It is now available as a general user service for any registered Cray user who wishes to use it.

The UNIX front-end complements the existing VM and VMS front-ends and allows you to choose the front-end which best suits your needs. But, I can hear you ask, lithe Cray itself runs UNIX, so why do we need a UNIX front-end?" Well, although the Cray is attached to JIPS (the JANET IP Service), it has no direct X.25 access, so that the many users on JANET with no JIPS access cannot log-in directly to the Cray. The UNIX front-end has both IP and X.25 access across JANET.

Another justification for a UNIX front-end is the Cray itself: because it requires contiguous real memory for a process address space and swaps complete processes in and out instead of paging, the Cray can support fewer processes than a comparable paging machine. It can be tuned to give excellent interactive performance, but this would always be at the expense of batch throughput, as there is an overhead in the repeated swapping and interrupt handling which characterise an interactive workload. In the circumstances, even with the increased CPU power and memory of the Y-MP, it seems sensible to target the general housekeeping tasks of editing, file management, and job submission to a separate machine, leaving the Cray to do what it does best: high performance numerically-intensive floating point work.

So, what kind of service does this machine (known as UK.AC.RL.UNIXFE) offer?

The basic tools that are provided initially are:

In addition to this basic service, all the usual facilities of a UNIX service are available. We have ordered the NAG Fortran + Graphics libraries, Pacific Sierra's Fortran 90 to 77 converter (both directions), the NAG Fortran 90 to C converter, and the UNIRAS Graphics software. If you have any suggestions for software suitable for a Cray front-end then contact me with them.

After reading so far, you might ask, Will I ever need to use the Cray interactively? Well, if you wish to interact with a Cray job and you have not developed a client-server version of your code, then you will still need to login. There are also a number of Cray-specific tools such as ATEXPERT, A TSCOPE, and the symbolic debugger cdbx, which require a UNICOS session to run them.

For these you can log into the Cray and have the tool display its output in an X-window on your local workstation.

Cray users who wish to use the UNIX front-end should contact Resource Management to have their userids registered.

John Gordon, Head of Applications & User Support

Upgrade to StorageTek Automatic Cartridge Store

By the time you read this, the Atlas Centre will have more than doubled the storage capacity in its Automatic Cartridge Store by taking delivery of a second Library Storage Module, or silo, from StorageTek. The new silo is physically identical to the existing one with its own robot arm, cartridge access port and storage slots for 6000 cartridge tapes. It is not planned to buy any more tape drives, at least initially, but instead to move one of the two existing drives (each of which has four transports) on to the new silo. Both sets of transports will be shared between the IBM and Cray mainframes so that the whole ACS can be used by both the VM and UNICOS operating systems. The ACS will continue to be used mainly for data migration, backups and transparent tape staging.

The new silo is being attached physically to the old one with a device called a Pass Through Port which allows the two robots to exchange cartridges, passing them from one silo to the other. This means that any of the 12,000 cartridges in the combined ACS can be read or written in any of the eight tape transports.

The new silo is being populated initially with longer length tapes which have a capacity of about 300 Mbytes compared with the original 3480 capacity of about 200 Mbytes. There are even longer tapes which will be tested, but assuming an average tape capacity of 300 Mbytes, the total capacity of both silos would be 3.6 terabytes. A future development planned by StorageTek is to increase the tape density by going from 18 tracks to 36 which would double the capacity again.

Tim Pett, Head of Marketing Services

AXIOM

AXIOM is installed on the RS/6000 system in the Atlas Centre, with a single user licence which allows use by one person at a time, but is available to any user who can access the RS/6000 system from a terminal running X-Windows. For further information please contact Jonathan Wheeler, preferably by sending electronic mail to JFWt@UK.AC.RL.IB.

Introduction

Since digital computers first became available, computational mathematics has been largely concerned with numerical analysis. Numerical methods have improved and evolved and have enabled the solution of problems that were previously impractical, if not impossible. Whilst the numerical solution of many mathematical models often produces satisfactory results, there are many areas that can benefit from a different approach, namely the treatment of those models in a symbolic form.

Recent advances in hardware performance and software technology have made the symbolic approach feasible even for potentially large and complex problems. Systems which support symbolic techniques effectively are at the forefront of a diffuse but profound revolution in computational mathematics, building upon established and recent mathematical theory and opening up new possibilities to people in almost every industry. Such systems represent a major step in the evolution of indispensable tools for engineers and scientists: from slide-rule and hand calculator, via general purpose scientific programming languages, towards integrated problem-solving environments incorporating symbolic and other computational techniques.

Symbolic Algebra

There are many real-life situations where a numerical solution is required, (for example, the prediction of physical variables such as position, time and quantity). However, investigation of the underlying principles expressed in symbolic form is required to achieve a more profound insight.

Mathematical models are used to represent these real-life situations. In order to evaluate the model and to use it effectively to predict behaviour, it is necessary to analyse and solve the model. Only for the simplest cases are analytic solutions readily available using pencil and paper. Many models are more complex, and until recently, numerical techniques have provided the only practical approach, giving specific numeric results for a given set of initial data.

Now powerful computers and symbolic systems have combined to provide the user with analytic solutions to more complicated models. Such solutions can display the explicit sensitivity of the model solution to initial data and can give further insight into model refinement.

Symbolic algebra is a basic tool of mathematics. For centuries, mathematicians have been representing the world (and later, the universe), using formulae, incorporating symbols to represent variables, constants and mathematical operations.

The use of symbolic algebra and associated analytic methods has created a wealth of knowledge and insight in mathematics, science and engineering. Before symbolic solvers, the vast majority of mathematical work required the analyst to have a strong understanding of the underlying mathematical principles involved. Moreover, the work was very laborious and error prone, with even routine tasks, for example finding the integral of a function, often taking many hours by hand.

Symbolic solvers are packages that can perform symbolic algebra. The user's problem is posed in the language of mathematics, algebraically. The problem can then be investigated symbolically and the solution given in symbolic form, or a message given as to why the operation cannot be performed, (such as the detection of a singularity in a function to be integrated). Symbolic solvers perform algebraic manipulations such as: polynomial factorisation, summation of series, symbolic integration and differentiation, and matrix operations.

Symbolic solvers give the user direct access to the knowledge base of the world's leading mathematicians, producing exact and reliable results. They are important tools for the analyst in mathematics, science, engineering and finance, opening up new fields of study and enabling new insights into existing areas.

Symbolic Solvers

Examples of Use

Symbolic solvers have already been used to great effect in a wide and diverse range of applications including: high energy physics, celestial mechanics, group theory, number theory, non-linear control systems, spacecraft dynamics, computational chemistry, robotics, geometrical modelling, financial modelling, radar design and mathematical biology.

Creating Models

Symbolic solvers allow the user to specify models that can be changed and improved quickly and easily. Financial institutions have been quick to realise the advantages offered, constructing complex and powerful economic models of economies and markets, realising that competitive advantage is gained from the analysis of information and the insight this provides. Symbolic solvers are ideal for creating adaptive, flexible predictive models that are easy to construct and simple to use.

Mathematical Applications

Symbolic solvers provide a tool that dramatically increases the productivity of the mathematical scientist and engineer. In mathematical research, for example, symbolic solvers are invaluable for testing conjectures, gathering insight through computational experiments and overcoming computational bottlenecks leading to the next stage of research. Cryptographers find symbolic facilities for elliptic curve factorization, finite fields, and discrete logarithms useful. Symbolic solvers can help solve some boundary value problems that occur in the modelling of many physical situations, including the flow of gases and fluids, electrical and magnetic fields.

Solving Equations

Newly developed algorithms from the symbolic solver research community have led to unprecedented problem solving power. For example, symbolic solvers can locate all solutions of systems of polynomial equations and compute them to any user-specified accuracy. For systems with an infinite number of solutions, the dimension of the solutions space can be calculated along with a description of each irreducible component. Among the triumphs of research are those which have led to complete algorithms for calculus and differential equations. A decision procedure can produce closed form solutions for integrals where they exist, thus obviating the need for tables which are necessarily incomplete. Differential equations can be solved either in closed form or by series expansions. Closed form expressions for limits and summations can also be computed.

Figure 1. Example graphs from AXIOM

Figure 1. Example graphs from AXIOM
Full image ⇗
© UKRI Science and Technology Facilities Council

Optimising Numerical Techniques

The analysis of many mathematical problems is best performed using a combination of symbolic and numerical techniques. The numerical solution of equations and functions can be difficult, and simple analytical approximations can make the solutions unusable. Symbolic solvers can recast the model in terms of functions that can be calculated accurately by forward or backward recursion.

The Differences between Numeric and Symbolic Computation

The advent of the modem digital computer made possible the solution of large problems using numerical techniques. This spurred the development of a new branch of mathematics known as numerical analysis, which studies the behaviour of numerical methods under the conditions of inexact computer arithmetic. New numerical techniques were discovered and developed.

Symbolic computation remained traditionally manual. However, recent advances in hardware and programming technology have enabled computers to perform symbolic computation with speed and accuracy.

In summary, numerical techniques use actual data values in a mathematical problem and employ specialised techniques to minimise the effects of inexact computer arithmetic. The results are expressed numerically.

Symbolic computation uses different techniques, in general, to manipulate formulae and symbols and bears a much closer affinity to pencil and paper mathematical techniques. Typically, results are expressed in terms of formulae and symbols.

AXIOM Overview

AXIOM is the powerful new symbolic solver developed (under the name Scratchpad) at IBM's T J Watson Research Facility, Yorktown Heights, New York, in collaboration with experts around the world. It is:

AXIOM Design

AXIOM is believed to be unique among computer algebra systems in its consistent, hierarchical, object-oriented approach to datatypes and operations defined on them. Users and system implementers alike use AXIOM's abstract data type programming language to modify or extend existing facilities.

Types in AXIOM

Fundamental concepts in the design of AXIOM are domains, categories and packages.

Every computational object in AXIOM belongs to one, and only one, domain. Domains correspond to the usual notion of abstract datatypes in the modem theory of programming languages, in that a domain is a set of values and a set of exported operations for the creation and manipulation of these values. AXIOM has the usual datatypes (e.g. integers, floats, strings, lists, hash tables, input files), as well as algebraic ones (e.g. polynomials, matrices, fractions, power series).

Datatypes are parameterized, dynamically constructed, and can combine with others in any meaningful way, e.g. lists of floats, fractions of polynomials with integer coefficients, matrices of matrices of power series, infinite streams of cardinal numbers. AXIOM domains are defined in the AXIOM programming language and converted into machine code by its compiler, representing a set of values with a set of exported operations which can be performed upon them.

Categories are second-order types which serve to define useful classification worlds for domains, such as algebraic constructs (e.g. groups, rings, fields), and data structures (e.g. homogeneous aggregates, collections, dictionaries). The categories of a given world are arranged in a family-tree (formally, a directed acyclic graph). Each category inherits the properties of all its ancestors. Thus, for example, the category of ordered rings inherits the properties of the category of rings and those of the ordered sets. Categories provide a database of algebraic knowledge and ensure mathematical correctness, (e.g. that matrices of polynomials is correct but polynomials of hash tables is not; and also that the multiply operation for polynomials of continued fractions is commutative, but that for matrices of power series is not).

Facilities for integration, group theory and the solution of linear, polynomial or differential equations are provided by packages. Packages are domains whose exported operations depend solely on their parameters and other explicit domains, for example, a package for solving systems of equations of polynomials over any field, e.g. floats, rational numbers, complex rational functions, or power series. Using packages, algorithms can be defined in their natural algebraic setting and compiled for run-time efficiency.

Structure of AXIOM

The structure of AXIOM consists of a Kernel and a Library of over 500 loadable modules. The Kernel itself knows very little algebra. Most of the algebraic knowledge - for example, the definitions of categories and domains - is supplied by the Library, which is written in a high-level language and compiled into machine code for speed of execution. This is the result of a continuing effort by many expert mathematicians around the world. Updates and extensions of the Library will be distributed with each release of AXIOM.

AXIOM has an Interpreter for interactive use. Users can write their own functions and programs that use the existing Library. AXIOM will compile or interpret such user code transparently. The Compiler emphasises strict type-checking, whilst the Interpreter is oriented towards ease of use. An enhanced Library Compiler will be available to users with Version 2 of AXIOM, allowing domains and packages to be added in a convenient and consistent manner.

AXIOM's mathematical facilities include arbitrary precision numbers, factorisation of polynomials, symbolic solution of algebraic and differential equations, symbolic differentiation and integration, limits, power series, transforms, linear algebra, group theory, number theory and a lot more.

Often additional valuable insights can be gained by employing numeric techniques in association with a powerful symbolic system such as AXIOM. Work has started to link the NAG FORTRAN Library with AXIOM Version 2 to combine the best of the symbolic and numerical worlds into one comprehensive system. The NAG FORTRAN Library contains over 1000 numerical algorithms.

HyperDoc

AXIOM features a powerful on-line documentation and help system called HyperDoc. HyperDoc is a mouse-driven hypertext system that runs under AIXwindows. The User's Guide is available in HyperDoc complete with graphics, active AXIOM commands and hypertext links. In addition, a Tutorial session and an introductory Basic Commands section are included. Users can write their own HyperDoc pages and link them to the system documentation. The Browser is a powerful HyperDoc utility that is used to examine the hierarchical structure of the AXIOM Library. Every single Library module and operation is accessible. The Browser can also display the appropriate Library source files (where available).

The Graphics System

AXIOM has an integral Graphics System which runs under AIXwindows. AXIOM transparently sends graphics information to the Graphics System when requested to produce a graph. The graph then appears in a separate window. The user can manipulate it by using an interactive mouse-driven control panel or by issuing AXIOM commands. Two- and three-dimensional graphs can be produced while various co louring, shading, lighting and perspective options can be specified. Graphics can be included in HyperDoc documents where the same degree of control is available. Graphs can be output in Bitmap, PostScript and Pixmap format for hard-copy generation.

The Interpreter

The Interpreter reads and analyses input expressions from the user and dynamically builds AXIOM structures in response to this input in order to perform indicated computations. The Interpreter uses sophisticated type-inferencing to determine appropriate types, searches the Library for appropriate operations, resolves type mismatches, and selects the correct operation. Output from computations is available in two-dimensional form, TeX, and FORTRAN. Users can trace AXIOM Library functions, internal Interpreter functions, and user-defined functions. Facilities are provided to maintain several interpreter workspaces concurrently, execute operating system commands, and to save results in a history file.

The Documentation

A hard-copy version of the documentation is available in book form as an AXIOM user's guide, published by Springer-Verlag. Copies are available via NAG or through the publisher's bookseller outlets. The AXIOM book provides a comprehensive guide to the use of the system, and features a large number of examples and graphical illustrations.

AXIOM Availability

AXIOM is marketed and supported by NAG. It currently runs on the IBM RISC System/6000, a comprehensive family of powerful workstations supported by a very large range of applications software. The RISC System/6000 family operates under AIX (IBM's open systems operating system) and supports X-windows in addition to many other industry standards. Versions for other IBM platforms which support AIX and AIXwindows are also planned. The minimum requirements to support AXIOM on the IBM RISC System/6000 are:

The distribution medium is a quarter inch cartridge tape or 8mm DAT.

Summary

AXIOM's design, performance, power and range make it a very powerful computer algebra system. The general availability of the IBM RISC System/6000, the primary development platform for AXIOM, makes AXIOM's facilities accessible to the people who need it - at their desk.

AXIOM incorporates HyperDoc - a powerful, on-line, help, tutorial and browser system providing easy-to-use, comprehensive documentation. The extensive use of a graphical user interface throughout the system and the efficient organisation of the on-line documentation helps the user climb the learning curve quickly and confidently.

Extensions planned for Version 2 include an enhanced AXIOM compiler (to provide improved performance for creating tailored extensions to the Library, in an object-oriented framework) and a link to the NAG Fortran Library (to create an integrated system of even greater scope and power).

Brian Ford and Steve Hague, NAG Lid

A Guide to the Multimedia Jargon Jungle

In common with many technologies, MULTIMEDIA has created a vast jargon to shroud the subject in mystery and protect its acolytes. This is a brief explanation of some of the more common acronyms, but beware: new systems seem to be appearing daily so no responsibility is accepted if the latest one is missing!

Warning: Each description of a topic starts with facts, (generally corresponding to Norman Wiseman's original article) but comments are then given on some of the topics. The CD formats are defined by a set of Coloured Books (no relation!).

CD (also known as CD-DA)
The original 5 inch Compact Disc for digital audio reproduction, defined in the Red Book, now ISO standard 10149. The usual transfer speed for bits from CDs is around 1.2 Mbits/ second. This rate was chosen to provide stereo sound reproduction to a quality where humans should not perceive any degradation caused by the digital medium.
CD and all its derivatives (CD-R, CD-ROM, CD-ROM XA, CD-I, Photo-CD) usually provide information - whether audio, video, data (or any mixture) - at this same rate, roughly 150 Kbytes per second. As this was designed for stereo sound, other uses (such as video) may either not be real-time or will require compression for real-time use.
Domestic CD-DAs are produced by a similar master to matrix to pressing sequence to that used to produce vinyl LPs.
CD-ROM
CD Read Only Memory - a method for storing digital data on the CD medium. It was defined by the Yellow Book, now enshrined in the ISO 9660 standard.
Some new CD-ROM devices provide 600 Kbytes per second, four times faster than the usual CD data rate.
In theory any CD-ROM disc should work on any CD-ROM reader but two standards were defined: mode 1 and mode 2. A series of extensions to ISO 9660 is being proposed to allow integration of CD-ROMs into the UNIX environment. CD-ROMs are good for shipping software and data around and are increasingly used for this purpose by software suppliers.
CD-ROM XA
An eXtended Architecture variant of the CD-ROM format that requires a Mode 2 drive. It allows the functionality of CD-I (see below) to be available on PCs and workstations and uses the same sound format as CD-I but different graphics and operating system environments. Photo-CD (see below) discs can also be read on CD-ROM XA drives.
CD-I
Compact Disc Interactive: a format that includes video, up to 16 audio tracks and control information. Developed by Sony and Philips, the main visible product of this is a turnkey system marketed by Philips that incorporates a 32-bit 68020 based-computer and a standard TV monitor. The user can steer through an application, but the "script" has to follow specified guidelines and the links within it are encoded on the disc. It allows interactive control via a mouse, which is used to click on menus or hot-spots on images on the screen.
At present all CD-I discs will play on all CD-I players. Unfortunately the aspect ratio of the pictures is different for PAL and NTSC CD-I discs, so PAL pictures are cropped on NTSC displays and NTSC pictures "letter-boxed" on PAL displays.
CD-I FMV
CDI with Full Motion Video. The original idea was that CD-I would be launched with Full Motion Video, but problems with getting adequate performance have meant that CD-I FMV is yet to be released. Full Motion Video is achieved by using MPEG (see below).
Photo-CD
Developed by Kodak and compatible with CD-I and CD-ROM XA; it is an extension of the Yellow Book standard. Personal photographs can be stored on a disc by High Street photographic developers for viewing at home on a Photo-CD (or CD-I) player or on a workstation with a CD-ROM XA drive. Photo-CD allows text and audio to be encoded on the discs as well as images, although this service is not currently provided by High Street stores.
Pictures are typically stored at five resolutions, the middle resolution corresponding to current TV resolution (albeit digital), the next to HDTV (see below) and the top resolution being around 3000 × 2000 pixels, adequate for excellent enlargements.
CD-MO
CD Magneto-Optical; a format for a rewritable CD, defined by the Orange Book, part 1. There are several restrictions on the type of drives that can read the disc.
CD-WO (also known as CD-R)
A Write-Once recordable version of CD (all variants) defined in the Orange Book, part 2. Discs can be written to CD-DA, CD-ROM (including XA), CD-I and Photo-CD standards. Recorders used to be exceedingly expensive but there are now CD-WO recorders available for £3750, with blank discs costing about £ 17. These cheap units are intended, at present, for the recording of music.
There is a complexity with CD-WO discs; they are of a slightly different format depending on whether all the data is written in one session or data is accumulated over several sessions (so-called Multi-Session Format). Drives, drivers and applications must all be aware of Multi-Session format if the application is to access such data.
CDTV
Commodore Dynamic Total Vision. Based on the Amiga PC, this is a proprietary CD-based system aimed at the home market using standard appliances such as a computer monitor or television.
CDXL
CDTV (see above) with full motion video in a small window on the TV screen.
Philips LaserVision
Analogue recording of video signals on a 12 inch disc. Much faster access rates than CDs and much higher capacity. Used in all major current computer applications featuring moving images. Particularly useful when a video sequence is to be shown repeatedly, as in an exhibition. Discs are produced commercially, not by the user, although there are bureaux that can provide the service from videotape masters.
Sony L VR video disk
Developed by Sony for industrial and scientific use; although the recorders and players are expensive (and the blank disks about £400) this allows users to record direct to video disk, including non-real-time recording. The disks are not compatible with LaserVision and are Write-Once media. In PAL format each disk (two sides) stores 42 minutes of video and sound.
DVI
Digital Video Interactive: a chipset developed by Intel for the compression and decompression of video, aiming at factors of 160:1. This will allow users to record video on the computer digitally, to store it economically and use video in applications with conventional peripherals.
MPC
MicroSoft's "standard" Multimedia PC: the minimum configuration required to run their multimedia software, which is currently a 286 compatible with 8-bit VGA graphics.
JPEG
Joint Photo graphics Expert Group. A joint lEC/ISO group responsible for formulating ISO standards for compression/ decompression of still images. JPEG is now widely implemented in both hardware and software, with some hardware implementations able to compress full motion video in real-time by a factor of about 40 with no appreciable quality loss compared with digital TV.
MPEG
Moving Pictures Expert Group. As JPEG, but for full motion video. A number of versions of MPEG have been defined, corresponding to different anticipated uses. At present MPEG-l, providing compression by about a factor of 150 and "VHS quality" pictures, and MPEG-2, aimed more at the studio and using less compression, are the leading contenders. The compression factor of 150 is a crucial target; this would allow Full Motion Video to be obtained from a CD.
Fractal Compression
A compression technique, developed by Michael Barnsley, that can achieve spectacular compression factors on certain pictures, but which is totally unpredictable in the time required to compress the image; since this can be quite long, this is not suited for real-time compression of full motion video.
HDTV
High Definition TV. A generic term for a large number of competing systems which have in common the doubling of the number of lines (to 1125, 1150 or 1250) and the widening of the picture to an aspect ratio (width:height) of 16:9; current TV systems use an aspect ratio of 4:3.
There are two main battlegrounds at present. The first is a format (and operating environment?) for the distribution of multimedia material. The contenders here, at present, are CD-I (FMV), CDTV, DVI and MPC. It is too soon to tell who will win, although CDTV may be losing at present and CD-I will be a strong contender when Full Motion Video becomes available.
The other area of hotly contested loyalties is HDTV. Suppliers of televisions and videos would be delighted if a new format, specifically designed for films, were a success with the public. HDTV could provide this but a large number of hurdles lie in the way:
  • Cost: every aspect of HDTV appears to be at least four times as expensive as current TV technology;
  • Technical Problems: whether to use analogue or digital transmission; where any extra channels could come from; how to handle the two aspect ratios; how to ensure a smooth changeover (as was achieved with black/white to colour).
  • User Reaction: several surveys of viewers' reactions to the format have thrown doubt on whether the superb quality of HDTV is actually appreciated by users!
If HDTV does take off, it will have been responsible for bringing to market a suitable medium for the recording of images at full workstation (1000+ lines) resolution and extensive technology for compression and decompression of Full Motion Video.
Norman Wiseman, NERC Computing Services (North) and Chris Osland, RAL CCD Graphics Group
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