Acorn User 4/AUCD4.iso/acorn/documents/appnotes/261-275/273c.arc/Text

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28th April 1995
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Support Group Application Note
Number: 273
Issue: 0.4 **DRAFT**
Author: DW
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CD ROM Drives and their Handling under RISC OS Explained
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Notes:
This Application Note details the interfacing of, and protocols underlying,
CD ROM drives
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Applicable Hardware:
All Acorn computers running RISC OS 3.1 or greater

Related Application Notes:
266: Developing CD ROM products for Acorn machines
269: File transfer between Acorn and foreign platforms


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Copyright (C) 1995 Acorn Computers Limited

Every effort has been made to ensure that the information in this leaflet is
true and correct at the time of printing. However, the products described in
this leaflet are subject to continuous development and improvements and
Acorn Computers Limited reserves the right to change its specifications at
any time. Acorn Computers Limited cannot accept liability for any loss or
damage arising from the use of any information or particulars in this
leaflet. ACORN, ECONET and ARCHIMEDES are trademarks of Acorn Computers
Limited.
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Support Group
Acorn Computers Limited
Acorn House
Vision Park
Histon
Cambridge
CB4 4AE
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Table of Contents

        Introduction

        Interfacing CD ROM Drives

        Features of CD ROM Drives

        CD ROM Formatting Standards ("Coloured Books")

        CD ROM Data Storage Standards

        CDFS and CD ROM Drivers

        Accessing Data on CD ROMs Produced for Non-Acorn Platforms

        Troubleshooting


        Appendix A: Useful Contacts
        Appendix B: PhotoCD Mastering Bureaux
        Appendix C: References



Introduction
------------
Considering the amount of data which has to be stored in today's Multimedia
applications (especially those incorporating moving video clips) it is often
impractical to distribute the software as a set of floppy discs. For this
reason, CD ROM is becoming an increasingly popular distribution medium. Even
with the high storage capacity (typically 600 MB) of this medium, however,
it is often necessary to feed the raw data through a compression system in
order to fit it all on the disc.

This application note aims to explain the terminology, interfacing, and
current capabilities of CD ROM drives and their respective data standards,
along with details of their software interfacing to RISC OS. Further data on
other multimedia capturing and rendering devices, and associated data
compression standards, is available in other supporting Application Notes.

Interfacing CD ROM drives
-------------------------
Currently, there are four ways of connecting a CD ROM drive to an Acorn
computer. These are:

SCSI: Currently the most popular method. SCSI (Small Computer Systems
Interface) is an industry-standard peripheral bus, which can move data
around in parallel 8-bit chunks. More recently, SCSI 2 has begun to emerge
as a standard on high-end systems, giving an effective near-doubling of data
transfer speed. The SCSI bus standard allows up to 7 peripheral devices to
be connected to the same bus; if you plan to have more than  one CD ROM
drive on a given machine, SCSI is the recommended option. The fastest SCSI
cards available for Acorn machines can transfer data at a sustained 3.5 MB
s-1 or so. Acorn SCSI interfaces can be fitted to the Archimedes 300 and 400
series, the  R140, A5000 and the Risc PC; the Archimedes 540 and R260 were
supplied with a SCSI card as standard. The Acorn card supports ANSI X3.131
1986 and CCS X3T9.2/85-52 Revision 4B of the SCSI standards; check with your
drive supplier for compatibility.

IDE: The emerging standard for hard drive interfaces in desktop computers,
with the exception of specialised workstations (which mostly use SCSI 2). A
number of CD ROM drives equipped with IDE interfaces have been released onto
the market, and it is one of these devices which is fitted in the Risc PC
600 CD. As IDE only supports a maximum of two peripheral devices on its data
bus, it is only possible to have one IDE CD ROM drive if you already have an
IDE hard disc. Bus data transfer speeds are on a par with SCSI 1. Suitable
IDE interfaces are fitted as standard to the A4000, A5000 and Risc PC.
Although the A3020 also has a suitable interface, cable length limitations
imposed by the IDE timing specifications mean that a secondary interface
must be used, as the physical size of the A3020 case requires that the drive
be housed externally.

Parallel: On Acorn machines equipped with a bidirectional parallel port
(these machines being the A3010, A3020, A4000, A5000 and Risc PC), it is
possible to interface a CD ROM drive to this port, and use a modified set of
drivers to access the drive. The hardware interface between the drive and
the computer usually has a "straight-through" parallel connector on it in
addition to the CD ROM drive connector, so that a printer may be attached to
the computer at the same time. The speed by which signal state can be
changed on these lines is sufficiently high that data can be transferred at
speed roughly equivalent to a SCSI 1 interface.

Proprietary: Some third party vendors have developed proprietary interfaces
for connecting CD ROM drives; the relevant third party should be contacted
directly for the latest details regarding data transfer  speeds and the
number of drives which can be connected via such an interface.



Features of CD ROM Drives
-------------------------
Speed
In all cases of data transfer between peripheral and computer, there is
always a "bottleneck," where one part of the system places a fundamental
limit on the rate of data transfer. In the case of hard drives, the
bottleneck is often the bus interface; this certainly became the case with
fast, cached SCSI drives, hence the advent of SCSI 2. In the case of CD ROM
drives, however, the physical mechanism of the CD ROM drive is the limiting
factor.

The first CD ROM drives were capable of a data access rate of 150K s-1; when
compared with the bandwidth sustainable by the SCSI bus, for example, this
is very slow. Successors to these drives were classed as "double speed," and
implemented such techniques as read-ahead cacheing, increased disc rotation
speed and multiple read heads to achieve 300K s-1 transfer. Subsequent
refinements have resulted in "quad speed" drives, capable of 600K s-1; these
are currently the state of the art, but still have a transfer rate well
below the bus bandwidth of SCSI or IDE.

Sessioning
A CD ROM drive may be described as either "single session" or
"multi-session." This distinguishes the capability of a drive's control
logic to access multiple catalogues for different parts of the disc, as they
were laid down at the time of mastering. As CD is a "write-once" medium, it
is not possible to produce a file catalogue, write the files and catalogue
to the disc, and then go back to the disc and add some more files without
adding a complete new catalogue after the end of the previously written data
to cater for the data being appended; in this circumstance, a "single
session" drive would only be able to read the data defined in the first
catalogue. Most modern drives are multi-session, but it is always wise to
check with the supplier.

Audio Output
Most CD ROM drives are capable of outputting audio information extracted
from Red Book Mode 0 (q.v.) CDs; this output is usually presented either at
a mini-jack on the CD ROM drive suitable for driving a pair of 35 Ohm (input
impedance) headphones, or (in the case of a drive fitted with an audio mixer
board) on a header plug to feed into the unfiltered external audio output on
the computer, or both. In the case of the Risc PC, the header plug can be
fitted onto link LK14; this will also allow audio to be produced via the
internal speaker.

The quality of sound output from Red Book CDs by the CD ROM drive is
determined solely by the Digital to Analogue Converters (DACs) built into
it. In the case of White Book (q.v.) CD ROMs the audio is converted by the
DAC unit on the appropriate expansion card fitted to the computer, and in
the case of CD ROMs containing Replay movies or other application-based
samples, the audio is converted by the on-board sound system. In all base
configurations, the on-board sound system is built around an 8 bit
logarithmic DAC, which gives sound output quality, after filtering, roughly
equivalent to a 12 bit linear system. The Risc PC, however, may easily be
upgraded to a true 16 bit linear audio system, giving CD quality
reproduction. Audio upgrades for earlier machines are available via third
parties.


CD ROM formatting standards ("Coloured Books")
----------------------------------------------
Red Book
This is the formatting standard which covers "ordinary" audio CDs, and is
defined by Philips and Sony. Dedicated audio data is recorded as CD-DA
(Compact Disc Digital Audio) in PCM (Pulse Code Modulated) format. Red Book
is the standard upon which all subsequent CD ROM standards are ultimately
based.

Red Book divides the disc into one or more audio tracks; each track normally
comprises a single "track" in the musical sense. These tracks are further
divided into sectors (also known as frames); each sector contains sufficient
data to supply 1/75 second of music, which at the standard CD digitising
rate of 44.1 kHz, works out as 2352 bytes.

In addition to the 2352 bytes of audio data, Red Book provides two levels of
error detection code (EDC) and error correction code (ECC) for each sector;
if part of a sector cannot be read for some reason, the ECC can be used to
reverse-engineer the data. Further to EDC and ECC, 98 control bytes are
added to each sector; these bytes contain such information as timing data to
enable an audio CD player to display the track playing time.

All CD ROM drives which are compatible with Acorn machines are capable of
playing Red Book audio via their own DACs, although most drives cannot allow
the computer to "read" CD-DA directly. Acorn's CD ROM Filing System (CDFS)
has facility to direct a drive to play a Red Book CD; either the appropriate
CD ROM drive icon can be clicked on when the disc is loaded to start it
playing from the beginning of the first track, or appropriate *commands may
be passed to cause the drive to play a given section of audio (see the CDFS
section below)

Yellow Book
This is the first set of standard definitions which detail the use of CDs to
store computer data. Yellow Book is based on Red Book, and indeed Yellow
Book Mode 0 supplies the same functionality as Red Book.

The Yellow Book standard defines three data modes; CDFS is capable of
handling all three, although not all CD ROM drives are capable of handling
them all. A CD containing tracks consisting of more than one mode is termed
a "mixed-mode CD."

Mode 0: This mode is used to store CD-DA in PCM format. Most drives cannot
"read" this data digitally and pass it to a computer, only play it.

Mode 1: This mode is used to store data, and is the normal mode which data
is stored in. The Red Book 2352 byte data area is split as follows:

12 bytes of synchronisation
4 bytes of header information
2048 bytes of user data
4 bytes of EDC
8 bytes of blanks
276 bytes of ECC

Mode 1 has an additional layer of ECC, which is included to provide the
increased reliability required to store computer data. This mode has an
uncorrectable error rate of 1 x 10-12 (ie one bit in every 200 CD ROMs). As
drives are capable of re-reading the data and correcting the information,
the data is hardly ever totally unreadable.

Mode 2: This is another data mode, designed particularly for storage of
video picture data and compressed audio data. Mode 2 is used where the
primary concern is density of data storage; by sacrificing most of the error
correction capability, a Mode 2 disc can store 14% more user data than a
Mode 1 disc. A 2352 byte sector is subdivided into:

12 bytes of synchronisation
4 bytes of header information
2336 bytes of user data

The extended error correction codes are missing from this mode so the error
recovery is not as good; the uncorrectable error rate is 1 x 10-9. This mode
is not used as often as Mode 1.

In all these modes, data is referenced by its position on the disc in units
of minutes, seconds and frames; a frame is a Philips-defined time unit
equivalent to 1/75 s.

Mixed Mode discs
As Red Book and Yellow Book use the same underlying sector size, it is
possible to produce "mixed mode" discs containing both computer data and CD
audio. The most common layout for a mixed mode disc is to have the first
track as Yellow Book Mode 1 data, and the remaining tracks as Red Book PCM
audio. The two most common methods used in Mixed Mode applications are:

a) To initially load the program into the computer and run it, and then
allow the computer to have continuous access to the audio tracks. The
limitation with this scheme is that sufficient free RAM must be available
for the computer to load all of the application executable and its
associated data.

b) To alternately read in portions of executable code and audio data. This
relieves the memory constraint above, but entails more track seeking for the
CD ROM drive and hence slower operation.

CD ROM /XA (PhotoCD)
This is a further extension of Yellow Book Mode 2. CD ROM /XA is distinct
from Yellow Book Mode 2 in that it is specified as suitable for computer
data, video data and compressed audio data. To do this, CD ROM /XA defines a
new track format; an 8 byte subheader is included in the 2352 byte sector,
so the sector takes the layout:

12 bytes of synchronisaton
4 bytes of header information
8 bytes of subheader information
2048 bytes of user data
4 byted of EDC
276 bytes of ECC

CD ROM /XA is also known as Mode 2 Form 1;  a slightly modified form of this
(to allow discs to be read by Philips CD-i machines) is is the standard
layout used in the Kodak PhotoCD system, hence CD ROM /XA is readable by
Acorn CDFS 2.21. A further iteration of CD ROM /XA, Mode 2 Form 2, also
exists; like Yellow Book Mode 2, this omits the ECC, and hence is rarely
used.

When compared to Mixed Mode discs, it is very important to note that a Mixed
Mode disc is unable to access both computer data and audio simultaneously;
data of different types must be on separate tracks. CD ROM /XA allows
heterogeneous data types to be interleaved within the same track, hence
allowing simultaneous access to executable code and audio; this is the
principal advantage of this format.

Green Book
This is a proprietary standard used by Philips for encoding computer data,
compressed audio and moving video (MPEG) CD ROMs for use with their own CD-i
system. Currently, Acorn systems cannot access Green Book CD ROMs.

White Book
This is the new "Open Standard" for storage of digitised video. White Book
discs use ISO 9660 (q.v.) filenames; the main thrust of the White Book
standard is to produce an explicit file hierarchy and filename set,
compliant with ISO 9660, into which all video data can be fitted.

Moving video data distributed using the White Book standard can be accessed
by CDFS; however, the movies can currently only be played at a suitable
frame rate using the Movie Magic card (available from Computer Concepts) and
a modified version of Acorn Replay. This modified version of Replay,
supplied only with the card, does not incorporate movie-decoding capability
within itself, but acts as the user interface to pass the movie data direct
to the C-Cube CL450 MPEG decoder chip on the Movie Magic card.

CD ROM data storage standards
-----------------------------
High Sierra
This is the earliest standard format utilised by CD ROM for storing computer
data in a hierarchical file structure. It has generally been superseded by
ISO 9660, which itself evolved from an enhanced High Sierra standard. In
addition to ISO 9660, CDFS is able to read most High Sierra CD ROMs.

ISO9660
This has become a de-facto standard as a logical format for information
storage and retrieval. The standard defines a hierarchical filing structure
for both files and directories. In order for all CD ROM supporting computers
to be able to map the names of the files on the CD ROM to their own filing
systems, file and directory names on ISO 9660 discs are restricted to:

Capital letters "A-Z"
Digits "0-9"
Underscore "_"

ISO 9660 Level 1 interchange format also restricts the naming system to:

Filenames: Maximum of 8 characters
Filename extensions: Maximum of 3 characters
Directory names: Maximum of 8 characters (no name extensions permitted)

To cater for RISC OS applications, which always exist in a directory
beginning with a pling "!", CDs destined specifically for Acorn platforms
are mastered with the initial pling replaced by an underscore. When
accessing the directory structure of such a CD ROM, CDFS looks for any
directories with names beginning with an underscore, and maps this
underscore to a pling "on the fly" and before presenting the filer display
to the user. Investigating such a CD ROM on another platform will therefore
result in application directories being displayed with an initial
underscore, and not a pling.

PhotoCD (Image Pac)
PhotoCDs are recorded in CD ROM /XA Mode 2 Form 1 format. Most of the disc
is taken up by files containing picture data stored in Photo YCC, which is a
Kodak-devised colour encoding metric. Each discrete image is stored 5 (or,
exceptionally, 6) times on the disc at different resolutions; the copies of
each image, once they have been fed through a visually-lossless Kodak
compression system, form an Image Pac. The Acorn PhotoCD viewer application
(!PhotoView) opens the Index on a PhotoCD, which contains the smallest image
from each Image Pac, in order to build a contact sheet; when a picture is
selected, the appropriate resolution of YCC image is selected from the Image
Pac and rendered. Each Image Pac contains scans at the following
resolutions:

Base / 16 (thumbnail resolution)       128 x 192
Base / 4                               256 x 384
Base (TV resolution)                   512 x 768
BaseX4 (HDTV)                         1024 x 1536
BaseX16 (photographic)                2048 x 3072
BaseX64 (photographic)                4096 x 6144 (Pro Master PhotoCD only)

PhotoCDs can be produced from ordinary 35mm slides or photographic
negatives; in addition to mastering facilities provided by some high-street
photographic processors, Kodak has set up a number of image transfer bureaux
dedicated to producing PhotoCDs in quantity for the commercial market; these
are listed in Appendix B.

Others
As detailed above, High Sierra, ISO 9660 and PhotoCD CD ROMs based on Yellow
Book or CD ROM /XA can currently be accessed by Acorn machines, and CD ROM
drives fitted to Acorn machines can play audio CDs which conform to the Red
Book standard.

Other formats also exist; Apple have a proprietary format (essentially,
Yellow Book Mode 1 with their own HFS filing system on top instead of ISO
9660) which is used to produce CD ROMs for their hardware, and high-end
dedicated workstations use further specialised formats such as RockRidge.
There are also discussions to extend the ISO 9660 standard to cope with
higher-capacity CD ROM discs which are under development.

Currently Apple-formatted and RockRidge CDs cannot be accessed using Acorn
hardware, and the extended ISO 9660 format has yet to be finalised. More
detail on ISO 9660 Levels 2 and 3, and the extended standard once it becomes
available, may be obtained from the British Standards Institute; see
Appendix C for further details.

CDFS and CD ROM Drivers
-----------------------
Supported Drives
Most CD ROM drives support a common subset of fundamental commands for
standard low-level operations. However, for more complex functions,
particularly when accessing discs formatted to standards other than Red Book
Mode 0, command sets differ between drives; this necessitates that each CD
ROM drive have a driver module written for it to interface correctly to
CDFS.

The difference in command sets is most graphically illustrated
by the fact that only some drives are capable of handling PhotoCD.

Drivers are currently available from Acorn for the following SCSI CD ROM drives:

Sony           CDU6111, CDU6211, CDU541, CDU561
Philips        CM131, CM231
Toshiba        XM2200A, 3301
Hitachi        CDR1650S, CDR1750S
Chinon         CDS-431

In addition, there is a modified version of the Sony driver, available via
Acorn dealers, which will interface to the Apple CD-300.

PhotoCD support is included with this modified Sony driver (the Apple drive
is PhotoCD capable), and with the Sony driver (the CDU561 is PhotoCD
capable).

The IDE drive available for the Risc PC is a Panasonic CR 562B unit. This is
a dual-speed PhotoCD capable drive, and is supplied with its own driver to
enable CDFS to access the IDE interface.

Other software drivers, and CD ROM drives, are available from third parties;
please refer to Appendix A for more details.

CDFS appears to the user as an ADFS-like filing system, and supports many of
the standard FileCore-compliant commands. In addition, CDFS has a number of
commands unique to itself: details of these follow:

*CDDevices displays all the CD devices connected, their product name,
capacity, SCSI ID (displayed as device, Logical Unit Number, and card) and
firmware revision.

*CDFS selects the CD-ROM filing system as the current filing system.

*Configure CDROMBuffers sets the configured amount of memory reserved for
CD-ROM buffering (maximum 512K). Syntax: *Configure CDROMBuffers <size>K

*Configure CDROMDrives sets the configured number of CD-ROM drives
recognised at power on. Syntax:*Configure CDROMDrives n

*Eject activates the eject mechanism (where possible) in the CD ROM drive;
this will eject any disc caddy present in the drive if it is a caddy type,
or open the loading tray on a non-caddy drive. Syntax: *Eject [drive]

*Lock prevents a CD being ejected from the drive, effectively disabling
*Eject. Syntax: *Lock [drive]

*PlayList lists the tracks - whether audio or data - on the disc in the
given CD-ROM drive, together with (on Red Book CDs) their start time and the
total CD time. Syntax:*PlayList [drive]

*PlayMSF plays a piece of audio from the disc in the given CD-ROM drive. The
start and stop times are specified in minutes, seconds and frames from the
start of the disc. Syntax:*PlayMSF mins:secs:frames mins:secs:frames [drive]

*Stop stops playing the disc in the given CD-ROM drive. Syntax:*Stop [drive]

*Unlock reverses the effect of *Lock, re-enabling the functionality of
*Eject. Syntax: *Unlock [drive]



To configure the number of CD-ROM drives, type:

*Configure CDROMDrives n

where n is the number of drives (from 0 to 28).

You will need to configure the size of the CD-ROM buffers, especially if you
expect to be using a variety of CDs. Type:

*Configure CDROMBuffers [size]K

where size represents the size of the buffers in K, a number in the range
0-512. 64K or 128K is a good starting buffer size.

Important: Incorrectly setting the number of drives causes the boot up
procedure to take longer.

Some Information on Driver Modules
----------------------------------
Owing to the differences in command syntax and availability between the
different supported CD ROM drives, CDFS does not communicate with a drive
directly; it translates user-level calls into a series of SWI calls which
are passed to an abstraction layer. This layer is in turn implemented by the
driver module, which is responsible for interfacing to the firmware on the
drive. As an example of what goes on at the abstraction layer level, the
SWIs provided by the Toshiba driver are:

cd_checkdrive
cd_control
cd_converttolba (logical block addressing)
cd_converttomsf (Minutes, Seconds and Frames)
cd_discused
cd_driveready
cd_drivestatus
cd_inquiry
cd_lasterror
cd_opendrawer
cd_prefetch
cd_readdata
cd_reset
cd_seekto
cd_stopdisc
cd_version
cd_identify
cd_register
cd_unregister

Clearly, the task of writing a CD Driver module is not a trivial one; the
command set above, for example, does not cover the PhotoCD extensions.
Registered Developers wishing to develop CD ROM drivers should, at the
outset, contact Acorn Developer Support.

Multiple Drives on Different Interfaces
---------------------------------------
It is possible to have multiple CD ROM drives connected using different
interfaces; althouh as a rule it is not possible to have multiple SCSI
interfaces in a given machine accessing CD ROM drives, it is perfectly
acceptable to have both a chain of SCSI CD ROM drives and (for example) a CD
ROM drive connected to an IDE interface (where fitted). What actually
happens at boot-up is that the driver software, comprising a version of CDFS
and copies of the relevant driver modules, for each interface loads in a
sequence. The ordering of the sequence is determined by whether the code is
on a podule ROM (in which case it loads first), or whether it is in the
normal boot sequence, in which case it loads in the order specified. As is
normal with relocatable modules, loading of multiple instantiations of a
module causes successive overwrites, such that the version of the module
which remains loaded once the boot sequence is complete is the last copy of
the module to be explicitly loaded.

Once loaded, the specific device driver modules remain loaded throughout the
boot sequence, unless subsequently overwritten. When CDFS (version 2.20 or
later) executes, it polls the loaded modules to check for the presence of a
preamble sequence unique to a CD ROM driver module; if this is present in a
given module, that module is invited to register with CDFS. Thus the
last-loaded version of CDFS can recognise and interface with all the
device-specific modules containing the preamble which were made available
during a boot sequence, and hence drive any suitably connected CD ROM drive
regardless of the physical interface. It is worth noting, however, that some
early third-party driver modules did not have the correct preamble present,
and therefore may produce unexpected results when interfacing to a current
version of CDFS; if an interface which appears to have a suitable driver
module refuses to interface with CDFS, contact the supplier of the driver
module quoting the version number of the driver module in question and the
version of CDFS.

Accessing Data on CD ROMs Produced for Non-Acorn Hardware
---------------------------------------------------------
One of the main benefits of standards such as ISO 9660 and the Coloured
Books is that, provided you have a driver capable of reading these formats
it should be possible to access data intended for use on other platforms.

However, although the raw binary data can be accessed, it is not necessarily
possible to make use of it. The likely possibilities are that files of
common formats, such as plaintext and graphic formats of types translatable
by !ChangeFSI, can be used; also Comma-separated variable (CSV) and
Tab-separated variable (TSV) files can be used in Acorn-native applications
which are specified to be able to read them. In addition, some third-party
programs which perform file compression (eg !SparkFS from David Pilling and
!ArcFS from VTI) can recognise and decompress a number of file archives of
certain standard formats, eg UNIX tar. If you have such a program, it is
worth checking on the formats it understands.

Problems arise when custom filetypes or proprietary codecs are used in the
software on the disc; as RISC OS cannot execute the binaries for the
decompressors / translators in the manner of the platform they are intended
for, it is not possible to extract and make use of files encoded in these
ways purely using RISC OS. As some discs use proprietary codecs and others
do not, Your Mileage May Vary; if you plan to extract data from a disc
designed for another platform, check with the supplier of the disc that the
data is in a format you can make use of. Acorn Customer Services Application
Note 269 gives further detail on file transfer and translation.


Troubleshooting
---------------
In the case of CD ROM drives, it is fortunate that only a relatively small
number of problems can arise, and none of these are fatal to the data
medium. Perhaps the most common problems are:

A SCSI CD ROM drive reports a target error on access.
There are several reasons for this behaviour, and it is not possible to
determine the root cause without examining the machine in question. Reasons
for this mode of failure are:

The SCSI bus is incorrectly terminated.
Make sure that a pack of terminating resistors is present on both the first
and last devices on the SCSI chain (the SCSI card will itself need to be
terminated if it is in such a position), and nowhere else.

Two or more SCSI devices have clashing device numbers.
 This can be diagnosed by issuing a *Devices command, and seeing if any of
the returned descriptions appear at odds with the known types and sizes of
peripherals on the bus. It is recommended practice, when only one or two CD
ROM drives are present on the bus, to start numbering them from Device 6 and
move upwards from there.

The installed version of CDFS, or one of its dedicated drivers, is out of
date.
 If a CD ROM drive responds correctly to a *Devices, and if it returns an
apparently correct disc size using *Free when a CD ROM has been inserted, it
is possible that the drivers are out of date. Contact the supplier of the
driver for more details, stating the version numbers of both the driver in
question and CDFS itself.

!PhotoView reports an error "CDFS::0.$.PHOTO_CD.OVERVIEW/PCD not found"
!PhotoView is not finding the file containing the index information for the
pictures on the PhotoCD. First check that you have a PhotoCD in your drive.
Corel Professional PhotoCDs do not have an Overview file on the disc;
individual Image Pacs may, however, be accessed using !ChangeFSI. If your
PhotoCD is not a Corel disc and the Overview file cannot be found, consult
your PhotoCD's supplier.

CD ROM access appears to be very slow
Remember that CD ROM drives are not high access speed devices! If access is
exceptionally slow, try increasing the buffer size allocated to CDFS. The
"Configure" submenu accessible from the CD ROM icon bar menu facilitates
this.

Appendix A: Useful Contacts
---------------------------
For SCSI, IDE, Parallel and Proprietary CD ROM drives, interfaces, and CDFS
Drivers:

Morley Electronics Limited
Morley House
West Chirton Industrial Estate
North Shields
Tyne and Wear
NE29 7TY
Tel: [phone]

Alsystems
47 Winchester Road
Four Marks
Alton
Hampshire
GU34 5HG
Tel: [phone]

Beebug Ltd
117 Hatfield Road
St Albans
Herts
Tel: [phone]

Computer Concepts
Gaddesden Place
Hemel Hempsted
Herts
HP2 6EX
Tel: [phone]

For MPEG rendering hardware (the Movie Magic card):
Computer Concepts (address above)

For Compression and Decompression software:

David Pilling
PO Box 22
Thornton
Cleveleys
Blackpool
FY5 1LR

VTI
The Shopwhyke Centre
Shopwhyke Road
Chichester
West Sussex
PO20 6GD

Appendix B: PhotoCD Mastering Bureaux
-------------------------------------
UK commercial transfer services, sponsored by Kodak:

Acorn Studios PLC       Tel: [phone]
B & S Visual, Glasgow   Tel: [phone]
Dunn's, Birmingham      Tel: [phone]
Grant's, Dublin Tel: (from UK) 010 353 1 660 4288
Laserbureau, London     Tel; 071 486 9260
Pro-Vision Digital Imaging      Tel: [phone]
Quadrant, Worcestershire        Tel: [phone]
Tapestry, London        Tel: [phone]
Wace Group, London      Tel: [phone]


Appendix C: Standards Documents
-------------------------------
For copies of the CD ROM Coloured Book (Red, Yellow and White) standards,
and SCSI standards:

BSI Standards
Linford Wood
Milton Keynes
MK14 6LE

Tel: [phone]