The Classic Amiga Preservation Society (CAPS)

http://www.caps-project.org

http://www.softsoc.org

Software Preservation Society

István Fábián

Introduction

CAPS founded in 2001

Ex-games developer

Frustrated with the state of software preservation

Aims of CAPS

CAPS changing into SPS (Software Preservation Society)

Game Preservation

GAMES ARE ART

Imprisoned by media

All disks will eventually die

Help from the community

Technical Issues

                                                                              

Technical Issues – Disk Formats

Disk Format is not copy protection

Floppy-based systems have standard “known” formats

Floppy Disk Controller (FDC) defines format on Atari ST/PC

Amiga FDC operation done mostly in software

System has to know format to be able to read it

                                                                              

Technical Issues – Copy Protection

Attempt to keep piracy under control

Non-standard “effects” created on media

Allow reading/detection data that cannot be written

                                                                              

Technical Issues – Protection Examples

Changing width of “bitcells”

                                                                              

Flakey/weak bits

“Stealth” data

Technical Issues – Disk Properties

Preserving the normal disk data is not enough

There are other sorts of information that is needed

                                                                              

Density of the bits across a track

Format description

Track geometry

Data “behaviour”

Media Unsuitable for Preservation

                                                                              

Media Unsuitable for Preservation - Errors

Damage to disks caused by:

                                                                              

Physical damageDrive failureBit rot

Magnetic Force Microscope visualisationof a damaged area of magnetic disk

Need detection of these errors

Integrity algorithms

Special handling of media that lacks integrity information

Media Unsuitable for Preservation - Modification

Modified disks not repairable

Disks manufactured write enabled

Sources of modification include:

                                                                              

Save gamesHi-scoresVirus damageUser hackingEtc.

A very big problem

Media Unsuitable for Preservation - Copies

Copying of a disk over a (perhaps broken) original

Cracks are easy to see by anyone

Hardware copies

                                                                              

Not easy to see without using our technologyAnalogue in natureLike copying a VHS tapeGeneration copies will eventually fail

Modification can not be determined after it has been copied

Cracks

Most common form of disk images

Represent piracy and “warez”, not developer friendly!

Frequently do not work, perhaps fail later in game

Game features often missing

Graffiti in credits and hi-score

Modifies game code!

                                                                              

The Solution

                                                                              

The Solution – Disk Imaging

Data normally read through FDC is not the same as on disk

DSP techniques used to get what is on disk surface bit-for-bit

Disk imaging technology produces raw signal information

To be usable, the data needs to be described

                                                                              

The Solution – Commercial Mastering (1)

Why define disk formats?

                                                                              

Same in commercial mastering

Trace 7500 ST Duplicator

Data meaningData verification

Master “gold” diskFormat description (Freeform)

Only then can we master disks

The Solution – Commercial Mastering (2)

Following commercial mastering principles

New formats researched and documented

“Layered” format descriptions

Result is IPF (Interchangeable Preservation Format) file

                                                                              

Contain both signal data and descriptions

Act exactly as real media

The Solution – Integrity

Integrity information described

Algorithms reproduced

Some formats do not contain integrity info

                                                                              

Check by encodingCheck by comparison

Some games have mastering errors, have to find good versions

If a disk does not pass integrity checks, it is useless for preservation

The Solution – Authenticity

Floppy systems are mechanical devices

Leave a “fingerprint” when writing

Commercial duplicators use high quality components and have very different fingerprints to those written on home equipment

We can see when a disk has been modified – as the fingerprints are different for one or more tracks

99.9% of games commercially mastered

Detection of copies in the same way

The shear amount of modified games is a very big problem

                                                                              

The Solution – Preservation Framework

Layer 1: Raw Image

Layer 2: Track Geometry

Layer 3: Disk Geometry

Layer 4: IPF File

Layer 5: Meta data

Layer 6: Digital Libraries

                                                                              

Density/Timing + Data

Descriptors

Self-describing format

Software collections

Description/Categorisation

All Layer 2 for Disk

Wrapping Up

We search until we find a game unmodified with no errors

IPF file describes everything the game needs to work. No program code is changed!

An IPF file is only sent to contributors and authors of the game

Currently focused on Amiga, as is the most complicated system.

Other systems supported by describing their disk format(s)

Resources available

Preserving software for the future...

                                                                              

The Classic Amiga Preservation Society (CAPS)

http://www.caps-project.org

http://www.softsoc.org

Software Preservation Society