The Classic Amiga Preservation Society (CAPS) http://www.caps-project.org http://www.softsoc.org Software Preservation Society István Fábián
Jan 03, 2016
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 – 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 – 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 - 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 – 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...