[game_preservation] Preservation of analogue game media

[Kieron Wilkinson]

I'm not sure how much interest there is in this, but I'll carry on  
regardless. :)

In my previous post, I summarised what I thought were the technical  
challenges faces in preserving games stored on floppy disk media. I  
them split those points into two categories, which I will now detail  
further.

a) Reading the disks in the first place

Getting hold of appropriate disk drives seems to be easy enough for  
the majority of disk types, the problem is getting the raw data off  
the disk. Floppy disks are an analogue storage medium, and data is not  
directly stored as 0's and 1's like on Compact Discs and flash drives,  
but as magnetic polarity changes ('flux transitions'). The problem is  
that you cannot generally read these flux transitions through a  
computer, as there is hardware in the way way to make accessing the  
data "easier" (and did it's job well, but now is a problem for  
preservation). This "raw" form is the ideal thing for preservation.  
Once you have this, you don't care about disk formats or copy  
protection - you are just doing a raw read of a disk - and it all  
comes along for the ride.

You might think that if the computer can read the data, there  
shouldn't a problem. Unfortunately that is not the case, the only way  
to get a computer to read particular things is to write it in a  
special way on special hardware, a concept that underlies many copy  
protection techniques.


b) Knowing that what you have read is correct

Secondly, there is knowing whether the disk image you have made is  
correct. There is little point of trying to preserve games if you  
cannot be sure whether those disk images are okay or not. With most  
types of storage media we use today, this is not a problem - the data  
is checked as it is copied. But games on floppy disks are a special  
case, you often do not know where the checksum/integrity information  
is stored on the disk, and even for known disk formats, games  
developers applied copy protection that deliberately wasn't covered by  
the integrity data. The disks are old already, the data may already be  
broken, and you won't know if you need to find another copy without  
being confident in your disk images.

You cannot play the game to check it, the corruption may not be  
apparent until, say, level 14. Also, how do you know the copy  
protection passed? It is not always obvious. Borrowed Time on the  
Commodore Amiga has very nice protection, if it fails, you can't find  
some items to allow you to proceed in the game, they simply don't  
appear - and that is not the only example.

It gets worse, what if somebody modifies a game disk (virus, accident,  
malicious intent, save games)? There will be no corruption, but it  
certainly is no longer an authentic copy suitable for preservation.

I firmly believe that any disk images produced also require some sort  
of checking to be confident in their preservation status. I'll drop a  
small note here that The Software Preservation Society check for all  
of above for every single game preserved (nearly 3000 so far).


I think all that covers the points raised in my last email.


With these sorts of difficulties, it is no wonder that game  
preservation (for computers at least) has historically been in such a  
poor state.
In my next post, I will detail some new developments that I believe  
makes the future brighter for everybody.

If anyone has any comments on any of this, please feel free to chime  
in with your thoughts.
Kieron


On 13 Feb 2009, at 23:05, Kieron Wilkinson wrote:


>

> Since I have been away for a while, I was trying to get a feel for  

> how things have changed, and I thought this was a good place to  

> start. I guess there doesn't seem to be many people here involved  

> with that side of things, perhaps it is still very much an ad-hoc  

> process.

>

> As I said before, there does seem to be a number of common technical  

> problems in preserving game media. Here are the ones I can think of:

>

> 1) Devices required to read the disks

> 2) The different and custom disk formats in use (I don't mean the  

> physical disk format here, but how the software data is structured  

> on the disk)

> 3) The presence of any disk-based copy protection (the whole purpose  

> of which is to hide itself)

> 4) Degradation of original disks, leading to corrupted reads

> 5) Authenticity (ensuring disks are original and unmodified)

>

> I'd like to cover these points as two distinct problems...

>

> a) Reading the disks in the first place (points 1, 2 and 3).

> b) Knowing that what you have read is preservable (points 4 and 5,  

> but also involves 2 and 3).

>

> I don't want to go into too much detail in one post, so I will leave  

> it at this for now, and follow up this two issues separately later.

>

> If anyone has any comments on any of this, please feel free to chime  

> in with your thoughts.

> Kieron

>

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