[game_preservation] Preservation of analogue game media (disks)

[Kieron Wilkinson]

Hi Devin,

Yes, I'm being very confusing, sorry. Maybe I should have said  
"analogue game disks" in the title, otherwise it could be confused  
with cassette tapes too. Just to make myself clear to everyone, I'm  
talking about floppy disks, such as the 3.5" and 5.25" variety - I  
just meant analogue in the sense of how the technology works. I don't  
mind people not replying though, I'm building up to something and it's  
good to get this stuff down in writing for other places like our  
website.

Authenticity. All good points. I guess the particular problem with  
disks is that on many of them you don't know where the CRC info is, or  
what the algorithm is, and so if the disk has errors, you have a  
problem because you can't tell. Our disk imaging software reads and  
stores each track 5 times, and we *still* find that perhaps, 5-10% of  
games need to be imaged again, or simply have unrecoverable errors.  
So, it is a good thing we do check :)

Copy protection data. I think that generally, if you need to treat  
(disk-based) copy protection in a special way when imaging floppy  
disks, you are doing it wrong :) However, you are absolutely right  
that when you are checking that the disk image is correct and  
authentic, the copy protection should be included in that checking,  
and stored in any resulting image file.

Kieron

On 1 Mar 2009, at 16:17, Devin Monnens wrote:


> Hi Kieron,

>

> Haven't posted any responses as I was on the conference track the  

> past week - makes it difficult to read things! Anyway, great detail  

> here and it's all quite fascinating! At first I thought this was for  

> scanning documents ( >.< ) but as I see, it's new information!

>

> Authenticity is a problem that hackers are dealing with, too, which  

> is why a lot of the sites that rip disc-based games are now  

> including MD5 and CRC check files. (Unfortunately, I think they are  

> encoding all their audio into FLAC, which has some advantages, but  

> is not a preservation standard. FLAC does contain the CRC  

> information of the original WAV though).

>

> Another thing to consider is whether (and sometimes how) to preserve  

> the copy protection data. I am assuming your backups include these  

> as well?

>

> On another note, I have found very little high-quality Super Mario  

> Bros. development art on the web despite the fact that it's in tons  

> of magazines and promo materials. You would think a site like The  

> Mushroom Kingdom would have it...

>

> Devin

>

>

> On Wed, Feb 25, 2009 at 3:16 AM, Andrew Armstrong <andrew at aarmstrong.org 

> > wrote:

> I'm interested in hearing more and how people can help. Responses on  

> this mailing list widely vary, and there isn't as many institutions  

> as I'd like to see involved here, we'll need to invite more people  

> on :)

>

> Andrew

>

> Kieron Wilkinson wrote:

>>

>> 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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>

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