How can you tell if disk images is real?

[per]

Lets say you have an old game, a "PC Booter", you really want to play, without gambling about that the disk is 100% as readable as it was new. Somehow, somehting keeps you from making an image of the disk (Copy protection, no dual 5.25/3.5 PC's, incompatible operating system, etc...). You get desperate and does a quick search on internett and find the image there.

But how can you be sure that the image is equal to the one on your disks? should it be "(C)" instead of "(c)" on the titlescreen of "Lode Runer"? Are you 100% sure the files "Discopy" "Does" "Da" "Deed..." should show up in the root directory when you write "DIR A:"?

So how can we be sure that the disk images aren't modified?

[Trixter]

Lets say you have an old game, a "PC Booter", you really want to play, without gambling about that the disk is 100% as readable as it was new. Somehow, somehting keeps you from making an image of the disk (Copy protection, no dual 5.25/3.5 PC's, incompatible operating system, etc...). You get desperate and does a quick search on internett and find the image there.

But how can you be sure that the image is equal to the one on your disks? should it be "(C)" instead of "(c)" on the titlescreen of "Lode Runer"? Are you 100% sure the files "Discopy" "Does" "Da" "Deed..." should show up in the root directory when you write "DIR A:"?

So how can we be sure that the disk images aren't modified?

You can't. If there is a crack message, obviously they've been altered, but otherwise you can't tell.

If you downloaded a booter image from Retrograde Station, you can be guaranteed they are as unaltered as humanly possible; only the protection has been removed. Don't ask me how I know this.

[tezza]

It's not easy. Programs (expecially games) can get hacked by people for various reasons (sidestep copy protection, work with a different configuration, increase speed, put their own names on the default hi-scores list etc.)

People who are wizards with machine code can make small changes to executables, even without having the source code.

The only sure way of having an original is to actually own the original. And even then, in the early days of computing, it's possible some publishers may have made minor "invisible" changes to code, without changing the version number at the retail level. In that case, what is "original"?

Tez

[per]

some publishers may have made minor "invisible" changes to code, without changing the version number at the retail level.

like "(c)" or "(C)" on the loderunner title? (I compared the outcome from the disk image at Retrograde Station with the images at MobyGames)

[dksinghh]

The 5 most common types of disk images you might come across are (identified by their filename extensions):

ATR: Nick Kennedy's SIO2PC Atari Disk Image format. This is the defaco standard disk image, used by APE, SIO2PC, and all Atari emulators. There are minor differences in the header use between these programs, but the images remain compatible regardless of what program they are created with.

XFD: Xformer Disk Image. This image is similar to the ATR but lacks the ID and format header, it is essentially a large unmarked blob of data. Compatible only with the PC-Xformer emulator.

DCM: Compressed Disk Communicator image. This is actually a native Atari file format which contains an entire Atari disk compressed with Bob Puff's Disk Communicator program. Must be decompressed to an ATR before use.

SCP: Spartados Compressed Disk Image. This is also a native Atari file format, an image of a complete disk compressed with the Spartados utility SCOPY. Must be decompressed into an ATR before use.

PRO: A proprietary disk image formatted used by APE and the ProSystem. Contains an image of a copy-protected Atari disk, useable only with APE.

[carlsson]

The 5 most common types of disk images you might come across are ...
... if you life is entirely about Atari 800 series. Per who started this thread seems more into vintage IBM PCs, and wanted to know that the files in a disk image are not tampered with.

In the C64 community, there has been an ongoing preservation project for a number of years now, where disk images (perhaps also tapes?) are duplicated at a very low level so you get the exact same bit patterns as the original disk. Many times some copy protections have to be bypassed to safely get an 100% duplicate. I don't know if there are similar projects with PC Booters.

[Trixter]

... if you life is entirely about Atari 800 series. Per who started this thread seems more into vintage IBM PCs, and wanted to know that the files in a disk image are not tampered with.

In the C64 community, there has been an ongoing preservation project for a number of years now, where disk images (perhaps also tapes?) are duplicated at a very low level so you get the exact same bit patterns as the original disk. Many times some copy protections have to be bypassed to safely get an 100% duplicate. I don't know if there are similar projects with PC Booters.

Retrograde Station is that project for PC Booters.