I have a couple of DOS game backups from a few years ago from a user called ibmpc5150. The backups are in .scp and .psi extensions. Are these considered good forms of disk backups for DOS software? Can these be linked/contributed?

SCP is a stream format, PSI is a "hybrid" format. You can find details in Moebius' old FAQ. Are these "good" formats? That's like asking which religion is the best Or, more seriously, it rather depends what you're trying to achieve, as there are (among other things) trade-offs between direct usability versus "perfect" preservation to be considered (to name just two of many dimensions).

On this site, we stopped archiving floppy images years ago. The only thing I can offer is to drop it to the Unprocessed Images folder and make them available. Though not sure how many people follow that.

I see what you mean, yeah. I guess, what I'm hoping is, if those formats are considered "accurate" in preserving the data on the DOS disks. Structure, whole content, etc.

I think an analogy would be like with dumping CDs. Unlike DVDs and newer including Blu-Ray, dumping a CD in .ISO format is unacceptable because that misses a significant amount of data from the disc. More accepted are the .bin; has to do with how DVDs can be completely imaged as ISO due to their 2048 bytes/sector structure (Mode 1). Meanwhile, the CDs are 2352 bytes/sector (Mode 2), and the .bin format of backup is much more appropriate for them. Both iso and bin files do reflect the layout/placement of files and other data on the disc, so they can just be fired up in an emulator.

So in a similar vein, do scp and psi capture all (or at least pretty close0 the data, and retain the same file structure/layout on the original disk? And with the tradeoff between usability and preservation accuracy, where do those 2 fall? If it's all on the same level as other imaging formats (like img, dsk, etc), yeah it does come down to opinion/priority rather than preservation quality. I hope that makes sense.

Thanks!

I can't say I really share what you say about optical media preservation. But anyway, the thing is this.

SCP is completely useless as is. You can write it back to real floppies, but only using dedicated hardware and specific bundled software. There are awkward ways to convert those files into something usable in emulators.

PSI is actually one of these converted formats. There are, as far as I know, only two obscure emulators which can use those.

I'm unable to judge the accuracy of both formats. The advantage of those (and similar), in general, is that they can be used to archive disks with on-disk copy protection.

I see what you mean. So would you say it would be better if the disks can be backed up in other formats, as far as usability and accessibility? I see .img and .dsk (I think dsk) almost always. They're more directly usable in emulators, too. Only in one case have I seen the scp + psi format, done by the aforementioned user.

Well, you're asking for my personal opinion. I would always go for the least complex format necessary to preserve. Is it a regular disk? I see no compelling reason to use anything but basic raw images ("IMG"). Is it a strange format, possibly features on-disk copy protection? Then go for a format which can handle this. But handle with care, don't jump to ultra-complex formats just because you can.

In those stream formats, what you also need to keep in mind is that essentially, no two disks will be identical, even if coming from the same production run. There will always be differences in the stream, due to differences in handling since production. These formats preserve many details of the disk which are not actually relevant differences. It makes it very hard to identify whether something is actually a different version of the same software or whether they are actually identical disks of which one has just spent more time in the sun.

Any format which is not openly documented, tied to one piece of proprietary software? Clearly out, that doesn't fulfil the basic objectives of preservation.

Sounds clear to me! Yeah I don't think this is particularly a complex software. AFAIK, it does have some sort of protection involving the disk, but I don't know the specifics. I'm pretty sure it could easily be imaged with the tools into the format of .img

I'm not big on the stream format now that you describe how it is.

FTR, these are the games Jackal and Contra. I'm more concerned about the latter and it seems there is yet to be a .img backup available of it. I will see what I can do for that.

Thanks for your insight!

EDIT: I found a listing on ebay. Not cheap and it's a risk, but I'm willing to bite. Do you or anyone you know backup floppy disks? I can pay for it to be sent for imaging.

BTW, do you know how I can reach moebius? Seems he kind of drifted away...

Sorry, I cannot help on either point. Moebius announced his own preservation project when he left, but that has disappeared from the Internet quite some time ago. I occasionally saw him visiting here still, but not sure whether he still does.

That's unfortunate. Hopefully someone has the equipment to be able to dump the disk to bootable image some day.

I would recommend the HxC project and use the software to convert unprotected images back into raw images that can be easily opened. I just used it on a random SCP stream file I had and it saved it as an IMG just fine.

https://hxc2001.com/download/floppy_drive_emulator/