When is a sector dump good enough?

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VonOben
Posts: 10
Joined: Fri Mar 18, 2016 12:14 am

When is a sector dump good enough?

Post by VonOben »

Hi. This must have been covered on this site in the past, possibly many times... but for some reason I can't find thoses threads. Could be the beers fault.

Would you consider a sector dump good enough if you had some nice gems to share, but not large amounts of stuff? What would be the crossing point to investing in a KryoFlux for you?

I have a (yet untested) release of Interactive Unix to share, and in my profession there will turn up some nice things now and then. But not very offten.

JustZisGuy
Posts: 271
Joined: Wed Dec 11, 2013 3:24 am

Re: When is a sector dump good enough?

Post by JustZisGuy »

Typically, an img/WinImage sector dump is "good enough" if the disk is in a standard DOS 360k, 720k, 1.2mb, 1.44mb, or DMF format and contains no copy protection.

For odd formats such as CP/M or DOS 1.x 160K/320k disks, ImageDisk format dumps may also be needed. But that still can be done with a DOS based PC.

However, the moment you cross in to copy protected territory, a Kryoflux or SCP becomes a must-have. Dumps from software tools like CopyIIPC are great, but you always risk missing something.

That said, Kryoflux (or SuperCard Pro) images do provide some additional information that is not present in a sector dump. Notably it is often possible to determine if a user wrote back to an original disk, and it may include duplicator mastering information sometimes found on the last track+1. They can also dump GCR encoded disks (Mac 400/800k, Apple II, C64) that a PC won't touch.

If you are mass-dumping disks, it can be handy to help ensure you don't accidentally miss something that actually is copy protected. But even with all that you still risk certain kinds of format mismatch such as dumping a high-density 5.25 disk as low-density, unmarked "flippy" disks, or a 100tpi disk in a 96tpi drive.

So the key is that you must be 100% sure of what you are dumping.

VonOben
Posts: 10
Joined: Fri Mar 18, 2016 12:14 am

Re: When is a sector dump good enough?

Post by VonOben »

So it mostly comes down to knowing what you're dealing with floppy-wize. I can't say I will always know that.

My VHS-preservation experiences have learned me that - if possible - do the transfer on the first go. Magnetic material will come loose due to some manufactures using inferior binding material during the early 80's. That will lead to drop-outs the second time playing the tape, and become even worse the third time etc. (Such tapes can be 'baked' to avoid some of the problem.)

That kind of precautions perhaps isn't as important when dealing with ancient floppys? Still, the read head is in fact touching the surface.

If the first-go approach isn't as important, then perhaps the best available dump technique isn't necessary a must that first-go.

VonOben
Posts: 10
Joined: Fri Mar 18, 2016 12:14 am

Re: When is a sector dump good enough?

Post by VonOben »

JustZisGuy wrote:Typically, an img/WinImage sector dump is "good enough" if the disk is in a standard DOS 360k, 720k, 1.2mb, 1.44mb, or DMF format and contains no copy protection.

For odd formats such as CP/M or DOS 1.x 160K/320k disks, ImageDisk format dumps may also be needed. But that still can be done with a DOS based PC.
Would you say that an ImageDisk-dump would be a better bet for the Interactive Unix disk set I mentioned, than a WinImage-dump?

I'll try to google them, to see if I can find anything about the inner workings.

JustZisGuy
Posts: 271
Joined: Wed Dec 11, 2013 3:24 am

Re: When is a sector dump good enough?

Post by JustZisGuy »

Unix install disks will typically have a boot disk with a Unix variant file system, and the remainder of the disks in file system-less tape archive format.

Either way, WinImage usually won't touch those because they are non-DOS. ImageDisk should work perfectly.

One of the advantages of using a Kryoflux or SCP is that you can dump a disk as a raw flux stream, and assuming there was no media-mismatch problem, you can go back and analyze the dump later. This even lets you dump really oddball disks for which no high-level decoding software may yet exist. In some cases this can be helpful for data recovery as it will save everything in one pass, and erroneous tracks can be analyzed and re-dumped individually.

Floppy disks can shed magnetic media if they were poorly stored, or if they were very low quality brands (especially Wabash). The better brands such as 3M or Dysan will usually still hold together but may suffer from dirt/residue/mold or other junk inside the disk jacket that can rip things up.

Professional data recovery experts also use a "baking" method where they remove the disk "cookie" from the jacket and bake the cookies. (Yummy!) But for collectible 5.25" and 8" disks, I have found that carefully washing them with hot water is sufficient to remove junk from within the jackets and reduce the chances it will shred itself, without destroying the jackets. That doesn't work so well for 3.5" disks as they won't dry easily.

VonOben
Posts: 10
Joined: Fri Mar 18, 2016 12:14 am

Re: When is a sector dump good enough?

Post by VonOben »

JustZisGuy wrote:Unix install disks will typically have a boot disk with a Unix variant file system, and the remainder of the disks in file system-less tape archive format.

Either way, WinImage usually won't touch those because they are non-DOS. ImageDisk should work perfectly.
I see. I thought WinImage more or less did a straight dd-image. Apparently it doesn't, then. It needs to understand the data.

Thank you.

VonOben
Posts: 10
Joined: Fri Mar 18, 2016 12:14 am

Re: When is a sector dump good enough?

Post by VonOben »

Nope, WinImage couldn't read the Unix-floppys. And ImageDisk doesn't play well with the floppy drive I had in mind for it. (An IBM Thinkpad from 1998.) I guess I'll have to find some other computer for this rip.

Edit: Currently thinking about if dd - or perhaps even better... ddrecue - from *nix/BSD could do this as good as DiskImage.

VonOben
Posts: 10
Joined: Fri Mar 18, 2016 12:14 am

Re: When is a sector dump good enough?

Post by VonOben »

I'm slowling getting around to this floppy-set once again, but this time armed with a Greaseweazle. Could be fun.

It's been so long since I used the ftp-server that things seems to have changed. I need to read up on that.

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