bjjones37 wrote:[quote="ijor ... They do can copy many disks that software copiers can't. But there are several problems associated with this type of copy....
OK, now you've done it. You went and got me curious. I used blitz for quite some time. While I only used it on programs I could not copy otherwise, I do not remember it causing any problems. What was your experience?
Disk analog copiers work very similarly as dubbing an audio tape. They just reproduce the signal from the source diskette into the destination one. The consequences of this are several:
- The copy won’t be aligned to the index hole. Using matching drives from the same manufacturer will help a bit. But both drives can never be synced well enough. So any protection that relies on some kind of index alignment will fail. This includes software that can easily be copied with a software copier.
- Any “soft” (recoverable) error will be reproduced on the destination and converted to a “hard” (unrecoverable) error. A soft error happens when you read a sector and get an error, but it reads ok after a retry. “Soft” errors are much more common than what people realize. You usually never note them because there is a lot of retry logic going on at different levels of the operating system.
Other type of copiers, both software and hardware, will retry on any error and will usually recover from soft errors. But an analog copier will not, it can’t because it has no way of detecting the error in the first place.
- No verification is performed. So errors produced when writing are not detected. Again, no verification is possible.
- No filtering, adjustment or precompensation is performed. Take in mind that we are taking about a mechanical device and a magnetical medium. The signal you read is not exactly what was originally recorded. Digital devices, such as the FDC or a hardware digital copier, perform a lot of filtering that here is not possible.
- Because no “digitalization” is performed, the signal is degraded further on each “generation” copy. After a small number of generations there is very little chance of getting a working copy. Third generation copies usually don’t work (a copy of a copy of a copy of an original).
With today’s electronics, it should be possible to make an analog copier that more or less overcomes some of the above limitations. But it wouldn’t make much sense when you can as easily make a digital device.
The digital hardware copiers I have some experience are (in order of preference):
- The Discovery Cartridge for the ST.
- The Catweasel for the PC.
- The Central Point Deluxe Option Board for the PC.