Why does copy to the destination external hard drive is easy, less problems and faster than copy to a DVD disc? Is the copy procedure same or different?
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Why copy to the external hard dive has fewer problems/erors than to the disc? Does anyone know it?
Copying the data to an external drive just makes a 1:1 copy. The problems you may have with external hard drives would usually be interface problems. Sometimes USB gets interference from the operating system during long data transfers, which could corrupt the data. This is uncommon, though.
Copying to a disc depends more on the quality of the disc and to a lesser amount, the quality of the burner and the software used. Also the playback device. (Usually a set top player.)
If you are just copying as data to disc, it should still be a 1:1 copy and unless you use crap discs, should be fine. If you are authoring or changing the file to burn to disc, then the software may be a issue. But that doesn't usually change the video quality. A cheap or poor quality disc is more likely to have skips or dropouts in the video, especially near the end of the disc. (The outer edge).
If this is what you are asking.
You provided helpful info. Why can the external drive do 1:1 copy but drive/burner canít? In addition, how the quality of the burner affect the copy assuming the source, DVD disc and software are flawless?
DVD Burner can do 1:1 copy, but most DVD are double layer type, so if you want to make 1:1 copy, you need dual layer burner and disc, also good software which will burn the disc correct way.
Now here comes the problem:
1) Not all double layer disc are of good quality to be burned without problem.
2) Not all DVD burners have a good firmware to recognize and burn all DVD/DL brands correctly.
3) Not all software will do a good job either.
To make copy to HD, it will copy data to any free space on HD.
To make a copy to DVD, there has to be steady stream of data because data is burned in continuous track not in random packets. Any buffer under run,(interruption in data stream) will result in a bad disc.
The DVD can be a perfect 1:1 copy on the disc, if everything works properly. This includes the burning program, the burner and the DVD media. Most times there is no problem. But with crappy media you could end up with corrupted data on the disc. Rare, but possible.
With the DVD burner, the problems would more likely be the wrong firmware for the media you are using or a failing burner. If you have a newer burner and newer media, not too likely.
I believe a external hard drive, or an internal one, uses on-the-fly error checking, but with DVD media, you use a 'verify' to check the data after a burn. And I have had 'verify' fail, though the disc works perfectly. This is more common with video files as a bit of missing or corrupted data isn't noticed most times on playback.
Even a external HDD with a USB connection can have problems transferring data if the OS decides to use the USB port or a program interferes with the transfer. Some antivirus programs may scan the data as it's transfered. This usually just results in slower transfers, but no data loss. Or another USB devices may try to use the same port at the same time. Worst case is the 'delayed write failure' where the OS loses contact with the USB device.
I prefer to use a eSATA external drive as the transfers are faster and less prone to USB problems. FireWire also works better than USB for large files.
Hopefully, I have all that mostly correct as I don't have any sources readily available to back it all up.