"Buffer" is the system RAM buffer... it's essentially where the program spools data into from the disc. If you lose disc synch (some other process needs it, some IO error occurs) then this buffer is used up while re-synching with the disc.
"Device Buffer" is the drive's hardware cache.
So essentially, what happens is this. Let's say that your device has 2MB of cache, and DVD Decrypter is using 64MB of RAM buffer.
The program reads 2MB from the disc. It puts that 2MB into the device cache. Then it reads ANOTHER 64MB from the disc, and puts it into RAM.
From then on out, it continuously does two things:
- Push data from RAM into the device cache.
- Pull data from the HDD into RAM.
The status of those two buffers is what you're seeing. Usually the device cache should stay at 99% all the time. If the device cache is fluctuating but the RAM buffer stays full, there's a problem with the device, like it's set to PIO instead of DMA, or has a bad cable or something.
On a properly setup system, you should see the device cache at 99% all the time, and the disc cache near that. If some other process hits the disk, the RAM cache might dip temporarily, and then fill back up. If you have some other process running continuously in the background, the RAM cache might stay stuck at 50% for example.
Only if the RAM cache hits 0% and stays there (some other process is using the disc heavily) should the device cache ever dip.
Does that help at all?
I concur that you need to just stick with media that works.