I have a DELL 5150c slimline PC ( like the current model C521) with a built in lap-top style vertical combo drive.
this works OK, but is not very tolerant of scratches on rentals , ( compared with my main DELL e520 desktop which has 2 "proper" drives.), and it's also much slower at reading entire DVDs onto the had drive ( again compared with the E520)
I'm pretty sure that the slow speed is due to the dell drive, not the pc's power, as it's a 3.0gb pentium 4.

Comparisons:
Dell E520 core duo 2.0gb , RAID 1 hard drive setup, twin dell DVD drives - copies a 7GB DL DVD to HD in about 20 mins
Dell 5150C P4 3.0gb, Dell combo drive - takes 40-60 minutes to do the same task and is much more likely to throw up read errors.

I use the 5150c for viewing movies as it is stashed behind the TV, & I usually place the movie onto HD beforehand as it's a tad awkward to get at the DVD drive.

So would I get faster speed & better reliablity from an external USB2 linked drive & if so could i have a recommendation please. I'm not fussed about burning speeds as I don't usually burn anything on this PC, but it does not seem possibel to buy a read-only external DVD drive. Or shoudl I look to upgrade the DELl drive, bearing in mind that it has to fit the SFF case ?

thinking about this some more, I guess there are 3 factors that govern the overall speed of copying a DVD to hard drive using DVDfab:
1. CPU power ( for decoding & converting)
2. DVD drive (read) transfer rate
3. Hard drive (write) transfer rate

but how does one determine which of the 3 is limiting the overall speed ?

First off wrong forum.

You be better off to get an internal drive and put it in a external enclosure. I'd recommend one of the new Pioneers or the classic BenQs (DW1620, DW1640, DW1650, DW1655).

I have moved it here to the Optical Drives Forum with a redirect in the other forum, so the OP can find his thread.

OK - I put in dvdfab forum because I was specifically wanting to understand what hardware factors limit DVDFAB platimum's copy from DVD to HD speed, but anywhere that leads to as response will do :-)

I don't want to buy a new DVD drive if the bottleneck is elsewhere on my DELL PC !