Components for Building Computers From Scratch/optical drive

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Question
I wanted to know with internal DVD and Blu Ray drives for computers, what is the speed dependent on for which stuff is backed up to the hard drive.  I have backed up DVD movies before from discs for which I own (since our kids tend to scratch the originals), and I've always wonder how the system determines the speed to "rip" or backup the disc.  Is it dependent on the read speed of the drive, like say 12x, 14x read speeds, or is it based on the connection in the computer, like SATA, or IDE, or is it based on the "ripping" or backup program used?  Sometimes it seems like it varies, with some backups taking 10 minutes, and others, taking much much longer.  I'm not sure if compression has anything to do with it or not.  I see advertised read speeds on drive, which seem fast, and I thought it was all based on this.

I am considering down the road getting a Blu Ray drive for this purpose as we get more Blu Ray discs, but if speed will vary, I couldn't imagine how long it may take to back up one Blu Ray disc.  Maybe the best thing in that case would be to let not the kids touch those discs at all, ever.

Thanks for any help and advice you may have.

Answer
It's a variety of factors - as you've alluded to. Conventionally (for CD-ROM, DVD-ROM, etc), the drive varies the rotational speed of the disc relative to where the read-head is located in the data track (which is different from how a phonograph works, where the disc spins at a constant rate). This is known as constant-linear velocity playback. The drive's goal in this scenario is that the read-head sees the same data-rate regardless of the increasing circumference of the disc. This is how a conventional DVD or CD player will access the data (and it maintains the same data-rate throughout playback of the disc). This is accomplished by decelerating the disc as the read-head moves outward.

However a computer-based drive may also employ constant-angular velocity, whereby the speed of the disc is held constant (as in a phonograph), and as the read head moves further away from the center of the disc, you will see the data-rate increase (because the read head is "seeing" a higher velocity). This allows such drives to achieve higher theoretical maximum transfer rates, however their average read speed is often lower than the stated numbers on the packaging (because the disc must spin up, and the read-head still has to track outwards). The software accessing the data can also contribute to this performance as well, especially if it's asking the media for random access (e.g. it wants data from different places on the disc surface, instead of wanting all of the data in one linear stream). The speed is both influenced by the ability of the receiving software to perform whatever calculations on the data, as well as (in the case of random access) the time it takes for the read head to seek to the requested sections of the disc (and for optical drives, this is generally a relatively large period of time, compared to a hard-drive or system memory). In general if the receiving software is doing relatively complex processing (like re-encoding the data) you should expect some slow-down; a faster CPU will improve this performance.

Also do keep in mind that the speed-ratings for different types of media are not equivalent; 1x CD-ROM is equivalent to 150 KB/s, while 1x DVD-ROM is 1.32MB/s, and 1x Blu-ray is 4.5MB/s. Put another way, 36x CD-ROM is equivalent to 4x DVD-ROM, which is roughly equivalent to 1x Blu-ray (36x CD-ROM is 5.27MB/s, 4x DVD-ROM is 5.2MB/s, and 1x Blu-ray is 4.5MB/s). The reason for these differences is primarily due to the density of the media - a Blu-ray is the same physical size as a CD-ROM, yet holds substantially more data. Higher density leads to generally higher transfer rates.

Ripping and encoding Blu-ray will be substantially more demanding on the machine than DVD, just as DVD is more demanding than CD - the computer has to deal with a much larger and more protected data-stream and produce an output file from it. While CD ripping is generally capable of running at faster-than-real-time speeds (that is, audio CD playback operates at 1x, and generally CDs can be ripped at 10-20x), and DVD ripping (with a modern computer) can generally be ripped at real-time or faster-than-real-time speeds, Blu-ray will more than likely run slower than real-time due to the encoding demands of HD video and HD audio (especially if you're having the encoder package compress the audio or video to save space; keep in mind that Blu-ray contains substantially more data than a DVD or CD (and will accordingly need more storage)).

On the upside, Blu-ray discs are physically treated with an anti-scratch material (it's part of the standard), unlike CD, DVD, and HD-DVD; they are designed to be more physically resilient. It should also be noted that many Blu-ray releases are now including a digital copy of the movie, often offered through a service like Hulu or UltraViolet, which may save you the hassle of ripping the discs yourself. Some retailers may also include a digital copy of DVD releases (Amazon does this with many titles).


Regarding the drive's interface to the system - this is generally a non-issue. SATA and PATA are both capable of substantially higher transfer rates than most hard-drives can deliver (which is what their specifications are primarily designed and improved in response to), let alone what an optical drive can deliver. PATA on a modern system is capable of 133MB/s, while the fastest theoretical Blu-ray transfer (16x) will only achieve 72MB/s. SATA has eclipsed PATA, and starts at 150MB/s (with more contemporary revisions seeing up to 600MB/s). It should be noted (and this is more theoretical than real-world (because again, ignoring that 16x BD drives are somewhat uncommon, that would be a maximum peak speed)) that most conventional hard-drives would have trouble keeping pace with a 72MB/s data stream (>70MB/s write speeds are exceptional for a hard-drive). Dealing with DVD or CD however, even a 24x DVD drive should be no trouble for a modern hard-disk (the peak theoretical throughput is just over 33MB/s).


If you have further questions, feel free to ask.

-bob  

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Bobbert

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I have nearly two decades of experience in IT, computer repair, and related fields and will attempt to provide the most solid, brand-agnostic advice when it comes time to purchase a new computer, or upgrade an existing machine. I can answer anything from the seemingly basic to the downright complicated - and will do my best to provide this information in a clear and concise manner.

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I have been an enthusiast of PC's for many years, and can answer questions about the purchase/use of a new computer or the purchase, installation, and use of upgrades for existing computers. There probably isn't a whole lot related to the home computer that I haven't seen over the years.

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