How Many CDs Can You Burn at Once?

kfs27 asks: "In an attempt to help a professor of mine record and duplicate his lectures. I have been asked to put together a CD duplicating box. Commercial products seem to be very expensive and I figured a PC with some SCSI160 Cards (HW or SW Raid maybe), SCSI Burners and a 15K RPM drive (size not an issue) could do the job for cheaper. But the question is, how many CDs can you burn at once of 30 minutes, mono audio. 10 at a time would be excellent I think. More of course better. Cost is not a huge issue, as long as it's less than Commercial Duplicators, it's more of an experiment, but must be stable and easy to operate (I'd be willing to script up a frontend)."

Comments

PCI bus is your bottleneck...

[stienman]

The only bottleneck you have then is your PCI bus.

You'll probably be fine with the 10 drives and one HD as long as:
1) You use a ramdisk
2) You make sure each burner has at least 2MB of buffer

With the 2MB buffer, fast scsi, ram disk and DMA you should run into no problems even with 24 or 32 speed burners. You'd be better off, of course, with a faster/wider PCI bus.

Integrate a robotic loading/unloading system, and 24x drives - you'll get 10 cds every two minutes. Your class of fifty can get their CD on the way out the door. It may be more cost effective to get twice as many drives that run at half the speed.

-Adam

Re:PCI bus is your bottleneck...

[hamjudo]

Don't make this too hard. The PCI bus on a cheap motherboard is 32bits at 33Mhz, or a peak bandwidth of 132Mbytes/second. A 1X CD-ROM is 44.1Khz * 2 channels * 16 bits (2 bytes) or 176Kbytes/second. If the PCI bus were perfect, it could drive a single 748X CD writer, or ten 74X CDWriters. It's not perfect, but you'll easily get more than half of the max bandwidth (assuming modern PCI cards). Since 32X is the fastest CDwriter available today, you can easily drive 10 of them with quite a margin.

If they're new CDwriters, they'll have protection against making coasters, so the penalty for running too many CDwriters, is they'll slow down.

If you're good with metal working tools, you can make a double wide case that can hold 10 drives. Plug a bunch of IDE controller cards into the PCI bus. Note: IDE cables are limited to 18 inches. So you have to do a little design work, before you start cutting metal.

If you're not into metal working, just take a few cheap PC's, max them out with CDwriters and network them with 100base-T ethernet cards. A little glue, and it will be like one big machine. This design can be expanded to hundreds of drives.

I'm assuming student labor, so you won't need a robot disk changer.

Let the students burn...

[martyb]

Let the students burn the CDs themselves. Just set up a server (ala napster), tell the students to download the lectures. Then, if the students actually want to burn them to CD, they're free to do so (set upa FAQ, if need be).

Why CDs?

[Jerf]

Why CDs? 30 minutes of mono audio, encoded in 32Kb/s MP3, is (30 * 60 * 32 / 8) = 7200 KB (with the last "/ 8" to get us to kiloBYTES instead of kiloBITS). There are MUCH better codecs then MP3 for this at this bitrate, I just use MP3 as a convenient and easily obtained example. Record the lecture, convert to (lossily-compressed-audio-format-of-your-choice), and load it on the web.

At the end of the semester, give each student ONE CD with the entire course on it!

Nowadays, if your student can use a CD, they can play an MP3. And even a 7MB download is doable over a modem connection. (And you might cut that down to perhaps 1 or 2 MB or less by using a codec designed to do voice-only, but you'll probably have to pay for it.)

Alternatives to what you want.

[Linuxathome]

Are you just burning audio or are you also including powerpoint slides or images? I'm also a student, and the lectures we have (1 hour lectures at a time) are recorded as wav files and then encoded as mp3 files at a 16K bitrate (trust me, I've listened to them and they work fine for lecture audio) and at that bitrate, the techs managed to squeeze 1 hour in 5 MB's (well, they also squeezed the sample rate down during recording too). That's the size of a regular music track at 192K bitrate, 44.1KHz samplerate--in other words, just the perfect size to publish online and download. Add less than 1 MB for the powerpoint file and you have enough info for most of the students to skip class and just listen to audio while flipping through the slides at home. Let me emphasize again that this is already implemented at my medical school and lots of students skip class due to this feature. ;-)

Ok, my question is: why spend the money on CD duplicators? I think it's more worthwhile to spend it on a computer station with all necessary drives for all available media that the students use. You can even turn it into a webserver if it has fast internet access. That way, all the lectures will be on this station and the students would only need to go to it and pop in their zip disk, jaz disk, cd-r or even better, a cd-rw, and then be able to copy what lectures they want. So, I think rather than spend your time trying to build the cd-duplicator, spend your time on writing the software/program that is running on the station that will allow the student to easily choose what they want and then instantly hit the "Burn" or "Copy" button and copy it to their media. In my view, this station is a much better use of your time.

Actually, if you wanted to make it a truly killer app, then instead of copying the mp3's and the powerpoint files separately, have them integrated with, say, a macromedia program that the students can run independently (without the need of either a mp3 player or even powerpoint) and it'll automatically play the audio and show the slides cued to the audio (no need for the students to guess which slide the prof is on).

But then again, I could be totally offtopic and your reasons behind building this cd-copying system far outweighs my suggestion. Anyway, these are just my thoughts.