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

Well at a glance..

[jonistron]

[(max bandwidth to drive)*(n disks)]/[(max bandwidth cd-r drive)*(n cdr's)] > 1

Umm, depends.

[polymath69]

Factors are going to include the speed of the drives holding the .iso images, the number of CD burners per SCSI bus, and the speed that you are trying to burn the disks at (eg. 4x). The idea of using a RAM disk to eliminate the hard drive variable has some merit, but unless you've got a gig of RAM or so, you'll only be able to burn one image at a time onto those multiple disks.

But here's an unrelated thought. You say these CDs are to contain 30 minute mono lectures. A CD will hold 60 minutes easily. Why not put two lectures per CD and save on your overhead in loading and unloading the disks?

You could take it even further by recording one lecture in the left audio channel, and another in the right, to fit four lectures per disk. It might be worth considering.

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.)

Re:Why CDs?

[Jerf]

"and load it on the web." The CD at the end of the course is a bonus. The rest of my point concerns getting the file size down to the point where this is feasible, even for modem users.

The fact that creating all of these CDs is difficult suggests that a different approach is probably called for; no matter HOW little is spent on this duplication scheme, the money is probably better spent elsewhere. Work smarter, not harder.

Don't mean to be a contrarian but...

[Anonymous Coward]

Why does he need to burn his lectures for mass distribution? If it's some sort of ego thing then it would be easier to post the lectures on a server and let the students decide if it's worth the bandwidth.

Re:RAM Disk, not Hard Drives

[joshsisk]

http://www.everything2.com/ I find their system far from perfect in other respects, but once you get used to the idea, I think the editable comments system is far superior.

Everything2 isn't a discussion/news site, though. It's more like a non-strictly-factual dictionary or encyclopedia. (I also find the site to be pretty useless, but that's another story.)

Whats the point of having a reply if it doesn't address points covered in the parent?

The point is to stop someone else from spreading untrue crap. Whether it's through responding to them (and hoping your response gets read), or having them change their original comment, it still accomplishes that goal. It's quite likely the reply would get moderated down to -1, so no one would have to actually read it once it's accomplished its purpose.

And that's exactly what editable comments would result in - more untrue crap. How can allowing people to change what they said "keep people from spreading untrue crap"? If anything, altering the record of what was said, when, reduces the veracity of a thread, not increases it. One would imagine that if someone said something honestly, from their heart, they wouldn't HAVE to edit it, except for spelling errors. The people who will are ones trying to change the flow of discourse, or make others look badly/themselves look good.

It seems to me that if you make a statement, you should stand by it, or recant/correct it- NOT delete your original statement and all record of it, then replace it with something else. Which is what an editable comments system would allow for.

The bottom line is, in a threaded/nested view, it would just be frustrating to try and read something like that. I like reading the comments in close to chronological order, and if comments at the top were ACTUALLY more recent then what are ostensibly supposed to be responses to the top comments, it seems like it'd be headache inducing.

I can also see it encouraging people to "frist post" some nonsense, just so they can copy and paste from later, more popular posts. Their frist post is higher up, so it will get read more.

Now, if they TOTALLY changed the comments system, maybe. But wouldn't that be a totally different website? And this comment system works relatively well. I have no problems understanding it and finding info I want while filter out the garbage. If it was made to be really complicated, I don't think it would be that much better...

And really, I don't see how it's that hard to post a correction reply to one of your comments if you realize you made a mistake. Isn't that easier than devising some new comments system?

The only way this would work is if you got rid of the karma system (among other things), because it's too easy to use editable comments to artificially lower someone else's karma.

It also seems you have a lot of faith in users to change their comments if they are wrong. I think this is unlikely. I'd bet most people who comment don't even go back and read the responses to them (though the new message options may be changing this). I also doubt most users would change their comment if proved wrong. More likely, they'll just change there comments to make themselves look smarter/anyone responding to them look stupid.

I also feel there is value in a thread where:

1. I post a unfounded opinion.
2. You refute it.
3. I add an arguement to my opinion, perhaps with a fact.
4. You post more well-founded facts than my facts.
5. Someone else verifies those facts.
6. I either stop responding, or, in an ideal world, agree that I was wrong.

With editable comments, you'd end up with:

1. My edited, opinion with verified facts.
2. You refute an opinion which no longer appears in the parent.
3. I edit this comment to mention that's already stated in my first comment.
4. You post more well-founded facts than my facts, but they are now present in my parent comment.
5. Someone else verifies those facts, but this verification is now present in the parent comment.

That just seems confusing to me, and hard to read. What's the reason for having the responses beyond my edited comment, since I summed them up and claimed the other people's opinions as my own? You could just have them fall off, but then you open up an avenue for people to delete/hide actually good and useful comments.

You could say it doesn't matter, since all the salient points are inside the parent (even though the good points are not my own), BUT- part of a site like this is finding people who's opinion you trust. The karma system tries to do this, as does the friend/foe system. If people can change their comments, absorbing the best comments of others, it seems like you can no longer really tell who is insightful and trustworthy. The people who post earlier and can copy/paste well instead seem to have the best opinions... Which would then lead to the people who's opinions were usurped responding "hey you just stole that comment from me!" and so forth...

Again, this is what I would love about it. If someone presented a single coherent post incorporating all the others, I'd much rather read that then a 15 post reply chain arguing the point.

You seem to have a lot of faith in the userbase. In an ideal world everyone will act nice and simply try to present the facts in the best manner. But in reality, there are trolls. And trolls will try to find ways to use any system to annoy other people and make slashdot (or any site) hard to read and less fun for others.

And besides, isn't that what happens when posts are archived? The threading is removed and all the garbage posts are stripped out? Or when you view a post at +4/+5?

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.

multi CDRs

[anthares]

DiscJuggler - Unlimited Recorder Version Full version supporting up to 32 CD-R/RW drives. Based on this CDR software you can connect up to 32 CDRs. http://www.padus.com/downloads/full.php