Here are some capacities for you:
You can look at the surface of the blank disk for the designation of which type of disk it is (CD-R, DVD+R, etc.)
DVD capacity Disk Type Data sectors
(2,048 B each)
Capacity bytes GB DVD-R (SL) 2,298,496 4,707,319,808 4.7 DVD+R (SL) 2,295,104 4,700,372,992 4.7 DVD-R DL 4,171,712 8,543,666,176 8.5 DVD+R DL 4,173,824 8,547,991,552 8.5 SL / DL – Single/Dual layer
CD-R, CD-RW Capacities: 700 MB
How much data can you fit on a Blu-ray disc?
A single-layer disc can hold 25GB.
A dual-layer disc can hold 50GB.
I pulled these off Google for you.
Hope this helps
Message was edited by: Radiation Mac
Thanks for the help guys.
Radiation Mac: Thanks for the info, but I already knew the capabilities of the different discs - the problem was that the discs themselves have nothing on the top of them but my company logo, so no indication of whether they're CDs, DVDs or BluRays (useful I know...)
Dashford: Thanks for this! I can select the Superdrive in the left pane, but it didn't give me any info in the bottom right. I had to go into 'Open System Information' and it had the disc type there under 'Media'.
I played with this a little in my Snow Leopard system, using both a blank CD-R disc, and also a CD-R disk that I had burned as a data CD using Finder.
I think what is happening is that when a burned CD is placed in the optical drive, it has already been formatted such that the system recognizes it as a "volume" and mounts it onto the file system the same way that it would mount a regular disk partition. Finder and Disk Utility can read the information on this mounted volume and report its capacity, free space, etc, the same way that an external disk drive would be reported. Although the icon of a burned CD appears on the Desktop, this icon does not represent a physical object in your Home/Desktop folder, but rather represents a mounted object with its "mount point" in the hidden /Volumes folder. If you Get Info on it with Finder, it will be of kind:Volume:
By contrast, when you insert an unburned, blank CD, it has not yet been formatted and cannot be mounted in the file system. You can see an icon on the Desktop that looks like a CD volume:
However if you show all file extensions, you can see that the icon carries the extension ".fpbf" and is actually a "burn folder," not a mounted volume:
Such a "burn folder" is a real folder that gets created in Home/Desktop. Like any "folder", it does not have a "capacity":
So basically, Finder and Disk Utility can give volume information for burned optical media that has been formatted and mounted, but not for blank media.