Came across an old CD-RW Phillips disc which has a rewrite speed of 4 to 12x. Shows on label the usual 700MB. I know I tried it out in 2005 as it showed the date when W7 finally saw something on the disc via 'computer' as I waited for the green bar on the top to load. So far so good.
Opening it was a no go. So W7 gave me two options;

A, Format like usb flash drive (576MB) so you can burn files on or erase off.

B, use for CD/DVD players but files can't be edited or removed after burning.

Did the 'like usb flash drive' bit and successfully burnt some zip files.

Then erased the disc and while erasing the disc the optical drive actually showed 700 MB in 'Computer'.

So to use an old CD-RW disk I lose 124 MB of storage.
I suppose the next step is to format to the 'B' option and lose the re-write option?