Memorex Disk Capacity On Mac


I have recently bought a pack of Memorex CD-R disks, which advertise 70 minutes and 700 megabytes of storage, but I am unable to get more than 600 mb on them while using my new Mac G4. Memorex has responded to my query with some questions, one of which is, are there any known or documented capacity isssues on this system (OSX Tiger 10.4.1). Haven't been able to get any information on this, and I wondered is anybody out there has had the same problem. Thanks.

PS: An idea just occurred to me; I will burn one on my Windows machine, and see how much it will hold.