This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
In April 2003, a few companies began announcing technologies that allow you
to store larger quantities of data on standard CD-R media. Unlike DD-R
and "ML" technology, special discs aren't required. The capacity and
compatibility is different for each.
Increases storage capacity by 40%, allowing up to 1GB on a 700MB disc.
The discs can be read on some unmodified CD-ROM drives.
Doubles disc capacity of an 80-minute disc from 700MB to 1.4GB. A
firmware change is required before a drive can read the discs.
Support for extended-length CD-RW media is planned.
Does it make sense to use these? The extra capacity is handy, but data
is only useful if you're able to read it. Check the compatibility of the
hardware you're going to use to read the discs.