GM release for IBM PowerPC

[needee]

1a, SLES 10 SP2 is available for IBM PowerPC as
"SLES-10-SP2-DVD-ppc-GM-DVD1.iso"
url for SLES-10-SP2-DVD-ppc-GM:
NOVELL: Downloads

1b, SLES 10 SP1 is available for IBM PowerPC as
SLES-10-SP1-ppc-DVD1.iso
url for SLES-10-SP1-ppc-DVD1.iso:
NOVELL: Downloads

here I want to know the difference b/w GM and the non-GM releases. SLES 10 SP2 for PowerPC is available as GM(...ppc-GM-DVD1.iso), but SLES 10 SP1 is available as non-GM(...ppc-DVD1.iso) i.e just plain iso image.

2a, Likewise iso images of SUSE Linux Enterprise Server 9 SP4 for IBM PowerPC are available as
SLES-9-SP4-CD-ppc-GM-CD1.iso

url for SLES-9-SP4-CD-ppc-GM
NOVELL: Downloads

2b, while iso images of SUSE LINUX Enterprise Server 9 Service Pack 2 for IBM PowerPC are available as
SLES-9-SP-2-ppc-RC4-CD1.iso

url for SLES-9-SP-2-ppc:
NOVELL: Downloads

here I want to know the difference b/w GM and the non-GM(in this case RC4) releases.
whats just plain iso image ?
whats GM ? whats the technical meaning of GM
whats RC ? whats the technical meaning of RC