The difference between the 970 and 990FX chipsets is the PCI Express slot functions (Multi-Graphics Technology). The Wiki encyclopedia has a chart which details the differences.http://en.wikipedia.org/wiki/Comparison_of_AMD_chipsets
The 990FX board also has:
2 x Marvell 88SE9172 chips:
1. 2 x eSATA 6Gb/s connectors on the back panel supporting up to 2 SATA 6Gb/s devices
2. Support for RAID 0 and RAID 1
The onboard sound chip is different. The 990FX board has support for Dolby Home Theater.