Bought a 4 Gb stick for DC7900 SFF. The BIOS does not see. But BIOS so limited this not too surprising. A Dell saw it in extended info but not Memory Count. But Windows 7 did not see it either unlike the Dell. Ran CPU-Z which did see it. This leaves me with only 3 Gb of Ram. I will get a second stick soon. The stick is new manf. date wk 9/14
Kingston 4Gb PC2-6400 99P5471-013.A00LF is the Part number.
BIOS only counts to 3 GB. Task manager only sees 3 Gb. Three 1 Gb sticks also installed. Position does not seem to matter except in the black slot where a warning message is no memory installed is given.
1.26 BIOS flashed did not matter though it did fix the sound on the PC to work with the HDMI sound. Did not see a newer BIOS.
Attached CPU-Z report.