Just played a quick session and on my Core i7 (overclocked to 3.4Ghz) D:OS uses 3 cores at 50% and a fourth at 10% so it does seem multicore capable. I'm also getting <600MB VRAM usage with all options set to max at 2560x1600 resolution and framerates in the 40s.
For those seeing single-core usage, I can only suggest checking affinity settings. Start D:OS, Alt-Tab to the Windows Desktop, fire up Task Manager, look for EoCApp.exe in the Processes tab, right click on it and selecct "Set Affinity" and make sure that all the CPU boxes are checked.
If only one CPU box is checked, then review the affinity settings for Explorer.exe - they'll probably be the same and try to find the cause of its settings (changing affinity settings will only apply while the process is running so would have to be done repeatedly). Creating a shortcut for D:OS (EoCApp.exe) using the instructions
here may suffice as a workaround in such a case.
