D90D7 Windows 7 Usable memory

We are looking at a demo unit for the D90D7 which runs Windows 7. All settings should be the factory defaults out of the box. The unit has 4 GB RAM. In System Properties it displays 4 GB (2.35 GB usable). Task manager shows 2404 MB total physical memory. We want to understand where the other 1.6 GB of RAM is being used. 384 MB is allocated for video in the BIOS. There is a 100 MB RAM disk and 128 MB setup for FBWF. I’m not sure if that should take away from the total memory or just available memory. Either way we are still missing over 1 GB of RAM. Our account rep and pre-sales engineer says it’s normal, but I don’t want to pay for a 4 GB unit and only get just over 2 GB. Can anyone suggest where the missing RAM might be allocated?