Ports

Picture 4 IS a serial port. The DB9 connector is typical of a 9 pin serial connection. While VGA is the same 'size' it's a HDDB15 - a high density DB15 connector.

The serial connector is for configuration before you have the network set up and is pretty common with network based devices - ala NAS, Routers, Switches, etc.

Personally, I think that it's either an ethernet controller or part of the Northbridge chipset (although I think that's whats under the green heatsink). I believe that on the 520, gigabit ethernet was standard and dual gigabit nics were an option, and I quote:

"Optional dual hot-swappable power supplies, hot-swappable SATA II drives, and dual gigabit Ethernet ports with Ethernet teaming for load balancing and port failover".

4ram slots and only one used by default. In the slot being used we have a (512MB PC3200 DDR SDRAM 400Mhz ECC Registered Low Profile) stick. So keep that in mind if you chose to add more RAM to the system.

We found the need to add more RAM after connection limits and server lockups from users running PST off the NAS.