Under The Covers
Figure 14: The DSM-520 with the cover off
As you can see in Figure 14, D-Link didn't really need all that space inside the DSM-520's enclosure. They apparently just wanted the device to fit nicely in an entertainment center. Figure 15 is a close up of the DSM-520 motherboard.
Figure 15: The motherboard (click for full-resolution image).
You can see that the main CPU is a Sigma Designs EM8620l, which has an ARM core and does all the A/V heavy lifting as well. I couldn't find any specific information on it, but an ALPHA Networks WMP-G09 mini-pci card provides the wireless capabilities. A RealTek RTL8100BL provides the wired network support.
I'm always interested in what operating system these boxes run. With this one, it wasn't easy to figure out. The DSM-520 automatically downloads firmware revisions from D-Link so there wasn't a firmware file to dissect. A network port-scan of the box turned up only a few open ports used for the UPnP subsystem. I did get one of the ports to tell me who did the UPnP implementation on the box. The internal UPnP subsystem was evidently supplied by Redsonic. A network fingerprint scan identified the operating system as: "Linux 2.4.X|2.5.X," so the internal operating is most likely Linux-based, but a fingerprint scan can be misinterpreted.