The Duo comes in a black metal enclosure that has high build quality and uses the same drive trays as the rest of the ReadyNAS lineup. The power supply has been moved outside the box to a largeish brick, however.
The processor is hidden under a heatsink, but since the Duo uses the same "RAIDiator" OS as the other ReadyNAS products, I suspect that it uses the same Infrant IT3107 Storage Processor. Due to the cabinet construction, I wasn't able to get a clear shot of the main board. But by peering between the vent slots, I was able to see a Via VT6212 4 Port USB 2.0 Host Controller and a Vitesse VSC8201 Single Port 10/100/1000BASE-T PHY.
The RAM complement didn't require much sleuthing, since the Unigen UG032D6686LM-GJF DDR400 256 MB SODIMM was clearly visible (and accessible) behind the removable left side cover. 64 MB of Hynix flash memory is also on the board.
The Duo is aimed primarily at home users but supports the same impressive assortment of network services as the quad-drive ReadyNASes. You get CIFS/SMB, NFS and AFP network file systems, HTTPS access (enabled by default), FTP for file transfer, Rsync for backup and both Bonjour and UPnP discovery services.
For media servers, there are SlimServer, iTunes, UPnP AV and a "Home Media Streaming Server", which will allow you to stream to just about anything you want. You also get a built-in "officially licensed" BitTorrent client and "ReadyNAS Photos" web photo sharing application. The last two apps are also available on other ReadyNASes when you upgrade to the latest version 4 firmware.
What you don't get with the Duo is support for Active Directory or NT Domains for user authentication. The Networking settings are also a bit simpler than those on the NV+ and 1100 and don't include VLAN support or DHCP and WINS servers. But you still get up to 8K jumbo frame support.
The other important limitation is that the automatic X-RAID mode can't be bypassed. So, unlike the NV+ and 1100, you don't have the option of changing to manual RAID configuration. This means that any second internal drive you add is used only for redundancy and can't be used to expand capacity.
Performance tops the 1000 Mbps RAID 1 average write NAS Charts at 16.8 MB/s for 32 MB to 1 GB file sizes, with the Duo essentially tied with the Synology DS207+. 1000 Mbps RAID 1 average read measured 21.6 MB/s, slightly behind the chart-topping Thecus N2100 and again, essentially tied with the Synology DS207+.
Note that performance with a single drive, which is shown in the 100 and 1000 Mbps non-RAID charts, was essentially the same as the RAID 1 performance. This is probably due to the fact that both modes were run under X-RAID, which appears to penalize throughput compared to other two-drive NASes running in JBOD.