We have built and sold hundreds of DW pc's and we have our own PC's built for us to our specifications in house. We always use SSD Drives for the Windows OS, but if you are savvy you can use Linux too, key here is a SSD drive for processing the video as we have found that with large systmes using spinning drives for the os cna miss video processing. Next we use Western Digital Purple Hard drives for our recording storage as well as in any NAS if we build them. We also use 2 network cards or dual port network cards to isolate the customers network from our own camera network. 8gb or 16gb of ram works great but feel free to go more if you like.
We use i5 processors for our smaller camera jobs approx 10 or less cameras and i7 for larger systems and DW can setup fail-over redundant server which we use on systems over 20-30 cameras or more. This allows us to balance the camera load and then if one pc should need to reboot or fail the other will carry the load within about 3-5 seconds.
The client software works in Linux, Windows & Mac, and the app works in IOS & Droid.
DW is great, and as mentioned the software is actually made by NX Optix or NX Witness software, but in the US you must purchase license & use DW Spectrum software through DW or now Samsung has their version for more money.
NX Optix has a great website for questions and specs and info as needed the DW & NX sales guys & tech support are all great to work with and the DW Spectrum software just continues to get better and better with each new release. The licenses are good for life and can be moved from pc to pc.
Our clients all love their systems and we remotely support them by installing a commercial license of TeamViewer so we can remotely manage any needs that arise thus saving a truck roll. We also strongly suggest managed network switches so you can reboot cameras as needed.
Lastly, the DW cloud is awesome and works thru almost all firewalls and allows the end user to view the cameras and manage users via the cloud without having to port forward any ports.