For the grief and anguish getting this to work I really want to give a 3 or maybe a 4 star rating at best. But I have to admit to contributing to the problems I had myself. But the thing is, at the end of the day this box works as advertised. Make sure you read the scant literature that's available, twice or maybe even thrice. I looked and looked but I couldn't find the manual for this box on Startech's website. There was a manual for the 4 port KVM and that was for the all DVI port model. A simple cabling diagram for this exact box would have saved a lot of time and gnashing of teeth.The manual only covers the SV431DDVDUA in great detail, including features that are not available on the two port model.This unit, SV231DDVDUA is only mentioned in passing, no pictures, no diagrams, no nothing.I was very close to sending it back.This KVM is for a vender certification lab project that I set up in my home.I purchased this unit to switch between two computers, one with only VGA, the other with only DVI outputs.Because the computers had different video outputs was the reason I thought this KVM would be what I needed.In the end it works.I will not cover all of the cabling trial and errors I went through so I'll skip to the chase and tell you what worked for me.The computer with the DVI video had a fairly high end dual DVI & Display port card.I replaced the card with a very low end card that had a single DVI port and a single VGA port.I don't even know why I still had this card. I should have thrown it out years ago.So, to you electronics pack rats...old does not mean not useful.In the manual under "System Requirements" does say: DVI and VGA enabled computer system/video card.While there may be other ways to get this box to work, it would not work for me until at least one of the computers had a dual video card.Once you understand that, then this box is all that and a bag of chips.I would rather have given 4.5 stars, but there are no half stars available so I'll give 5 stars.StarTech: how about including an accurate manual/user's guide of THIS box on your website that includes a cabling diagram.StarTech: how about making this series of KVMs a little larger or arranging the DVI connectors so that two DVI connectors can be plugged into the box next to each other. Right now the connectors are so close you cannot get two connectors side-by-side.Lastly, because this ends well I'll be generous and include a plug for another StarTech product.The certification lab project requires me to connect to the console ports of routers, switches, and firewalls.Most modern desktops don't come with a serial port/connector any more.I bought a StarTech PCI2S550 2 port PCI RS232 Serial Adapter and it works great.Once again the documentation is less than desirable and the ports are not labeled, so you have to be a little persistent.Windows recognized the card and the 2 ports without needing to use the included drivers disk.