Having 2 desktops refers that getting increased rate of work as of survey. Also there is an argument related to more desktops comparing with rate of work.
Check graphic card
Before operating multi desktops, check your desktop indication of operation capability. In order to check it, please view your desktop back side checking graphic card ports. (DVI ,HDMI ,Display Port and VGA)
If there is no compact graphic, you may view only two video ports. Most motherboard has installed graphic cards. In this case, it’s available to operate two desktops. If there is a compact graphic card, you may view additional three ports with motherboard port at least.
Desktop, port and cable
If you learn about graphic card, now focus on selection of additional desktop which is interesting point. Additional desktop price is getting decreased nowadays. Imagine that 24 inch desktop is around 170 dollar and 27 inch desktop is around 250 dollar. If you want to buy perfect desktop, there are a lot of influences of course. For example: What is the current desktop size and for what will you use your desktop etc.