[alexjplant]

Wikipedia says "Remote Desktop Protocol (RDP) is a proprietary protocol developed by Microsoft" and that "[the] Terminal Services Edition of NT 4.0 relied on Citrix's MultiWin technology, previously provided as a part of Citrix WinFrame atop Windows NT 3.51, in order to support multiple users and login sessions simultaneously". Based on this it sounds to me like the protocol itself was the work of Microsoft and that Citrix built an extension to the server that multiplexed it. It also later remarks that "[the] T.128 application sharing technology was acquired by Microsoft from UK software developer Data Connection Limited", so it would seem that the protocol itself is a series of extensions developed on top of an open standard that they got via acquisition.

Years ago I worked in defense contracting. The US Department of Defense uses Citrix (which is easily Google-able; don't come at me about "OpSec") and my experience with it was always abysmal compared to RDP. I have a funny feeling that even with Microsoft in the mix it'd be cheaper and better for everybody involved to just pay M$ for the RDP CALs and ditch the dinosaur that is Citrix altogether.

[jiggawatts]

My understanding is that back in the early 2000s the Citrix ICA and Microsoft RDP protocols were nearly identical. Common code and all that.

One of the reasons companies licensed Citrix is because Citrix kept investing in ICA and it was about 2-3 times as bandwidth efficient. In the era of 64 Kbps ISDN WAN links this was critical.

Microsoft did something around 2008 and now RDP seems better overall. It can handle 4K at 30 fps without difficulty.

Meanwhile Citrix did weird random things to ICA that made it markedly worse.

It says a lot that all of the Citrix engineers I’ve worked with (including myself) prefer to RDP into a Citrix server instead of using its native ICA protocol!

Other deliberate breakage was Citrix deprecating SSL support directly on the session hosts. They did this to force customers to buy their overpriced Netscaler / ADC appliances. These slow down connections and can’t handle many 4K streams.

Generally they seem to have become an acquisition-driven company instead of an engineering-led one.

[ROTMetro]

Don't forget that Citrix had a Terminal Server offering before Microsoft incorporated it into Terminal Server. That was the big offer in my mind, not the RDP client, but the ability to connect multiple end users to one Windows NT server back in NT 3.51/4's early days.

[because_789]

I worked at Citrix from 1996 thru 2000. In the early days, Citrix was licensing Windows NT (source code) from Microsoft and selling a modified version of it such that (a) one could remotely control/display Windows apps, and (b) multiple users could do this simultaneously. At a certain point (‘98?) Microsoft announced they would soon offer the same functionality as Citrix, and the stock got crushed. In the end, though, it seemed Microsoft decided the practical thing to do would be to roll their own version of “(a)” (dubbed “RDP”) and license “(b)” (back, as it were) from Citrix. At least I think it was something like that.

[Melatonic]

I have managed large Citrix farms and if you have the bandwith RDP blows it away. Lot less options and control but with decent bandwith and high settings RDP is pretty nice.

That being said I hear VMware Horizon blows away Citrix too

I will never touch Citrix again.

[alexjplant]

It took an act of God to get the Horizon client working last I used it (weirdness with client SSL libraries... on Windows no less) but it worked pretty well once I got it set up.

[grosswait]

Citrix is typically used over WAN or internet and RDP over fatter pipes. Citrix gives a more complete desktop experience using less bandwidth. Not typical concerns where RDP is dominant.