Why do you need both GDS2 and Tech2Win for GM MDI?

Because GDS2 works for the new GM MY2010 only while Tech2Win works for the old.
Attach a chart: GDS2 vs. Tech2Win

Functions/ Software	GDS2	Tech2Win
Tool to work with	GM MDI	GM MDI
Diagnostics	Yes	Yes
ECU Programming	No. But you can log in www.acdelcotds.com to do programming	No. But you can log in www.acdelcotds.com to do programming
Key Programming	Yes. But you have to program new keys online via www.acdelcotds.com	Yes. But you have to program new keys online via www.acdelcotds.com
SPS Programming	No	Yes
Vehicle Coverage	Working for new GM motors 2010-	Working for old GM motors

Part 1: GDS2
In 2010, GM made a change in their vehicles moving to a Global platform to simplify marketing their vehicles all around the world.
The communication systems changed and the Tech 2 scan tool was no longer able to access them.
In preparation for this change, years earlier, GM had released a laptop based Multiple Diagnostic Interface or MDI . The blue box.
Note that the MDI 2 is used for reflashing only but the dealers loved it because it is twice as fast because of its USB connection to the laptop. (The Tech 2 is a Serial connection system and slower to transfer data for reflashing)
Back to the MDI. Global cars like the 2010 :
Chevrolet Camaro
Chevrolet Volt gas/electric hybrid
Buick Lacrosse
Cadillac SRX SUV
GMC Terrain
Chevrolet Equniox
We are now onto GDS2 which is simply a newer and better version than GDS1.
GDS2 requires renewing of the license to use it by visiting the Tis To WEB website at least once a month (if you have a yearly subscription).
Tis To Web as it is called is GM's website to download the scan tool or reflash data to update a vehicles computer.
You download vehicle software to your laptop and then you run the vehicle choice or program to scan from your laptop with the MDI 2 as the interface between your laptop and the vehicle.
You do not HAVE to be 'online' to use GDS2, only download the latest software license to use it by visiting Tis To Web monthly.
When you start GDS2, the bottom of the screen shows how many days left till an update is required.
If expired, simply log in to Tis to Web before you work on a GDS2 vehicle and renew your license then.
The above license requirements don't apply with a 2 day paid pass to use GDS2.
Part 2: Tech2win
GM also came out with a software program called Tech2Win.  (Tech 2 for Windows)
This is a Tech 2 emulator that runs on your laptop and simulates the Tech 2 screen and keypad to operate it.
Unfortunately, it leaves something to be desired with limited functions and some lack of actuator tests and incomplete coverage. It does not replace a Tech 2 and is a yearly subscription purchase but it is cheaper.
  Tech2Win also cannot be used for Saab or Izusu or Suzuki! 
GM really needs a laptop with a Intel I5 quad processor and 4 GIG of RAM plus Windows 7 Professional.
I recommend a refurbished Panasonic Toughbook CF19 tablet with 2.5 GHZ I5 quad processor with 4 partitions. You can use 1 terabyte solid state hard drives for speed and durability.
1 year warranty though you will probably never have a problem with one of these since they
are solid as a rock. If something were to go wrong after the warranty, I can get it repaired very cheaply. No sweat.
Keep GM by itself to prevent software conflicts and still get use of other operating systems to maximize laptop use with other software programs like Ford, Mazda etc.
When you first start up, the laptop pauses and offers you a screen with the 4 Windows operating systems. Pick which one you want and you are on your way. I also label them to make it more clear what is being chosen.
Example :
Windows 7 GM MDI 2
Windows 7
Windows 7
Windows 7
It's easy to name them anything you want.

http://www.chinacardiags.com/

VXDIAG VCX NANO GM Windows 10 Review

VXDIAG VCX NANO GM Windows 10 Review:
The software of  VXDIAG VCX NANO includes two parts: tech2win and GDS2. 
Version of tech2win: V33.003
Version of GDS2: V2016.1.0
Recently ran into an issue where i wanted to replace my aftermarket pioneer (didn't like it and much prefer my smart phone) with a stock unit. Found a cheap OEM unit on eBay. After install, i realized that factory head units are tied to the original cars VIN. No problem, i'll pay the dealership to fix the issue. Only problem they outright say they CANNOT guarantee they can fix the locked status of my radio and i'd still have to pay. As an IT/Network technician, i couldn't imagine telling people i can't guarantee i can fix your network or pc problems, but you still owe me full price plus tax.
Enter the VXDIAG VCX Nano. I was looking into gm tech 2 clone's for the past couple weeks and stumbled onto this gem. There is very little info on this product, but i still had more faith in this thing and myself more than my own dealership so i took the plunge. For $119 on chinacardiags.com, i basically have the software version of a tech II device. I was able to unlock my radio in a matter of minutes. Have never used a real or upscale scan tool device so i can't compare but just poking through some of the menus, it looks like i can do anything a tech II can. Cool thing is that the tech2win software runs just fine on my Windows 10 64bit laptop. Would be even cooler with a surface pro or similar tablet. I'm sure there are reasons for owning an actual tech II device over just software, but i wanted to try something different out of curiosity and explore other options for those that want an even cheaper alternative.

I am impressed so far....
Good tool!
I was only speaking for the tech2win software. That i did run straight from a Windows 10 64-bit laptop. Website says that GDS2 only runs from a Windows XP/7 32-bit computer. If there is a simple GDS2 test that anyone can think of for me to try, i then confirm or deny this claim. FYI i have a windows XP, 7, 8, and 10 32 & 64 bit laptops. So i could try on any operating system.
Important tips - Tech2Win GDS2 on Windows 10
On tech2win, although the op is stating that its working in 64 bit mode, really want to go through it to double check if it needs to run in win 7 compatible mode for everything to work "correctly" instead.
Putting tech2win into win 7 compatibility mode is the way and it’s not hard to do.
Go to the start icon for tech2win, right click it and go to properties, and see if you can click the box and make it run it in win 7 mod.
If the box is grayed out and you can not do it this way, click on the windows icon, type in run in the search box, then find run program made for a previous version of windows in list it will bring out and click on that to open that program. From here, it pretty straight forward to find Tech2 win, and change tech2 win so it running in win 7 compatible mode.
As for SDS, need to see that if it has for any type of account already set up in it's memory. Hence in VM, gds2 should run fine.
I fired up the GDS2 software and that indeed runs off Windows XP. But it does come with the VM software. So far everything works under my Windows 10, but like i said the GDS2 is running in the VM software
But without a active account in SDS, it’s never going to connect to GM to pull firmware files down that way instead.
Hell who knows, and if the SDS program on the disco does not have a hidden account on it, maybe you can access GMvia the cloud software instead.

Original:VXDIAG VCX NANO GM Windows 10 Review