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.

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