Windows 7: Mis-insert Dual Channel RAM memory modules?

As far as I can see I have currently dual channel DDR3 RAM memory modules.
Assume it would not be written on a label sticker on the ram modules:
How can I find out if a ram modules support dual channel or not?

As I learned I have to put dual channel mondules into different channel slots to get full speed.

My motherboard has current 4 slots:
Channel A: slot 1 + slot 2
Channel B: slot 1 + slot 2

Assume I put the 2 modules into the 2 slots of channel A.
How much performance/speed loss do I get approximately?

What happens when I have two single channel ram modules:
Does it matter where (in which slots) I put them?

Peter

You can buy sets of RAM that work together,
If you have more RAM modules that are the same you can try them out in your PC It will work or it won't
Dual Channel is selected in the BIOS (this can happen automatically on some boards)
Refer to your motherboard manual or have a look here as a guide only; RAM issues Windows 7 Ultimate 64 Bit

The ram should have a sticker on the module that will tell you exactly what it is and the timings. Most motherboards have 4 slots. 2 slots will be one color and the other 2 will be a different color. each color is a channel. so you would want to put 2 sticks of ram in the same color sockets. Download this free program, CPUz. It will tell you what kind of ram you jave installed in each slot, It is a good program. It will also tell you about your motherboard, CPU memory and graphics. The memory tab will tell you what type of ram (DDR2, DDR3) and whether it is in dual channel mode. Also, it would help if you went to the user CP link at the top of this page and filled out your system details. It helps when you ask questions.