I am thinking to get a pair of new memory (2x2G) to my computer since their on sale. If combined these rams to my existing ram (1x4G), will my computer motherboard consider dual channel operation?
My motherboard Asus M4A88T-M/USB3
Welcome, Newcomer. Mixing RAM is never a good idea. While some have been successful with it, many have not. Generally, you're wasting potential. In a mixed set of RAM, you'll be bound by these limitations:
1. Lowest frequency achieveable
2. Loosest timings
3. Highest voltages
And this is just the tip of the iceberg. If you're lucky, all you'd have to do is underclock the RAM with the higher potential to the settings of the RAM with the lower potential. This is due to physical limitations, in that you cannot exceed the max settings of the RAM. For example, if the 4GB KIT can operate at 1600 MHz, but the 4GB STICK can only go up to 1066, you'd have to use the 4GB KIT at 1066 MHz as well.
In many, many other circumstances, you'll probably wind up with lower density than expected; BSOD after BSOD, and horrible performance.
But to answer your question... Typically, DC mode is achieved by using pairs of RAM; however, in many Intel-based mobos, Flex Mode exists. Flex mode allows you to install RAM and have DC mode enabled for the RAM that meets the criteria, while the remain RAM that doesn't will operate in SC mode.