“Channel” refers to how many DIMMs are running in synchronization with each other and has a great impact on speed. Single-Channel is a single RAM stick. This will achieve only half of its rated speed, and serve to bottleneck the CPU. A Dual-Channel is two RAM sticks. These will reach their rated speeds, and serve a literal 2x performance improvement over SC setups. A Quad-Channel is four RAM sticks. These will reach their rated speeds and do offer more performance than Dual-Channel.