A memory slot, memory socket, or RAM slot allows RAM (random-access memory) to be inserted into the computer. Most motherboards have two to four memory slots, which determine the type of RAM used with the computer. The most common RAM types are SDRAM (synchronous dynamic random-access memory) and DDR (double data rate) for desktop computers and SO-DIMM (small outline dual in-line memory module) for laptop computers, each having various types and speeds. The picture below shows what memory slots may look like inside a desktop computer. This picture has three open and available slots for three memory sticks.
When buying a new computer or motherboard, pay close attention to the types of RAM the memory slots can accept. Make sure you know exactly the type of RAM to buy for your computer. It is also important to note how many memory slots are available on your computer. It is not uncommon for computers to have all memory slots occupied. If all slots are full and you want to upgrade the computer memory, you must remove some or all of the existing memory.
Why are the memory slots different colors?
When a motherboard has different colored memory slots, it indicates the memory slots are dual-channel, and pairs of memory should be installed on the same channel (color). For example, a motherboard could have two yellow and two black memory slots. The yellow memory slots could indicate Channel A, and Channel B could be indicated by the black slots. If you were only installing two memory sticks, you'd want to install both in Channel A (yellow slots) for optimal performance.