DIMM slots are found on most motherboards and can hold either RAM or hard drive storage. RAM is much faster than hard drive storage, so it is typically used for the operating system, programs, and data files. DIMM slots are also used to add more hard drive storage to a computer. Most computers only have one DIMM slot, so adding more hard drive storage will require purchasing a separate expansion card.
Some DIMM slots are also found on laptop computers and can hold both RAM and hard drive storage. Laptop computers typically have less space for other components, so adding more RAM or hard drive storage is a common upgrade.