Memory modules
The number of individual modules included in RAM kit. One module occupies one slot on the motherboard, so to install the entire kit, the number of free slots must be equal to or greater than the number of modules.
If there is an even number of modules in the set, they can be paired. This mode significantly increases the speed, but is not supported by all models of motherboards, so in each case this point should be clarified separately.
Now on the market? there are modules supplied in such quantity:
one modules,
set of 2 modules,
set of 4 modules,
set of 8 modules.
Memory rank
The number of ranks provided in the memory bar.
The rank in this case is called one logical module — a chipset with a total capacity of 64 bits. If there is more than one rank, this means that several logical ones are implemented on one physical module, and they use the data transmission channel alternately. A similar design is used in order to achieve large amounts of RAM with a limited number of slots for individual brackets. At the same time, it should be said that for consumer computers, you can not pay much attention to the memory rank — more precisely, peer-to-peer modules are quite enough for them. But for servers and powerful workstations, two-, four- and even eight-rank solutions are produced.
Note that other things being equal, a larger number of ranks allows achieving larger volumes, however, it requires more computing power and increases the load on the system.