Memory Slots and External Cache

Memory or random access memory (RAM) slots are the next most prolific slots on a motherboard, and they contain the modules that hold memory chips that make up primary memory, the memory used to store currently used data and instructions for the CPU.

Many and varied types of memory are available for PCs today

For the most part, PCs today use memory chips arranged on a small circuit board. Certain
of these circuit boards are called Dual Inline Memory Modules (DIMMs).

Today’s DIMMs differ in the number of conductors, or pins, that the particular physical specification uses.

Some common examples include 168-, 184-, and 240-pin configurations. In addition, laptop
memory comes in smaller form factors known as Small Outline DIMMs (SoDIMMs) and MicroDIMMs.

Memory slots are easy to identify on a motherboard. DIMM slots are usually black and
placed very close together.

The number of memory slots varies from motherboard to motherboard, but the appearance of the different slots is similar.

Metal pins in the bottom make contact with the soldered tabs on each memory module.

Small metal or plastic tabs on each side of the slot keep the memory module securely in its slot.
Sometimes primary memory gets a bit overwhelmed with the requests coming from the processor.

To get its bearings, the RAM must obtain the information the CPU wants immediately, but
RAM is not as fast as the CPU, and the CPU must wait.

The result is that the entire system slows down noticeably, on average. One solution for this is to use the hard drive as RAM.

This space on the hard drive is known as virtual RAM (VRAM). VRAM is a contiguous, optimized space that can deliver information to RAM faster than if it came from the general storage pool of the drive.






picture of different memory modules






There is something that can be done on the CPU side of RAM to speed things up a bit as well.

That something is adding cache memory. Cache memory is a very fast form of memory forged
from static RAM, which is discussed in detail in the “Identifying Purposes and Characteristics
of Memory” section of this chapter.

Cache improves system performance by predicting what the CPU will ask for next and prefetching this information before being asked.

This paradigm allows the cache to be smaller in size than the RAM itself. Only the most recently used data and code or that which is expected to be used next is stored in cache. Cache on the motherboard is known as external cache because it is external to the processor.

Also called Level 2 (L2) cache, this is as opposed to the Level 1 (L1) cache built into the processor.