There are a lot of different types of computer memory. To anyone who hasn't spent years studying them, it can seem like a lot of information that goes straight over the head. To be sure, computer memory is complicated, but the knowledge is not quite as unattainable as most people think.
RAM stands for Random-Access Memory. It was first invented in 1949, though it looked much different back then. Even in 1949, when the personal computer screen was a science fiction ideal, RAM was instrumental in the functioning of a computer. RAM allows data to be stored in any order, and the computer to access it in any order. Before RAM was popularized, computers had to follow a string of unrelated data every time they wanted to access anything. RAM is used in modern computers as a short-term memory and data storage. It is a flash memory, so it can be rewritten as many times as needed. Because it is a volatile form of data storage, it requires a power supply constantly. But this constant power means that it has much faster access times than nonvolatile memory such as hard drives, and it stores programs and files that are in use.
Another type of RAM is DDR RAM. DDR stands for Double Data Rate. DDR RAM is twice as fast as the old versions of RAM. What most people think of as RAM today is actually DDR RAM, which was first released in June 2000. And in 2003, even that was improved on with DDR2 RAM, which is even faster than DDR RAM.
All DIMM is RAM (or more specifically DDR2 RAM these days), but not all RAM is DIMM. DIMM stands for Dual Inline Memory Module. A DIMM is essential just a stick of RAM. This circuit board is long, thin, and narrow with tabs on one edge. These tabs are studded with flat metal pins. The pins are responsible for transferring data between the DIMM and the computer. If you look at a stick of DIMM, two main things will stick out; the green metal part and the black squares that stick out. Those black squares are the RAM. The green part, the part that makes it DIMM, connects these squares in an efficient and speedy manner.
In terms of what is available today, the only difference that matters is what the specific computer's compatibilities are. And IBM computer must have a 5913-8202 DIMM or the like. An HP computer must have HP DIMM, so on and so forth. Other than speed capabilities and computer compatibility, there really is no difference between RAM, DDR RAM, and DIMM. Because essentially, they all incorporate aspects of each other anyways.