Thread: Types of Memory

Various types of memory have been used in PCs throughout evolution. At present, 2 types are popular that is high-speed, thin bandwidth memory produced by Rambus known as Rambus Dynamic Random Access Memory, and high-bandwidth memory known as Double Data Rate Synchronous DRAM.

Rambus DRAM runs at higher frequencies in comparisons to DDR memory. RDRAM is available at 800MHz, 1066MHz, and 1200MHz. Only few Intel chipsets supports RDRAM, and it’s costlier than DDR memory. The different speeds are considered as PC800, PC1066, and PC1200. Like DDR memory, RDRAM moves data twice in each clock cycle.

DDR memory is accessible at efficient speeds up to 400 MHz. It’s known as both PC3200 as well as DDR400. 400MHz DDR memory basically runs at 200MHz, but performs data moves double per clock cycle. DDR RAM is also available with efficient frequencies of 266MHz (PC2100), 333MHz (PC2700), and at higher speeds than 400MHz, but today’s motherboards don’t support anything more than 400MHz.

Memory. A single word for a very complicated brain process. It is memory that allows us to learn from our elders, and that allowed them to learn from their elders, so that a modern person can benefit from the knowledge of generations: how to harvest crops, make fire, speak a language, read and write, cook a pizza, brush teeth, play baseball—without having to reinvent the wheel. It is also memory that enables us to reminisce, to form attachments to others, to feel that we’ve lived a good life. But what is “memory”? It actually takes many different forms. The biggest categories of memory are short-term (or “working”) memory and long-term memory. Both can weaken with age, or due to a variety of other reasons.
Even within short- and long-term memory, there are different categories, as you can see in this graphic. We’ve described these types below.

Short-Term Memory
Short-term memory—closely related to “working” memory—is the very short time that you keep something in mind before either dismissing it or transferring it to long-term memory. Short-term memory is shorter than you might think, lasting less than a minute. It’s what allows you to remember the first half of a sentence you hear or read long enough to make sense of the end of the sentence. But in order to store that sentence (or thought, fact, idea, word, impression, sight, or whatever else) for longer than a minute or so, it has to be transferred to long-term memory.
Long-Term Memory
A long-term memory is anything you remember that happened more than a few minutes ago. Long-term memories aren’t all of equal strength. Stronger memories enable you to recall an event, procedure, or fact on demand—for example, that Paris is the capital of France. Weaker memories often come to mind only through prompting or reminding.


Long-Term— Explicit
Explicit memory (also called “declarative memory”) requires conscious thought—such as recalling who came to dinner last night or naming animals that live in the rainforest. Explicit memory is what most people have in mind when they think of “memory,” and whether theirs is good or bad.


Long-Term—Explicit—Episodic Memory
Episodic memory is one type of explicit memory. Episodic memory provides us with a crucial record of our personal experiences. It is our episodic memory that allows us to remember the trip we took to Vegas, what we had for dinner last night, who told us that our friend Maryann was pregnant. Any past event in which we played a part, and which we remember as an “episode” (a scene of events) is episodic. This form of memory appears to be centered in the brain’s hippocampus—with considerable help from the cerebral cortex. To read more about this type of autobiographical memory


Long-Term— Explicit—Semantic Memory
Another type of explicit memory is semantic memory. It accounts for our “textbook learning” or general knowledge about the world. It’s what enables us to say, without knowing exactly when and where we learned, that a zebra is a striped animal, or that Paris is the major city in France. Scientists aren’t sure where semantic memory happens in the brain; some say in the hippocampus and related areas, while others think it’s widely spread throughout the brain.


Long-Term—Implicit
Implicit memory (also called “nondeclarative” memory) is different from explicit memory in that it doesn’t require conscious thought. It allows you to do things by rote. This memory isn’t always easy to verbalize, since it flows effortlessly in our actions.
Long-Term—Implicit—Procedural Memory
Procedural memory is the type of implicit memory that enables us to carry out commonly learned tasks without consciously thinking about them. It’s our “how to” knowledge. Riding a bike, tieing a shoe and washing dishes are all tasks that require procedural memory. Even what we think of as “natural” tasks, such as walking, require procedural memory.
Though we can do such tasks fairly easily, it’s often hard to verbalize exactly how we do them. Procedural memory likely uses a different part of the brain than episodic memory—with brain injuries, you can lose one ability without losing the other. That’s why a person who has experienced amnesia and forgets much about his or her personal life often retains procedural memory: how to use a fork or drive a car, for example.
Long-Term—Implicit—Priming
Implicit memory can also come about from priming. You are “primed” by your experiences; if you have heard something very recently, or many more times than another thing, you are primed to recall it more quickly. For instance, if you were asked to name an American city that starts with the letters “Ch,” you would most likely answer Chicago, unless you have a close personal connection to or recent experience with another “Ch” city (Charlotte, Cheyenne, Charleston…) because you’ve heard about Chicago more often. In the brain, the neural pathways representing things we have experienced more often are more salient than those for things with which we have fewer experiences.