Machine perception of time, if only nanoseconds were seconds
Let's just discuss the time scale. The processor of your computer lives by the nanoseconds: the majority of the CPU can do several things for one nanosecond; generally, these are the simple math and the comparisons. To make this perception easer, we assume that you are the processor, and instead of nanoseconds you live and work second by second. In order to make it clear, we apply this metaphor to the single-core processor.
You are able to keep simultaneously a few things in your mind (the register). Not more than a dozen or two in your active memory, however you are capable to recall any of them almost instantly. You keep the important information handy, whether it is on the scratch pad on the desk (L1 cache) that is available in a couple of seconds or one of the books that is on the shelf (L2 and more cache), which is so well organized that every piece of information you cannot get in a dozen seconds or so.
If you cannot find what you are looking for there, you have to go to the library on the street (it is RAM). Fortunately, it is pretty close, so that you can walk over there, take a book and return to the work in only eight and a half minutes, and it is a lot, because some libraries are thousands of times greater than the size of a typical book store. It is a little inconvenient, until you remember that the library has the free delivery service, so you do not have to worry at all, if there is work to do while you are waiting.
But the local library keeps only the popular books (which is quite true, because your book shelf, the scratch pad, and even a dozen or two factors in your head are usually made on the same principle). The problem is that if you need something, and it is missing there, you will have to wait a little longer. How long? Well, let’s imagine Amazon.com in the age of discoveries. They send out an old wooden ship, and it may take weeks, perhaps months, and often you have to wait three years before you get a response.
Welcome to the hard drive world where your information is extracted by the rapid unwinding of metal plates. Many metric tons of sweat were shed in order to speed up the process as fast as possible, but it's hard to compete with the electrons that are flying over the wires.
So when someone says that the SSDs are splendid, because they are able to turn this slow unpredictable old sailing ship into a powerful steam engine vessel. A good SSD can often make a voyage in less than a week, and sometimes it could do in less than a day. It can also make the thousands of trips for information per year.
(If you are looking for information in terms of various SSD, I recommend you read http://www.anandtech.com/tag/storage, I recently have bought OCZ Vertex 3, but there I have learned that they have unresolved and very serious bugs.)
Sources of inspiration for this article:
1. http://www.phy.duke.edu/ ~ rgb/Beowulf/beowulf_book/beowulf_book/node24.html
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