disk as a handy place to swap out programs or data that can’t fit in main memory at a particular point in time. So, if you have several windows open on your computer, and only 64 megabytes of main memory, you might see the hourglass form of the cursor appearing quite often because the operating system is constantly swapping the different applications in and out of main memory. From Figure 1.4, we see that the ratio of access times between the hard disk and main memory can be 10,000 to one, so any time that we go to the hard disk, we will have to wait. The moral here is that the best performance boost you can give to your computer is to add as much memory as it can hold.Finally, there are several symbols used in Figure 1.4 that might be strange to you. We’ll discuss them in detail in due course, but in case you were wondering what it meant, here’s a little preview
Hopefully, these numbers will soon become quite familiar to you because they are the dimensions of modern computer technology. However, one note of caution: The terms kilo, mega, giga and tera are often overloaded. Sometimes they are used in the strictly scientific sense of a shorthand notation for a multiplication factor of 103, 106, 109 and 1012, respectively. So, how do you know the computer-speak versions, 210, 220, 230, 240 are being used, or the traditional science and engineering meaning is being used? That’s a good question. Sometimes it isn’t so obvious and mistakes could be made. For example, whenever we are dealing with memory size and memory issues, we are almost always using the base 2 sense of the terms. However, this isn’t always the case. Hard disk drives, even though they are storage devices, use the terms in the engineering sense. Therefore, an old 1 gigabyte hard drive does not hold the same amount of data as 1 gigabyte of memory because the “giga” term is being used in two different senses. In any case, you are generally safe to assume the base 2 versions of the term in this text, unless I specifically state otherwise. In the real world, caveat emptor