Microsoft Office Tutorials and References
In Depth Information
The speed of a microprocessor is determined by its clock speed, word size, and cache
size. Think of the clock speed as the pulse of the processor. It is measured in millions of
cycles per second, or megahertz (MHz), or gigahertz (GHz), a billion cycles per second.
Word size refers to the number of bits that are processed at one time. A computer with a
large word size can process faster than a computer with a small word size. The earliest
personal computers had an 8-bit word size, but now a 64-bit word size is common.
Cache , sometimes called RAM cache or cache memory , is special high-speed memory
reserved for the microprocessor’s use. It speeds up the processing function by accessing
data the computer anticipates you will request soon, while you are still working on some-
Take another look at the computer advertised in Figure 1. What is the type and speed of
its microprocessor? Your answer should be that it has a Pentium 4 microprocessor that can
operate at 2.66 GHz and has 512 K cache.
Computer memory is a set of storage locations on the motherboard. Your computer has
four types of memory: random access memory, virtual memory, read-only memory, and
complementary metal oxide semiconductor (CMOS) memory.
Random access memory (RAM) is active during the processing function. It consists of
electronic circuits on the motherboard that temporarily hold programs and data while the
computer is on. RAM is volatile , which means that it is constantly changing as long as the
computer is on and is cleared when the computer is turned off. The microprocessor uses
RAM to store and retrieve instructions and data as they are needed. For example, if you
are writing a paper, the word processing program that you are using is temporarily copied
into RAM so the microprocessor can quickly access the instructions that you will need as
you type and format your paper. As you type, the characters are also stored in RAM, along
with the many fonts, special characters, graphics, and other objects that you might use to
enhance the paper. How much you can include in your paper depends on the RAM
capacity of the computer you are using. Most personal computers on the market today use
SDRAM (synchronous dynamic RAM) or RDRAM (Rambus dynamic RAM). SDRAM is
plenty fast for the average computer user and inexpensive. RDRAM was originally
designed for use in computer game systems and is more expensive than SDRAM. When
paired with a microprocessor of 1 GHz or faster, RDRAM can improve a computer sys-
tem’s overall performance.
Look at the computer ad in Figure 1. Notice that this computer has 512 MB of SDRAM.
In other words, it has the capacity to temporarily store over 512 million characters at any
one time. Although your paper might not be that long, the computer uses a lot of that
available memory for programs and other data it needs to process your paper. The nota-
tion “expandable to 2 GB (2048 MB)” tells you that you can add more RAM to this com-
puter. Expandability is an important feature of any computer; you need to be able to
change your computer’s capability as your needs change.
When the programs running on a computer use all the available RAM, the software
uses space on the computer’s storage devices to simulate RAM. This extra memory is
called virtual memory . Figure 15 explains how it works. The disadvantage of using virtual
memory is that it is much slower than RAM, so expanding the RAM capacity of a com-
puter will improve its performance.