Information Technology Reference
In-Depth Information
or the purchase of a new one. Many computers come with expansion
slots. Often,
expansion slots
represent additional connecting places to
an internal bus, allowing connections for future components. When a
computer has such connections available, adding new capabilities can
be easy—perhaps as simple as just plugging in the new hardware.
However, when all bus connections are already in use, there may be
no free connecting points, making expansion difficult or impossible.
Therefore, when purchasing a machine, a buyer may want to
consider what expansion is possible. Typically, one can expect new
devices and capabilities to enter the market over the lifetime of a
computer. These can be added to an existing machine if it has some
appropriate free expansion slots—perhaps extending the useful life
time of an existing machine.
hardware elements do?
Although the basic CPUmemoryI/Obus model is sufficient to
run most computer programs, the applications may run very slowly.
In many cases, this poor performance has three basic causes:
1.
The movement of data from one location (such as main mem
ory) to another (such as the CPU) takes time.
2.
Connection of components with a single bus limits data
movements to one at a time.
3.
The CPU coordinates all activities and performs all process
ing, so any processing must wait until the CPU can monitor
or handle it.
Latency: All activities within a computer take some time to com
plete. For example, the CPU may request a piece of data from main
memory, but it takes time for main memory to retrieve that infor
mation and make it available on the bus. As a different example, the
addition of two numbers within the CPU requires time. We might
think of these time delays as being insignificant by themselves—and
they may be in some circumstances—but in other cases, such delays
combine to consume considerable amounts of time. More generally,
any work within a computer takes some time, and this time delay is
called
latency
.
