Hardware Reference
In-Depth Information
Figure 1.16 Modern system architecture based on a North Bridge/South
Bridge chipset
read/write memory of the system. What makes all this possible is the availabil-
ity of fast semiconductor random access memory (RAM) devices. This section
explains what these devices are and how they are incorporated into a PC system.
Modern PCs require large amounts of RAM in order to run increasingly
powerful software applications. Today, memory capacities of 64 MB or 128 MB
are commonplace. Early PCs, on the other hand, were designed to operate with
a mere 640 KB or 1 MB of memory.
Memory operation
Unfortunately, it takes a finite time in order to access data stored in a memory
device. Since program execution involves constantly reading and writing data
from/to memory the amount of time taken to transfer data has an important
bearing on the time that it takes to execute a program. Access time is the average
time (usually specified in nanoseconds) for a RAM device to complete one data
access. Access time itself is comprises the initial address setup time and the time
it takes to initiate a request for data and prepare access (this is known as latency ).
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