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Chapter 1 Introduction to Information Technology 11
played, or otherwise used. The most familiar storage locations are the
computer system’s memory and hard disk drive, but flash drives and fl
other forms of external storage devices are also common.
Storage devices are usually automatically named by the operating
system. The device drive name is a letter followed by a colon. For example, C:
is the primary hard drive, and it is referred to as the “C drive.” Additionally,
the name of the device itself is called the volume label or volume name.
Memory is the part of the computer that stores information for
immediate processing. It stores the code for the computer programs, data
used for the programs, results from executing the programs, and much more.
Some memory is involatile, which means it is kept even when the computer
is turned off. The basic startup program in a computer is stored in persistent
memory. Other memory is volatile, which means it is erased when the power
is off. There are two types of memory:
• random-access memory
• read-only memory
Random-Access Memory
Random-access memory (RAM) is memory
that can be changed. This hardware holds
instructions that the processor can immediately
use. RAM is what most users think of when the
word memory is mentioned.
As various programs are used, the constantly
changing instructions are loaded into RAM.
When the computer is turned off, all data and
instructions that were stored in RAM are erased.
Therefore, RAM is volatile memory. It is just a
temporary holding area for data and instructions.
The physical chips that hold RAM look like
small black rectangles with many pairs of metal
feet, as shown in Figure 1-8.
Read-Only Memory
Read-only memory (ROM) is memory that cannot be changed. ROM
contains static information the computer will always need to operate and
that cannot be subject to variation. ROM holds its information even if the
computer is turned off, which means it is involatile memory.
Measuring Memory
The capacity of memory is measured in how many bytes it can
hold. One byte holds enough information for one character. Figure 1-9
describes the prefi for various quantities of bytes and the approximate fixes
data storage capacity.
Storage Media
Magnetic media are made of iron oxide-coated disks that can be
selectively magnetized to store on-off signals. The computer’s internal
Radu Bercan/Shutterstock.com
Figure 1-8. The green board is a RAM unit, which
holds many RAM chips. The RAM chips are black in
this example. The metal feet are hidden because the
chips are surface mounted.