Copyright Goodheart-Willcox Co., Inc. 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 fl ash drives and 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 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 xes for various quantities of bytes and the approximate 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.