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CHAPTER 6

RAM

In this chapter, you will learn how to

Identify the different types of DRAM packaging

Explain the varieties of RAM

Select and install RAM

Perform basic RAM troubleshooting

Whenever people come up to me and start professing their computer savvy, I ask them a few questions to see how much they really know. In case you and I ever meet and you decide you want to “talk tech” with me, I’ll tell you my first two questions just so you’ll be ready. Both involve random access memory (RAM), the working memory for the CPU.

1. “How much RAM is in your computer?”

2. “What is RAM and why is it so important that every PC has some?”

Can you answer either of these questions? Don’t fret if you can’t—you’ll know how to answer both of them before you finish this chapter. Let’s start by reviewing what you know about RAM thus far.

* * *

EXAM TIP The CompTIA A+ certification domains use the term memory to describe the short-term storage used by the PC to load the operating system and running applications. The more common term in the industry is RAM, for random access memory, the kind of short-term memory you’ll find in every computer. More specifically, the primary system RAM is dynamic random access memory (DRAM). For the most part, this book uses the terms RAM and DRAM.

When not in use, programs and data are held in mass storage, which usually means a hard drive but could also mean a USB thumb drive, a CD-ROM, or some other device that can hold data when the computer is turned off. When you load a program by clicking an icon in Windows, the program is copied from the mass storage device to RAM and then run (Figure 6-1).

You saw in Chapter 5, “Microprocessors,” that the CPU uses dynamic random access memory (DRAM) as RAM for all PCs. Just like CPUs, DRAM has gone through a number of evolutionary changes over the years, resulting in improved DRAM technologies with names such as SDRAM, RDRAM, and DDR RAM. This chapter starts by explaining how DRAM works, and then moves into the types of DRAM used over the past few years to see how they improve on the original DRAM. The third section, “Working with RAM,” goes into the details of finding and installing RAM. The chapter finishes with troubleshooting RAM problems.

Figure 6-1 Mass storage holds programs, but programs need to run in RAM.

Historical/Conceptual

Understanding DRAM

As discussed in Chapter 5, “Microprocessors,” DRAM functions like an electronic spreadsheet, with numbered rows containing cells and each cell holding a one or a zero. Now let’s look at what’s physically happening. Each spreadsheet cell is a special type of semiconductor that can hold a single bit—one or zero—by using microscopic capacitors and transistors. DRAM makers put these semiconductors into chips that can hold a certain number of bits. The bits inside the chips are organized in a rectangular fashion, using rows and columns.

Each chip has a limit on the number of lines of code it can contain. Think of each line of code as one of the rows on the electronic spreadsheet; one chip might be able to store a million rows of code while another chip can store over a billion lines. Each chip also has a limit on the width of the lines of code it can handle, so one chip might handle 8-bit-wide data while another might handle 16-bit-wide data. Techs describe chips by bits rather than bytes, so ×8 and ×16, respectively. Just as you could describe a spreadsheet by the number of rows and columns—John’s accounting spreadsheet is huge, 48 rows × 12 columns—memory makers describe RAM chips the same way. An individual DRAM chip that holds 1,048,576 rows and 8 columns, for example, would be a 1 M×8 chip, with “M” as shorthand for “mega,” just like in megabytes (220 bytes). It is difficult if not impossible to tell the size of a DRAM chip just by looking at it—only the DRAM makers know the meaning of the tiny numbers on the chips (see Figure 6-2), although