Buying A Computer For Dummies, 2006 Edition (2005)

Finally, the terabyte (“TAYR-uh-bite”) has approximately 1 trillion bytes — an awful number that’s beyond human comprehension. It’s abbreviated T or TB. Because it’s a relatively new value in computerdom, you may see it referred to as 1,000GB for a while.

Table 6-1 puts these values in perspective.

These terms — kilobyte, megabyte, and so on — are used to describe both temporary and permanent storage in a computer — how much room you have for the stuff you create.

Gigabyte is pronounced “GIG-a-byte,” not “JIG-a-byte” or “giggle-byte.”

Note that that there’s a difference between approximate and exact storage — chump change, really. It accounts for the fact that the computer is counting in binary, or base 2, which doesn’t always work out to the base 10 values we humans use. It’s trivial, really.

Memory Madness

You may have heard the term RAM. And, you may have a brief understanding of computer memory. Although it’s important to know memory quantities, as covered in the preceding section, the rest of the details regarding computer memory are truly boring. That’s because they’re technical.

For buying a computer, knowing how much memory your new computer needs is just about enough. Beyond that, you’re faced with a slew of memory terms to boggle, baffle, and bewilder. Because there seems to be no getting around it, I’ve written this section to help describe these memory terms and

Or, if you have any deuterium pellets handy, plus a powerful laser, it takes one nanosecond to compress the pellet with the laser. Again, that’s fast.

Back in the world of computers, you may see a RAM chip advertised as “6ns.” That term means that the memory hums along at 6 nanoseconds.

The speed describes how fast the memory can be accessed. This speed depends on your computer’s configuration; adding faster RAM chips to a slow PC doesn’t (unfortunately) perk things up.

Memory speed isn’t seriously important when you buy a computer. The dealer installs whichever memory works best in that system. Memory speed becomes an issue when you buy more memory for your computer. The speed of that additional memory should match the speed already used in your computer.

Upgrading memory is covered in Chapter 27.

Again, the faster the memory, the more you pay for it.

Another aspect of RAM speed is how fast the computer’s bus runs. You need to match the RAM speed to the PC’s bus speed, or a multiple thereof — though this is a more technical aspect that’s handled by the manufacturer or computer dealer than a choice you must make.

Goodbye, Mr. Chips!

To make handling the chips easier, memory manufacturers solder a whole bank of chips together on a single tiny strip of fiberglass about the size of a pocket comb. That strip is called a DIMM, as shown in Figure 6-1, and it does indeed make up one whole bank of memory. This is very handy.

Figure 6-1:

A DIMM.

Honestly, the only places you see these terms are in memory ads. In the real world, even engineers just call it RAM or memory. The rest is all scientific fluff that makes good (or bad) ad copy:

Bank: The slot into which a DIMM is inserted. Most computer motherboards come with two or four banks, numbered 0 and 1 or 0 through 3. Bank can also refer to a chunk of memory, such as a 64KB bank of RAM. See the section “Banks o’ Memory (RAM),” later in this chapter.

DDR: Acronym for Double Data Rate, a type of SDRAM that’s twice as fast as regular SDRAM.

DDR-xxx. The xxx here is a number that specifies the memory’s speed with regard to the motherboard’s data transfer rate — a technical thing, but if you plan to build your own computer, the xxx number on the RAM chips you buy must match the motherboard’s xxx number.

DRAM: Another term for RAM. Pronounced “DEE-ram,” it stands for Dynamic Random Access Memory. It’s more impressive than RAM, I suppose, but not as impressive as SDRAM or EDO RAM. Whoa! No way!

ECC: An acronym for Error Checking and Correction, which can require extra circuits to ensure that memory is being properly written to and read from.

EDO RAM: An acronym for Extended Data Out, another fancy-schmancy type of memory and more powerful than mere SDRAM.

FPM: Acronym for Fast Page Mode, often used with RAM, as in FPM RAM. It’s faster. Smarter. Better. Using it implies that the neighbor’s dog is ugly.

Nonparity: Memory chips that don’t use parity, as described next.

Parity: Another nerdy term; refers to a self-check that memory chips can perform on themselves every time the memory is accessed. Do you need parity? Maybe. A computer manufacturer decides whether it wants to put parity in its PCs. Other than that information, anything else I could say about parity would put you to sleep.

PCxxx: Refers to the speed of the computer’s front side bus, where xxx is a numeric value (in megahertz). The SDRAM that’s used should match the front side bus speed, though you can use slower memory on a faster bus (but I don’t see why you would want to).

RDRAM: Special Rambus DRAM, which operates at superhigh speeds — but only on motherboards that use the Rambus chipset.

Again, this is advertisement-only information. Whenever you see VRAM or SGRAM or any other type of video-RAM-whatever, know that it’s memory used by the computer for displaying graphics.

Your computer needs both main and video memory.

Some computers boast shareable memory, in which the main RAM is used to supplement video memory. This type is often a cheap alternative to stuffing a computer with both types of RAM. Yes, it works. No, I do not recommend this type of system — unless graphics or games are not one of the reasons you’re getting a computer.

Banks o’ Memory (RAM)

Science fiction TV shows typically feature computers with banks of memory.

Although that term is accurate, it’s also vague.

The computer you buy will indeed have banks of memory. The DIMM cards plug into these slots inside the computer. Each slot is known as a bank. What’s important is how those banks are filled. Ideally, you want them filled in a manner that wastes no memory, in case you ever decide to upgrade.

When you order your computer, try to get the manufacturer to install all your computer’s memory into as few banks as possible. For example, Figure 6-2 shows a setup with four banks of memory. A 128MB DIMM is plugged into each bank, which gives that computer a total of 512MB of RAM — a goodly amount for now, but what about future expansion?

Yes, one 512MB DIMM usually costs more than four 128MB DIMMs.

Some computers insist that all memory banks have the same amount of memory. If you have three 265MB SIMMs in three banks and want to add a 128MB DIMM to the last bank, you can’t do it. (Don’t blame me! Beat up an engineer!) Also, some systems require you to install DIMMs in pairs, which requires additional thinking when you’re buying additional memory.

How Much Memory Do You Need?

How much memory will your new computer need? The answer depends on your software. The bottom line is that you need memory (or RAM) in your computer. Memory in your computer is measured in megabyte units. The standard quantity for most new computers is 256MB of memory, or RAM. Some come with more memory — typically, 512MB. On a PC, Windows XP needs 128MB just to start, but it runs better with 256MB — best with 512MB.

Watch out for computers advertised with no memory or 0K or 0MB of RAM. This sales ploy makes a computer look cheaper than other models sold with memory. All computers need it, so you have to pay for it one way or another.