You don't need to be a genius to figure out your system's RAM needs, but you do need to know where to look and what questions to ask. These guides will explain everything there is to know about RAM. So, what are you waiting for? Get RAMbunctious!

Where to begin? It all depends on your experience and confidence level. If you're new to RAM, or want to brush up on the basics, start from "RAM explained." Once you master the basics, read the step-by-step installation instructions in "Plug it in" to get your RAM up and running. If you've already installed RAM and are experiencing problems, go straight to "Troubleshooting and beyond."

Contents

	RAM explained Think SIMM and DIMM are characters from a Dr. Seuss book? Don't be intimidated by acronyms. We'll help you figure out what separates your RAM from your DRAM.
	Plug it in Got a bargain on your RAM? Good! Don't blow your savings by forking over a wad of cash to a tech pro who'll take care of the installation. Empower yourself with this step-by-step installation guide.
	Troubleshooting and beyond Having problems with bootups, broken memory components, or PC compatibility issues? Use these common troubleshooting solutions to get your RAM up and running correctly.

RAM explained

Think SIMM and DIMM are characters from a Dr. Seuss book? Don't be intimidated by acronyms. We'll help you figure out what separates your RAM from your DRAM.

Your computer uses at least two types of memory: long term and temporary (you may also find memory chips on components such as video adapters, but we'll save that discussion for another day). Long term memory is found in hard drives and other storage devices; temporary memory is memory that is used only when the computer is on and functioning. Once you turn off your computer, the temporary memory vanishes. Temporary memory in your computer is referred to as RAM.

RAM is rated in terms of megabytes (MB), and a typical computer will ship with 64MB to 128MB installed. However, you can increase that total to 256MB, 512MB, or even a whopping 1GB, if your system supports it.

There are two basic types of RAM available today: SDRAM (Synchronous Dynamic RAM) and RDRAM (Rambus Dynamic RAM). And, there are three incompatible forms of SDRAM memory modules currently in widespread use. The form you need depends on the RAM sockets installed on your motherboard. Most systems available on the market today take SDRAM in 168-pin DIMMs (dual in-line memory modules); older Pentiums and later 486 PCs take 72-pin SIMMs (single in-line memory modules), while earlier 486 desktops take 30-pin SIMMs.

RAM modules are usually a little over an inch wide and four to six inches long--look for a row of slots projecting from the motherboard with at least one module plugged in. The number of pins refers to how many gold (or tin) contact strips are on the edge connector side of the SIMM or DIMM.

You can buy DIMMs that hold up to 256MB or more, but note that not all motherboards support all module sizes. To get an idea of the limitations of your system, check your motherboard or PC manual. 30-pin SIMMs are rarely produced anymore and expensive. If you're thinking of getting 30-pin SIMMs to speed up an older machine, shop around first because in the long run, it may just be cheaper to purchase a whole new system.

By Samuel Brown Baker II, Margaret Chesler, Robert Vamosi, Special to ZDNet

What about the fine print?

Depending on the type of motherboard you have, memory modules can also be of a certain type, speed, or in some cases, a specific metal lead type.

The types of RAM used in PCs over the past few years include, from fastest to slowest: SDRAM (used only in DIMMs), EDO (extended data out), old-fashioned FPM (fast-page mode) DRAM (found only in SIMMs), and DRAM (used in both DIMMs and SIMMs). Most motherboards require that you use only one of these four types. Some motherboards can handle more than one type, but still don't allow you to mix them. Consult your manual to find out which type of RAM you need, and whether you can use two different types at the same time or not.

The speed of SDRAM produced today is measured in megahertz (MHz). Your SDRAM must match the speed of your system bus or it won't perform as well as it's rated. Most new computers with SDRAM use PC100 or PC133 RAM. In other words, the RAM communicates with the CPU via a 100MHz or 133MHz bus. PC66 RAM was once de rigueur, but Intel popularized the PC100 standard with its 400BX motherboard, which supports Pentium II and Pentium III CPUs.

Older DRAM (EDO and FPM) speeds are measured in nanoseconds (ns). The lower the number, the faster the RAM. You can install DRAM with a faster speed rating than your system requires, but it won't improve performance. You cannot, however, install slower RAM or mix EDO and FPM DRAM in the same system and expect it to work.

SIMM socket contacts, or leads, are plated with tin or gold. Most manufacturers will insist that you buy SIMM modules that are made out of the same metal as your motherboard, or else run the risk of oxidising the module contacts over time. Manufacturers of DIMMs addressed this issue by making all contacts out of gold.

Until a few years ago, virtually all PCs depended on parity RAM, which supported a primitive form of error checking through the use of a ninth parity bit for each 8-bit byte stored. In the early days of the Pentium era, when memory was hard to come by and prices were high, many PC manufacturers switched to non-parity RAM. Most systems you'll encounter don't support parity at all; on others, it's an option at setup. If you're upgrading an older machine, make sure you don't mix parity and non-parity SIMMs.

Error Correction Code (ECC) RAM not only checks for errors, but also corrects some of them along the way. ECC RAM is more expensive than other types of RAM, and it's typically used only in machines that used for mission-critical applications, such as file servers. ECC and non-ECC RAM cannot be mixed.

What about newer types of RAM?

Today's computers have such fast processors that new types of memory are being developed just to keep up with them. RDRAM (or Rambus, for short), a higher access speed memory originally designed for graphics applications, has now found its way into some cutting-edge (1GHz and above) systems.

However, if you decide to go with RDRAM, you won't be able to swap out your SDRAM DIMMs and plug Rambus memory in their place. To take advantage of the RDRAM, your computer's motherboard must have a chipset that can support it, as well as the proper Rambus controller circuitry.

RDRAM is packaged in RIMMs (Rambus Inline Memory Module), which are roughly the same size and shape as DIMMs. A few dozen manufacturers--including Hitachi, IBM Kingston, Micron, NEC, Samsung, Toshiba, and Viking--are already in the RIMM business. One feature that's particular to RIMMs is a heat sink.

Since individual chips are mounted more closely together on RIMMs than on DIMMs or SIMMs, manufacturers had to come up with a way to direct heat away from them. That's where the sink comes in.

Another newcomer to the RAM game is DDR SDRAM (Double Data Rate SDRAM). DDR SDRAM is roughly twice as fast as standard SDRAM, and like RDRAM, it is not compatible with older systems. If you want to upgrade your RAM to DDR SDRAM, your PC's motherboard needs to support 184-pin DIMM slots, and your processor must be one of the newer ones designed to handle the extra bandwidth (such as the 1GHz and faster AMD Athlon chips) or all that speed just goes to waste. PC1600 DDR SDRAM is made for motherboards and processors with a 200MHz (100 MHz doubled) bus, and PC2100 DDR SDRAM is designed for motherboards and processors with a 266MHz (133MHz doubled) bus.

PC2100 RAM will work on motherboards with a 100MHz bus, but you won't see any dramatic boosts in performance.

What type of RAM do I need?

Earlier types of RAM were rated in ns (nanoseconds), while SDRAM is rated in MHz (megahertz), because its speed is somewhat dependent on your system's bus. Your motherboard's bus rating will determine whether you can use 66MHz, 100MHz, or 133MHz SDRAM. You can use RAM with a higher rating on a slower motherboard, but only if you plan to upgrade your motherboard someday, since the RAM will only run as fast as your motherboard will allow. On the other hand, since the price for 100MHz SDRAM is so low these days, you might as well pick some up simply to take advantage of the resale value.

PC100 is standard issue for Intel processors that conform to a 100 MHz bus. A 100MHz RAM module without PC100 on the label may not run as fast in your system, since it is only required to peak at that speed, and not necessarily sustain it. The same principles apply to 133MHz modules and the PC133 standard.

Don't just pick RAM at random. The simplest way to ensure you get the right kind of memory is to visit a memory vendor's Web site, and look for a memory configuration page that will match your system up with the correct memory type. When in doubt, check your motherboard manual or call the manufacturer and ask. If you can't get anyone on the line, give the serial number and model name of your computer to the memory supplier. If you have a generic PC or if you built your own, jot down your motherboard model and serial number, and contact your supplier. Based on that information, the supplier should be able to provide the exact memory type you need (and possibly even help you identify which modules are compatible with your system).

If all else fails, take a stick of your current RAM to a local PC repair shop. (Make sure you ground yourself before removing one of the sticks of RAM!) If you see more than one type of RAM, take one stick of each. Put them in an anti-static bag, and then take them to a local PC repair shop. (If you don't have an anti-static bag, pick one up at the repair shop first, or borrow one from a friend or the IS department at work.) They should be able to help you upgrade or replace it. Some shops can even test your RAM to see if it still works.

How do you determine just how much RAM you need? Take inventory. Make a list of the minimum RAM requirements of everything you run on your system and be liberal in your estimations. You'll definitely need more than what the vendor recommends if you want your system to run optimally. You can run Windows on 8MB of RAM, but you'll be doing a lot of waiting between mouse clicks. Calculate the total memory required to run all the programs you'll be using at the same time on your system, and then step up that number a bit.

RAM recommended by Microsoft Microsoft suggests the following minimum RAM amounts for its operating systems: Windows 95: 8MB Windows 98: 16MB or more Windows Me: 32MB or more Windows XP: 128 MB or more Windows NT 4.0: 16- to 32MB Windows 2000 Professional: 64MB or more

Go over the minimum if you can, especially if you're using applications that require a lot of memory. Photoshop, for example, keeps duplicate copies of your files. If you're editing photos that are 20 to 30MB, those files can really add up. Factor in at least twice as much RAM as the size of your largest photo. If you spend a lot of time editing video, you'll definitely want to invest in more RAM.

If you run games on your machine, keep in mind that your PC's main system memory determines how all the gameplay elements fit together: game rules, sound, AI, maps, and networking. While most games will run with 64MB, you'll get better gameplay with 128MB. Games that have very large maps or highly detailed gameworlds can eat up a full 256MB of memory. See this list from Kingston Technology for more OS recommendations for specific types of users.

Before you settle on a number, take your current system into consideration. The maximum amount of RAM you can install is subject to the limitations of your motherboard. Check your computer manual and see how much RAM your system supports. For example, if you own a Pentium system with a TX motherboard, anything more than 64MB is too much. The L2 cache on that particular motherboard only supports that much--any more than that will actually slow your system down.

Your system RAM is divided into banks so that your CPU can read one bank while it writes to another. So, if you're upgrading a system outfitted with DIMM sockets, you'll either add a DIMM that matches what you already have, or replace the existing DIMM with one or more higher-capacity modules. The general rule for SIMMs is that their banks must be filled in even multiples. If you have an older system (a 486 or earlier) with eight SIMM sockets, you'll need to add or replace four identical SIMMs at a time (because there are two banks with four sockets each). DIMMs, on the other hand, can be added one at a time because each socket is a complete bank.

Plug it in

Learn how you can add RAM to your system the right way with this step-by-step installation guide.

Once you have the right kind of RAM in your hot little hands, it's just a matter of matching modules to sockets, right? If you want to save yourself headaches later, the most important thing you can do to ensure a smooth installation is a little prep-work. Of course, it would help if your modules were oriented correctly in your sockets, too. Keep reading to learn how to install RAM the right way with this step-by-step guide.

Some systems require you to use pairs of matching modules to fill a bank of sockets on your motherboard; if you fail to match them up correctly, your system might not work properly. If you want 64MB of RAM, you may need to install two matching 32MB modules, instead of going with just one 64MB module, or one 32MB module plus two 16MB modules. Check your manual before you buy.

While it's in your best interest to shop around, don't skimp on quality. Get only grade A memory. It's amazing how many program crashes can be attributed to cheap RAM. If you can only afford generic, low-cost memory, make sure you get it from a reputable dealer who will refund your money if some chips turn out to be defective and you need to send a module back. If you buy from a store that's not online, ask the salesperson to test the memory first before you pay for it.

By Margaret Chesler, Bill O'Brien, Samuel Brown Baker II.

Installation

Before you install
Once you have your new RAM, take your time in setting up your workspace before you install. Make sure you have a clear workspace (if necessary, move the computer to another table). You should also be equipped with a tool kit that includes screwdrivers and pliers. If any of your tools have magnetized tips, do not touch any chip pins with them. Keep your new RAM in its anti-static packaging until you have your case open and you're ready to plug it in. You should also consider getting yourself a grounding strap.

Once your case is open and the power cord is unplugged, locate the SIMM or DIMM sockets. Look for the small circuit boards inside the case that match the size of the memory you purchased. DIMMs are typically longer than SIMMs. Many standard motherboards available today carry only DIMM slots, while some have sockets for both SIMM and DIMMs. You shouldn't mix DIMMs and SIMMs on the same motherboard. The voltages are generally different, and mixing memory types can actually shorten the working life of RAM. Check the motherboard manual to see if mixing is allowed.

While you're scrutinising the module and its socket, take note of the tiny latches on either side. SIMMs usually have metal tabs, while DIMMs tend to have plastic ones. Before you can remove your RAM, you'll need to gingerly pry these latches away from the module.

After you've pried the tabs off your SIMM, carefully rock the module forward past the latch on the socket using only your fingertips. If you use a screwdriver for this task, one slip could cost you a motherboard. Use your fingers. You don't want to end up using too much force or applying force to the wrong parts of the module. Once the module has moved past the latches, slowly pull it out.

168-pin DIMM slots
DIMM modules are much easier to remove. After you've unlocked the tabs, simply hook a finger alongside both edges of the module and pull it straight out of the socket.

Install a SIMM by sliding the module into the socket at an angle, pulling it up so that it's vertical. Chips should be facing the front of the motherboard. You can tell that the SIMM is oriented correctly if the small notch on one side of the SIMM matches the corresponding plastic tab on the SIMM socket. If it seems to be bowed rather than perfectly straight when you install it, you may need to reinstall it.

Installing a DIMM is much easier than installing a SIMM. Pull the small plastic tabs on either side of the DIMM socket outward so that they're slightly away from the socket. You should see a pair of notches on the DIMM that correspond to each key in the socket. Match the direction so the notch matches the key, then push the DIMM straight down. If you do it correctly, the plastic tabs you originally pulled out will click back into place by themselves. It will require some force so don't hesitate to lean into it just a bit.

That's really all there is to installing RAM!

A note about static

Static electricity is the buildup of electrical potential. When that little blue spark jumps from your fingertip to a nearby object, it's because that object has a lower electrical potential than you do at that given moment. Although it might pack several thousand volts, static electricity's amperage is so low that the "shock" you feel is no more than a tickle. However, that tickle carries more than enough amperage to harm your motherboard and almost anything plugged into it.

The electrical cord connected to your computer provides grounding, but only when it's plugged into an outlet that's properly grounded. While you can safely leave an AT case plugged in while you work inside, most ATX systems have a feature that supplies power to the motherboard even when it's turned off. You could end up frying one of your vital components if you leave it plugged in. Unplug the power connectors from the motherboard itself, but leave the cord to the power supply plugged in. This way, touching the bare metal of your case will diffuse any built-up static, and anything going into your motherboard will be safe from potential arcs.

If you don't want to be bothered with plugging and unplugging the power to the motherboard (which can be a real hassle when you're troubleshooting a hardware installation), at least get rid of the higher electrical potential by frequently touching a metal chair or table--preferably not the one the computer's sitting on. If you want to be extra cautious, touch a nearby cold water pipe to ground yourself.

Your best bet is to slap on a grounding strap, which is typically a bare, braided wire that wraps around your wrist and connects to the center screw of an electrical outlet. You can find one at most electronics stores.

Troubleshooting your RAM and beyond

Congratulations! You managed to install your newly acquired RAM. But, just when you thought everything was perfect, you notice a glitch in the system. If you've come this far, why not try to fix your own PC before you panic and call in a technician? Hopefully, you've left the cover off your PC and still have your grounding strap on. If not, review our directions and static precautions before you do anything.

Contents

	My new RAM won't work!
	What if my PC won't boot?
	What if my PC beeps after installing RAM?
	What if some of my RAM is bad?
	What if my PC won't recognise the chips?
	What if my RAM socket is broken?
	What if my RAM fails intermittently?
	What if you lose RAM while operating Windows?

By Robert Vamosi, Stephen Bigelow, Margaret Chesler

My new RAM won't work!

Certain characteristics of the memory module, such as speed, size, error checking, type, and so on, can make the difference between whether your computer accepts or rejects the installation. Check the product package and take a close look at the memory you bought. Make sure it meets your computer's requirements. If you're having problems, you may have simply selected the wrong type of RAM for your system.