Installation

In general, the memory of your computer will work throughout the life of the machine without requiring any attention. Memory has no moving parts that require service or lubrication. The only time you're likely to tangle with memory is when you decide to add to your computer's native endowment , either by adding to its main memory on the motherboard or by adding an expansion board to enhance the size of a disk cache or video frame buffer.

Memory installation is a process that requires care but does not demand expertise or extreme precision. You can usually add a few megabytes in a few minutes without worrying about damaging the memory, your computer, or yourself.

The care required involves taking simple precautions . Avoid static electricity, which can damage any solid state circuitry, including memory chips. The most cautious sources usually recommend that you ground yourself to a cold water pipe before you dig into the circuitry of your computer. Most people just plug in chips or modules without a thought to static. Unless you draw sparks when you touch things on your workbench, you're probably safe to install memory modules.

In that one of the primary design goals of memory modules is simplified installation, modules make expanding the memory of your computer easy ”or at least easier than it would be with a box full of discrete chips. Modules do not, however, make memory installation or expansion "trouble free." You still must match modules with your computer and insert them in their sockets properly.

Memory Speed

Memory speed is one of the most critical factors in computer performance. Faster memory can move data to the microprocessor faster. Today's microprocessors are so fast that they outrace any kind of memory, so anything you do to make your system's memory faster can help performance.

Most of what you can do to speed up memory requires an advanced degree in tinkering . You can experiment with the advanced setup adjustments in your computer's BIOS (if it affords you such adjustments) to see how many corners you can cut before your computer freezes up and dies.

Mostly what you do with memory makes your computer slower. The design of your computer limits the top speed at which its memory can operate (even though faster memory might benefit your computer). Adding faster memory won't break through this speed limit. On the other hand, add memory that's too slow when you expand your system, and your whole system might shift into low gear. Modern memory systems can detect the speed rating of memory modules, and they will slow down their operation to match the slowest memory in your computer.

The best strategy when adding memory to your computer is to duplicate what you already have. If your system has PC100 memory installed, always install more PC100 memory.

Mixing Modules

Modern memory module design precludes you from using the wrong kind of memory in your computer. Because memory modules are made from discrete chips, they use the same underlying technologies. SIMMs made using static, dynamic, video, and page-mode RAM technologies are available. As with discrete chips, different module technologies are not completely interchangeable, so you need to specify the correct type when ordering memory for your computer.

At one time, however, the different memory types ”fast page-mode, EDO, and Burst EDO ”all used exactly the same style of module: the standard SIMM. In general, a computer designed for fast page-mode SIMMs could use other SIMM technologies but derives no benefit from doing so. Similarly, the higher speed of the more advanced memories could be wasted . Sliding a fast page-mode SIMM into an EDO socket would slow your entire system down to the fast page-mode speed.

With DIMMs, you ordinarily do not need to match modules. Each one constitutes a full bank of memory. You should be able to mix different sizes and install modules in any order. Mixing module speeds will only result in your system operating at the speed of the slower module (if it doesn't reject the laggardly memory as too slow). In reality, you may find slight differences between modules and motherboards. (A motherboard can sometimes be persnickety about where you put the modules.) That said, upgrading memory is much easier than it used to be, and you're much less likely to encounter problems if you just slide modules into the sockets that they fit into.

Contact Material

At one time, the contacts used by memory modules sometimes came plated with tin and sometimes with gold. The purpose of this plating is to prevent oxidation or corrosion that would increase the resistance of the contact and lower the reliability of the connection. In the abstract, gold is the preferred material because it oxidizes less readily. Gold also costs substantially more, encouraging manufacturers to opt for tin.

One manufacturer of electronic component sockets, AMP, points out that the material is not so important as the match. You should choose memory modules with contacts plated with the same material as used in the sockets in your computer. The explanation goes deeper than the plating.

According to AMP, putting tin in contact with gold and exerting pressure on the contact results in a problem called fretting . Part of the tin rubs off, attaches to the gold, and oxidizes there, thus building up a thin layer of tin oxide. The longer the two materials contact one another, the thicker the oxide build up.

Gold is not the only material susceptible to this oxide buildup. It can develop when tin contacts nearly any dissimilar metal. The problem does not arise when tin-plated contacts press against other tin-plated contacts. Of course, the tin surface will naturally oxidize on the tin-plated contacts, but when you insert a tin-plated edge connector into a tin-plated socket, the soft tin gives way. Pushing the contacts together squeezes or wipes the tin oxide away from the contact area so that tin presses against tin.

Today, nearly all DIMMs and their sockets use gold plating, so you're unlikely to encounter problems with modern computers. With older SIMMs, however, you'll find both contact materials are prevalent . Matching material is the best bet. If you have an older computer with a metals mismatch in its sockets and memory errors, you may be able to correct the problem by cleaning the contacts on the memory modules. Although special contact cleaners are available, you will get good results wiping the contacts clean with an ink eraser (the kind that is slightly abrasive). Don't clean too hard, though, because you may wipe the contact material entirely off.

Orientation

When installing memory modules, remember that their orientation is important. In general, all modules in a computer will face in the same direction. Of course, with two-sided modules with components on both sides, you can't easily tell which direction anything is facing . The key is to look at the notches in the edge connector at the bottom of the module. You'll see the notches line up with tabs in the socket when the module is oriented in only one direction ”the right way. Should you try to insert a module and discover that it refuses to fit, you probably have it in the wrong orientation or improperly seated.