By David Gabel
Senior Reviews Editor

Of all the ways to improve your system's performance, a memory upgrade will likely give you the most for your money. That's because Windows 95 works around a PC's memory constraints with a simple procedure called disk caching. Here's how it works. Say you want to have Word, Excel and PowerPoint active so you can use OLE to work on a spreadsheet inside a Word document that will be the basis of a presentation. All of these apps are data intensive, but you have only 4MB of memory. That's not enough to have everything you need in active RAM. Nonetheless, Windows 95 will let you keep them all open. The OS takes the data that won't fit into active memory and writes it to the disk cache, a special area on the disk drive reserved for data that exceeds active memory capacity. If you're working in Word and then switch to Excel, Windows 95 will first "page out" portions of Word. Then it will retrieve Excel and its data from the cache.

There's no such thing as a free lunch, though. The cost for all this disk caching is execution speed. Disk access times are on the order of milliseconds, while memory access times are measured in nanoseconds--a million times quicker. If you can load all your applications into RAM, your computer will operate much faster.

So let's discuss the process of adding more RAM. There are several things you need to know before upgrading your computer's memory: how much it has, how much it can use and what kind it uses.

To find out how much memory you already have, click on Help/About in any Microsoft Office 95 application, then click on System Info. This will show you the amount of physical memory present in your computer. You can also go to the Start button and click on Run. Type mem in the dialog box to see how much memory you have installed. Then consult your system documentation or call technical support to find out the maximum possible RAM your PC will support.

Memory comes in the form of SIMMs (single in-line memory modules). These small circuit boards contain a number of memory chips of a given size, and are characterized by the number of contacts, or pins, that plug them into the motherboard. Common sizes are 1MB, 2MB and 4MB, while common pin counts are 30 and 72. The former pin count is used on many 486-based computers, while the latter is used on Pentium PCs. You can also call tech support to check out the type and speed of memory chips your system takes.

Also make sure you have open slots for memory--if you don't, you may have to replace the RAM you already have. Some manufacturers save money by filling all available RAM slots with less expensive, small-capacity modules rather than fewer modules of high capacity. This limits your upgrade options, unless you can afford to replace the memory you already have with larger-capacity SIMMs.

Access time, in nanoseconds (ns), tells you the amount of time it takes for your CPU to get data from memory. Common RAM access times are 60ns for Pentium-based PCs and 70ns for 486s. You can put faster memory (shorter access time) than is called for into a computer with no ill effect-but don't install slower memory, or you will lose data and slow your system's performance.

You also need to know if your computer uses standard DRAM or one of the less common types, such as EDO RAM or synchronous DRAM. Match the type, pin count and access speed to existing SIMMs.

Shop around. Mail-order houses often offer better prices than retailers. Check guarantees as well as price, and make sure the supplier you choose offers a money-back guarantee. It's also wise to pay with a credit card, since the card company may offer its own guarantee or assistance in case of a dispute.

Now that you've acquired your SIMMs, it's time to install them.

• First, and most importantly, ground yourself by touching your PC's frame. Do so while the computer is plugged in but turned off. Unplug the machine and open the case. It should be easy to locate your SIMMs--they'll likely be sitting slantwise in sockets on the motherboard.
• If you have to remove memory, push the catches on the side of the socket and rotate the SIMMs to the vertical. They should lift out.
• SIMMs go in only one way. Match the cutouts on the module to the notches on the sockets, then rotate each new module so that it's on a slant. The catches will snap into place.
• Once this is finished, close your computer case and fire up the PC. It should automatically recognize the new memory. You may have to go into the BIOS to upgrade your configuration information. If that happens, follow the on-screen instructions and access the BIOS, make and save the necessary changes, then exit.

Installing more RAM will almost always improve your machine's performance--and it's easier than you may think. Thanks to falling memory prices, RAM upgrades are also easy on your pocketbook. Windows 95 and today's memory-hungry apps demand more from a PC, so why not give them what they need?