It's unfortunate that memory�one of the most important factors in measuring your computer's capabilities�is made so intimidating by the coded language used to describe it. But don't be scared off. It's worth your time to sort out all the letters because you'll use that information to understand your current components and decide if you want to, or can, make a change.

But before we delve into the subtle difference between EPROM and EEPROM, let's cover the basics.

RAM vs. ROM.

Memory itself comes in the form of memory chips, the integrated circuits that hold information. These chips store information in binary form, consisting of 0s and 1s that represent on and off.

Memory can be sorted into two categories with vastly different tasks: RAM and ROM. Most often, when you hear about memory, you're hearing about RAM, the place a computer temporarily holds information currently being used so the data can move quickly between the central processing unit, or CPU, and the operating system. Essentially, RAM is where the CPU, the computer's main processing chip, does its "thinking." Information in RAM can be stored and accessed randomly, and therefore, more rapidly (as opposed to the linear access of data on, say, a tape cassette).

RAM should not be confused with storage, which is where information is permanently held on your computer, much like a file cabinet where you keep your folders. This often confuses people. Just remember that when you open a file, it's loaded from storage (usually your hard drive or a diskette) into memory.

RAM is the vital workspace of computing; the more RAM a system contains, the more information it can handle, and the more programs it can run at one time. (Note that the arrangement of information in RAM also determines how much data your PC can handle.) RAM is often compared to the top of a desk, where you spread out a group of files so that you can quickly access information in any of them. The programs you use determine how much RAM you need. Graphical programs, for example, handle a lot of information and require much more RAM than word processors or spreadsheets.

How To Better Your BIOS Because the BIOS instructions stored in ROM tell the motherboard how to relate to hardware, BIOS upgrades are necessitated by new hardware: a larger hard drive, perhaps, or an upgraded microprocessor chip. Sometimes, a new operating system calls for a different BIOS; many computers needed a BIOS upgrade to support Windows 95's Plug-and-Play capabilities. Other times, BIOS upgrades are necessary to fix a bug with the original version, as with some software. If you need a BIOS upgrade, start by contacting the computer's manufacturer, who should be able to tell you what type of ROM you have (probably EPROM or flash ROM) and how you can upgrade its BIOS. You also might visit the manufacturer's World Wide Web site. If you can find information about changing the BIOS for your particular setup, that's a good indication that it can be changed. (See main article for more information about different types of ROM.) EPROM can be removed from the motherboard, reprogrammed by the manufacturer, and replaced, but it's usually less expensive to replace the old chip with a new one, says Robert Braver, president of Micro Firmware, a BIOS manufacturer. On the other hand, changes to flash ROM work like this: You find the specific BIOS needed for the motherboard and get an installation program, usually through the manufacturer. The program, stored on a diskette or downloaded from the Web, allows the motherboard to put the chip into a mode where it can be reprogrammed. Then, the installation program uses electricity to erase the data and rewrite the new data. This process is known as "flashing." But be careful. The wrong BIOS can cause a major�and majorly expensive�disaster. "You have to be really, really certain that you know what you're doing, and that you're getting the right BIOS for the right motherboard, and that you follow the directions carefully in regards to installing it," Braver says. In other words, don't mess with the BIOS unless it messes with you first. If you do make a mistake, different chips have different recovery modes, but at any rate, it won't be the most joyous of tasks to "recover" the system. In a bad situation, you'd have to send the whole motherboard to a repair facility so the flash ROM chip could be removed with special tools and reprogrammed, Braver says. In the worst case scenario, if the ROM chip is soldered to the motherboard, you may have an ever bigger problem on your hands. You can change a computer's BIOS, or have it changed, but you can't change the type of ROM itself, he says, with very few exceptions. For instance, if a computer has EPROM, it generally can't be upgraded to flash ROM because EPROM and flash ROM are set up in totally different ways. "BIOS is done as part of the actual design of the motherboard at the time the team of engineers is sitting down and laying it out," Braver says. "It (the BIOS) has to match the way the motherboard design is implemented."

Though RAM holds your information while you're working on it, it's no place to leave data between work sessions. When the computer loses power, RAM loses all of the information it contained. Even if power is gone for only a few seconds, RAM still forgets because it is volatile, or nonpermanent. That means a blink in the power can erase hours of work if you haven't been continually saving your work to permanent storage on a hard drive or diskette. RAM's volatility comes in handy, however, when you can "fix" a computer by just turning it off and then on again to clear memory.

Aside from its unfortunate acronym, you might have a bad association with RAM because it usually introduces itself by punching you in the face with a notice that you're short on memory. Sometimes you can free up memory by shifting some files around. (See "Avoid The RAM Cram" in this issue.) Even if you need to physically add more RAM chips to meet your needs, the news isn't all bad. Upgrading your RAM often is the cheapest way to speed up your computer. (See "Buying & Installing RAM" in this issue.)

The other common type of memory, ROM, as its full name implies, is a type of memory that�for the most part�only can be read and not changed; it also retains its contents even when the computer is powered down. ROM contains many of the basic instructions a computer needs to operate in BIOS (Basic Input/Output System, pronounced "BY-ose"). Without looking at the BIOS instructions stored on ROM, a computer won't even know how to read important files such as the Config.sys and Autoexec.bat files that are integral parts of starting up DOS.

The BIOS is always stored in ROM, and for the most part, it's all that's stored there. For that reason, ROM and BIOS are so interconnected that you'll hear the terms ROM BIOS and BIOS ROM used interchangeably. BIOS controls a computer's start-up processes and basic components such as the keyboard, display, and disk drives.

"It's a layer between the hardware and the software," says Frank Lazaro, marketing specialist at American Megatrends Inc., which manufactures BIOS. "If the software wants to access the hard drive, it has to go through the BIOS to make sure that the hard drive is working." The BIOS translates between the two because hardware speaks a machine language and software speaks a programming language.

Because of this, BIOS is considered a type of firmware, which is neither hardware nor software. BIOS is like software in that it contains instructions, but unlike software, it is an intricate part of the motherboard's circuitry that generally isn't changed by the user. (The motherboard is the computer's main circuit board.)

The BIOS traditionally was built into the ROM chip during the manufacturing process. Later technology let ROM be programmed after the manufacturing process�but only once. Now, as we'll explain later, an increasing number of computers have ROM that can be erased and reprogrammed. Instead of being stuck with the original BIOS instructions, users can customize ROM to fit user needs. (See the sidebar for more information on upgrading BIOS.)

Note that your computer's main ROM and BIOS�located on the motherboard�are usually the ones you hear about, and they're the ones we'll focus on. However, your computer may have other components with their own BIOS and ROM. For instance, a video card used to speed up graphics may have ROM programmed with video BIOS, which contains instructions that initialize the hardware on the video card. The technology of the chips themselves may be the same as the chips on the main ROM, but they're programmed differently.

Now that you have a general idea about how RAM and ROM work, you're ready to sort things out a little further.

Bad Memory.

We mentioned earlier that RAM loses the information it contains once the computer loses electricity. RAM's way of remembering anything, for any amount of time, is one of the major factors leading to different types of RAM.

The most common type of RAM, known as dynamic RAM (DRAM, pronounced "d-ram"), has such poor retention that it has to remind itself every few milliseconds what it's supposed to remember. That's because the electric charges representing information only store data for a brief time, like a bucket with holes in it. To compensate, the chips continuously read and rewrite the information in a process known as refreshing. If the computer loses power, all the water drains away.

DRAM chips contrast with static RAM (SRAM, pronounced "s-ram") chips. SRAMs consist of tiny transistors that are on/off switches. These switches don't require refreshing, although they still lose their memory if the PC loses power. SRAMs are faster but more expensive and bulky than DRAMs, so your computer probably uses DRAM chips. SRAM is used only in special situations where speed is most critical.

DRAM is broken down even further, but the "guts" of the three main types of DRAM are all the same, says Lucas King, a memory product manager at Kingston Technology Corp., a memory module manufacturer.

If you have a 386 or 486 microprocessor, you most likely have fast-page mode (FPM) memory, which locates information like you would in a book�by turning to a particular page, then selecting the appropriate information from that page.

Most PCs with Pentium CPUs, on the other hand, have RAM that uses a technology called extended data out (EDO), which is almost the same as FPM but faster. EDO lets the computer begin accessing new data even before it has finished reading the previous data. This shaves off enough time so that the chip can operate about 10% to 15% faster.

When you enter the realm of 200 megahertz (MHz) Pentium and Pentium Pro CPUs, you see synchronous DRAM, which just began appearing on desktop computers. Synchronous DRAM has a clock connecting the memory to the system clock, which controls the operations of the microprocessor's different chips. Having the input and output processes in sync makes the computer operate more efficiently.

The Memory Family Tree

In essence, says Gary MacDonald, vice president of marketing at Kingston, "each one of these is incrementally a bit faster than the preceding architecture. It's part of the game of catch up with the microprocessor." That's because today's speedy microprocessors often handle data more quickly than memory can handle it.

When it comes to types of RAM, your PC has what it has. You can't upgrade from, say, EDO RAM to synchronous DRAM, and the type of RAM isn't a key consideration even when it comes to buying a computer. What's important is how much RAM you have.

Understanding different types of RAM, however, will help you when the time comes to add more RAM to your machine�if for no other reason than you'll be able to nod intelligently at the salesperson and boast to your friends that your RAM is the grooviest.

Separate from all of this is a type of RAM called video RAM (VRAM, pronounced "v-ram"), a special, more expensive type of RAM chip. VRAM chips can send information to the monitor at the same time they receive new information. This type of chip, which is frequently needed for graphics-intensive software such as three-dimensional games or graphics applications, often is placed on a video card to speed the creation of on-screen images. (See "Video RAM To The Rescue" in our April 1997 issue.)

Can/Can't Be Changed.

ROM has about as many variations as RAM. Remember how we said that ROM instructions usually were built in during the manufacturing process and couldn't be changed? Exceptions to the rule lead to the different types of ROM.

For cases where ROM isn't being manufactured in large capacities, with the BIOS instructions as part of the manufacturing process, newer technologies let ROM be programmed. This type of ROM is often called programmable ROM (PROM, pronounced like the high school dance).

Almost all new computers will have some type of PROM, but you'll probably want to check what kind of ROM a computer has before you buy it, just for future reference. Some PROM can be written to only one time.

One of the most popular kinds of PROM is erasable PROM (EPROM, pronounced "e-prom"), which can be erased and reprogrammed when removed from the motherboard and exposed to ultraviolet light. EPROMs have a clear window covered with a label of some kind. Lifting the label exposes the semiconductor chip and lets it be reprogrammed. The correct dosage of ultraviolet light quickly erases the chips, and manufacturers change EPROMs with a special hardware device called a PROM blaster.

Electrically erasable PROM (EEPROM, called "double-e-prom") can be erased and reprogrammed with an electrical process in which a higher-than-normal voltage is applied to the chip. The BIOS can be rewritten right in the machine, but because EEPROM is more expensive than EPROM, it's less popular and is rarely used on the motherboard of a PC.

Newer computers store BIOS on flash ROM, which is sort of like EEPROM in that it can be electrically rewritten. It started becoming common in about 1995 because it's cheaper than EPROM and easier to reprogram, says Robert Braver, president of Micro Firmware, a BIOS manufacturer.

Once you find the correct installation diskette, updating the BIOS instructions is�theoretically�a simple task, thanks to flash ROM. You won't even have to open your PC.

Better still, with only the word "flash" tacked onto ROM, there's not yet another ingredient in our acronym soup of memory terms.

by Sarah Scalet