Memory Packaging

Like processors, memory is made from tiny semiconductor chips and must be packaged into something less fragile and tiny in order to be integrated with the rest of the system. However, in many cases the chip packages are themselves further integrated into larger packages. There are many different kinds of memory packages in the PC world today, and it can be difficult to know which type needs to be used with a given system design. This section discusses the types of packaging available and the issues involved in selecting and using memory packages and DRAM chips in a PC. If you are looking for specific installation instructions for memory modules, see this procedure.

Dual Inline Packages (DIPs) and Memory Modules

Most memory chips are packaged into small plastic or ceramic packages called dual inline packages or DIPs. A DIP is a rectangular package with rows of pins running along its two longer edges. These are the small black boxes you see on SIMMs, DIMMs or other larger packaging styles. The DIP has been the standard for packaging integrated circuits since the invention of the PC, and in fact the earliest processors were also packaged as (large) DIPs.

Older computer systems used DIP memory directly, either soldering it to the motherboard or placing it in sockets that had been soldered to the motherboard. At that time most systems had a small amount of memory (less than one megabyte) and this was the simplest way to do things. However, this arrangement caused many problems. Chips directly soldered onto the motherboard would mean the entire motherboard had to be trashed if any of the memory chips ever went bad.

Chips inserted into sockets suffered reliability problems as the chips would (over time) tend to work their way out of the sockets. Due to thermal contraction and expansion as the machine was turned on and off, the chips would actually slowly come loose, a process called chip creep. Anyone who has worked at keeping an old XT running for many years probably remembers opening up the box and pushing all the memory chips back into their sockets with their thumbs to fix a memory problem. Dealing with individual chips also made upgrading or troubleshooting difficult.

Newer systems do not use DIP memory packaging directly. The DIPs are soldered onto small circuit boards called memory modules; the two most common being the single inline memory module or SIMM and the dual inline memory module or DIMM. The circuit boards are inserted into special sockets on the motherboard that are designed to eliminate the chip creep problem. This arrangement makes for better reliability and easier installation. Also, since SIMMs and DIMMs are (for most PCs) industry standard, it makes upgrades much simpler as well.

Parity, Non-Parity and ECC Memory

Most memory modules are available as either non-parity or parity. Some also are available as dedicated ECC-only modules. Non-parity is "regular" memory, including one bit of storage for each bit of data. Parity memory includes one extra bit of storage for every eight bits of data, used to store information about the data that the system can later use for error detection or correction. It can be used in parity or ECC mode. ECC modules are newer and also include extra bits of information, but can only be used in ECC mode. See this section for a full description of the differences between these memory forms.

Parity or ECC memory is generally more expensive than non-parity. Originally, this was because of the extra 12.5% worth of memory chips needed (one bit for every eight). Now, the increase in cost is more due to supply and demand issues, since non-parity memory is produced in much larger quantities. ECC is beginning to become popular again, and the price differential is shrinking as a result.

Parity memory will usually work in a non-parity system; the extra parity bits are ignored. However, non-parity memory will not work in a parity system (unless parity checking is turned off in the BIOS setup program, and some older systems don't even allow that). If you use non-parity memory in a parity system, a parity error will be generated as soon as the system boots up.

Standard and Proprietary Memory Modules

The three common sizes of memory modules (30-pin and 72-pin SIMMs and 168-pin DIMMs) are fortunately pretty close to being an industry standard. The vast majority of PCs use the "standard" or generic type of SIMM/DIMM. This gives the machine's owner the flexibility to shop the market and get the best deal on new memory.

There are still some companies however, that insist on using proprietary memory module formats. In many cases it can be difficult to distinguish these from industry standard SIMMs or DIMMs. If your PC uses proprietary memory, you must get upgrade memory from the manufacturer or from certain companies that manufacture third-party memory compatible with the manufacturer's proprietary format. Either way, you will have much less choice and your memory will cost significantly more. Check your system manual or talk to your vendor if you are unsure of whether or not your machine uses standard memory.

Single Inline Memory Modules (SIMMs)

The single inline memory module or SIMM is still the most common memory module format in use in the PC world, largely due to the enormous installed base of PCs that use them (in new PCs, DIMMs are now overtaking SIMMs in popularity.) SIMMs are available in two flavors: 30 pin and 72 pin. 30-pin SIMMs are the older standard, and were popular on third and fourth generation motherboards. 72-pin SIMMs are used on fourth, fifth and sixth generation PCs.

SIMMs are placed into special sockets on the motherboard created to hold them. The sockets are specifically designed to ensure that once inserted, the SIMM will be held in place tightly. SIMMs are secured into their sockets (in most cases) by inserting them at an angle (usually about 60 degrees from the motherboard) into the base of the socket and then tilting them upward until they are perpendicular to the motherboard. Special metal clips on either side of the socket snap in place when the SIMM is inserted correctly. The SIMM is also keyed with a notch on one side, to make sure it isn't put in backwards.

The 30 pin SIMMs are generally available in sizes from 1 to 16 MB. Each one has 30 pins of course, and provides one byte of data (8 bits), plus 1 additional bit for parity with parity versions. 72-pin SIMMs provide four bytes of data at a time (32 bits) plus 4 bits for parity/ECC in parity/ECC versions. Package bit width is discussed in detail here.

SIMMs are available in two styles: single-sided or double-sided. This refers to whether or not DRAM chips are found on both sides of the SIMM or only on one side. 30-pin SIMMs are all (I am pretty sure) single-sided. 72-pin SIMMs are either single-sided or double-sided. Some double-sided SIMMs are constructed as composite SIMMs. Internally, they are wired as if they were actually two single-sided SIMMs back to back. This doesn't change how many bits of data they put out or how many you need to use. However, some motherboards cannot handle composite SIMMs because they are slightly different electrically.

72-pin SIMMs that are 1 MB, 4 MB and 16 MB in size are normally single-sided, while those 2 MB, 8 MB and 32 MB in size are generally double-sided. This is why there are so many motherboards that will only work with 1 MB, 4 MB and 16 MB SIMMs. You should always check your motherboard to see what sizes of SIMMs it supports. Composite SIMMs will not work in a motherboard that doesn't support them. SIMMs with 32 chips on them are almost always composite.

Warning: Lately, some 16 MB and 64 MB SIMMs have been seen that are composite. These can cause significant problems with some motherboards, since they are specified to support 16 MB SIMMs on the expectation that 16 MB SIMMs will all be single-sided. You may not be able to use double-sided 16 MB SIMMs in some systems, especially older or cheaper ones.

Most motherboards support either 30-pin or 72-pin SIMMs, but not both. Some 486 motherboards do support both, however. In many cases these motherboards have significant restrictions on how these SIMMs can be used. For example, only one 72-pin socket may be usable if the 30-pin sockets are in use, or double-sided SIMMs may not be usable.

Dual Inline Memory Modules (DIMMs)

The dual inline memory module or DIMM is a newer memory module, intended for use in fifth- and sixth-generation computer systems. DIMMs are 168 pins in size, and provide memory 64 bits in width. They are a newer form factor and are becoming the de facto standard for new PCs; they are not used on older motherboards. They are also not generally available in smaller sizes such as 1 MB or 4 MB for the simple reason that newer machines are rarely configured with such small amounts of system RAM.

Physically, DIMMs differ from SIMMs in an important way. SIMMs have contacts on either side of the circuit board but they are tied together. So a 30-pin SIMM has 30 contacts on each side of the circuit board, but each pair is connected. This gives some redundancy and allows for more forgiving connections since each pin has two pads. This is also true of 72-pin SIMMs. DIMMs however have different connections on each side of the circuit board. So a 168-pin DIMM has 83 pads on each side and they are not redundant. This allows the packaging to be made smaller, but makes DIMMs a bit more sensitive to correct insertion and good electrical contact.

DIMMs are inserted into special sockets on the motherboard, similar to those used for SIMMs. They are generally available in 8 MB, 16 MB, 32 MB and 64 MB sizes, with larger DIMMs also available at a higher cost per megabyte. DIMMs are the memory format of choice for the newest memory technology, SDRAM. DIMMs are also used for EDO and other technologies as well.

DIMMs come in different flavors, and it is important to ensure that you get the right kind for the machine that you are using. They come in two different voltages: 3.3V and 5.0V, and they come in either buffered or unbuffered versions. This yields of course a total of four different combinations. The standard today is the 3.3 volt unbuffered DIMM, and most machines will use these. Consult your motherboard or system manual.

A smaller version of the DIMM is also sometimes seen; called the small outline DIMM or SODIMM, these packages are used primarily in laptop computers where miniaturization is key.

Gold and Tin Connectors and Sockets

Most people don't pay attention to the color of their memory module connectors and sockets, but they should. :^) There are in fact two different types of metal used. Most older motherboards use gold sockets for SIMMs. Newer ones use tin sockets (which is a silvery color).

It is important to make sure that you use gold memory modules in gold sockets, and tin modules in tin sockets. When gold and tin are mixed by putting gold in a tin socket or vice-versa, the direct contact between the two dissimilar metals causes a chemical reaction over time. It can take months or even years to happen, but tin oxide will build up on the gold and eventually, cause the electrical connection between the socket and connector to become unreliable.

While many people get by mixing metals, it is not recommended. I have seen gold memory in tin sockets produce errors after a period of time. There is really no reason to take the chance; just make sure to specify the right metal type when buying memory. (Don't be surprised if you get a funny look asking for a particular metal type. Many PC component vendors understand their product a lot less than their customers do.)

The current standard in newer systems using SIMMs is tin; the change from gold was made mainly as a cost-savings measure, but tin can be just as reliable as gold when used properly. Interestingly, gold is now coming back in vogue in most of the newest PCs, which use the DIMM memory packaging format. This is likely due to how "picky" SDRAM can be, which uses the DIMM format. Here are the three most common memory packaging styles and an assessment of their general availability in gold or tin:

• 30-Pin SIMMs: The oldest module type, these are most often found with gold contacts. I have seen tin ones, but they are not easy to find today.
• 72-Pin SIMMs: These are usually, in my experience, found with tin contacts. Gold ones are available for use in older systems and not too hard to find.
• 168-Pin DIMMs: The latest packaging technology, DIMMs are generally found only with gold contacts. There may be tin ones out there but I have not found a major vendor offering them for sale. Please let me know if this is incorrect (I got this one wrong once before. :^) )

Memory Banks and Package Bit Width

As discussed in the section on memory buses in the memory section and processor section, data from the memory flows to and from the processor along the data bus. The width of the data bus dictates how much information can flow in each clock cycle. In order to take advantage of the full width of the processor's data bus, it is necessary to arrange the system memory so that each clock cycle, the full data bus width can be transferred at once. In fact, most systems require the system memory to be arranged so that this is the case.

A quantity of memory that is wide enough to match the bit width of the data bus is called a bank of memory. Most of today's PCs have a data bus width of 32 bits (fourth generation processors) or 64 bits (fifth and sixth generation CPUs). A computer will not read a partial bank of memory; the result of setting up a partial bank ranges from the memory in it being ignored, to the system not booting at all. The PC definitely will not start if the first bank is incomplete, since then it has no usable memory at all.

Most PCs have room for more than one bank of memory; some support two banks, some three or more. Banks are usually numbered starting from zero, although sometimes starting with bank one. The lowest-numbered bank should always be filled first, and they should always be filled sequentially.

Each of the different types of memory modules arranges its memory so that a certain bit width can be accessed simultaneously. 30-pin SIMMs have a width of 8 data bits, 72-pin SIMMs have 32 data bits, and DIMMs have 64 bits. In addition, when parity is used, an extra bit is added for error detection. So 30-pin parity SIMMs have 9 bits, 72-pin parity or ECC SIMMs 36, and parity or ECC DIMMs 72 bits. Each module can be made up of various types of DRAM chips, as long as the right width is maintained.

Choosing memory packaging is an exercise in matching the width of the packaged RAM to the data bus width of the processor to make sure that a full bank of memory is provided. Fortunately, this is not as difficult as it sounds. The table below shows how this works (the 8088 and 8086 are not shown since they used individual memory chips, not SIMMs):

Note that a PC with a 64 bit data bus could use 8 30-pin SIMMs, except that this older technology is not supported on these newer machines; too much motherboard "real estate" is required with 30-pin SIMMs. Also, a 486 motherboard could actually make use of a single 168-pin DIMM to make up 2 banks of memory since the DIMM is 64 bits and the motherboard 32, but in practice this isn't done.

As you can see, Pentium-class and later PCs require two 72-pin SIMMs to make up a single bank. This is why you are always told to use a pair of SIMMs when buying memory for these machines. While this is generally true, there are in fact some Pentium motherboards that don't require a pair of 72-pin SIMMs. How is this possible? Basically, the chipset "cheats" by doing two consecutive accesses to 32 bits of memory at a time, allowing these machines to use a 32-bit bank size. This is a non-standard setup and leads to lower performance. It is found generally in older designs and is done mostly as a corner-cutting measure. In doing this, the bandwidth of the memory is cut in half for really no good reason. All else being equal, these motherboards should generally be avoided.

You should always use identical SIMMs when you require more than one to comprise a bank. Using different brands or speeds, or SIMMs with different types or quantities of DRAM chips, can cause motherboard system timing problems.

Memory Size Specifications

A specific notation is used to indicate the size and bit width of memory modules. These can be quite confusing to many memory buyers, especially if they don't understand the concept of bit width. However, knowing what these notations mean can help you make sure that you get the right kind of memory for your PC.

Memory modules have a specific width. Each module of the same type has the same width, so all 72-pin parity SIMMs for example have the same width and all 72-pin non-parity SIMMs have the same width. Larger SIMMs of the same format (say a 16 MB 72-pin SIMM as opposed to an 8 MB 72-pin SIMM) have more storage because they have a greater depth of storage for each bit of width. A memory SIMM or DIMM is usually specified using a notation that looks something like this: "2x32-60". The "x" is read as "by", just as a "2x4" in the lumber yard is called a "two by four", so this SIMM would be a "two by thirty-two sixty". A more generic way to express the notation is "DxW-S". Here is what each of the numbers means:

• D: This is the depth of the module in millions. For each bit of width, there are this many megabits (not bytes) of storage. This number is usually 1, 2, 4 or 8. For smaller SIMMs, it can be 256 or 512; in this case it represent the number of kilobits of depth, instead of megabits.
• W: This is the width of the module in bits. Each SIMM or DIMM type has the same width. This number is usually 8, 32 or 64 for non-parity modules, or 9, 36 or 72 for parity or ECC modules.
• S: This is the speed of the module in nanoseconds. It is sometimes not specified directly as part of the specification but each module should be rated with its speed.

What is confusing is that the actual amount of storage in megabytes is usually not shown. You have to be able to figure that out from the numbers given, although it's not that hard once you get used to it. So how do you interpret a "2x32-60"? This is a 72-pin SIMM (because it has 32 bits of width). The size of the SIMM is 2 million (depth) x 32 bits (width). 32 bits is 4 bytes, so the size of the SIMM is 8 MB (2 million times 4). The speed of the SIMM is 60 ns. To take another example, let's look at a "4x9-70". This is a 30 pin SIMM (because it has only 9 bits of width). The depth is 4 million bits. The size of the SIMM is therefore 4 million x 9 bits. The "9" tells us that it is a parity SIMM; only 8 of the bits are used to store data, and the ninth is for error detection. So the total size is 4 million x 8 bits which is 4 MB. The speed is 70 nanoseconds.

This table shows the different size specifications for common modules. Note that not all of these modules are necessarily available; I don't think that 8 MB 30-pin SIMMs even exist, as 1 MB and 4 MB are the only ones I ever see used. 2 MB SIMMs existed at one point but now are almost never seen. Notice the difference between the specifications of a 4 MB 30-pin module (4x8) and a 4 MB 72-pin module (1x32). This shows how the 30-pin module is narrower than the 72-pin (only 8 bits) but deeper (4M instead of 1M):

Tip: A simple rule of thumb to find the size in megabytes of any module from its "DxW" specification is as follows: take the D and W numbers and multiply them together (if D is 256 or 512, use 0.25 or 0.5 instead). Then, take the product and divide by 8 (for non-parity memory) or 9 (for parity). The result is the size in megabytes.

DRAM Size and Quality

For most people, it is not terribly important to pay attention to the number and type of DRAM chips that are used to make the SIMM or DIMM they plug into their PC. After all, the whole point of using these modules was so that it wouldn't be necessary to worry about all the little chips. However, all SIMMs are not created equal. Some older PCs will only work properly with SIMMs that have the right configuration and types of chips. There are also important quality issues associated with the DRAMs that the SIMM is made from.

Much as SIMMs are specified using a "depth x width" notation, the individual DRAM chips are as well. There are DRAM chips of various sizes available on the market, which have different depths and widths as well, and a SIMM can be made up (in general) of any combination of DRAM chips that adds up to the proper depth and width. For example, a 1x9 30-pin 1 MB parity SIMM is typically made up of either 9 1Mx1 DRAMs, or 2 1Mx4 DRAMs plus 1 1Mx1. In both cases, the total memory is the same: 1Mx9.

DRAMs are labeled using part numbers, usually a long string of letters and numbers. The exact part number is manufacturer-specific; however, many manufacturers' part numbers are similar in their last few digits, which can help you to identify the exact chip type and size if you need it. However, first, you have to be able to identify the manufacturer! This isn't always that easy, for two reasons.

First, they use a short code instead of the company name in many cases. Second, manufacturers often resell lesser-quality parts under a different name, a little-known fact. Manufacturers will often sell their top-quality parts (sometimes called "A grade") to their bigger customers and label them with their primary name. They will also have lower-quality parts (sometimes called "C grade"), perhaps not with as much margin on their marked speed or maybe not tested as well, that they will sell under a different label (for less money of course). The exact difference between high and low quality parts depends on the manufacturer. The high-quality parts may have passed more tests, or may have more speed margin compared to their rating. Either way, know that there is a difference.

This table shows common DRAM manufacturers and what the codes are that they typically use on their chips. I only know of some of the codes for the second-quality chips; another thing to look for in general is the name of a country on a chip. If it just says "JAPAN" or "KOREA", then the manufacturer has decided to leave their name off of their product--why do you suppose they would want to do that?:

It is important to realize that not all DRAMs are created equal. For the mostpart, a SIMM made from DRAMs manufactured by one of the major manufacturers is likely to be a good quality part. DRAMs that are either seconds as identified above or "mystery parts" with no known markings on them may easily be of lower quality (however, the latter could also be perfectly good parts made by a good company whose markings you don't recognize). Some companies have unfortunately even been known to sell partially damaged DRAMs on the market, which are bought by "price conscious" SIMM manufacturers and made into poor-quality memory modules.

The following table shows the different sizes of DRAM chips commonly used in memory modules, and the different bit widths that each size is typically available in. For each one, the configuration of the chip is shown (depth x width) and then in parentheses, the most commonly found last four digits of the part number found on the chip:

Note: The four digit codes above are the typical ones you'll find on FPM memory modules. EDO memory chips will have different numbers, and usually the pattern with 16 Mbit EDO chips is that they have a non-zero last digit where the FPM digit is zero. For example, a 4Mx4 FPM chip may have a 7400 code, while an EDO chip may have a code like 7404 or 7405. See this web site for a pretty comprehensive list of chip part numbers that you can use to find out specifically what's in your modules.

Chip Composition of Memory Modules

Better quality SIMMs/DIMMs generally speaking use fewer, higher-capacity DRAM chips. Cheaper modules generally use more, lower-capacity DRAM chips, because older technology costs less. Since SIMM sockets are close together, using modules with many chips makes it harder for them to cool. This is especially true of double-sided SIMMs. Also, more chips means more of an electrical load on the motherboard.

Cheap 8 MB SIMMs are often made with 16 4Mbit DRAMs. Many lower-quality motherboards will croak if you try to put 4 of these SIMMs in them, because they can't handle driving 64 individual DRAM chips. (They almost never mention this in the manual, either.) Some 64 MB SIMMs are made with 36 DRAMs a piece--try getting 4 of those to work on a motherboard! In addition, many SIMMs with tons of chips on them (24 or more) are composite, and these present other problems for many motherboards.

Despite the fact that better modules use fewer chips, some older motherboards can have problems with them. In particular, some older PCs that use 30-pin parity SIMMs will not work with 3-chip versions. This has to do with the additional complexity of using different-sized DRAMs on the same SIMM: a 9-chip 30-pin SIMM uses 9 chips each 1 Mbit in size, but a 3-chip SIMM uses two 4-Mbit chips and one 1-Mbit chip. The motherboard manual may say if 3-chip SIMMs will work (or you may find that your system is already using them). If unsure, use the 9-chip SIMMs; 9 isn't a large number of chips for a SIMM in any event.

This table shows the typical chip composition of non-parity 30-pin and 72-pin SIMMs, which are usually found in 2, 4, 8, 16 or 32 chip configurations. Note that some of these are more commonly found than others, and that there are also other combinations that can exist. Manufacturers will tend to use whatever chips they can buy economically that will make up the right blend of depth and width; in particular for many SIMMs there isn't much difference between a 4Mx4 and a 1Mx16 for example, so there may be several different ways to set up the larger modules:

Here is the same table for parity or ECC SIMMs, usually found as 3, 9, 12, 18, 24 or even 36 chip modules:

Memory Module Quality Factors

Assuming that "memory is memory" is one of the biggest mistakes made by people who buy RAM upgrades for their PCs. I know, because I used to make it myself. It's easy to walk into a computer show, or scan on the net for the lowest prices, and just buy whatever is cheapest. Even the vendors often have little understanding of the product they are selling, and some of them say as little as possible about the memory intentionally, because they know its quality is so low. So all they say is "16 MB EDO $xx". I've seen buyers make the decision to spend over 300 dollars on SIMMs at company A based entirely on the fact that they had a SIMM for $150 and company B's were $152. They just handed over the money, no questions asked (well, maybe "were these tested?", which always is answered in the affirmative by every vendor.) Would these people purchase a car, or even a stereo system in this manner? Unlikely.

The reason this happens is that the competition amongst vendors is fierce, and buyers have little knowledge of what they are purchasing. The perception is that all memory is the same, and so many people just buy whatever is cheapest. This is exacerbated by the fact that most systems today do not use parity memory, so users often don't realize that the random system problems they are having are due to poor quality memory. Many vendors are quick to pass off errors that are being caused by their memory as a "software glitch" or "motherboard defect", and in fact some of them are counting on you doing this when they sell you their junk (not all or even most, but some). The result of all this is that a lot of junk is being sold on the open market, especially by small companies to home builders and upgraders, and especially at computer shows or swapmeets.

Here are some quality factors to bear in mind specifically when evaluating memory modules:

• DRAM Quality: Inspect the manufacturer of the DRAMs used on each module you buy, or if buying by phone ask who makes the chips. If the person you are talking to doesn't even know what you are talking about, then you probably should consider buying somewhere else. If you can't determine who made the DRAMs, or if they are not marked as first quality DRAMs made by one of the big manufacturers listed in the table in the section on DRAM size and quality, keep shopping.
• Number of Chips on the Module: Avoid SIMMs that have more than 12 chips on them if at all possible.
• Module Quality: Do not assume that because you buy a SIMM that has chips saying "Toshiba" all over them, that the module itself was made by Toshiba. While DRAMs are made by big companies in large plants, the SIMMs themselves are assembled by many different kinds of companies. Some of them are rather unscrupulous and will cut corners in any way possible to save on cost. You are always best off to buy from a large reputable company, which is far more likely to be selective about where they get memory chips from, and conscientious about how they assemble them onto SIMMs.
• Warranty: A good company will give you a one-year warranty on your memory. Very good companies offer a lifetime warranty (even though these are rarely ever used if the memory doesn't fail in the first 90 days). If someone offers you the deal of the century on modules with no warranty, well, think about it.

Warning: Beware of parity modules that are actually what is called "logic parity"; they are not real parity memory and provide no error detection capabilities at all.

One final tip: beware of modules that have too many chips on them. I have seen (and even bought, before I realized what they were) 4x36 SIMMs with 12 DRAM chips on them. Now 12 chips is a normal configuration for a parity SIMM, but 4 of the chips should be smaller than the other 8. These chips were all the same size, and turned out to be 4Mx4 DRAMs, yielding a total of 4Mx48 bits worth of memory. Since the SIMM only needs 36 bits of width, why would they waste money putting the extra chips on the SIMM? The reason is simple: because only part of the DRAMs actually works. Some companies will sell damaged 4Mx4 DRAMs, where 3 of the 4 quadrants are still functional, as 4Mx3 chips. Then 12 of these can be used to make a 4x36 SIMM. You can see small resistors on these SIMMs which are used to control which portions of these damaged 4Mx4 are actually used. I saw these for sale at a "great price" at a computer show a long time ago and I got suckered. TANSTAAFL.

Next: Memory Errors, Detection and Correction

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The PC Guide Disk Edition - Version 1.8 - January 1999 Based on The PC Guide web site (http://www.PCGuide.com) Visit online for the latest updates, or to order Disk Edition upgrades. © Copyright 1997-1999 Charles M. Kozierok. All Rights Reserved. The Disk Edition is licensed only under the terms of the Disk Edition License Agreement and may not be distributed.
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