RAM - (Random Access Memory) Usually described in terms of how many Megabytes (Meg or MB). This is the type of memory used in personal computers today. Older computers usually have 16-32 Meg ram installed in them. Newer computers frequently have from 64-256 Meg of ram installed in them.

Why do people need to add more RAM to their computers? Because if a computer doesn't have enough RAM (chips) the computer will use the hard drive to manage data during processing instead of memory chips. Since memory chips are substantially faster than a hard drive, if the computer runs out of available space on the memory chips, then the entire system will slow down to the speed of the computer's hard drive, which causes a substantial decrease in performance of the computer regardless of the speed of the hard drive.

How do I know if I need more RAM? This answer is a little complicated. A general rule is that more is better unless you already have plenty. The fact is, if you don't need more RAM, then adding more RAM will not speed up your PC. But, if too little RAM in your system is causing a 'bottle-neck', then adding more RAM will surely speed up you PC. More specific examples of when to add memory follow:

a. If you're running Windows XP, you will need at least 128MB, but you'll run much smoother with 256MB. If you are running windows 98 or Windows ME on your computer then you should have at least 64MB but you computer will almost surely run faster if you have 128MB, although 256MB is best. 512MB couldn't hurt especially if keep several programs open at once or if you are a heavy gamer.

 

b. If you are running windows 95 on your computer then you should have at least 32MB. If you have any less than 32, then adding more RAM will almost definitely speed up your system. 64MB to 128MB is recommended.

 

c. If you are running Windows NT workstation or Windows 2000 Professional, then you should have at least 64MB, but 128MB or 256MB is much more common and will certainly speed up your system.

 

d. If you PCs HDD (hard disk drive) light flickers a lot during standard processing, you almost definitely need more RAM. This is an indication that the computer is running out of available space on your memory chips, so it is therefore relying more heavily on the swap disk portion of your hard drive to process data. Since your hard drive is much slower than your RAM chips, your entire computer system is slowing down to the speed of your hard drive. Adding more RAM will allow your PC to perform more processing entirely within the RAM chips and that will speed up your computer.

 

e. The System Resources of Windows 9X, ME or 2000 indicates less than 65%. Right click on the MY COMPUTER icon, scroll down to properties and then click on the PERFORMANCE tab. Check the % of available resources that are free.

 

f. You multitask a lot of programs at the same time in Windows. If you use several utilities and programs simultaneously having extra memory will increase performance.

 

g. You receive error messages indicating that you don't have enough memory.

 

h. You don't need more memory if you already have plenty. If memory is not a bottleneck in your system then adding more will not increase performance. Spend your money on something else.

Some definitions

SIMM - (Single In-line Memory Module) These are circuit boards that have memory chips soldered on to them. They are usually installed in groups or 'banks'. SIMMs usually come in two major types. 30-Pin and 72-Pin. A 30-pin SIMM measures about 3 inches and a 72-pin SIMM is about 4 inches long. 72-pin SIMMs have the value of 4 30-pin SIMMs. For example, four 1Meg 1X8 30-pin SIMMs, (which has 8 data bits), is equivalent to one 4 Meg 1X32 72-Pin SIMM, (which has 32 data bits).

 

DIMM - (Dual In-line Memory Module) Similar to SIMMs but the arrangement is slightly different. DIMMs have the value of 2 SIMMs and are therefore added individually (not in pairs). The DIMMs commonly used in PCs today have 168 pins (count them if you want). DIMMs generally use Synchronous DRAM and are therefore referred to as SDIMMs.

 

Fast Page Mode (FPM) - The standard variety of RAM that has been in use for many years. Also known as 'regular' or 'non-EDO' to the less informed.

 

EDO - Extended data output. This is a newer standard for RAM that came into use in 1995. It has a greater throughput than standard Fast Page RAM. The last generation of systems to use EDO RAM were the first Pentium-IIs.

 

PINS - The number of contacts on a memory module that make contact with the SIMM socket. Try counting them if you wish.

 

Parity and Non Parity - Refers to additional bits of memory on a SIMM module. Parity checking is a method of verifying the integrity of the computers data. Some computers perform parity checks during data processing.

 

Logical Name - The industry descriptor used to identify value of a memory the module. Examples are 8X32-60 (32Meg 72-pin SIMM) or 4x64 (32Meg DIMM). Here is a guide to understanding this nomenclature.

 

168-pin DIMMs - There are 32 Meg, 64 Meg, 128 Meg, 256 Meg and 512 Meg DIMMs in popular use. They are identified as somethingX64 (non-ECC) or somethingX72 (with ECC). The sixty-fifth through the seventy-second bits are the ECC bits. The formula to determine the megabytes on a DIMM is (xXn)/8 for non-ECC and (xXn)/9 for ECC DIMMs. For example, a 16x64 DIMM is equal to 128 Meg. (16x64=1024, 1024/8=128).

 

72-pin SIMMs There are 4 Meg, 8 Meg, 16 Meg 32 Meg and 64 Meg SIMMs in popular use. They are identified as a somethingX32 (non-parity) or somethingX36 (parity). The thirty-third through the thirty-sixth bits are the parity bits. The formula to determine the amount of memory on a 72-pin SIMM is (xXn)/8 for non-parity and (xXn)/9 for parity SIMMs. For example, a 2X32 SIMM is equal to 8 Meg. (2X32=64, 64/8=8).

 

30-pin SIMMs There are only 1 Meg and 4Meg 30-pin SIMMs in popular use. They are identified as a 1Xsomething or a 4Xsomething. There are non-parity, (1X8), and parity, (1X9), versions of these SIMMs. The ninth bit is the parity bit. Another convention of naming the SIMMs is to identify the number of chips on a 30-pin SIMM. Therefore a 1X3 is just like a 1X9 except that it uses 3 chips to make the same thing. The three chip SIMMs are comprised of two chips which have the value of 4 each, totaling 8, and one more chip to make the ninth (parity) bit. These SIMMs are functionally and logically equivalent to a 9-chip SIMM and can be used in place of a 9-chips SIMM in almost all cases. Sorry, but we don't sell 30-pin SIMMs anymore. Why? Because no one makes them anymore.

NS - Nanoseconds. The -60, -70 or -80 number at the end of each logical descriptor refers to the rated nanosecond speed of the module. The lower the number the faster the rating of the SIMM or DIMM module.

How do I know what type and quantity of memory modules I should buy to upgrade my computer? This is by far the most difficult question for most end users. There are several keys to determining what you need. Here is a handy upgrade guide. It will hold true in almost all cases, although there are certain non-standard types of system designs which may not conform to this guide.

a. Check your users manual. Most manuals will have a chart indicating the various combinations of modules that are appropriate for your PC. If you can't decipher this chart, just bring your manual in to PCs for Everyone and we will help you read it. 

 

b. Check the memory modules in your PC. What is already there will usually indicate what you must buy. Open up your system and look for some sign of the type of memory module. Many module manufacturers will clearly indicate the type, the megabyte size, and the speed of the module. There may also be some indication of whether the type of RAM chips used on the module, such as SDRAM, EDO RAM, Fast-Page RAM, etc. Additional RAM features such as parity, ECC and buffering may be indicated as well.  

 

c. Depending on the processor-type of your PC, you can figure out what you need. To find out what your 'processor'  (CPU) is, either check your user's manual or the invoice for your PC. Almost all PCs will tell you the processor type during boot up. As the system is turning on you will most likely see a BIOS screen. Press the 'pause' key on your keyboard when the BIOS screen appears. This will allow you to take your time to study the information provided. Does it mention the processor/CPU type?

Keep in mind that you can usually substitute faster RAM for slower RAM (about 98 percent of the time) and then under-clock the memory module. This circumstance will often happen because your system is getting on in years (we usually equate 1 human year to 20 computer years), and RAM and module manufacturers may no longer produce the exact memory product for your PC any longer because the demand has subsided. So, for example, if your PC needs PC66 SDRAM, you can probably use PC100 modules set to run at 66MHz. 

 

 

Pentium-III - Its all over the place!

Unfortunately this platform is becoming more and more complicated because the RAM you need depends on the MHz speed of your PC, the FSB (front side bus) speed of your system and the type of memory that is already installed in your PC as well. Did you know that your CPU speed is a function of the FSB speed of your system and a multiplier. For example, a Pentium-III 500 uses an FSB speed of 100MHz and a multiplier of 5. So the motherboard is running at 100MHz and the CPU is running at 5 times the speed of the motherboard. Get it?

 

If you have a Pentium-III 450, 500 or 550, 650, 700, 750 or 850, which use an FSB speed of 100MHz, you definitely need PC100 SDRAM. While it is remotely possibly that your PC could have PC133 SDRAM installed, it is very unlikely. Some systems let the memory BUS to run independently if the front side bus speed. So the motherboard might be running at 100MHz, the CPU at a function of the motherboard FSB (say, 500MHz from the example above) and a memory bus speed of 133MHz. Confused?

 

If you have a P-III 533, 667, 733, 866 or 933, which use an FSB speed of 133MHz, you probably need PC133 SDRAM, but since it is possible that your system has PC100 SDRAM (your PC maker could have used RAM and set the memory bus at 100MHz, a speed which is slower than your CPU's FSB speed), look for some indication on your BIOS screen of the type of RAM (PC100 or PC133) that your system is using. If you have already opened up your system, you can look at the memory modules themselves. There could be a sticker on the module that indicates the speed of the RAM. Confused yet?

 

If you have a P-III 600, or 800MHz system, your FSB speed could be 100 or 133MHz. (Of course 600 and 800 can be divided neatly in either 1 or .5 increments by 100 and by 133). How can you tell which one you have? Look at the opening BIOS screen for some giveaway information. Intel labels their CPUs with a suffix that indicates the CPU's FSB. E refers to a Pentium-III coppermine core at 100MHz and EB refers to a coppermine Pentium-III core at 133MHz. Generally, the core MHz speed will be the same as the speed of your RAM. If you have a P-III 600 and there is no suffix, you likely have a 'classic' P-III with a Klamath core, (which has 512K of 1/2-speed cache), which means that your FSB speed will be 100MHz, so you will need PC100 SDRAM.

 

The CAS Latency rating of the SDIMMs that are installed in your PC determine the type of RAM you need to buy too! Obviously, most people have never heard of CAS Latency, let alone know the CAS Latency of the RAM installed in their PCs. The lower the CAS Latency rating of your RAM, the faster the system can write information to the RAM and therefore there is a performance gain from using lower CAS Latency RAM. Lower CAS Latency is also an indication that the RAM is of a higher quality and may perform better in the long run as well.

 

Not knowing the CAS Latency of your SDRAM is generally not a problem because of the SPD chip on your module! SDIMMs have a very tiny chip on them known as the SPD EEPROM which stands for Serial Presence Detect Electronically Erasable Programmable Read Only Memory. This chip has been programmed by the module manufacturer and holds the information about the specifications of your SDIMM module. Most motherboards will, when set correctly, automatically read the specifications of the module through the SPD and set itself up correctly. If you mix two different types of CAS Latency modules in the same PC, your motherboard should automatically run at the lowest common denominator of the CAS Latency speeds. Problems can occur, however, if your system is manually set to a faster CAS Latency setting (thereby overriding the automatic SPD settings) and you inadvertently add slower CAS Latency RAM. Because your system will try to run the RAM at a CAS latency speed that your RAM can't handle, your PC may experience instability as the system tries to write to the RAM faster than it is able to reliably accept the data.

 

 

Pentium-II - The RAM Depends on the chipset!

Your motherboard is controlled by a 'chipset'. These are the chips that soldered directly into your board. Who makes the chipset, and the chipset generation (usually identified by an alpha or alpha-numeric name) is very important in determining what RAM your system needs.

 

The first P-II motherboards originally would only take EDO ram because they were based on the older Intel FX chipset, which was developed for Pentium-Pro chips. Almost all FX chipset based Pentium-II motherboards had sockets for 168-pin EDO DIMMs only. Very few were designed to take EDO SIMMs.

Starting at approximately February 1998, P-II motherboards began shipping with the newer Intel LX chipset which had an FSB (front-side bus-speed) of 66MHz. LX boards run at a maximum bus speed of 66MHz and do support PC66 SDRAM DIMMs, (also known as SDIMMs). PC66 SDIMMs are usually 10 nanoseconds. By the summer of 1998, motherboards started shipping with the newer Intel BX chipset, which could run at 100MHz. The BX chipset boards take PC100 SDIMMs. You can add SDIMMs to your Pentium-II motherboard one at a time.

 

Depending on the MHz speed of your P-II, you either need PC66 or PC100 SDRAM. P-II 233, 266 and 333 CPUs run at an FSB speed of 66MHz so you need PC66 SDRAM (or PC100 or PC133 modules set to run at 66MHz, underclocked). If you have a P-II 350 or 400 you need PC100 SDRAM (or PC133 SDRAM underclocked). If you have a P-II 300 your CPU's FSB could be 66 or 100 MHz, but since hardly anyone sells PC66 SDRAM anymore, just get PC100 or PC133 SDRAM modules. Your system will run them at either 66 or 100MHz anyway, so don't worry about it. :-)

Intel specifies the use of an SPD EEPROM (serial presence detect electrically erasable programmable read only memory, whew!) chip mounted on the surface of the SDIMM when used on the 440LX or 440BX chipset motherboards.

 

Another popular option, especially for critical workstations and servers is the use of memory modules containing ECC, (Error correction code). These modules require an extra memory chip for every 8 chips on the module for a total of 9 or 18 chips.

 

Motherboard approved RAM is very important too! Although this is not required, it is certainly recommended for the in any system. Not all memory modules are made alike! Even though they cost a little more than the standard SDIMMs, we strongly encourage the use of the motherboard approved SDIMMs that we carry.

 

Lastly, another important factor in purchasing SDIMMs is the technology of the chips on the DIMM model themselves. For example, when purchasing 512 Meg SDIMMs, it is recommended that users pay the additional amount to get the 16-chip (non-ECC) or 18-chip (with ECC) designs rather than the 32-chip or 36-chip designs. Why? Because when it comes to DIMMs, the fewer chips on the module, the better. So why do some DIMMs have double the number of chips? It is because the modules employ different densities of chips. Going back to the 512 Meg example from above, the 16-chip design uses 16 of the 256-megabit chips and the 32-chip design uses 32 of the 128-megabit chips. 256-megabit chips cost more per megabyte than 128-megabit chips. Therefore, the 32-chip module is less expensive than a 16-chip design. But, having too many chips on a memory module can be unstable. We definitely prefer to build systems with the 16 and 18-chip designs.

 

 

Pentium(P5) or AMD K6 or Cyrix 6x86 Socket-7 or Socket-8 . 

How do you know if your board has a socket-7 or socket-8? Just look at the CPU socket. It will be clearly labeled with the socket level.

 

If you are running an older Pentium level socket-7 computer system, then you will almost definitely need a pair 72-pin SIMMs, either EDO or Fast-Page type. This group includes Intel Pentium, Pentium Pro, Cyrix/IBM 6x86 and AMD K-5 processor-based computers. Pentium level systems, which have a 64-bit BUS, require that SIMMs be added in pairs, (each 72-pin SIMM has 32-bits). Older Pentium class systems (when the maximum processor the board will take is a Pentium-100 or Pentium-133 CPU), usually are designed for 'Fast-Page' SIMMs. Later Pentium-class machines (usually Pentium 166 or higher) take EDO SIMMs but fast-page SIMMs will likely work too.

 

Again, look at the SIMMs already installed in your PC. If you already have EDO, stay with EDO. If you already have fast-page, stay with fast-page. To identify which SIMMs are already installed look at the module. Is there a sticker that says EDO, for example? Another giveaway is to look at the speed of the RAM chips on the SIMM module. If you see a -6 or a -60 it means that the SIMM runs at 60 nanoseconds. This is usually an indication that the SIMM is EDO, since the EDO spec is 60ns. If it has a -7 or -70 it must be fast-page since 70 nanoseconds is too slow for EDO RAM.

 

If you have a Pentium-166-or-higher socket-7 Pentium-class machine, then you may also be able to use DIMMs. DIMMs have 168 pins. count them if you like (snore). Most boards made at that time have sockets for both 72-pin SIMMs and 168-pin DIMMs. Different boards had different limitations regarding the what SIMMs and what DIMMs they would accept and also had limitations about taking different combinations of SIMMs and DIMMs together. Check your user manual. Hopefully there will be a chart that specifies what you can and cannot add.

 

You board may also have on-board jumpers that must be reset depending on the memory combination that you are using. 

 

If you are adding SIMMs to the motherboard you MUST add them two at a time, Why? Because SIMMs are 32-bit and your motherboard's memory BUS is 64-bit, so you have to add two at a time to cover the 64 bits.

 

If your board takes DIMMs, you can add them one at a time since a 168-pin DIMM is 64 bits wide and it exactly covers the motherboard's 64-bit BUS.

 

DIMMs for socket-7 boards will come in either EDO or SDRAM versions. Depending on the motherboard chipset of your computer it may not accept SDRAM. Earlier Intel FX and HX chipset motherboards did not accept SDRAM. Newer Intel VX and TX motherboards will usually take SDRAM DIMMs or EDO SIMMs . SDRAM only comes on DIMMs, and not on SIMMs.

 

Your computer may require parity SIMMs or ECC DIMMs. Some computers REQUIRE parity memory, while some computers will optionally use parity memory and still others have no facility to utilize parity memory. Even if a computer is not utilizing parity or ECC checking, the presence of the parity or ECC bit on the memory module will generally not be problematic and is simply over-kill. Parity and ECC modules are more expensive than non-parity SIMMs due to the addition of the parity/ECC bit, so you can save money by not buying parity or ECC SIMMs if you don't need to. How do you know if you need parity SIMMs or ECC DIMMs? Here's a handy way to determine whether to buy parity or ECC modules or not:

 

Check your users manual. It may refer to the type of memory needed in your system. It may also refer only to the number of bits, 8-bit (30-pin non-parity) or 32-bit (72-pin non-parity) RAM, or 9-bit (30-pin parity) or 36-bit (72-pin parity). The manual may also specify the logical industry descriptor, such as 1X32 (4Meg 72-pin non-parity SIMM) or a 1X36 (a 4Meg 72-pin parity SIMM). In the case of DIMMs the manual may state 64-bit (non-ECC) or 72-bit (with ECC).

Since the use of parity and ECC memory is usually optional, (the motherboard and BIOS may support it, but the computer may not have been purchased with it), you should try to determine the type of module actually installed in your PC. The opening BIOS screen (as you start up your PC) may indicate whether parity or ECC is installed. Press the 'pause key' just when your PC shows this screen and read it carefully. Is there any information there that may indicate the type of RAM installed? 

You can also Look at the memory you have in the computer now and by counting the chips on the module you can determine what type of RAM is there now. If your system uses 72-pin SIMMs, check to see whether it has either eight or sixteen chips on the module, which indicates non-parity. If it has twelve or twenty four chips then it is has parity. If your system uses DIMMs, check to see whether it has eight or sixteen chips on each side. Eight or sixteen indicates non-ECC and nine or eighteen chips on each side indicates ECC (error checking).

Check your BIOS setup information. Is there a section for parity or ECC checking? If there is, is it enabled or disabled? If it is enabled you may consider disabling it and buying the less expensive non-parity or non-ECC SIMMs. Most computer industry experts agree that based on the slim chance that the average user would ever experience a data processing error for which parity memory is designed to check, and the marginal benefit you would receive from such a successful detection is generally not worth the added expense of parity SIMMs. But this is for you to decide.

 

 

486 and 386 Computers

If you are running a 486 processor based system it may require either 30-pin or 72-pin SIMMs or a combination of both. 30-pin SIMMs will always be added in groups of four. 72-pin SIMMs can usually be added one at a time. You will also need to determine whether you should purchase EDO or Fast-page type ram on the SIMMs. Look in your user's manual or on the BIOS screen at boot up for any reference or mention of EDO (extended data output) ram. IF you don't see anything that refers to EDO, you should probably get the older style Fast-page RAM. If EDO is mentioned, then get EDO ram since it is a little faster and usually less expensive!

 

Another way to check for EDO is to look at the 72-pin SIMMs themselves (30-pin SIMMs never use EDO chips). If the speed on the SIMM is described as -60 or -6 it may indicate EDO type. If you see -70 or -7 it cannot be EDO since the spec for EDO is 60ns or faster. (The lower the number the faster it is.)

If you are running a 386DX, 486SX, 486DX, 486DX4, or 586 (a 586 really runs from a 486 motherboard), processor based computer then you need to add memory 32-bits at a time.

 

This means you might add four 30-pin (8-bits each) SIMMs in a single group or 'bank' or a single 72-pin (32-bit) SIMM which also constitutes a 'bank'. If you are adding 30-pin SIMMs (4 at a time of course), each SIMM within the bank must be of equivalent value.  Also, you should not mix-and-match manufacturers and types of SIMMs (e.g. 1Meg vs. 4Meg, 9-chip vs. 3-chip, 60ns vs. 70ns), within a single bank. You will need to consult your users manual or physically open up your computer to determine which type of SIMMs you currently have and which banks are open and can accept additional SIMMs. If you are uncomfortable with opening up your computer, bring it in to PCs for Everyone and we will check for you and install the memory if you wish. (A $10 charge will apply if you ask us to install your SIMMs).

 

If you have a really old 486 system which has eight SIMM sockets, (i.e. two banks of four), and both banks are filled with 1Meg 30-pin SIMMs then you need to remove four of the 1 Meg SIMMs, (i.e. one bank), and replace them with four 4 Meg 30-pin SIMMs, leaving you with a total of 20 Meg.

Older computers (produced summer of 1994 and before) usually require 30-pin SIMMs and newer computers usually need 72-Pin SIMMs

 

If you are running a 386 processor based system you almost definitely need 30-pin RAM.

 

If you are running a 386SX or 486SLC processor based computer system then you need to add 30-pin SIMMs, two at a time. This is because the motherboard BUS on your computer is 16-bit. So you need two 8-bit 30-pin SIMMs to cover the 16-bit BUS.

 

How do you know what speed SIMMs to buy for your computer? In general, it is wise to purchase the same speed of SIMM that you already have, or faster. Most 486's need at least 70ns fast-page SIMMs and most Pentium level systems need 60ns EDO ram.