FAQs and Troubleshooting Tips

Frequently Asked Questions - Memory


  1. What is a SIMM?
  2. What is a DIMM?
  3. What is a SODIMM?
  4. Is 168 Pin PC 100 SDRAM memory downward compatible with 168 Pin PC66 SDRAM memory? (In other words, can I put PC100 SDRAM in my computer that uses PC66 SDRAM?)
  5. What is Serial Presence Detect? 6. What is the difference between Registered SDRAM and Unbuffered SDRAM?
  6. What is CAS Latency?
  7. How do I figure out what type of memory requirements (PC 100/PC 133 SDRAM) are for my motherboard?
  8. What are some of the popular chipsets these days?
  9. What kind of memory do these chipsets support?
  10. Will PC 133 SDRAM work in a system that uses PC 100 SDRAM memory?
  11. Can PC 100 Unbuffered ECC SDRAM and PC 100 Registered SDRAM memory on be used on the same motherboard?
  12. Will 800MHz Rambus memory modules work in a system that uses 600Mhz Rambus memory?
  13. I have a Gateway G6 and/or GP6 series computer and have recently purchased a memory upgrade for this. After installing the RAM the computer either doesn't recognize the additional memory, or the system becomes unstable. What's wrong?
  14. When I attempt to install a 168-pin DIMM it doesn't quite fit or I have to really force it in the socket to get it to fit.
  15. My computer does not recognize the RAM upgrade when powered up. The memory fits but nothing happens. Why?
  16. My new RAM doesn't seem to be working at all, what can I do?
  17. The system is only recognizing a portion of the total RAM installed. What do I do?
  18. I purchased a RAM upgrade recently for my Windows NT computer in an attempt to eliminate the "out of memory" messages. After the RAM upgrade, I am still getting that message. Why?
  19. I have purchased SDRAM for my 66Mhz (FSB) Front Side Bus system and noticed that it says "100mhz" on the packaging. Will this memory work in a 100mhz Front Side Bus?
  20. After adding memory I got the error message, "Invalid system disk. Replace disk and press any key," and my system won't boot. Why?
  21. Will SimpleTech memory work with memory from another manufacturer?
  22. I have more than 512MB RAM. Why does Windows say I'm out of memory?
  23. What is the difference between ECC and non-parity memory? Is there a performance difference?
  24. Can you mix and match parity and non-parity modules?
  25. Will adding more RAM make my Internet browsing faster?
  26. My computer came with 32MB of RAM. I added 32MB in the second slot. Can I add 64MB or more in the third slot, or do I have to remove the 32MB modules and put in all 64MB modules?
  27. Can I use a 128MB PC100 SDRAM DIMM with a 128MB PC133 SDRAM DIMM?
  28. What is the performance difference between CL2 and CL3?
  29. Why did my computer slow down after I installed more RAM?
  30. Can I use PC133 memory on a system with a 200MHz front side bus?
Troubleshooting Tips - Memory Modules Pages

1. What is a SIMM?

SIMM (Single Inline Memory Module) is a device containing one or several random access memory (RAM) chips on a printed circuit board (PCB) with pins that connect to the motherboard. SIMMs are typically made in 30 pin and 72 pin packages and come in densities of 4MB-128MB. Most Pentium (64 bit data path) based systems require SIMMs to be installed in pairs. This was one reason for the invention of the DIMM, to save space.

2. What is a DIMM?

A DIMM (Dual Inline Memory Module) comes in sizes from 8MB to 1GB (currently) and is twice the bit path of a SIMM. This allows for only one DIMM instead of two SIMMs to make up the 64-bit data path.

DIMMs are typically made in packages of 72 pin, 144 pin (SODIMMs for portables) and 168 pins (Desktop, workstations and servers).

3. What is an SODIMM?

Small Outline Dual Inline Memory Module (SODIMM) is a DIMM made specifically for portable computers. SODIMMs come in 72 and 144 pin configurations. An SODIMM is smaller than a 168 pin DIMM.

4. Is 168 Pin PC 100 SDRAM memory downward compatible with 168 Pin PC66 SDRAM memory? (In other words, can I put PC100 SDRAM in my computer that uses PC66 SDRAM?)

PC 100 chips are downward compatible, however, the SPD (Serial Presence Detect) on a memory module must be programmed to PC66 (revision 1.0) before it will function properly in some computers which require PC66 SDRAM only.

5. What is Serial Presence Detect?

Serial Presence Detect (SPD) is a small EEPROM mounted on the DIMM that contains information about the DIMM module's size, data width, speed, voltage, etc. The Serial Presence Detect helps the system bios identify the memory as the correct type and properly configure the memory.

6. What is the difference between Registered SDRAM and Unbuffered SDRAM?

Registered SDRAM utilizes incoming address and control signals that are latched into a register during the leading edge of one clock cycle. On the leading edge of the next clock cycle, the signal is presented to the SDRAM components. This relieves the potential loading on the memory socket. The difference with the Unbuffered SDRAM is that the control signals are sent to the SDRAM component without a propagation delay (pipeline burst).

7. What is CAS Latency?

CAS Latency defines the number of clock cycles after which data is available on the bus once the Column Access Strobe has been asserted. CL2 represents 2 clock cycles. CL3 represents 3 clock cycles.

8. How do I figure out what type of memory requirements (PC 100/PC 133 SDRAM) are for my motherboard?

First, try usng Upgrade Navigator, our online Configurator.

Look for your motherboard's make and model there. If it is listed, you will find the correct Simple part numbers. If your motherboard is not listed in the Configurator, look for the PCI or AGP chipset of your motherboard in the user-manual. The chipset will give you the information regarding what type of memory it is able to manage.

9. What are some of the popular chipsets these days?

Some of the popular chipsets are Intel's 440BX, 440GX, 820, and the 840i.

10. What kind of memory do these chipsets support?

The 440BX chipset supports either Unbuffered Non Parity PC 100 SDRAM or Unbuffered ECC PC100 SDRAM (Up to 256MB).

The 440GX chipset supports Unbuffered Non Parity PC 100 SDRAM, Unbuffered ECC PC100 SDRAM, and Registered PC 100 SDRAM.

The 820 chipset supports Non Parity PC 100 SDRAM (No ECC support), Non Parity Rambus memory, and ECC Rambus memory.

The 840 chipset supports either Non Parity PC 100 SDRAM, ECC PC100 SDRAM, Non Parity Rambus and ECC Rambus memory.

11. Will PC 133 SDRAM work in a system that uses PC 100 SDRAM memory?

PC 133 SDRAM is downward compatible with PC 100 SDRAM memory.

12. Can PC 100 Unbuffered ECC SDRAM and PC 100 Registered SDRAM memory on be used on the same motherboard?

PC 100 Unbuffered ECC SDRAM and PC 100 Registered SDRAM memory can not be mixed in any stem.

13. Will 800MHz Rambus memory modules work in a system that uses 600Mhz Rambus memory?

A system that uses 600MHz Rambus memory can also use a 800MHz Rambus memory module as it is downward compatible.

14. I have a Gateway G6 and/or GP6 series computer and have recently purchased a memory upgrade for this. After installing the RAM the computer either doesn't recognize the additional memory, or the system becomes unstable. What's wrong?

More than likely you need to upgrade the bios on your system. Power down the system, remove the memory upgrade and download the latest bios update that's appropriate for your motherboard. After a successful bios upgrade is performed, reinstall the additional RAM and power up the system.

15. When I attempt to install a 168-pin DIMM it doesn't quite fit or I have to really force it in the socket to get it to fit.

First of all, make sure the clips on each end of the socket connector on the motherboard are retracted outward before attempting to install a memory module.

Second, verify that the module you are installing is compatible with your motherboard. On a 168-pin DIMM, there are two "notches" on the module. The notch in the center of the module determines the voltage of the module (typically 3.3V or 5V). The notch off-centered (to the side) determines whether the module is "buffered" or "unbuffered". The memory socket on your motherboard is "keyed" to discourage individuals from installing incompatible DIMMs. You may encounter some resistance when attempting to insert the module in a socket but it should not be excessive.

16. My computer does not recognize the RAM upgrade when powered up. The memory fits but nothing happens. Why?

Is the module seated correctly? It is possible to install a memory module incorrectly. Please remove the module, and reseat it making sure that all the contacts are seated and that any locking tabs are located correctly.

Does the module have the correct DRAM? Modules are available with different DRAM chips. Fast Page Mode (FPM), Extended Data Out (EDO) and Synchronous (SDRAM). If you have ordered "standard memory" for your system, you may have incorrect DRAM. Please refer to your owner's manual, or contact the computer manufacturer to identify which memory type is appropriate for you.

Have you installed the required quantity of modules?

Some machines require that memory modules are installed in kits of 2 or 4 modules. This is especially true on Pentium systems that use 72-pin SIMMs.

17. My new RAM doesn't seem to be working at all, what can I do?

Verify that you have the right type of RAM for the motherboard. Not all computers use the same type of memory. You'll have to look in the manual for its supported memory types. Is the memory the right size? Obviously, you can't stick 30-pin SIMMs into a 72 pin SIMM slot and expect it to work. Make sure that your new memory is the same type as your old memory (i.e. FPM/EDO/SDRAM, parity/non-parity/EEC, buffered/unbuffered). Using EDO or SDRAM in a system that does not support it will not work, often resulting in a blank screen and no POST (power on self test), or a BIOS/CMOS setup error.

Remove and reinstall the modules to make sure they are seating correctly in the socket.

Is it installed correctly? Plugged all the way in to the slot? Is the bank completely full? Are there any jumpers that need to be changed on motherboard (memory type, size, voltage, etc)? You could try cleaning the metal contacts if the memory is old. Also, make sure there is no limitation to how much memory the motherboard or the CPU can handle. Most fill your slots starting with the largest density and working to the smallest (put the largest module in slot 0, and the second largest in slot 1, and so on). Some systems go in reverse order, so if this doesn't work, try reversing the procedure.

If your DIMM module will not fit in the slot it is because you have an incompatible module. The two notches on a DIMM module are moved for 3.3V vs. 5V and for Buffered vs. Unbuffered.

If your system won't boot up with only the original modules in it, check all of your connections inside your PC. It is easy to bump a cable and pull it out of it's connector, disabling your hard drive or CD ROM.

If you are using MS DOS version 6.22 or earlier and are getting memory errors, consider running Memmaker to reconfigure your memory settings.

If you get a memory mismatch error follow the prompts to enter the BIOS setup utility, then select save and exit. Refer to your systems documentation for instructions on how to correctly enter the BIOS setup utility. (This is not an error - some systems must do this to update their CMOS settings.)

If your system is only reading half of the new module's memory, and the module has chips on both sides, then your system probably will only recognize single-banked or single-sided modules. Please return the memory and request single-sided modules with the same density.

18. The system is only recognizing a portion of the total RAM installed. What do I do?

Follow the same basic tips above for memory not working. Some motherboards have jumpers or switches on them, which govern the size of the modules. Refer to your user's guide for jumper settings.

19. I purchased a RAM upgrade recently for my Windows NT computer in an attempt to eliminate the "out of memory" messages. After the RAM upgrade, I am still getting that message. Why?

NT may be telling you that you are out of "virtual memory" not "system memory" (RAM). From Start button go to "settings", "control panel", "system", "performance". You may need to increase the "paging file size for selected drive" "Total paging file size for all drives" explains the minimum and maximum allowed. An experienced Information Systems technician should only modify these settings.

20. I have purchased SDRAM for my 66Mhz (FSB) Front Side Bus system and noticed that it says "100mhz" on the packaging. Will this memory work in a 100mhz Front Side Bus?

Most 66Mhz parts are made with 100Mhz dram chips, which may or may not be suitable for a PC100 environment. All SDRAM modules have an EPROM chip on the module that is programmed with an SPD (serial presence detect) code. The SPD is a line of code that allows the computer to identify the memory's functional makeup and how to interact with it. The system bios will attempt a "handshake" with the memory at power up to identify its characteristics such as dram type, speed, etc. The label on our generic SDRAM says "100mhz" on it. This refers to the speed of the dram and not the actual speed of the module. The modules are programmed to work in systems that require 66mhz SDRAM and will not work in systems that have a 100Mhz Front Side Bus. These 100Mhz FSB systems require "PC100" memory which can use selected 100Mhz dram or faster.

21. After adding memory I got the error message, "Invalid system disk. Replace disk and press any key," and my system won't boot. Why?

This error message is consistent with a couple of problems. The most common is that when reaching to install your memory, you accidentally bumped a cable (perhaps a hard drive cable). The first thing we suggest is to reseat all the cables in your computer; this includes the cable to the hard drive and hard drive power. When you turn on the computer, do you hear the hard drive start to spin or see the hard drive light flicker?

The second and much simpler solution may be that you have a floppy disk (that is not a boot disk) in your floppy drive. Please check to see that there are no disks in your floppy drives.

22. Will Simple memory work with memory from another manufacturer?

Yes. You can mix and match modules from different suppliers. The important things to remember when mixing module types are that you typically can't have more than one type of memory in the same motherboard (i.e., 1 EDO DIMM and 1 SDRAM DIMM), and you should always install the largest module (in MB) in the lowest numbered slot.

23. I have more than 512MB RAM. Why does Windows say I'm out of memory?

If you have more than 512MB RAM and are running Windows 95, 98, 98SE, or ME, you may not have enough cache to handle all of your memory. Solutions to this problem can be found at the Microsoft's Web site.

24. What is the difference between ECC and non-parity memory? Is there a performance difference?

If you already have a PC and are unsure which type you have, count the number of small, black, IC chips mounted on one of your existing DIMMs. If the number of chips is evenly divisible by three, then you need ECC. If the number of chips is NOT evenly divisible by three, you have non-parity memory.

If you are building a PC and deciding which type to use, the following guidelines should help. If you plan to use your system as a server or a similar mission critical type machine, it is to your advantage to use ECC. If you plan to use your PC for regular home, office, or gaming applications, you are better off with non-parity.

ECC (Error Checking and Correcting) performs "double bit detection and single bit correction." This means that if you have a single bit memory error, the chipset and memory will find and repair the error on the fly without you knowing that it happened. If you have a double bit memory error, it will detect and report it. Using ECC decreases your PC's performance by about 2%. Current technology DRAM is very stable and memory errors are rare, so unless you have a need for ECC, you are better served with non-parity SDRAM.

25. Can you mix and match parity and non-parity modules?

No. When adding new memory, you need to match what is already in your system. Parity modules have an extra chip that detects if data was correctly read or written by the memory module, depending on the type of error. However, a parity module will not correct the error.

You can determine if your system has parity by simply counting the number of black memory chips on each module. Parity (and ECC) memory modules have a chip count divisible by 3. Any chip count not divisible by 3 indicates a non-parity memory module.

26. Will adding more RAM make my Internet browsing faster?

Maybe. Internet browsing speed depends on a huge number of factors, including your connection speed, traffic on the site you're visiting, and the other components in your system. You will probably notice the biggest improvement from additional RAM if are viewing or working with large files (such as photos and digital audio and video) or if you switch between your browser and other applications often.

27. My computer came with 32MB of RAM. I added 32MB in the second slot. Can I add 64MB or more in the third slot, or do I have to remove the 32MB modules and put in all 64MB modules?

Different sizes of SDRAM modules can be mixed together. In other words, you do not need to fill each memory slot with the same size module, and yes, you should be able to add a 64MB module to the existing open slot on your motherboard. Keep in mind; the largest module should always be placed in the first slot for best performance.

28. Can I use a 128MB PC100 SDRAM DIMM with a 128MB PC133 SDRAM DIMM?

Generally you can mix PC100 and PC133 memory in the same system. The faster memory will run at the slower memory's speed (in this case PC100). However, there are some systems that will not correctly run this memory configuration. It is rare, but we suggest you contact your computer manufacturer or motherboard manual for specifics.

29. What is the performance difference between CL2 and CL3?

CL2 parts process data a little faster than CL3 parts, in that you have to wait one less clock cycle for the initial data. However, after the first piece of data is processed, the rest of the data is processed at equal speeds. Latency only affects the initial burst of data. Once data starts flowing, there is no effect. A clock cycle for a PC100 module is 10 nanoseconds so you probably won't notice a significant performance difference. Most systems will accept either latency part. However, there are some systems that require either CL2 or CL3 parts.

30. Why did my computer slow down after I installed more RAM?

In most cases additional RAM improves system performance. However, there are a few rare times when additional RAM actually makes the system slower. The most common reason for the problem is that the system doesn't have enough cache to handle the addressing for the additional RAM. If this is your case, the only solution is to upgrade your system or motherboard, as cache cannot be upgraded.

31. Can I use PC133 memory on a system with a 200MHz front side bus?

Sometimes, Yes. Some motherboards with 200MHz front side bus can take PC133 memory modules. Please check your system specifications and requirements.
Usually, PC133 memory is designed for use on systems with a 133MHz front side bus or slower. If your 200MHz front side bus is on a system with an AMD Athlon processor, you probably need PC1600 or PC2100 DDR modules. If your system uses an Intel Pentium 4 processor, you probably need RDRAM. In all cases, please check your system specifiations to decide which memory module is compatible with your system.

Troubleshooting Tips - Memory Modules Pages