Frequently Asked Questions About Computer Memory

Over the years we have been bombarded with memory questions about what works, what doesn't, as well as which motherboard should have which memory. Sometimes some of the questions are rather zany or crazy, while others are rather serious quests for information. Here you will find a grouping of the most frequently asked questions that we have received, to which we have added those asked of memory manufacturers such a Micron/Crucial, Samsung, Kingston and NEC to name a few. We have even left questions in our FAQ relative to 386 machines, as we still receive questions about them. 

Just click the numerical link to the left of the question to go to the answer. If you don't find your answer here, we're certain you will find it in our Performance and Technical Centers.

1. Why the transition from SIMMs to DIMMs?
2. By looking at a module can you tell if it is SDRAM, FPM or EDO?
3. Other than speed, what are the advantages of SDRAM?
4. How are PC100 specifications different from standard SDRAM specifications?
5. Can you mix SDRAM and EDO modules?
6. On some motherboards built for SDRAM is there some sort of bus width restriction which makes the SDRAM perform no better than an EDO motherboard?
7. Can you use SDRAM in older machines?
8. Why is it so important to get SDRAM designed specifically for your motherboard?
9. Why is it so much more difficult to come up with a good SDRAM module than an FPM or EDO module?
10. What is the difference between buffered and registered?
11. Ho do I determine whether I need buffered, un-buffered or registered SDRAM?
12. What is the performance difference between EDO and FPM (fast page mode) DRAM?
13. If a SDRAM DIMM module is assembled with a -10 SDRAM chip, is it considered PC100 compatible?
14. Are PC133 speed-tested SDRAMs backward compatible with PC100?
15. Several Memory module suppliers are offering PC133 modules with a performance setting of 3-2-2. What advantage does a 2-2-2 module provide?
16. Can you explain capacity on SDRAM - how does it work?
17. What is the difference between 72 bit and 64 bit memory, and the difference between 32 bit and 36 bit memory?
18. What is the difference between 2-clock and 4-clock?
19. Please explain ECC support vs. non-parity.
20. What's the difference between 2K and 4K SDRAM?
21. What is the difference between 100MHz and 10ns?
22. What is the difference between buffered and un-buffered DIMMs?
23. What is CL or CAS Latency?
24. What is the difference between CL2 and CL3?
25. What does refresh rate and self refresh mean?
26. What is an EPROM or EEPROM?
27. What is the difference between SPD and PPD?
28. What will happen if my memory is not PC100 compliant?
29. How do I recognize compliant PC100 or PC133 SDRAM memory?
30. What voltage is SDRAM?
31. What is the difference between "2-clock" and "4-clock" SDRAM?
32. What is PC SDRAM, PC100 SDRAM and Registered SDRAM?
33. What are the general guidelines for memory upgrade based on a CPU?
34. Do I need PC100 SDRAM for my PC system?
35. How Much Memory Do I Have?
36. How do I know when I have enough memory?
37. Okay, then how much memory do I need?
38. Memory for 386 Computers
39. Memory for 486 Computers
40. Memory for older Pentium Computers (586 Computer)
41. Memory for Pentium Pro Computers (P-6 (686) Processor)
42. Memory for Apple Macintosh Computers
43. Will more memory speed up my computer?
44. What do I need to Remove, Install or Replace defective modules and upgrade to new modules?
45. I have just installed memory into my 486 and have a blank monitor and the system refuses to boot. What's wrong?
46. I just installed 16MB of memory in my 486. I turned on the computer and get a message: Invalid configuration/run setup. How do I fix this error?
47. My Pentium 100Mhz computer came with EDO memory. I installed two new EDO 60 nanosecond SIMMs and now my screen is blank when I boot the computer. Why?
48. I want to purchase Fast Page Mode memory for my 486 computer, but the retailer only has EDO and Parity memory. What do I purchase?
49. What is the difference between EDO memory and Fast Page Mode memory?
50. Will EDO modules work in my 486DX2-66?
51. How many modules do I need to upgrade my Pentium?
52. I installed EDO memory in my Pentium system and am now encountering boot-up problems, why?
53. I own a Pentium 200MHz computer which has SDRAM memory. I have one memory slot available on the motherboard for upgrading. Do I have to remove the existing module and install in matching pairs to upgrade my memory?
54. What does ESD mean?
55. What does CL2 & CL3 mean?
56. Will DDR SDRAM memory work on my current PC system using PC133 memory?
57. What is a "Virtual Channel" or VC SDRAM Memory?
58. Can my PC-133 memory be backward compatible to my older PC system?
59. How can I tell if my PC133 memory is a 6 layer or 4 Layer PCB board?
60. What is OEM Memory?
61. Why do memory prices fluctuate so much?
62. How can I Troubleshoot my memory using the BIOS Beep Codes?
63. Troubleshooting Memory Failures using Award BIOS Beep Codes
64. How do I clear the printer memory after each page is printed?
65. My PC boots up okay but seems to hang up after running for one hour or so. How can I find out what is wrong?
66. If I have regular memory sizing error during POST (boot up), how should I trouble shoot the failure?
67. How do I troubleshoot a memory failure without a memory tester?
68. A Simple Guide to Troubleshooting Memory Failures without a Memory Tester
69. What do the AMI BIOS Beep Codes mean?

 

Q Why the transition from SIMMs to DIMMs? [Top]
A 72-pin SIMMs transmit data 32 bits at a time, while 168-pin DIMMs transmit data 64 bits at a time. As systems moved to 64-bit memory bus widths, it makes more sense to use DIMMs than SIMMs as the standard memory form factor. SDRAM technology itself has nothing to do with the transition from SIMMs to DIMMs. It’s just that the transition from EDO to SDRAM technology and the transition from SIMMs to DIMMs happened at about the same time.
 
Q By looking at a module, can you tell if it is SDRAM, FPM or EDO? [Top]
A An SDRAM chip looks just like a similar FPM or EDO chip. Both types of chips are used on the same kinds of modules (e.g. 168-pin DIMM). The best way to tell the difference is to reference the part number on the chip. Most DRAM chip manufacturers have reference pages on their WEB sites that list the chip specifications by part number. In our "How to Visually Identify Your Memory" and "How to Identify PC133 Memory" sections, you will find the references you need.

By looking at a memory module one can attempt to guess what it is. A general guideline is to look at the IC type and size. The EDO and FPM chips are typically packaged in SOJ form and are thicker when compared to that of the SDRAM chips which are typically packaged in slim-line TSOP form. The EDO/FPM chips typically have a marking of -60 at the end of the string of numbers, while SDRAM chips typically have markings of -12 -10 -8 -7.5. A SDRAM module typically has a row of resistors or a resistor array above the contact tabs.
 
Q Other than speed, what are the advantages of SDRAM? [Top]
A Memory speeds must increase in order for the computer to benefit from ever-increasing CPU speeds. SDRAM Technology enables more efficient communication between the CPU and memory. This means data can be accessed faster, which increases the overall performance (or speed) of your computer system. This is the single advantage of SDRAM over older memory technologies, but it is crucial.
 
Q How are PC100 and PC133 specifications different from standard SDRAM specifications? [Top]
A PC100 and PC133 specifications are far more stringent than 66MHz SDRAM because there is less time allowed for memory access.
 
Q Can you mix SDRAM and EDO modules? [Top]
A Some motherboards support the simultaneous use of both EDO and SDRAM modules, but this is not common practice. In order for the system to take full advantage of the benefits of SDRAM, all memory in the system should be SDRAM. By mixing the two, faster SDRAM memory will be slowed to that of the speed of EDO. See our Memory Speeds Review.
 
Q On some motherboards built for SDRAM is there some sort of bus width restriction which makes the SDRAM perform no better than an EDO motherboard? [Top]
A The 66Mhz system bus does limit the performance increase of 66MHz SDRAM over 66MHz EDO technology to slightly less than 10%. However, new PC100 class motherboards supporting 100MHz SDRAM have enabled performance increases of approximately 20% over prior 66MHz technology.
 
Q Can you use SDRAM in older machines? [Top]
A In order to take advantage of SDRAM technology, you must have a system board that includes SDRAM support. Most memory manufacturers offer SDRAM for all systems that support it. For older machines that do not support this type of memory, we provide the correct technology based on what each motherboard will support.
 
Q Why is it so important to get SDRAM designed specifically for your motherboard? [Top]
A If the module has not been qualified for your system, it may not be fully compatible with your motherboard. This means the system might not boot up at all, or if it does you may get intermittent failures and lost or corrupted data. We provide system specific modules which are controlled to guarantee compatibility with your system.
Q Why is it so much more difficult to come up with a good SDRAM module than an FPM or EDO module? [Top]
A SDRAM components operate at higher speeds and require much tighter design parameters. This includes matching trace lengths for clock and data lines, as well as impedance matching. FPM and EDO modules do not require as stringent controls.
 
Q What is the difference between buffered and registered? [Top]
A A buffer is a device used on EDO or Fast Page Mode modules. A register is used on SDRAM modules. Registers and buffers “re-drive?or “amplify?signals as they enter the memory module.
 
Q How do I determine if I need registered or un-buffered SDRAM? [Top]
A Generally, your motherboard manual will provide the necessary information, however if the manual isn't available, we can provide it for you with our system configuration library.
 
Q What is the performance difference between EDO DRAM and standard (Fast Page Mode) DRAM? [Top]
A EDO DRAM speeds up memory transactions by as little as 5% or by as much as 25% over conventional DRAM, depending upon how much Cache you have on your motherboard. Less Cache on the motherboard will result in a larger speed increase when adding EDO DRAM. EDO eliminates a wait state between the execution of sequential-read commands from memory, giving the CPU significantly faster access to memory.
Q If a SDRAM DIMM module is assembled with a -10 SDRAM chip, is it considered PC100 compatible? [Top]
A No - An SDRAM DIMM with -10 (100 MHz) chip will support only 66 MHz Systems. This type of module is not guaranteed to run consistently in a PC100, 100 MHz system.

In order for the module to be PC100 compatible the components need to be marked with -8A, -8B, -8C, -8D or -8E (or 125 MHz) and example taken from micron chips.

Micron Modules with -8A through -8C SDRAM chips will run at 100 MHz at a CAS latency of 3.

Modules with -8D or -8E components will run at 100 MHz at a CAS latency of 2.

Refer to the original manufacturer data sheet to determined the correct CAS latency setting.
 
Q Are PC133 speed-tested SDRAMs backward compatible with PC100? [Top]
A Yes. The AC timing specifications on a PC133 device are tested to allow a system bus to run at 133 MHz.

The PC100 and PC66 timing specifications are more relaxed on these timings.

Majority of PC133 chips should work at PC100 and PC66. In fact, a -75 device is specified for PC100 timings using CAS latency = 2.

Please refer manufacturer data sheet for AC timing table in the appropriate data sheet tCK at CL = 2.
 
Q Several Memory module suppliers are offering PC133 modules with a performance setting of 3-2-2. What advantage does a 2-2-2 module provide? [Top]
A The first number of the 2-2-2 designation refers to CAS latency, so in short you are asking the advantage of a CAS latency of 2 over one of 3.

Adjusting a device to CL = 2 from CL = 3 will speed up access time from a READ command to the point at which data is available on the data bus (1 clock quicker).

Based on benchmark testing results, better performance improvements were found in the 2-2-2 setting over the 3-2-2:
 
Q Can you explain capacity on SDRAM - how does it work? [Top]
A The capacity of an SDRAM module is calculated the same way as an EDO or FPM design. For 168-pin modules, multiply the depth x 8 to determine the capacity. For example, a 4M x 64 memory module is 32MB.
 
Q What is the difference between 72 bit and 64 bit memory, or the difference between 32 bit and 36 bit memory? [Top]
A 72 bit memory is commonly known as ECC memory. It has an additional 8 bits for Error Correction Check 64 bit memory is non-ECC. 72 bit or 64 bit configuration are typically found in 168 pin DIMMs

36 bit memory is commonly known as parity memory. It has an additional 4 bits for parity checking. 32 bit memory is non-parity. 32 bit or 36 bit configuration are typically found in 72pin or 30 pin SIMMs
 
Q What is the difference between 2-clock and 4-clock? [Top]
A SDRAM requires clock lines running from the system clock to the memory module. Two clock means there are two clock lines running to the module, and four clock means there are four clock lines running to the module. Four clock designs are faster because they allow less chips per clock line, enabling a quicker interface with data.
 
Q Please explain ECC support vs. non-parity. [Top]
A Parity is a form of error detection, which can detect memory errors and halt the system to prevent data corruption. The term Non-parity evolved to describe modules that did not have error detection capability. ECC (Error Correction Code) memory is a more complex form of error detection which not only detects, but also corrects most memory errors while your system is running. ECC support means the system is capable of supporting ECC memory, but can also run with non-parity modules.
 
Q What's the difference between 2K and 4K SDRAM? [Top]
A The SDRAM has multiple internal banks. The 16M SDRAM has 2 banks, the 64M has 4 banks. When you tell the SDRAM a ROW or COLUMN address you must also specify which BANK you are referring to. The way to do this is by the 'bank address' (BA). Herein lies the problem. For some unknown reasons, suppliers have lumped together the ROW address pins with the BANK address pins and simply refer to them as 'address' pins. For the 2Mx8 SDRAM some suppliers claim to have 11 ROW address plus 1 BA, other just say 12 addresses. That's just addressing, for refresh requires you also specify the refresh interval (tREF). For a distributed refresh scheme you simply divide tREF by the number of refresh cycles to get the auto-refresh interval. In both cases (for SDRAM) it works out like:

Address bits Refresh Cycles tREF Auto-refresh interval
11 row 2^11 = 2048 = 2K 32ms 32ms / 2048 = 15.6 us
12 2^12 = 4096 = 4K 64ms 64ms / 4096 = 15.6 us

The upside is that for distributed refresh schemes these two devices are identical in both addressing and refresh. (For a burst refresh scheme, the 32ms tREF is a subset of the 64ms.)

For the general PC application the 2K device works fine. The 4K device offers no advantage. Note that this is not the case for asynchronous DRAM where there truly is a difference in addressing between 2K and 4K.
Q What is the difference between 100MHz and 10ns? [Top]
A With respect to SDRAM chips, the terms are used interchangeably. “MHz?is a speed, and it means the “number of cycles per second? “ns?means “nanosecond? an actual period of time. A nanosecond is one billionth of a second. 100MHz means there are 100 million clock cycles per second. That means one tenth of a clock cycle per nanosecond, or one clock cycle in 10ns. 100MHz SDRAM chips are marked as 10ns, because there are 10ns between clock cycles.
 
Q What's the difference between buffered and un-buffered DIMMs? [Top]
A High density DIMMs have lots of chips on them and therefore possess a higher capacitive load on the address and control signals in comparison to lower density DIMMs. Some designers use re-drive buffers on the DIMM to boost the signals to reduce system loading when compared to the same high density module without buffers. But, the buffers introduce a small delay into the electrical signal, so adding buffers to a standard density module would have the effect of slowing down the signal, compared to the same low density module without buffers.
Q What is CL or CAS Latency? [Top]
A CL stands for CAS Latency. It is a programmable register in the SDRAM that sets the number of clock cycles between the issuance of the READ command and when the data comes out. Smaller number for CL indicates faster SDRAM within the same frequency.
Q What is the difference between CL2 and CL3? [Top]
A CL2 (CAS Latency 2) is a little bit faster than CL3 (CAS Latency 3) because during one step in the column accessing process you only have to wait two clock cycles instead of three clock cycles. The overall performance difference is minor, but some systems are designed to only support one type of memory or the other. When ordering memory, use Kingston’s configuration tools to find the part number you need. Kingston’s system- specific part numbers guarantee that you will get the correct technology based on what your motherboard supports.
Q What does refresh rate and self refresh mean? [Top]
A A memory module is made up of electrical cells. The refresh process recharges these cells, which are arranged on the chips in rows. The refresh cycle refers to the number of rows that must be refreshed. The common refresh cycles are 2K, 4K and 8K. Refresh cycle together with refresh period determines how often refresh is needed, which is defined as Refresh Rate. For the same refresh period, 4K refresh parts needs to be refreshed more frequently than 2K parts. For the same size DRAM, 4K refresh part consume less power than 2K refresh parts. Some specially design DRAMs feature self refresh technology, which enables the components to refresh on their own, independent from the CPU or external refresh circuits. Self refresh, which is built into the DRAM itself, reduces power consumption, and it is commonly used in notebook computers.
 
Q What is an EPROM or EEPROM? [Top]
A

EPROM (Erasable Programmable Read-Only Memory) was designed to allow changes to the ROM chips through the use of ultra-violet light. A window on the top of an EPROM chip allows you to reprogram the chip using a chip burner. This system works, but because outside equipment was required not many people used this system. The chip can be programmed with various types of information about the memory module, and the CPU uses this information when booting up to understand what kind of memory is in the system and adjust its settings accordingly.

EEPROM (Electrically Erasable Programmable Read-Only Memory) allows technicians to flash an electric charge through the ROM chip to reprogram it's code. Most current BIOS's have EEPROMs, and can be flashed while still connected to the motherboard. This means that a simple software utility can re-write an entire BIOS.

EEPROM's are used on most present day SDRAM modules. When a memory module is assembled, in addition to the precision SDRAM chips, there must also be a correctly programmed SPD (Serial Presence Detect) EEPROM. The SPD EEPROM is a small little black chip found near the edge of the module. It is normally located on the right hand corner of the module, near pin 84 if you count from left to right.

 
Q What is the difference between SPD and PPD? [Top]
A When a computer system boots up, it needs to “detect?the configuration of the memory modules in order to run properly. PPD (Parallel Presence Detect) is the more traditional method of using a number of resistors to relay the required information, and SPD (Serial Presence Detect), a more recent method, uses an EPROM to store information about the module. SPD can store over 400 times as much information as PPD, and is becoming more prevalent.
 
Q What will happen if my memory is not PC-100 compliant? [Top]
A It means you may experience system errors in a 100mhz system because the memory's performance cannot keep up with the system requirement. The system will operate at the speed of the slowest component. For example, installing 66MHz SDRAM memory in a PC-100 system will cause the bus to operate at 66MHz, rather than the speed it was designed to operate at.
 
Q How do I recognize compliant PC100 or PC133 SDRAM memory? [Top]
A A PC100 or PC133 compliant memory includes a label affixed to it which identifies the module as "PC100 compliant" or "PC133 compliant" . An attempt can be made to verify it by looking at the chip marking which should indicate "-8" or "-7.5" after the string of manufacturer part number, though this may not be entirely accurate.
 
Q What voltage is SDRAM? [Top]
A SDRAM specifications state that all SDRAM has to be 3.3V.
 
Q What is the difference between "2-clock" and "4-clock" SDRAM? [Top]
A The early SDRAM DIMM design has 2 clock inputs to drive all the SDRAM chip. This was found to be insufficient due to loading on these inputs. Some 4 clock modules will not work in systems that are designed for 2 clock, but some will. SOME 2 clock modules might not work in systems designed for 4 clocks, but then again some will. 4 clock modules are the current standard and it is unlikely to change again.
 
Q What is PC SDRAM, PC100 SDRAM and Registered SDRAM? [Top]
A PC SDRAM is a loose general term for SDRAM that runs at 66 MHz and has an SPD chip for compatibility with P-II motherboards.

PC100 SDRAM refers to PC100 SDRAM chips or DIMMs that meet the Intel PC100 Standard specifications. These parts are designed to run at 100 Mhz front side bus (FSB) speeds, and must run at 125MHz without errors.

Registered SDRAM modules have a Register for Address and Control Signals. Registered DIMMs reduce the load to the DIMM and thus to the motherboard so that larger capacity DIMM modules and more DIMMs can populate the motherboard. It is a technique used widely on servers to increase the amount of memory the system can support. A Registered DIMM is a little slower in access timing versus that of its un-buffered counterpart.
 
Q What are the general guidelines for memory upgrade based on a CPU? [Top]
A The next group of questions will provide you with a general guideline on memory upgrades based on your computer systems CPU. This is intended only as a broad guideline. Please consult your PC users manual for further details of your system requirements, or contact us and we will help you.
 
Q Do I need PC100 SDRAM for my PC system? [Top]
A You do only if you have a 100 MHz system bus, and no, if you have a 66 MHz or 133MHz system bus. On certain systems, a non-PC100 module may be "pushed" to run in a 100 MHz system, and likewise a PC100 or PC125 module may be "pushed" to run in a 133MHz system, but the results are not guaranteed and may lead to system instability and data loss.
 
Q How Much Memory Do I Have? [Top]
A It's easy to find out how much memory your PC has!

Start with your PCs or motherboards User/Owner's Manual. Consult your user/owner's manual for details about the original memory configuration and capacity. If you've misplaced the manual, you may be able to contact the retailer where you bought the PC from.

If you have a hand-me-down PC or inherited a pre-owned PC, you may not have the user manual or know any of the details of the original memory configuration or the memory configuration may have been changed. In that case, you may want to try one of the following options:

1. Ask Your PC - If your PC is running Windows NT/98/95, use your mouse and right-click on "My Computer" then select "Properties". The total memory is calculated and displayed under the Tab indicated as "General" in the system property dialog box.

2. If your PC is running Windows v 3.1 or older, go to the DOS prompt and type in "MSD."

3. Ask Your Mac - If you're a Mac user, select "About This Macintosh" or ("About This Computer") from the Apple menu on the upper left corner of your Desktop. This will provide information about your Mac's total memory (built-in memory plus DIMMs or SIMMs installed).
 
Q How do I know when I have enough memory? [Top]
A Determining your memory needs:
The amount of memory you need is determined by several factors; the software, operating system and the number of programs you want to have open at the same time. When you determine memory needs, you'll also want to consider what your needs will be six months down the road. If you think you may be upgrading your operating system or adding more software, it's a good idea to factor that into the equation now. The following user profile will also help guide your decision:

Business user (64MB-128MB)
~~~~~~~~~~~~~~~~~~~~~
Light to Medium usage: runs 2 or 3 applications at one time. Mainly used for word processing, e-mail, fax and communication, database type of application

Home multimedia user (64MB - 128MB)
~~~~~~~~~~~~~~~~~~~~~~~~~~
Light to Heavy usage: runs 2 or 3 applications at one time. Mainly used for word processing, e-mail, surfing the internet, with Heavy user may include use of database, Graphics & 3D intensive games.

Graphics user (128MB - 512MB)
~~~~~~~~~~~~~~~~~~~~
Light to heavy: runs 3 or more applications at one time. Graphic page layout, illustration/graphics. and Heavy users also need photo editing, font packages, multimedia and presentation software.

CAD Design (256MB - 2GB)
~~~~~~~~~~~~~~~~~~
Light to heavy: CAD and CAM software. Heavy users need 3D CAD and solid modeling CAM.
 
Q Okay, then how much memory do I need? [Top]
A These days most people are looking for speed and performance, and most especially for systems capable of handling huge graphic and multimedia applications. In order to insure smooth and efficient operation with some of these new memory hungry software packages, considerably more memory is required than had been in the past. In the past, 8MB or 16MB or 32MB used to be plenty, but with today's software programs, with their increasing need for memory, 64MB is the least that a Windows based PC should have.

Today's PC are being shipped with 64MB, 128MB and even more as minimums. If you plan on taking advantage of the latest technology in software, you should either choose to upgrade your PC's memory, or purchase one with at least 64MB or more pre-installed. Keep in mind though that there is no clearly defined criteria for determining how much memory is necessary, just a broad guideline to help you make this determination. We have prepared a help section purely for the purpose of helping you make this determination, just follow this link to see How Much Memory you may need.
 
Q Memory for 386 Computers [Top]
A The majority of 386 computers uses 30 Pin SIMMs, though some 386 computers may use 72 Pin SIMMs. When upgrading 386 computers, the modules must be installed in pairs, inserting two 30 Pin SIMMs per bank. This would usually be Fast Page Mode (FPM or FM)
 
Q Memory for 486 Computers [Top]
A Most 486 DX computers uses 72 Pin SIMMs. Modules may be installed one SIMM at a time or 1 socket per bank

Most 486 SX computer utilize 30 Pin SIMMs. Modules must be installed in 4 pieces at one time or 4 sockets per bank.

Some 486 computers (both SX & DX) utilize both 30 Pin and 72 Pin SIMMs on the same motherboard.

Memory Type: (FPM) Fast Page Mode DRAM, both Parity or Non-Parity, depending on the motherboard requirements.
 
Q Memory for older Pentium Computers (586 Computer) [Top]
A Many early Pentium computers with CPU's in the 60MHz to 166MHz range have 2 banks of two SIMM sockets on the motherboard, each bank must have a pair of the same value and type of memory to be utilized by the system.

These early Pentium computers use 72 Pin SIMMs, and installation requires 2 SIMMs per bank to upgrade as there are 2 sockets per bank.

Many of the later generation Pentiums with frequencies of 166MHz through 233MHz have both 72 Pin SIMM sockets as well as 168 Pin DIMM sockets and use either 72 Pin SIMMs or 168 Pin DIMMs. Some motherboards were able to use a combination of both on the same motherboard. Usually, those Pentium computers utilizing 168 Pin DIMMs require at least 1 DIMM at a time, or one socket to be filled per bank.

The memory types usually consisted of EDO (extended data out) DRAM in matching pairs for later generation Pentiums, with older Pentiums (60MHz -100MHz) requiring FPM (Fast Page Mode DRAM.) Newer 100MHz to 200MHz MMX computers, CYRIX 6X86 and AMD 586 class processors uses EDO or FPM. The latest generation of the x86 Pentiums use SDRAM DIMMs, DR DRAM and now some motherboards are being released that support DDR DRAM.
 
Q Memory for Pentium Pro Computers (P-6 (686) Processor) [Top]
A The majority of Pentium Pro or P6 or 686 Computers use 72 Pin SIMMs, and installation requires 2 SIMMs per bank in order to upgrade. (2 sockets per bank) The memory types used in these early Pentium Pro units consisted of either Parity or Non-Parity FPM or EDO (A large number were configured with Parity FPM). Later releases of Pentium Pro motherboards used 168 Pin EDO in DIMM format.
 
Q Memory for Apple Macintosh Computers [Top]
A Mac Quadra 700, 900, 950, and Macintosh II series computers use 30 Pin SIMMs. Installation requires 4 SIMMs per bank of the same value.

Mac IIfx uses 64 Pin SIMM modules.

Mac Plus, Mac SE, Mac Classics, Classic II, Color Classic, Mac LC, LCIII, Performa 200,400, 405, 410, and 430 utilize 30 Pin SIMMs.

New Quadra's, newer Performa's, and Centris series utilize 72 Pin SIMMs.

Most Macintosh computers come with onboard permanent memory and can utilize 72 Pin SIMMs 1 at a time.

Mac Performa 6400/180 & 200 models require 168 Pin DIMMs to upgrade.

Memory Type: Fast Page Mode DRAM
 
Q Will more memory speed up my computer? [Top]
A More memory will not increase the speed of the CPU, but it will reduce the time a CPU spends waiting for information from a hard drive. Since RAM provides data to a CPU faster than a hard drive, you will not have to wait as long for programs to execute.
 
Q What do I need to Remove, Install or Replace defective modules and upgrade to new modules? [Top]
A Things you will need:

  • Your new memory modules
  • A screwdriver to remove the pc case
  • The manual for you motherboard or PC
  • An Anti-Static Wrist Strap
Tips on Memory Module Installation

  1. Insure that your environment is static safe by removing any unwanted plastic from your work area.
  2. If you have one available, use an anti-static wrist strap.
  3. Make sure that the computer system is unplugged from the AC electrical outlet before you start working on it.
  4. If possible, attach one end of a ground wire from the center screw on the AC outlet (ground screw) and attach the other end to the PC case to ground it. This will reduce the possibility of damaging the module or system from ESD (Electro Static Discharge).
  5. After removing the casing cover, and if you are not using an anti-static wrist strap, ground yourself by touching any of the metal surfaces on your computer casing. Doing this will discharge any static built up on your body and clothing.
  6. Visually locate and identify the memory expansion slots on the motherboard (main board). These are normally instantly visible, but if you are unsure, refer to your PC's or motherboards operation manual.
  7. Insert you memory modules according to the illustration in provided in the manual. Make sure you take note of the modules keyed notches and match them to the socket on the motherboard when inserting them.
  8. Make sure to use even pressure when inserting the modules, as they should snap into place. Do not force them!
  9. Most SIMM and DIMM sockets have locks on both ends to lock the modules into place. If they appear to be locked, then the module should be inserted correctly. If your manual doesn't provide an illustration for memory installation, click here and look at our illustration.
  10. Replace the case cover to complete the installation.
  11. Note: When restarting your computer, take careful note of any error messages that may be displayed and update your motherboards configuration settings accordingly.
Q I have just installed memory into my 486 and have a blank monitor and the system refuses to boot. What's wrong? [Top]
A Make sure you are not trying to install EDO memory into your system. EDO will not work in the 486 based computer.
 
Q I just installed 16MB of memory in my 486. I turned on the computer and get a message: Invalid configuration/run setup. How do I fix this error? [Top]
A This is not an error. This is exactly what should happen when installing memory. Your system "sees" the new memory, but your BIOS (the software that operates your motherboard) does not. You must run the CMOS setup utility to allow the BIOS to 'write' the changes in extended memory to the CMOS setup. There are several ways to access your setup, but the normal method is to hit your F1 or F2 key when you first boot up. Some systems require Control + Alt + Esc, while others require the delete key to enter setup. Check your manual for the exact key strokes.
 
Q My Pentium 100Mhz computer came with EDO memory. I installed two new EDO 60 nanosecond SIMMs and now my screen is blank when I boot the computer. Why? [Top]
A Generally speaking, EDO is for Pentiums 120Mhz and up. Most early Pentiums (60MHz -100MHz) prefer Fast Page Mode (non-EDO) memory. Some earlier Pentiums can use EDO, but it may require replacing the slower standard EDO memory, and changing your BIOS. This is not recommended for most users.
 
Q I want to purchase Fast Page Mode memory for my 486 computer, but the retailer only has EDO and Parity memory. What do I purchase? [Top]
A EDO memory will not work in 486 computers. Parity memory, which is actually Fast Page Mode with 4 bits for parity checking, works in all computers. If your system does not use parity, it will ignore it. However, if your system does require parity, then you must use parity modules. Newer Pentium systems can be configured to use either parity or non-parity modules but need to have the BIOS set up accordingly.
 
Q What is the difference between EDO memory and Fast Page Mode memory? [Top]
A EDO memory has a faster read timing than FPM but has the same write timing. FPM is commonly used in 386 and 486 computers, while EDO is for Pentiums only. Apple computers should be configured with Fast Page Mode memory.
Q Will EDO modules work in my 486DX2-66? [Top]
A No. EDO memory is designed for Pentium style motherboards (64 bit) and will cause errors or no-boot if used in a 486 system. Install 72-pin non-EDO memory.
 
Q How many modules do I need to upgrade my Pentium? [Top]
A Pentium motherboards require the installation of matching pairs when using 32 or 36 bit 72-pin memory. The motherboard is 64 bit and would necessitate the use of two 32 bit or two 36 bit modules to equal the 64 bit motherboard.
Q I installed EDO memory in my Pentium system and am now encountering boot-up problems, why? [Top]
A Try installing the EDO modules in the bank containing the OEM (original) factory SIMMs and moving the OEM SIMMs to another bank. Many times this will resolve the conflict. If this does not resolve your problem, you may need to exchange the EDO modules for Fast Page Mode (FPM) memory available at your place of purchase. Also remember, EDO memory does not work in 486-based systems.
 
Q I own a Pentium 200MHz computer which has SDRAM memory. I have one memory slot available on the motherboard for upgrading. Do I have to remove the existing module and install in matching pairs to upgrade my memory? [Top]
A No. SDRAM or Synchronous DRAM systems utilize 64 bit, 168-pin DIMMs rather than 72-pin SIMMs. Leave your existing memory and install one additional module. (168-pin DIMM) Make sure the memory is SDRAM.
Q What does ESD mean? [Top]
A ESD (Electrostatic Discharge) is Static electricity . This energy is found in air surrounding us and can damage electronics components in a computer such as Hard disk drive, Floppy Disk drive , motherboard , CPU, memory modules etc.. ESD occurs when one touch an object that conduct electricity.

To protect your memory module from getting damage by ESD, always keep electronic components in its Anti-Static packaging until you are ready to use them.
 
Q What does CL2 & CL3 mean? [Top]
A CL2 parts process data a little quicker 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. Bear in mind, a clock cycle for a PC100 module is 10 nanoseconds so you probably won't notice a significant performance difference.

While most systems will accept either latency part, there are some systems that require either CL2 or CL3 parts.
Q Will DDR SDRAM memory work on my current PC system using PC133 memory? [Top]
A The quick answer is "NO" although DDR) SDRAM is an evolution from the current PC133 SDRAM, it will not work since both the frequency, voltage and pin out are completely different.

DDR Memory actually doubles the bandwidth available to your system and runs twice as fast as regular SDRAM.

Some of the current application of DDR SDRAM chips are found in graphics cards and game consoles.

Right now only a handful of developmental motherboards from Micron, AMD, VIA and Ali will take DDR SDRAM modules.
 
Q What is a "Virtual Channel" or VC SDRAM Memory? [Top]
A VC SDRAM is a proprietary non standard type developed by NEC of Japan. The VC-SDRAM memory is supported by a handful of PC systems and is said to provide better performance.

The performance between VC133 is somewhere between PC133 CAS 3 and PC133 CAS 2.

PC133 is the standard adopted by the industry for 133MHz modules.
 
Q Can my PC-133 memory be backward compatible to my older PC system? [Top]
A Most SDRAM is backward compatible and can run at any bus speed slower than it is rated to run. For instance, a PC133 SDRAM DIMM is capable of running at 133MHz, 100MHz, and 66MHz. There are some older motherboards that require 66MHz SDRAM and that will not accept PC100 or PC133 SDRAM, but they are the exceptions to the rule.
 
Q How can I tell if my PC133 memory is a 6 layer or 4 Layer PCB board? [Top]
A All PC100 and PC133 SDRAM DIMMs that are manufactured by the original manufacturer such as Micron, Samsung, NEC, Toshiba are built on 6 layer Printed Circuit Boards (PCBs), except for modules build by 3rd party manufacturer especially from Taiwan which typically are 4 layers. Physically you will not be able to tell the difference between the 4 or 6 layer just by looking at the PCB board. The best way is to visit the manufacturer website for more information or call their toll free number to find out.
 
Q What is OEM Memory? [Top]
A OEM is an acronym for "original equipment manufacturer" and OEM memory means that the memory chips and PCB boards are made by the semiconductor manufacturer themselves, and the same memory that the largest PC manufacturers worldwide such as Dell, Compaq, Apple buy for use as original equipment in their systems.
Q Why do memory prices fluctuate so much? [Top]
A Supply and demand will cause the memory price to dip or rise on a daily basis. Changes in market demands will also alter inventories thereby causing prices to raise or lower prices.
 
Q How can I Troubleshoot my memory using the BIOS Beep Codes? [Top]
A The BIOS on the motherboard will always perform a "power-on self-test" or “POST?during power up. Usually this test is performed to ensure proper system function and if a failure should occur, the “POST?will identify the failure and emit a beeping sound to prompt the service technician to take corrective action ASAP.

The exact meaning of the beeping codes varies from different BIOS developers, there are 4 basic BIOS developers today, and they are “American Megatrends? AMI, Award and Phoenix. The beep codes for AMI & Award BIOS developers are provided below. We do not have, at present, a beep code reference for the Phoenix BIOS or other custom BIOS's written by other companies other than then these two.

Beep codes are not entirely consistent in detecting the exact failure. Generally accurate troubleshooting depends diagnose a fault by opening the PC can and using diagnostic software and test equipment.
 
Q Troubleshooting Memory Failures using Award BIOS Beep Codes [Top]
A Award is the another popular BIOS developer and they use the fewest beep codes by far.

Procedures ?The normal procedure is to power up the PC system, and watch for any error messages on the monitor screen while listening to the PC beep tone. A single beep during boot-up process is normal and does not indicate a failure as long as the system continues to boot-up.
  • 1 Long Beep tone - Memory Problem
  • 1 Long Beep and 2 Short Beeps - DRAM Parity failure
  • 1 Long Beep and 3 Short Beeps - Video error
  • Continuous Beep tone - Memory or Video memory failures
Q How do I clear the printer memory after each page is printed? [Top]
A
  1. Open the file you wanted to print.
  2. Click on File, Print, or simply press "Ctrl P".
  3. In the Current Printer box, click on the Select menu bar.
  4. Click on Setup -> Options -> Advanced.
  5. Click on the Clear Memory per Page check box.
  6. Close and Click on Print to print the file, or return to the current file by clicking on Close.
 
Q My PC boots up okay but seems to hang up after running for one hour or so. How can I find out what is wrong? [Top]
A This type of problem can be tricky to diagnose. Typically you may want to begin by finding out if it's a memory related problem. DocMemory PC Memory Diagnostic software is designed for this very purpose. You can start by downloading a copy of the software from DocMemory, and follow the setup instructions and run a diagnostic test on your PC memory. DocMemory diagnostic information can be located here.

If the Memory tests return good results, you will then need to isolate and examine other possibilities such as CPU, Motherboard or other peripherals that you have in your PC.
 
Q If I have regular memory sizing error during POST (boot up), how should I trouble shoot the failure? [Top]
A One of the most common memory problems you will face in older PC systems during boot-up is “incorrect memory sizing? or the error number 164. Sometimes these failures can be caused by incorrect software settings, and sometimes they can be caused by hardware problems that can be easily fixed if you know where the faults lies.

Many times these hardware failures are caused by the natural aging process of the memory components, defective memory module socket, dirty contacts, cold solder joints during assembly or a memory module not seated properly in the socket due to vibration.

It is important to view cleaning and maintenance as a cause of intermittent memory failure before you make any decision to replace a memory module- try cleaning the memory module contacts for both old and new ram to see if the problem can be fixed:

Here's how, along with what you will need:
  • Contact Clean (Purchase from local computer hardware store)
  • Cotton Bud or Q-Tip (For cleaning with Contact Clean)
  • Piece of clean dry cotton cloth (an old T-shirt is great)
  • Screwdriver (pc case removal)
  • PC users manual
  1. Insure environment is static safe by removing any unwanted plastic from your workbench.
  2. Unplug the computer system from the AC source, but attach a ground wire to the ground screw in between the two sockets. This insures that case is grounded, thus reducing the risk of damaging the module or system from ESD (Electro Static Discharge).
  3. After removing the casing cover, ground yourself by touching any of the metal surfaces on your computer casing. This step discharges any static built up on your body and clothing.
  4. Visually locate the computer memory expansion slots. This is normally visible but if in doubt, refer to your PC's operation manual.
  5. Next, remove the memory module and visually inspect it and the memory socket. Make sure all the pins are straight, and there are no cracks or broken pins.
  6. Wet the end of a cotton swab with the solvent, the swab should be wet but not dripping.
  7. Using a circular motion, clean the contacts on the memory module. Now take your cotton cloth and remove any remaining fuzz from the cotton swab and dry the module.
  8. Set the module aside and allow the surface of the contacts to dry thoroughly.
  9. Replace the memory module into the socket.
  10. Repeat steps 5 through 8 for each module you have.
  11. Insert a MS-DOS boot disk into the floppy drive and then power on the computer to test the RAM. This will prevent you from inadvertently booting to the operating system on the hard drive.
  12. If there are no memory errors, replace the PC's case and power-up.
Additional Tips:
  • While using contact cleaner is the preferred method, in an emergency you can clean the contacts with a pencil eraser.
  • Continuous RAM errors are usually a sign of a bad memory module. If cleaning the contacts doesn't solve your problem, try to isolate the faulty module and replace it.
 
Q How do I troubleshoot a memory failure without a memory tester? [Top]
A Simple techniques to isolate possible memory problems.
Remove the modules one by one from motherboard.

The simplest method of isolating a possible failing memory module is by moving modules, swapping them between slots on the motherboard. If the motherboard has "SIMM" modules, the slots must be filled in pairs, therefore this form of testing is only valid if you have 2 pairs of SIMM modules. If your motherboard uses "DIMM" memory modules, and you have 2, then you can remove one, run the tests and then swap it for the one removed and test again. By selectively removing one module one at a time from the system and then running tests, you should be able to isolate the bad module quickly. Be sure to mark which module passes or fails and then switch that one with the other. Always place the modules in the slots by filling slot 0 (zero) or slot 1 (if the is no slot 0) first. Most motherboards using SIMM modules require that slots be filled in pairs, therefore plan accordingly. If you only have two SIMM modules, you'll need to borrow or purchase another pair.

Swap the modules out.

If you only have two memory modules, such as in the case of 2 SIMMs, swap and rotate modules to find which module is defective. This technique can only be used if there are two or more modules in the system. Change the location of two modules one at a time. As an example, place the module from SIMM slot 1 into slot 2 and place the other module from slot 2 in slot 1. Run the diagnostic test, and if either the failing data bit or address changes, you know that one of the modules you have just swapped is defective. If the PC boots fully with the first combination and then you swap the modules and the PC fails to boot, you then know that the module's) in slot 0 (zero) is defective. By using combinations of module swapping, you should be able to find the defective module.

Replacing modules with known good ones.

If neither of the above two methods are available to you, or you are unable to make a determination by following those methods accurately, you are left with two possible alternatives, either sending your memory modules to a testing facility or swapping them with known good modules. Use known good modules and selectively replace one module at a time to identify the memory failure. This is the easiest of all of the methods to detect memory failure.

Last ditch effort - Remove and Clean the metal contacts.

If your PC system is older, sometimes dust and oxidation will cause poor contact in the SIMM/DIMM slot. Remove the module and clean the gold or tin contact following the procedure outlined above. Usually contact cleaner or video and audio head cleaners work the best, although a good grade of nail polish remover will work as well. Make sure you remember which slot is being used, and be careful not to reverse the module while reinserting into the SIMM/DIMM slot.

You can also try to identify a memory failure by using the motherboards BIOS beep codes.
BIOS beep codes are normally used when adequate diagnostic methods are not available. Most BIOS developers and motherboard manufacturers have devised a simple way of telling you if your system is having problem by having the BIOS emit beeping tones from the built in speaker on the motherboard.

 
Q A Simple Guide to Troubleshooting Memory Failures without a Memory Tester [Top]
A This section of our FAQ is written with the presumption that you have at least a general understanding of the PC operating system and that you are capable of performing the diagnostic procedures detailed below.

We will attempt to describe the entire process in detail, however it is beyond the scope of this FAQ to provide all the necessary information to cover all possible PC memory failures. For further assistance with non-memory related failures, please consult our technical support department or our online support system. If your particular question is not addressed in this section ?please send us an e-mail and we will do our best to provide you with the right answers.

When you are experiencing memory or other failures on your PC, there are several issues to be determined. Run through each of the following to try and determine as much information as possible. The following are typical of memory failures:

* PC system does not boot-up
* HIMEM.SYS does not load
* Memory failure due to system hanging up, or system rebooting after running a large program.
* Failure during the installation of win3.1, Win95, Win98 and Windows NT
* Windows programs are unstable
* Continuous beeping sound emitted by system during power up
* Continuous ram count during boot-up , without loading Windows program
* No display other than blue screen on the monitor during boot-up
* Totally no video display on the monitor.
* System hang or rebooting after prolong usage.

If you have followed our earlier suggestions regarding the swapping and cleaning of memory modules and the above problems persist, you may need a well trained technician to perform further diagnostics and apply corrective measures.

Once a memory failure has been detected, identifying the defective module is not an easy task. With such a large variety of motherboards provided by so many different manufacturers, and with the many different combinations of SIMM/DIMM slots, it is difficult, if not sometimes impossible, to assemble complete information about a particular memory error mapping to a specific failing memory module.
 
Q What do the AMI BIOS Beep Codes mean? [Top]
A The AMI BIOS is the most popular of the BIOS's used by motherboard manufacturers. You can usually determine quite allot about your computer systems BIOS by reading the screen display on the Top screen during power up and listening for beep tones if there is a problem.

Here are some basic procedures:

The usual procedure is to power up the PC and watch the monitor for error messages on the monitor screen and listening for the beep tones from the speaker on the motherboard inside the PC case. A single beep tone during the boot (startup) process is normal and does not indicate a failure as long as the system continues to boot up.

Here is a list of the most common beep tones
1 Beep tone - DRAM refresh failure
2 Beep tone - DRAM Parity failure
3 Beep tone - Base 64K RAM failure
4 Beep tone - System timer error
5 Beep tone - CPU failure
6 Beep tone - Keyboard controller error
7 Beep tone - Virtual mode error
8 Beep tone - Display memory read/write error
9 Beep tone - ROM BIOS checksum error
10 Beep tone - CMOS register read/write error
11 Beep tone - Cache memory error
Continuous Beep tone - Memory or Video memory failures

You can learn more about AMI and Award BIOS issues by visiting our Technical Center!

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If you would like to review more about memory related issues, you may want to follow these links:

Memory, Evolution or a Revolution?

How Memory Speeds Are Determined

How to Identifying Different Memory Types

How to Identify PC133 Memory

Does your memory meet the Standard?

Troubleshooting Memory Problems

Megabyte (MB) vs. Megabit (Mb)

Memory Trends in 2001

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This page updated: 1/27/2001