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MEMORY FAQ (please read before posting)

June 17, 2010 2:33:34 PM





CL: Short for CAS Latency, where CAS is short for Column Address Strobe. CL latency is one of the most important parameters of a memory chip. It is the time it takes to get data to the data pins. Immediately following the CAS Latency, the data is available on the memory Data-pins.
Command Rate (CMD): The command rate specifies how many consecutive clock cycles need to be sent to the memory modules before the modules can send data. Because wires often have natural capacitance on them, sometimes it takes longer for a wire to transition from a 1 to a 0. The CMD setting is typically one or two clocks and can often be adjusted between the two. It's represented as 1T or 2T.
CPU: Stands for Central Processing unit. Also called processor, the CPU is the active part of a computer where arithmetic operations are performed.
Core speed/frequency: The speed of the innermost component of an electronic device, measured in MHz.
Example: A DDR-400 module has core speed of 200MHz.
DRAM: Dynamic Random Access Memory
Dual-channel: A property of the motherboard where the memory bus is split into two 64-bit channels, effectively doubling the bandwidth in relation to a single-channel setup. Dual-channel is not a property of the memory modules.
Effective speed/frequency: The actual speed of a device in practice, measured in MHz.
Example: A DDR-400 module has an effective speed of 400MHz.
Form factor: The physical size and shape of a device.
FBGA or BGA: Fine Ball Grid Array
FSB: Stands for front side bus. The FSB is the data path that runs between the CPU and main memory (RAM).
IC: Integrated Circuit, commonly referred to as a memory chip, an IC is a small electronic device made out of semiconductor material.
Latency: Physical delay of the memory module represented discreetly in clock cycles. Usually pronounced as 'C-L three', where the three represents the delay, measured in clock cycles. The delay normally ranges from two to six clock cycles for DDR.
Memory module bank: Logical division of chips on a PCB board. A single memory bank can be composed of any number of chips. Some banks are composed of only 2 chips, whereas some other modules have 18 chips or more per bank. Not to be confused with memory Rank, see next term.
Memory rank: The physical side of a memory module. The side of the module is referred to by Rank0 or Rank1.
PCB: Stands for printed circuit board. A PCB is a small plate on which chips and other electronic components such as resistors or capacitors are placed.
Semiconductor: A material such as germanium or silicone which allows current to flow under certain circumstances. Semiconductor materials make it possible to make energy-efficient and fast nano-scaled transistors, which are the basic units of computer logic. Semiconductor materials are used in the fabrication of integrated circuits, which are used to build memory modules.
TSOP: Thin Small Outline Package


SIMM: Single in-line memory module. An older technology, a SIMM is a PCB (Printed Circuit Board) that typically holds 8 or 9 memory chips on a single 32-bit data bus. Typically comes with 72-pins.
DIMM: Dual in-line memory module. A DIMM is a PCB (Printed Circuit Board) that can hold up to 18 chips on a single 64-bit data bus. DIMMs make up a range of different pin configurations: 168-pins for SDRAM, 184-pins for DDR, and 240-pins for DDR2.
RIMM: A Rambus trademark name for a module that uses RDRAM chips, similar to a DIMM, but with different pin configurations. The number of pins: 184-pins for 16-bit modules, 232-pins for 32-bit modules. RDRAM modules have heat-spreaders on them and use RAMBUS technology
SO-DIMM: Small outline DIMM. An SO DIMM is about half the length of a DIMM and is typically used in notebook systems. An SO-DIMM has the following pin configurations: 144-pins for SDRAM, and 200-pins for DDR and DDR2.
SO-RIMM: A small outline RDRAM module for notebook systems, similar to an SO-DIMM, but uses RAMBUS technology.
MICRO-DIMM: Basically a small form factor SO-DIMM. Micro-DIMMs are used primarily in small notebooks and mini PCs.


UNBUFFERED MODULE: A buffer is used to re-drive and refresh a signal as it travels on a wire. An unbuffered memory module has no such buffer. Unbuffered memory modules are the most common for desktop systems.
FULLY-BUFFERED MODULE: A module whose data signals are re-driven and refreshed before sent. These modules are typically used for server applications where many high-speed DRAM components are required. FBDIMM modules are a new technology complementing current registered memory technology.
ECC MODULE: Stands for error-correcting code. An ECC module has an additional memory chip per memory bank that is responsible for detecting and correcting 1-bit data errors as data passes through the memory module.
REGISTERED MODULE: A registered module contains an extra memory chip per memory bank that is responsible for holding data for one clock cycle. This process increases the reliability of data. Typically, registered modules are only used in data-sensitive or server stations where the focus is on the integrity of data. Registered modules are not compatible with desktop motherboards.


FPM: Fast page mode RAM. Popular at one time, FPM RAM allowed for faster access to memory, but was replaced by newer technology such as SDRAM.
EDO: Extended data out DRAM. Essentially modified FPM technology, EDO RAM allows the possibility of fetching the next block of data at the same time it sending the previous block.
DRAM: Dynamic random access memory.
SDRAM: Synchronous DRAM. The clock speed of an SDRAM module is synchronous with the CPU bus.
RAMBUS: A bandwidth driven bus technology where high speed data transfers are possible through a feature where operations occur on both the rising and falling edge of the clock signal. Rambus technology uses a packet-switched bus where addresses/data are multiplexed, instead of using row and column address strobes like in SDRAM and DDR systems.
DDR SDRAM: Double data rate SDRAM. The core-clock speed of a DDR SDRAM module is synchronous with the CPU bus, however data is sent on both the rising and falling edge of the clock signal effectively doubling the memory chip's throughput.
DDR2 SDRAM: Next generation DDR technology, DDR2 memory offers greater bandwidth and density in a smaller chip-package. DDR2 requires less power than its DDR predecessor, and is composed of a technology that allows for greater speeds of 400, 533, 667, 800 MHz, and above.


Q: For the modules installed in my system, how do I find the following?

A: You can find the type of RAM in the memory section of CPU-Z (from Also, you can check the motherboard's manual to see what type of RAM it supports.

A: You can find the size of memory installed using CPU-Z.

A: double-click the 'system' icon in the control panel.
Start --> Settings --> Control Panel --> Syetem. Look under the general tab, you should see something similar to "512 MB of RAM"

You can also use CPU-Z.

A: You can normally find the brand by looking directly at the modules themselves. If no sticker, label or logo exists on the module, sometimes you can find the brand labeled on the chips.

A: Please refer to section: MEMORY CHIP IDENTIFICATION.

A: Under the memory section of CPU-Z you will find a text box labeled as 'Frequency'. This is the core speed of the module. Keep in mind for DDR the effective speed is double the core speed.


A good way to identify a module is by looking at its chips. Sometimes it's difficult to identify the chips, either because the chips are non-major brand, or covered by a heat spreader.

To identify the part numbers on major brand chips or modules, please refer to the following documentation (you can also check the chip part numbers on the modules with the manufacturer's web): SAMSUNG MICRON INFINEON HYNIX ELPIDA

For other modules, you can check the manufacturer's web site for further details if the module is not listed here: OC FORUMS


Picking the right memory is typically a preference; there is no single memory module that is better than the others.

Memory can be classified into the following general classes:

Memory Classes: (note: sort these by classes/tiers)
1. Performance modules
2. OEM or third party
3. Major original
4. Major third party
5. Second-tier
6. Downgrades
7. Counterfeit

Performance Modules
Typically any module rated to perform above the market standard.
Examples: DDR500+ or PC-3200 CL2 modules.

Third party modules
Any module manufactured by one company using chips built by another company. For example, a module built by Kingston using Samsung chips is a third party module.

OEM (original equipment manufacturer) is a confusing and misleading term. OEM is normally described by: A company uses original equipment, such as memory chips, to manufacture the modules. The original equipment (memory chips in this example) is typically branded with the company's name who manufactures the module from the chips; however, the equipment is not usually built by the company, but used by the company. This term is not normally used to describe major or high quality modules, because many OEM modules are built using lower quality parts.

Major original
Any major brand module where the chips and the modules are built by the same company. The standards of testing and manufacturing are normally higher for the major brands.
Major brands:
Class1: Samsung, Micron, Infineon, Hynix
Class2: Elpida, Mosel, Toshiba, Nanya

Major third party
Modules manufactured by one company using major branded chips built by another company.

Second tier originals
Original modules built by major manufacturers, but because the testing standards are usually lowered, the cost of the modules becomes more competitive in the market. Popular Examples: Spektec (Micron), Elixir (Nanya), Aeneon (Infineon).

Modules built using downgraded chips, often called half-bit modules. Sometimes, the chips fall short of their intended standard and have to be passed down to a new standard. Many of the chips are intended as 32M chips for example, but fall short of the memory density and thus are passed off at 16M chips instead.

The typical counterfeit case involves blank or UTT chips being marked and illegally passed off as major brand chips. They are sold at a higher price, and because the quality is not as good as major brand modules, the reputation of the major brand companies, who provide good quality modules, suffers. Counterfeit chips make up approximately 10% of the market total.


There are only a handful of chip manufacturers. The value of the chip is determined by the testing process and the availability of the chip in the market. It is fair to say that a large manufacturer whose chips are widely available will be higher in cost than a similar manufacturer whose chips are rarely seen. This is because the reputation and value of a manufacturer is built over time.

MAJOR BRAND IC (tier-one):
The current leader in chip production is Samsung, followed closely by Micron, Hynix and Infineon. These companies have a reputation of maintaining high standards for their ICs. And because the chips are consistently available in the market sets them apart from other major brands.

MAJOR BRAND IC (second-tier):
Other major brands include: Elpida, Mosel Vitelic, Nanya, Powerchip, and Winbond. Not to say the quality is any different than tier-one major brand, the main factor setting them apart is their rank in terms of market share, and availability of chips in the market.

Contrary to its name, UTT chips are tested, but not as thoroughly as major chips. As a result, some have adopted to call them ETT (Effectively TesTed) Chips. Because testing standards have been lowered, the cost of UTT is better than other major brands. Some companies have elected to perform additional testing on UTT chips thereby raising its cost. As a result, performance, quality and cost are random from company to company. Often, UTT chips are remarked and passed on as new specification.


Memory standards have been in place to provide a medium for the general computer system. Of course, many applications and systems can go safely beyond the standards, but knowing how far a module can go requires some expertise. Thus, the standards have been decided by JEDEC and followed by most manufacturers as a general measure of safe operation for the common computer system. However, many advertised and retail modules deviate from these standards to make the modules more attractive to enthusiasts and general consumers.

Below you will find the official memory standards currently set by JEDEC:

DDR2-400 = PC2-3200 (200MHz @ CL=3, tRCD=3, tRP=3)
DDR2-533 = PC2-4200 (266MHz @ CL=4, tRCD=4, tRP=4)
DDR2-667 = PC2-5300 (333MHz @ CL=5, tRCD=5, tRP=5 OR 4-4-4)
DDR2-800 = PC2-6400 (400MHz @ CL=6, tRCD=6, tRP=6, OR 5-5-5)

*DDR-500 = PC-4000 (250MHz)
DDR-400 = PC-3200 (200MHz @ CL=3, tRCD=3, tRP=3, or 3-4-4)
DDR-333 = PC-2700 (166MHz @ CL=2.5, tRCD=3, tRP=3)
DDR-266 = PC-2100 (133MHz @ CL=2.5, tRCD=3, tRP=3 OR 2-3-3, 2.5-3-3)

PC-100 (100MHz @ CL=2, tRCD=2, tRP=2)
PC-133 (133MHz @ CL=3, tRCD=3, tRP=3 OR 2-2-2)

PC-800 (400MHz)
PC-1066 (533MHz)

*Non Standard Specification (not officially supported)


How much memory do I need?
It depends on your type of work. 512MB is enough for most desktop applications such as windows office tools. Some workstations can benefit from upwards of 1GB to 2GB of memory and server stations can use as much as 16GB or more. 1GB seems to be the "sweet spot" for the majority of Windows XP users.

How much memory will my system recognize?
Every system has its own limit on the memory size which varies with each Operating System and motherboard. Check with your motherboard manual on how much memory your motherboard supports. Desktop motherboard limits are typically 3GB or 4GB.

What kind of memory is compatible with my system?
Check with the motherboard manual.

How many sockets are open and how should I fill them?
Motherboards typically have 2, 3, or 4 slots for memory. You'll need to check with the motherboard manual to see if there are limitations on the memory setup.

How do I determine the quality of memory?
The quality of memory lies with the integrity of the module's manufacturer and the type of chips used.

What should I know about memory prices?
Prices vary from company to company- even for the same product. Shopping around is always a good idea. In many cases modules that perform only slightly better may be significantly higher in price. Thus, choosing the right module is often a balance between how much performance you want versus the price of the module.

What kind of service and support do I need?
Some modules come with limited, lifetime or no warranty at all. It is a good idea to buy from a reputable source because almost always the modules will come with a return policy. Of course you want to cross the return policy from several sources before making a decision.

What other issues should I consider?
It is also a good idea to be familiar with different brands, and pay attention to the speed and latency of the module. Some modules are better than others. Matching performance, stability and cost is not always an easy thing to do. If you have other questions regarding your purchase you can always post on the message forums, check with the vendor's website, or consult a professional.


1. Make sure you have the correct type of memory module for your system.
2. Make sure the module does not exceed the maximum capacity supported by your motherboard. You can check with the motherboard's manual what capacity is supported.
3. Make sure the module is firmly seated in the slot with the clips locked in. Clean away any dust to ensure good contact between the module and the slot.
4. Make sure the processor and graphics card are firmly seated. They may have been accidentally dislodged by you while installing the module.
5. Check that each module installed on the motherboard is not defective and are not in conflict with one another. Test by first removing all modules from the motherboard. Install each module by itself on the motherboard and try to boot the system. If everything appears to work properly, then install one module, then add back the remaining modules one at a time, booting up the system between each addition, to find any possible sources of conflict.


Q: My system does not recognize the full capacity of the modules I installed. How do I fix this?
1. If the system memory appears to be off by several megabytes, then check to see if you have an on-board graphics processor on your motherboard. Often, on motherboards with integrated VGA, a portion of the system memory, such as 8MB, is placed aside for video memory.
2. If the system is recognizing only a fraction, such as 1/2 or 1/4, of the total capacity of the module, then the problem is most likely due to you using modules with memory chips that are too high in density. Many older systems require lower density memory parts. As memory modules with higher megabytes are developed, the density of the memory chips also must increase. Older, lower density memory parts are phased out and become harder to find. Current modules with high density memory components may not work with the older systems.

Q: I added more memory to my system, but I still get warnings that my system resources are low. How can I fix this?
A: System resources and system memory are not the same thing. System memory refers to the physical memory installed on the system- if you have a 128MB module installed on your motherboard, then you should have 128MB of system memory. System resources are areas of memory used to keep track of the windows that are open and displaying objects on the screen. If this area becomes full, programs may not load properly and Windows may become unstable, no matter how much free system memory you have. Closing some running applications can free up your system resources, but some software may not release its resources as readily and you may need to reboot Windows.

Q: I added more memory in my system, but now I get "Out of Memory" error messages in Windows. How can I fix this?
A: If your system memory is 512MB or above and are running Windows 95/98/Me, please consult Microsoft for the fix.

Q: How do I test my memory for errors?
A: Memtest86 (from



Can I use PC-133 memory in PC-100 system?
A: Yes. All PC-133 modules will work as PC-100. Keep in mind the following:
-PC-133 CL3 may not work in a system that requires PC-100 CL2. It's best to match the latency of the module with the system's specification.
-Some systems may have a problem using x16 memory chips, or higher density 32M chips.

Q: Can I mix DDR and SDRAM together?
A: Absolutely not. Don't try this at home.


Can I use DDR-400 in a DDR-266 system?
A: DDR-400 modules are capable of running at slower speeds i.e. DDR-333 or DDR-266.

Q: Can I use DDR2 in a DDR system?
A: Nope. DDR2 is not compatible with DDR memory.


What is DDR2?
A: Please refer to section: RAM Technology.


What is Rambus?
A: Please refer to section: RAM Technology.

Q: Is Rambus compatible with DDR or SDRAM?
A: No.


Q: How do I find out what my modules latency is?
A: The modules latency is normally programmed into the SPD (Serial Presence detect) chip on the module itself. There are many programs that can be used to read this. CPU-Z (from is one of them. Using CPU-Z, you can read the SPD data from the SPD timings table under the SPD tab.

Q: What are the two most common ways in which memory bandwidth is increased?
A: Bandwidth can be increased either by increasing the number of memory channels (i.e. dual-channel) or by increasing the clock speed of the memory.

Q: How does memory access work, and what do the timings stand for?
1. tRCD (RAS to CAS Delay) 2-3 cycles, The row is selected by the Memory Controller.
2. CAS (Column Address Strobe) 2,2.5,3 cycles (DDR), The Memory Controller selects the column and now the ROW is
ACTIVE, and the READ COMMAND is sent.
3. Data is sent to the DQ pins after CAS delay.
4. tRAS (Row address Strobe) 6 cycles, The module waits a certain period of time for the data to be active.
5. tRP (RAS precharge) 2 cycles, The Memory Controller DEACTIVATES the row.
6. Memory Cycle repeats as requested by the Memory Controller.

The timings are represented as follows:
2-3-2-6 1T (CAS, tRCD, tRP, tRAS)

The 1T is the command rate (see key term: command rate)

Q: How do I adjust the latency timings of my memory modules?
A: Some motherboards allow the latency settings to be adjusted in the system's BIOS. To enter the system BIOS you will need to press either the 'delete' or 'tab' key before your system starts. However, many Dell, HP, and Compaq systems do not allow for changes to the latency timings.

Q: What is the difference between 1T and 2T memory timings?
A: A 2T command rate means that commands are presented to DRAMs for two consecutive clocks, as opposed to one consecutive clock for a system with a 1T memory setting.

Q: How do I calculate my memory's bandwidth?
The maximum bandwidth is calculated below for DDR-400
DDR-400 = 200MHz * 2 (double data rate) = 400MHz
400MHz * 64-bit data bus * 1bit/8bytes = 3200MB/s

Note: Not every memory bus is 64-bit. Dual-channel, for example, is 128-bit. And some older memory busses are 32-bit or 16-bit.

The calculation above assumes no latency. Of course, in the real world there is always latency. The latency add anywhere from 2 to 5 clocks per memory instruction, and is nearly impossible to calculate by hand. There are some benchmark tools that can be used to determine the bandwidth more accurately. Sisandra is one of the more popular tools:

What is Dual channel?
A: See key term: dual-channel.

Q: I currently have two sticks of 512mb pc3200 memory in DIMM 1 and 3 to reach the performance of dual channel DDR. Can I also add two sticks of 256mb PC3200 in dimm's 2 and 4 to reach 1.5GB of ram and still maintain dual channel performance?
A: As long as you have matched memory pairs on each channel, you should be able to run dual channel.

The only potential problem: Because you are using 4 memory modules, which require more power, your system may clock the speed of the modules down to maintain stability.

Q: How do I know if dual-channel is working in my system?
A: An easy way to tell is to use CPU-Z (from You can check if dual-channel is enabled by looking at the memory tab. In the General section, you will see a field labeled as 'channels #' which will indicate if dual-channel is working.

Q: Can I add 256MB and 512MB modules together?
A: Yes. Make sure you do not exceed the total memory size.

Q: Do I have to install memory in pairs?
A: It depends on your motherboard. Consult with your motherboard's manual to see how dual-channel works on your board. For most dual-channel boards the memory modules must be identically sized, and have the same number and type of chips. Typically, the motherboard requires the modules to be inserted in pairs on either slot0 and slot1, or slot2 and slot3. For some other motherboards three modules can run in dual-channel (the numbers of chips, not the modules themselves, are divided between the two channels). In any case, it is best to match the latency and speed of the modules, though it is not required.

How much memory do I need?
A: Please refer to section: Before you purchase.

Q: How do I find out how much memory I have running in my system?
A: You can check the memory running in your system in the 'System Properties window':
START --> SETTINGS --> CONTROL PANEL --> SYSTEM.general tab under Computer.

You will see something similar to: 512MB of RAM

To check the memory setup in greater details you can use CPU-Z (from

Q: Can I use registered memory on a desktop board?
A: No. Registered memory is only compatible with boards that support it, such as server boards.

Q: How do I find what type of memory I have installed in my system?
A: CPU-Z (from will usually tell you the size and type of RAM from the memory section of the program.


Virtual memory is required by nearly all operating systems as a way of providing seemingly unlimited memory for computer applications and programs. It's called "virtual", because the memory is borrowed from the computers hard drive data storage.

As an application is executed, it normally requests a large amount of memory for its operation- much more than it typically needs just in case it may use it. So the operating systems needs to setup a PAGE FILE to accommodate the application's memory needs. The PAGE FILE contains pages (or blocks of memory) where the blocks of memory are mapped from one set of addresses (virtual addresses) to another set (called physical addresses). The physical address is typically stored on the hard drive.

Virtual memory simplifies the loading of a program for execution. Because the memory addresses are translated to the hard drive, this eliminates the need for memory addresses to be stored in one long continuous block. The operating system only needs to find a sufficient number of pages in the main memory.

How to check page file size set by windows?
Windows will set the page file size automatically. You can check it by using DirectX Diagnostic Tool:
START --> RUN --> "dxdiag" and hit ENTER
Q: How to check the peak amount of memory since my last boot?
1. Open the Windows Task Manager (CONTROL + ALT + DELETE)
2. Look under Performance tab at the Peak value.
It is best to record the peak value over a period of time, and just not assume that any single reading is the peak. After a period of review, you can easily determine what page files size if right for your computer.

Q: How to change the Page File Size?
A: The recommended minimum page file size is about 1.5 times the amount of RAM in your system, and the maximum recommended is about 3 times. By default windows will set this value for you. However, you can determine using the steps above what page file size is best for your system and change it manually:
START --> SETTINGS --> CONTROL PANEL --> SYSTEM --> ADVANCED --> performance.SETTINGS --> ADVANCED --> virtual memory.CHANGE


There are a few top-rated memory manufacturers out there, who do the right thing in making memory that works. These are companies that work closely with CPU and motherboard manufacturers as new machines are being developed, and make sure that all of their modules are following the standards set in their specification.

Manufacturers are typically the best source for memory modules in that they offer better terms of service and returns for their products than the brokers or middlemen. Good service typically comes with lifetime warranty, and knowledgeable staff who can answer specific questions relating to the technology and respective applications. Companies that work closely with the manufacturers and distributors are the best source for memory modules.

Because Manufacturers and good vendors take extra steps to ensure the service and quality of their memory, the prices may be a little higher than buying from a broker or middleman. The extra price is probably worth it given the extra care and support that comes with it.


A broker is typically an individual who works with memory manufacturers and distributors in negotiating purchases, contracts or sales in return for a fee. Little to no value is added to the product, but instead the broker is looking to mark up and move out the product at a profit. Because there are many brokers in the memory market, it sometimes becomes very difficult to tell the brokers apart from the dedicated distributors.

There is very little regulation over the products in the memory market and so the level of quality can vary significantly from product to product- at times you may not even know what you are getting until you receive it. And because it is normal for products to trade many hands before they are consumed, the prices are very inconsistent.


What is Counterfeiting?
Definition: The deliberate attempt to deceive product purchases by copying and marketing goods bearing well known trade marks, generally together with packaging and product configuration, so that they appear to be made by a reputable manufacturer when they are, in fact, unauthorized and generally inferior copies.

Why is it bad?
There are many reasons, but most importantly a counterfeit module is always inferior in quality to the product it intends to be.

How do I identify a counterfeit module?
Any reputable manufacturer can easily identify a counterfeit module. But for the average consumer, it is not so easy. There is, however, one easy technique that can be used to identify a module as counterfeit. The normal counterfeiting process involves re-marking of memory chips after the module is assembled. Normally, the chips are marked prior it its assembly. This means, that the markings of each chip on a counterfeit module are identical and the markings from one chip to the next are perfectly aligned in a straight line. The real modules normally come with different markings per memory bank and the markings from one chip to the next are not perfectly aligned. This is just a general technique and should not be used to confirm a module as counterfeit.

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