Memory modules 101:
Motherboard Specs

An explanation of terms used to describe your new Crucial memory and its compatibility with a particular motherboard

Chipset
This line tells you what kind of chipset your motherboard uses. Your chipset enables many of the devices in your computer (processor, memory, keyboard, mouse, etc.) to communicate with one another. Unlike processors and memory, chipsets are an integral part of a motherboard and generally cannot be upgraded.

Accepts PC133 SDRAM
This line tells you whether or not your system will accept PC133 synchronous dynamic random access memory (SDRAM). SDRAM delivers bursts of data at very high speeds using an interface that is synchronized to the CPU clock. PC133 SDRAM meets Intel's requirements for use with 133MHz motherboards.

In general, PC133 SDRAM can also be used with a 100MHz or 66MHz front side bus; however, your memory will only operate as fast as the slowest "link" in your system. For example, if you install a PC133 module in a system with a 100MHz FSB or in a system containing a 100MHz module, the PC133 module will operate at 100MHz.

Accepts SDRAM 100MHZ
This line tells you whether or not your system will accept 100MHz synchronous dynamic random access memory (SDRAM). SDRAM delivers bursts of data at very high speeds using an interface that is synchronized to the CPU clock. PC100 SDRAM is a particular type of 100MHz SDRAM that meets Intel's requirements for use with 100MHz motherboards.

In general, 100MHz SDRAM can also be used with a 66MHz front side bus; however, your memory will only operate as fast as the slowest "link" in your system. For example, if you install a PC100 module in a system with a 66MHz FSB or in a system containing a 66MHz module, the PC100 module will operate at 66MHz.

Accepts SDRAM 66MHZ
This line tells you whether or not your system will accept 66MHz synchronous dynamic random access memory (SDRAM). SDRAM delivers bursts of data at very high speeds using an interface that is synchronized to the CPU clock. 66MHz SDRAM is used in systems that have a 66MHz front side bus.

Accepts Registered SDRAM
This line tells you whether or not your system will accept registered SDRAM. Registered modules contain a register that delays all information transferred to the module by one clock cycle. Like buffered modules, registered modules are typically used only in servers and other mission-critical systems where it is extremely important that the data is properly handled.

Accepts EDO
This line tells you whether or not your system will accept extended data out (EDO) memory. Enhancements its addressing system allow EDO to operate 10 to 15% faster than FPM; however, it is not as fast as SDRAM.

Accepts Fast Page Mode
This line tells you whether or not your system will accept fast page mode (FPM) memory. FPM is the oldest type of memory that Crucial sells. In the FPM scheme, information from the same row of DRAM can be accessed an infinite number of times after supplying the row address only once.

Max EDO/FPM
This line tells you the maximum amount of EDO or FPM memory (in megabytes) that your motherboard will recognize. The total memory on all the modules installed in your system cannot exceed this amount.

Accepts DDR
This line tells you whether or not your system will accept double data rate (DDR) SDRAM. DDR SDRAM is the most recent addition to Crucial Technology's memory offerings. It reads information on both the rising and falling edge of the CPU's clock cycle, roughly doubling the speed of memory processing over standard SDRAM.

PC1600 DDR SDRAM is used in systems with a 100MHz front side bus. PC2100 DDR SDRAM is used in systems with a 133MHz front side bus.

Accepts ECC
This line tells you if your motherboard will accept error checking and correcting (ECC) modules. ECC modules have an extra chip that detects if the data was correctly read or written by the memory module. If the data wasn't properly written, the extra chip will correct it in many cases (depending on the type of error). Non-ECC (also called non-parity) modules do not have this error-detecting feature.

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-ECC. 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-ECC SDRAM or DDR SDRAM.

Accepts Parity
This line tells you if your motherboard will accept parity modules. 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, unlike an ECC module, a parity module will not correct the error.

If you plan to use your system as a server or a similar mission critical type machine, it is to your advantage to use parity. If you plan to use your PC for regular home, office, or gaming applications, you are better off with non-parity. Current technology DRAM is very stable and memory errors are rare, so unless you have a need for parity, you are better served with non-parity DRAM.

Accepts RDRAM (Rambus)
This line tells you if your motherboard will accept Rambus (RDRAM) memory. Rambus is a proprietary memory of Rambus Inc., and manufacturers who produce it are required to pay a royalty. Rambus and SDRAM modules are not interchangeable and do not fit into the same size slots.

DIMM Socket Count
This line tells you how many dual inline memory modules (DIMMs) can be installed in your system at once. A DIMM consists of a number of memory components (usually black) that are attached to a printed circuit board (usually green). The gold or tin pins on the bottom of the DIMM provide a connection between the module and a socket on a larger printed circuit board. The pins on the front and back of a DIMM are not connected, providing two lines of communication paths between the module and the system.

DIMMs come in several sizes. 168-pin DIMMs, the most common size for PCs, are approximately 5.375" long and 1.375" high. 100-pin DIMMs, the most common size for printers, are approximately 3.5" long and 1.25" high. 184-pin DIMMs, used for DDR SDRAM, are approximately 5.375" long and 1.375" high. While 184-pin DIMMs and 168-pin DIMMs are about the same size, 184-pin DIMMs have only one notch within the row of pins while the 168-pin DIMMs have two notches.

Sockets per DIMM Bank
This line tells you how many DIMMs must be installed at the same time. In most cases, DIMMs are installed individually. However, if there were two sockets per bank, you would need to install two modules at the same time. In this scenario, if you wanted to add 64MB, you would need to purchase two 32MB modules and install them together.

72-pin SIMM Socket Count
This line tells you how many 72-pin single inline memory modules (SIMMs) can be installed in your system. A SIMM consists of a number of memory components (usually black) that are attached to a printed circuit board (usually green). The gold or tin pins on the bottom of the SIMM provide a connection between the module and a socket on a larger printed circuit board. The pins on the front and back of a SIMM are connected, providing a single line of communication paths between the module and the system.

Each 72-pin SIMM provides a 32-bit data path, so they can be installed singly in 32-bit systems (486 models) but must be installed in pairs in 64-bit systems (Pentium and Athlon models). 72-pin SIMMs are approximately 4.25" long and 1" high, though the heights may vary. They have one notch on the bottom left and one notch in the center of the module.

Sockets per 72-pin SIMM Bank
This line tells you how many 72-pin SIMMs must be installed at the same time in your system. In general, they can be installed singly in 32-bit systems (486 models) but must be installed in pairs in 64-bit systems (Pentium and Athlon models). If you have two sockets per bank, you would need to install two modules at the same time. In this scenario, if you wanted to add 64MB, you would need to purchase two 32MB modules and install them together.

30-pin SIMM Socket Count
This line tells you how many 30-pin single inline memory modules (SIMMs) can be installed in your system. A SIMM consists of a number of memory components (usually black) that are attached to a printed circuit board (usually green). The gold or tin pins on the bottom of the SIMM provide a connection between the module and a socket on a larger printed circuit board. The pins on the front and back of a SIMM are connected, providing a single line of communication paths between the module and the system.

Each 30-pin SIMM provides an 8-bit data path, so they must be installed in banks of 4 in order to communicate with 32-bit systems (such as 486 models). All 30-pin SIMMs use FPM memory technology. 30-pin SIMMs are approximately 3.5" long and .75" high, though the heights may vary. They have a single notch on the bottom left to ensure that they are installed correctly.

Sockets per 30-pin SIMM Bank
This line tells you how many 30-pin SIMMs must be installed at the same time in your system. In general, 30-pin SIMMs are installed in banks of 4. That means that if you wanted to add 64MB, you would need to purchase four 16MB modules and install them together.

Buffering
This line tells you whether your system takes buffered, unbuffered, or registered modules. Unbuffered modules are the most common. In unbuffered memory, the chipset controller deals directly with the memory. There is nothing between the chipset and the memory as they communicate. Buffered modules contain a buffer to help the chipset cope with the large electrical load required when the system has a lot of memory. Registered modules are unbuffered modules that contain a register that delays all information transferred to the module by one clock cycle. Buffered and registered modules are typically used only in servers and other mission-critical systems where it is extremely important that the data is properly handled.

DDR and SDRAM modules can be registered or unbuffered; EDO and FPM modules can be buffered or unbuffered.

Max Unbuffered SDRAM
This line tells you the maximum amount of unbuffered memory (in megabytes) that your motherboard will recognize. The total of all the modules installed in your system cannot exceed this amount. In unbuffered SDRAM, the chipset controller deals directly with the memory. There is nothing between the chipset and the memory as they communicate.

Max Registered SDRAM
This line tells you the maximum amount of registered memory (in megabytes) that your motherboard will recognize. The total of all the modules installed in your system cannot exceed this amount. Registered modules contain a register that delays all information transferred to the module by one clock cycle. is usually done on modules with a lot of memory to help ensure that the data is properly handled.

CL=3, CL=2, and CL=2, 2-clock
In our Memory Selector, the CAS latency of our parts is designated with "CL=3," "CL=2," or "CL=2, 2-clock." (You may see this written elsewhere as "CL2, etc." or "CAS=2, CAS=3, etc.") CAS latency is the amount of time it takes for your memory to respond to a command. It only affects the initial burst of data. Once data starts flowing, latency has no effect.

Latency is measured in terms of clock cycles. For example, a CL=2 part requires two clock cycles to respond, while a CL=3 part requires three clock cycles. Thus, CL=2 parts complete the initial data access a little more quickly than CL=3 parts. However, a clock cycle for a systems with a 100MHz front side bus is only 10 nanoseconds (10 billionths of a second), so you probably won't be able to tell the difference between a CL=2 and a CL=3 part.

Most systems will accept either part; however, some systems require one or the other. These requirements are built into our Memory Selector.



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Memory modules 101: Motherboard Specs

64MB PC100

128MB PC133 ECC

256MB PC2100 DDR ECC

64MB PC100

128MB PC133 ECC

256MB PC2100 DDR ECC

64MB PC100

128MB PC133 ECC

256MB PC2100 DDR ECC

64MB PC100

128MB PC133 ECC

256MB PC2100 DDR ECC

64MB PC100

128MB PC133 ECC

256MB PC2100 DDR ECC