Memory module frequently asked questions - RIMM, DIMM, SIMM,

What is a SO-DIMM?

Small outline dual in-line memory modules (SO-DIMMs) are used in notebook computers. They are smaller and thinner than other DIMMs, so are used when there is less space within a chassis.

SO-DIMM modules for HP computers must meet the following requirements:

The number of pins on the SO-DIMM must match the socket type.


SO-DIMM memory requires a 200-pin slot.


DDR2 SO-DIMMs are not compatible with DDR1 DIMM and DDR2 DIMM memory modules.


DDR3 SO-DIMMs are not compatible with DDR1 or DDR2 and use a 204 pin slot.


With a computer running at a system bus of 533 MHz or 667 MHz, use a PC2-4200 (DDR2 DIMM 533) type.

What is a DIMM?

Dual in-line memory modules (DIMMs), used in most desktop computers, are small circuit boards that can hold groups of memory chips. DIMMs provide a wider path with two rows of pins on a side, allowing for faster data transfer than single in-line memory modules (SIMMs). Like SIMMs, DIMMs might be manufactured single or double-sided. DIMMs do not have to be added in pairs and can be mixed with other DIMMs that have the same number of pins. For example, a 1-gigabyte (GB) DIMM can be added to the motherboard next to a 2 GB DIMM.

NOTE: DIMMs can only operate as fast as the speed of the system bus. If two or more DIMMs of different speeds are installed, the total speed of all installed memory is as fast as the DIMM with the lowest speed.

DIMM modules for HP computers must meet the following requirements:

The number of pins on the DIMM must match the socket type.


DDR memory requires a 184-pin slot and 2.5 operating voltage.


DDR2 memory is not compatible with DDR1 memory and requires a 240-pin slot and 1.8 operating voltage.


DDR3 memory can operate about twice the bandwidth of DDR2.
DDR3 DIMMS are not compatible with DDR1 or DDR2 memory.
DDR3 DIMMS require a 240-pin slot and 1.5 operating voltage. A slot for DDR3 memory is keyed differently than DDR2 or DDR. Do not attempt to install DDR3 memory into a motherboard designed for DDR or DDR2. Doing so can permanently damage the motherboard and DIMM.


Synchronous dynamic random access memory (SDRAM): Only use DDR type SDRAM memory if the computer came with DDR-SDRAM.

What is a RIMM?

Rambus in-line memory modules (RIMMs) are 184-pin memory boards that permit transfer rates of 600-800 MHz. RIMMs used with the Intel Pentium® 4 processors run on a 400 MHz system bus, allowing data transfer rates of 3.2 Gigabytes a second.

RIMM modules for HP computers must meet the following requirements:

HP computers require PC600 or PC800 RDR modules (184-pin Rambus dynamic Random access memory [RDRAM]).


Non-ECC (non error-correcting checking).


Rambus/Intel specification compliant.


All four RIMM sockets must be filled, either with a RIMM or with a continuity module called a Continuity RIMM (C-RIMM). C-RIMMs do not contain memory, but are placeholders to close the memory circuit.


RIMMs work in pairs, and they must be from the same vendor. RIMMs must also have the same memory size density within each channel.


When C-RIMMs fill empty sockets, they must be placed in the RIMM A2 and B2 sockets.


The RIMMs must be inserted in the RIMM A1 and B1 sockets.

What is a SO-RIMM?

Small outline Rambus in-line memory modules (SO-RIMMs) are 160-pin memory boards used in notebook computers. They are smaller than other RIMMs, so are used when there is less space within a chassis.

What is dual channel or triple channel mode?

Certain memory modules can operate in multiple channel modes. The motherboard specifications for your computer contain dual channel mode information, if available and supported. Dual channel and triple channel memory mode provides increased performance over single channel mode.

The following requirements must be met for the DDR memory to function in multiple channel mode:

All DIMMS must be of the same density (256 MB, 512 MB, etc.)


Same DRAM chip technology (x8 or x16).


All either single-sided or dual-sided.


DDR2 and DDR3 support Dual Channel mode. The same type of memory must be matched into the same matched slot for Channel A and Channel B. Usually the memory slots are color coded to make it easier to understand.


DDR3 memory can support 3 DIMMs in Triple Channel mode. The same memory size and type needs to be installed into the matched DIMM slots for channels A, B and C. Usually the memory slots are color coded to make it easier to understand.

NOTE:Motherboards with Intel i945G or i945P chipsets; with DDR2-667 memory modules using one Gigabit technology perform as DDR2-533 memory modules. If faster DDR2-667 memory modules are used, they must be 256 or 512 Megabit.