Module Form

On Sep. 10th (week 37th), we discussed that there is no possibility of SDRAM substitutes for DDR in terms of new specs in motherboards' socket. Now, for a more detailed analysis....

SIMM

Prior generations, when CPU processed in 8 bits or 32 data bits (which is 1Byte or 4 Bytes), there were Single In-Line Memory Module (SIMM) in 30 and 72 pin configuration modules to support 8 data bit or 32 data bit CPUs, respectively. With SIMMs, memory chips are soldered onto a modular printed circuit board (PCB), which inserts into a socket on the system board. As shown in the graph, the golden parts are the pins and there are 72 pins in this type. Some refer to these golden parts as "Golden fingers".

Graph 1. 72 pin SIMM.

Graph 2. 72 pin SIMM.

DIMM

Dual In-line Memory Modules (DIMM) closely resemble SIMMs. The difference between SIMM and DIMM is on a SIMM, pins on opposite sides of the board are "tied together" to form one electrical contact; on a DIMM, opposing pins remain electrically isolated to form two separate contacts.

DIMM are often used in computer configuration that support a 64-bit memory bus. SDRAM are more soldered onto a 168-pin PCB to transfer 64 bits of data at a time. But DDR tendes to be soldered onto a 184-pin PCB.

Graph 3. 168-pin DIMM. (SDRAM). Both sides have 84 golden fingers.

Graph 4. 184-pin DIMM. (DDR). One side has 92 pins.

So-DIMM

Small Outline Dual In-line Memory Modules ( SO- DIMM) used in notebook computers requires significantly smaller sides than the standard DIMM.

Graph 5. 144-pin SO-DIMM. (SDRAM).

Graph 6. 200-pin SO-DIMM. (DDR).

RI-DIMM and SO-RIMM

RIMM is the trademarked name for a Direct Rambus memory module. RIMMs look similiar to DIMMs, but transfer data in 16-bit batches. The faster access and transfer speed generates more heat, therefore RIMM usually covers a heat spreader (made by aluminum sheath) to protect the chips from overheating.

Graph 7. 184-pin RIMM.

This is why different types and number of pins need different sockets which are not substitutable.