Types of RAM Modules: DIMM, DDR, RIMM, FB-DIMM, GDDR, SO-DIMM

Memory Modules

Small printed circuit boards built on different memory chips:

• DIMM (Dual In-Line Memory Module): Similar to the SIMM, physically larger, and have 168 contacts. They are distinguished by having a notch on both sides and two more in the row of contacts. The mounting of the sockets is different than that of the SIMM. DIMMs are found in 32, 64, 128, 256, 512 MB, and 1, 2 GB capacities.
• DIMM DDR: Has gradually replaced the standard DIMMs. It has a total of 184 pins instead of the 168-pin DIMM of SDRAM. Physically, they resemble the above but have one notch in the row of contacts.
• DIMM DDR2: Has 240 pins and a notch in a different position than DDR DIMMs.
• DIMM DDR3: Also has 240 pins but is neither physically nor electrically compatible with DDR2 DIMM since the notch is in a different position.
• RIMM (Rambus In-Line Memory Module): Similar to DIMMs but slightly larger and covered by a heatsink. Initially appeared with 168 pins. Currently, 232 pins are used. They are faster than the previous ones but with higher prices. They are used in reports that can be found in RDRAM devices.
• FB-DIMM (Fully Buffered DIMM): A variant of DDR2, these modules are used in servers (fast, effective, and coordinated), which require fast, effective, and coordinated data transport. The data between the memory controller and the module are transmitted in series, so there are fewer connection lines. This provides dramatic improvements regarding speed and memory capacity. They have the inconvenience of their high cost, and the heat generated increases with speed and latency. These modules have 240 pins, and the positions of the grooves are different from that of DDR2.
• GDDR (Graphics DDR): Memory chips embedded in some graphics cards or the motherboard where the card is integrated. They are very fast, controlled by the graphics card processor. Also known as DDR RAM for graphics, they are used in consoles like PlayStation 3 and Xbox 360.
• SO-DIMM and Micro-DIMM (Small Outline): The first is a compact version of conventional DIMMs with 144 contacts. Micro-DIMMs are smaller than SO-DIMMs. Used for laptops, PDAs, notebooks, compact equipment, etc.
• Buffered and Unbuffered: Buffered modules incorporate registers, i.e., circuits that ensure stability at the expense of losing performance. They act as storage between the CPU and memory. They increase system reliability but delay data transfer time between memory and the system. They are used in servers where data integrity is important. They have ECC (Data Detection and Correction) to differentiate them from unbuffered, which have several small chips. Unbuffered modules communicate directly with the Northbridge, making memory faster but less secure than buffered.