Brief Outline Computer memory types are referred to by the term’s dual inline memory module and unbuffered dual inline memory module. While most memory modules fall under the general category of UDIMM, notebook computers almost exclusively use SO-DIMM modules.
UDIMM
A buffered memory module uses a microprocessor to pass data before it enters or exits the module’s memory chips. As a result, a computer can install multiple memory modules without overloading the motherboard’s memory controller and resulting in system instability. Buffered memory is necessary for many computers with more than four memory slots. Since most desktop and notebook computers only have four memory slots available, buffered memory is unnecessary. As a result, UDIMMs are present in the majority of computers.
SODIMM
Full-sized memory modules are challenging to fit in a notebook and small-form-factor desktop computers due to a lack of available space. These computers use memory modules with more compact circuit boards as a result. Small computers now have memory capacities similar to those of larger computers thanks to SO-DIMMs.
Identification to UDIMM
A SO-DIMM or a full-sized DIMM can both be unbuffered DIMMs. All SO-DIMMs are UDIMMs because only workstation and server computers require buffered memory. Furthermore, the majority of full-sized DIMMs are UDIMMs. The microprocessor in the middle of buffered memory modules is absent from UDIMMs.
Identification to SO-DIMM
The size of a SO-DIMM, which is slightly longer than 2.5 inches compared to a standard DIMM’s somewhat over five inches, is the primary way to recognize one as a SO-DIMM. There are 204 pins on a DDR3-SDRAM SO-DIMM and 240 pins on a DDR3-SDRAM DIMM.
Small computer expansion cards called SODIMMs (Small-Outline Dual Inline Memory Modules) are used for RAM. It is a scaled-down DIMM frequently found in laptops, all-in-one computers, and other small form factor PCs. The type of RAM it carries will determine the pinout, but most modern SODIMMs have 288 pins.
Here is an example of a DDR3 SODIMM:
UDIMM Vs. SODIMM
What is UDIMM?
Unbuffered Dual Inline Memory Module, or UDIMM as it is more commonly known, is a volatile memory chip used primarily in desktop and laptop computers. It is a typical form of RAM. A class of UDIMM is contemporary DDR memory chips.
UDIMM typically performs better than RDIMM (registered dual inline memory module) in systems with only one or two modules per memory channel. However, RDIMM can boost performance and lower latency in computers that use three or more modules per channel, like high-end workstations and servers.
What is SODIMM?
Small Outline Dual In-line Memory Module is referred to as SODIMM. SODIMMs are smaller than DIMMs, as you might guess from the name. The JEDEC specifications state that SODIMMs must be 3.8mm thick and 30mm high. The width of SDR, DDR, DDR2, and DDR3 SODIMMs was 67.6mm. SODIMMs for DDR4 and DDR5 was 2mm wider, measuring 69.6mm. The other measurements are comparable to PC DIMMS, which have a 133mm width, nearly twice as wide.
No generation of SODIMM form factored RAM is compatible, just like the DIMM form factor. This is so because their form factor is the only real distinction between DIMM and SODIMM. Beyond the smaller form factor’s increased thermal restrictions and physical capacity limits, there are no performance effects.
Each generation of SODIMM RAM uses a unique cut-out “key” to maintain the generational distinction and prevent hardware damage brought on by the variations in voltage requirements between ages. DDR and DDR2 SODIMM memory shared a similar key position. They are making it difficult to distinguish between them without direct side-by-side comparisons. Key locations on older SODIMM RAM generations are more distinct.
Similar to desktop DIMMs, SODIMMs have grown in pin count over time. DDR and DDR2 SODIMMs used 200 pins, while SDR SODIMMs had 144 pins. The pin count increased from 204 in DDR3 to 260 in DDR4 and 262 in DDR5. This further ensures electrical incompatibility among SODIMM memory generations.
Where is SODIMM Used?
The SODIMM form factor is perfect for use in computers with minimal space due to its small volume. As you may have inferred from the introduction, SODIMMs are primarily utilized in laptops. However, not all laptops use SODIMM memory. As convenient as it may be for users who desire the capability of future RAM upgrades. Compared to simply soldering the RAM chips directly to the motherboard, it is a little more difficult and expensive to implement. Comparable to what you might see on a smartphone.
Some small form factor motherboards may use SODIMM slots rather than full DIMMs. In addition, a SODIMM slot rather than a full-sized DIMM slot is part of the Nano-ITX motherboard standard. SODIMM slots may also be used by some routers, NASs, and upgradeable office printers. The alternative to using full-sized DIMMs would be to solder the memory chips directly to the motherboard.
Capacity Issue: The main problem with SODIMMs historically has been that they have less physical capacity than full-sized DIMMs. It is obvious that as memory density has risen, single DIMM and SODIMM memory capacities have as well. Due to the extreme lack of space, the available accommodations in SODIMM form factors have typically been about half that of full-sized DIMMs.
Bandwidth and Latency:
In terms of latency and bandwidth, UDIMMs excel. But when multiple DIMMs are installed in a memory channel, a completely different scenario emerges, causing the clock cycle for UDIMMs to change due to heavy electrical loading on the address and control lines. Higher latency and lower bandwidth than RDIMMs result from a single clock cycle being doubled to account for settling time.
Therefore, when there is more than one DIMM per memory channel, RDIMM’s superior performance is revealed, delivering an 8.7% faster data transfer rate than UDIMMs for two DIMMs per channel.
Most desktop and laptop computers use volatile memory chips called UDIMMs (Unbuffered DIMMs). It is a typical form of RAM. A class of UDIMM is contemporary DDR memory chips.
Conclusion:
Brief Outline Computer memory types are referred to by the term’s dual inline memory module and unbuffered dual inline memory module. While SO-DIMM modules are almost exclusively used in notebook computers, UDIMM is a general term that applies to most memory modules.
