Memory - RAM

RAM (Random Access Memory) is where data the CPU is working with is temporarily stored. More RAM is generally better, although there are diminishing returns and 32-bit versions of Windows only support a maximum of 4GB. Speed, measured in MHz, is another consideration, but most importantly memory needs to be compatible with your motherboard: it'll either be DDR, DDR2, DDR3 or DDR4. Smaller SODIMM modules for laptops and mini PCs and ECC memory for servers are all available in this category.

DDR4 Single/Dual Channel 2133MHz RAM Memory Kits

DDR4 SDRAM is the fastest and most efficient consumer memory available. It's compatible with Intel's Broadwell-E which run in quad-channel and Kaby Lake & Skylake CPUs which run in dual-channelmodes. It is also compatible with AMD's latest RYZEN CPUs running in a dual-channel configuration. The modules found here are designed for Intel Kaby Lake, Intel Skylake & AMD RYZEN, so they're sold in matching kits of two modules for best performance or single modules for a cheap upgrade. These are the most basic kits around, with a speed of 2,133MHz.

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DDR4 Single/Dual Channel 2400MHz RAM Memory Kits

DDR4 SDRAM is the fastest and most efficient consumer memory available. It's compatible with Intel's Broadwell-E which run in quad-channel and Kaby Lake & Skylake CPUs which run in dual-channelmodes. It is also compatible with AMD's latest RYZEN CPUs running in a dual-channel configuration. The modules found here are designed for Intel Kaby Lake, Intel Skylake & AMD RYZEN, so they're sold in matching kits of two modules for best performance or single modules for a cheap upgrade. These are the mid-range kits, with a speed of 2,400MHz.

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DDR4 Single/Dual Channel 2666MHz+ RAM Memory Kits

DDR4 SDRAM is the fastest and most efficient consumer memory available. It's compatible with Intel's Broadwell-E which run in quad-channel and Kaby Lake & Skylake CPUs which run in dual-channel modes. It is also compatible with AMD's latest RYZEN CPUs running in a dual-channel configuration. The modules found here are designed for Intel Kaby Lake & Skylake, so they're sold in matching kits of two modules for best performance or single modules for a cheap upgrade. These are the mid-range kits, with a speed of at least 2,666MHz.

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DDR4 Single/Dual Channel 3000MHz+ RAM Memory Kits

DDR4 SDRAM is the fastest and most efficient consumer memory available. It's compatible with Intel's Broadwell-E which run in quad-channel and Kaby Lake & Skylake CPUs which run in dual-channel modes. It is also compatible with AMD's latest RYZEN CPUs running in a dual-channel configuration. The modules found here are designed for Intel Kaby Lake & Skylake, so they're sold in matching kits of two modules for best performance or single modules for a cheap upgrade. These are the high-end kits, with a speed of at least 3,000Hz.

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DDR4 Quad Channel 2800MHz+ RAM Memory Kits

DDR4 SDRAM is the fastest and most efficient consumer memory available. It's compatible with Intel's Broadwell-E which run in quad-channel and Kaby Lake & Skylake CPUs which run in dual-channel modes. It is also compatible with AMD's latest RYZEN CPUs running in a dual-channel configuration. The modules found here are intended for use with Intel Broadwell-E or Haswell-E CPUs, using an Intel X99 motherboard which runs in quad-channel mode. That's what these modules are designed for, so they're sold in matching kits of four or eight. These are the high-end kits, with a speed of at least 2,800MHz.

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DDR3 Single/Dual Channel 1600MHz+ RAM Memory Kits

DDR3 SDRAM is an evolution of DDR2 SDRAM. Designed for todays systems which support DDR3, the primary benefit of DDR3 being the ability to transfer data at a much higher rate than DDR2 due to the higher clock rate. This allows you to take advantage of the high speeds offered by todays CPU's. These memory modules are available in single, dual and quad packs, and have a clock speed of 1600Mhz.
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Tekspek An in-depth guide into tech: Gigabytes and Gibibytes System Buses & Bandwidth DC Ram DDR3
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DDR3L SO-DIMM 1600MHz+ RAM Memory Kits

SODIMM memory is smaller than standard modules, and is used in laptops and mini-PCs. As long as you can access your system's memory slots, you can upgrade it. The kits here come in a range of speeds and capacities, so make sure your system is compatible with the memory you choose.

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Server DDR4 2400MHz RAM Memory Kits

DDR4 server memory brings maximum speed and efficiency to Intel's quad-channel Xeon E5 and six-channel Xeon Scalable platform and AMD's eight-channel EPYC platform.

Server memory is designed to have rock solid stability 24/7. ECC (error correcting code) modules are immune to errors, while registered/buffered sticks reduce memory controller load and ensure additional stability when using many modules together. Motherboards need to support ECC and registered memory for these features to work. These particular modules are rated up to 2400MHz.

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