Memory - RAM

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.

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.

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.

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.

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 3,600Hz.

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 most basic kits around, with a speed of 2,133MHz.

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 mid-range kits, with a speed of 2,400MHz.

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 mid-range kits, with a speed of 2,666MHz.

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.

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 fast premium kits with speeds of at least 3200MHz.

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 fastest & most premium kits around with speeds of at least 3600MHz.

DDR3 SDRAM is an evolution of DDR2 SDRAM. Designed for todays systems which support DDR3, the primary benefit of DDR3 is 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 of todays CPU's. These memory modules are available in single, dual and quad packs, and have a clock speed of 1333Mhz.
Updated

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.
Updated

DDR3 memory is the most common memory. Excluding Intel X99, all current generation Intel and AMD desktop chipsets (and many previous generations too) use it. These high-end kits range from 4GB to 16GB with speeds from 1,866MHz to 3,000MHz – you may need to enabled the memory's XMP (Extreme Memory Profile) in your motherboard's BIOS to run it at full speed. Each kit has two identical sticks – they're designed for motherboards with just two slots or with four slots that need to be filled in pairs.

DDR3L differs from traditional DDR3 as it runs at 1.35V rather than 1.5V. This means it consumes less power and runs cooler. DDR3L is required for Intel Skylake CPUs using the Z170 chipset. For the best performance choose a pair of DIMMs running together in dual-channel mode at the highest frequency you can afford. These are the entry-level kits, with speeds between 1,600MHz and 2,133MHz.

DDR3 memory is the most common memory. Excluding Intel X99, all current generation Intel and AMD desktop chipsets (and many previous generations too) use it. The modules here come in all shapes, sizes and colours so you can match your system's aesthetic, but are all clocked at 1,600MHz. They come either in kits of two or as single units, but it's best to use matching modules if you need multiple sticks.

DDR3 Quad Channel Memory is a set of four matched memory modules, specifically for Intel X79 Chipset Motherboards which feature four or eight memory slots. Quad channel memory will have a higher bandwidth than a triple (3 memory module) channel memory system. These Memory modules come with a clock speed of 1800Mhz or more (check product specifications), and are available in packs of four modules. Always fit Quad channel memory modules as a complete set to your motherboard.
Updated