A-Tech 16GB DDR4 2666 MHz UDIMM PC4-21300

Only the specifications this product actually carries.

DDR4

DDR4 is the memory generation that dominated desktops and laptops from about 2015 until DDR5 arrived in late 2021. DDR4 kits typically run between 2133 and 3600 MT/s and use 288-pin desktop modules or 260-pin laptop modules. DDR4 is not compatible with DDR5 motherboards; the slots are keyed differently. For buyers on an existing DDR4 platform, the practical question is price against the kit's own history, since DDR4 pricing has moved independently of DDR5 during the 2025 to 2026 surge.

Speed (MT/s and MHz)

Memory speed is quoted in megatransfers per second (MT/s), though retailers and manufacturers often label the same number as MHz. A DDR5-6000 kit transfers data 6000 million times per second. Higher speed generally helps in memory-sensitive workloads and on AMD Ryzen systems up to the platform's sweet spot, beyond which gains shrink. Kits at the same capacity but different speeds are different products with separate price histories, which is why MemRadar tracks them on separate pages.

CAS latency (CL)

CAS latency, written CL followed by a number such as CL30 or CL36, is the number of clock cycles between a memory request and the start of data delivery. Lower is faster at the same speed. Because faster kits run more cycles per second, a CL36 kit at 6000 MT/s can have similar real latency to a CL30 kit at 5200 MT/s. CL is one of the specs that most often separates two kits that otherwise look identical, and it usually carries a price premium at the low end.

UDIMM and SODIMM

UDIMM is the full-size unbuffered module used in desktops; SODIMM is the shorter module used in laptops and small-form-factor systems. The two are not interchangeable. Desktop DDR5 UDIMMs have 288 pins and laptop DDR5 SODIMMs have 262 pins. A kit listed as "laptop memory" is a SODIMM, and MemRadar's product name states Desktop or Laptop wherever a listing's title left it ambiguous.