SDRAM – Synchronous Dynamic Random Access Memory can accept one command and transfer one word of data per clock cycle, typical clock frequencies are 100 and 133 MHz. Chips are made with a variety of data bus sizes (most commonly 4, 8 or 16 bits) but chips are generally assembled into 168-pin DIMM modules that read or write 64 (non-ECC) or 72 (ECC) bits at a time. For space constrained designs, 144-pin SODIMM modules are a smaller form-factor alternative. SDRAM 168-pin and 144-pin modules are now considered legacy product, which Wintec is committed to continue supporting based on availability of raw materials. From the original SDRAM, further generations of modules are now available, DDR1, DDR2 and DDR3 (which is becoming the mainstream technology in 2010), with DDR4 currently being designed and anticipated to be available in year 2012.