What is the difference between DDR3-1333 (PC3-10600), DDR3-1600 (PC3-12800), DDR4-2133 (PC4-17066), and DDR4-2400 (PC4-19200)?
Although these are all types of double data rate (DDR) memory, the varying numbers refer to the different speeds of memory, and even different memory generation types. When looking at the Data Rate (DDR), or speed PC (Per Clock transfers), it is important to note that systems can only handle certain types of memory - this is why it’s important to use either our Crucial Memory Advisor™ or System Scanner, when looking for compatible memory to install in your system.
It is easy to get data rate and speed mixed up because they are often interchangeable when someone is talking about how “fast” memory is. In layman’s terms data rate is how many bits a module can transfer in a given time, and speed is how many bytes it can transfer. Since there are 8 bits in a byte, we simply multiply the data rate by 8, and get the speed of the memory: 1600x8=12800, 2400x8=19200, where these results are your transfer rates in Megabytes per second (MB/s). When looking at both the data rate and speed, the particular generation of memory will be listed as well - for example PC3 prefaces DDR3 speeds, and PC4 prefaces DDR4 speeds.
Below is a list of common memory speeds and associated data rates. There may be some higher- and lower-end speeds that are missing, and slight differences depending on how numbers are rounded, but it is a good general overview of common memory performance attributes.