What is the cas latency of RAM

What-is-the-cas-latency-of-RAM

RAM latency are various parameters that indicate how many clock cycles it takes for RAM to process a column of data and send it to the CPU. However, this definition is probably not clear enough, but it is the shortest definition and let’s dig a little deeper now for clarity.

These parameters are denoted by 5 or 6 different abbreviations, but we usually only look at 2 of them to characterize the latency of a RAM module. They are identified by the following abbreviations: CAS (or CL), tRCD, tRP, tRAS, tRFC and CR.

What is RAM latency?

The lower the RAM latency, the faster the memory because it takes less time to execute the action of sending a column full of data. This data will then be interpreted by the processor, but this is already independent of RAM.

The main parameters to look at are CAS (sometimes referred to as CL) and CR. The first stands for Column Address Flash and the second stands for Command Rate. Let’s explain them all briefly and in detail below.

  • CAS (or CL): Indicates the number of cycles required from the moment the RAM controller receives a command and the data is sent to the CPU by the pins.
  • tRCD: Loops required to pass data from a column to a row.
  • tRP: Cycles required to flush a row’s cache and load new data into the row.
  • tRAS: Minimum number of cycles required for RAM to repeatedly process and store data
  • tRFC: Loops required to update a row.
  • CR: Cycles required between identifying the memory chip to be used and starting to use it.

All these parameters have a direct impact on both the performance and stability of the system. To change them, you need to enter the BIOS, but if you do not understand what you are doing, it is better to leave them as standard.

XMP profiles are responsible for setting all these parameters. RAM modules contain JEDEC-approved profiles using standards compatible with all motherboards, so all these RAM latency parameters are determined from the moment they are manufactured.

What should be the RAM latency?

The latency of the RAM serves to give us an idea of its performance. As we said at the beginning, two basic parameters are important. Typically, RAMs are specified by their speed (in MHz), voltage (in v), and latency (in clock cycles). In this way, we can find RAM specifications like this: 4000 MHz 19-23-23-45 1.35V.

Where they only show four parameters, the first four from the list we made above. In this case, if the first number, CL, is 19, the RAM latency is said to be CL19. The lower the number, the better, but you also need to take into account the speed of the RAM, since this number as we say indicates the number of clock cycles required to execute an operation from start to finish.

The speed of the clock is determined solely by frequency, and the higher the speed, the faster the cycles are completed. It’s common to see latencies increase significantly with each step taken in DDR, but the overall gain is better as higher speeds mean shorter cycles.

In this way, changing the latency of RAM can improve the performance of the computer, but it is true that it is often largely unnoticeable in daily tasks. One change to consider is choosing a higher voltage memory profile, as it is not easy to calculate each of these numbers.