What are memory timings

by Crucial Employee on ‎06-07-2016 11:49 AM - edited on ‎06-09-2016 01:29 PM by Community Manager Community Manager (2,807 Views)

When the topic of memory performance comes up, most people usually think of a memory module speed. Module speed is a measure of a memory’s ability to transfer data, like: DDR2 800MHz, DDR3 1600MHz, and DDR4 2400MHz (or MT/s). In addition to module speed, we have other attributes we call timings, which determine how fast your memory can respond to requests for performing actions.

 

If we were to think of memory as a racing car, the module speed (MH/z) would be like the raw horse power of the engine, and the timings would be the driver of the car. As the driver of the car gets better at handling turns, responding to obstacles on the race course, the car inevitably will perform faster, so much so, that you can have a car with lower horsepower, outperform one with more, if the driver (timings) are faster than the other.

 

When we look at timings of memory, they are typically displayed in a numerical format; 9-9-9-24 is as an example of a generic DDR3 memory timing. Below is a table that displays some standard timings for different types of DDR memory.

 

Timmings table.PNG

 

Timings are most commonly broken down to the four values: CAS Latency (CL), Row Column Delay (TRCD), Row Precharge Time (TRP), and Row Active Time (TRAS). If you noticed the table above has the TRAS missing for DDR4, this is because this value has been merged into another number with the new memory technology, so it is no longer relevant.


latencies.PNG

 

The most widely recognized timing for memory would be CAS Latency. This value is typically ubiquitous with performance, it however can be very misleading sometimes. Logic would tell you that the lower the CAS Latency the better, since that means your memory is more able to quickly respond to new information; however newer memory types typically have much higher CAS latency times as you may have noticed already.

 

So why do new memory types have slower latency times?Along with different timings, there is an attribute called Clock Cycle Time; which is a measurement of how quickly the memory can be ready for a new set of commands. New memory types like DDR4 have significantly faster Clock Cycle Times than older memory, and as the chart below illustrates; this effectively means the True Latency (real speed) is much faster. If you would to know more about Speed vs Latency, check out this in-depth article we have.

speed vs latency.png

 

So should I really worry about my timings?

 

In most cases no. So long as you purchase memory that our System Scanner or Advisor Tool says is compatible with your base computer, you can be assured that you have memory that is capable of running in your system; there is however an exception to this rule when purchasing high performance Ballistix parts for custom built system. Some CPUs are limited with the memory speed and latencies they will support, so it’s always a good idea to check the max memory speed your CPU will support, before paring it with any higher end memory.  If you have any further questions be sure to reach out to Crucial support.