Most would think that the lower the CAS Latency the better, as this value refers to your memory's ability to quickly respond to new information. This isn't completely accurate as newer memory types typically have much higher CAS latency times than their older counterparts.
Why do new memory types have slower latency times? Along with different timings, there is an attribute called Clock Cycle Time. This is a measurement reflective of how quickly the memory can be ready for a new set of commands. As the chart below illustrates, this effectively means the True Latency real speed is much faster.
If you would like to know more about speed vs latency, check out this in-depth article. In most cases you shouldn't worry about your memory timings. If you have any further questions be sure to reach out to Crucial support. All rights reserved. RAS Precharge is the time between the command is issued to close the row, and a new row becoming available for use.
This has a reduced effect on performance than that of CL. Example timing: 2 The time taken from the memory being activated to the possibility of an action being delivered to it. Whilst a topic of much debate, it is generally agreed that CR1 gives better performance, whilst CR2 gives potentially more stable overclocks. There you go, DDR explained. There you have it. A breakdown of each memory timing in a manner that is hopefully easy to digest. This is listed in MHz, or units of 1,,Hz.
However, modern memory is DDR double data rate , meaning data is transferred on the rising and falling edge of each clock, so advertised frequencies are twice the real clock frequency. Latencies have gradually increased over the years with the physical distance that signals have to travel the speed of light is a hard limit , but frequency has increased as well, and therefore performance has still improved. There are many, many different timings, but they deal with a fairly small list of commands: when they can be issued, how long it takes for them to execute, how many cycles pass before a response.
These are Active-Low signals, so they can be either H igh or L ow , 1 or 0. Together they form a four-bit code that specifies a command to be executed. The signals have changed a bit over the years, but for the most part DDR4 has the same list of commands that SDRAM has always had, and therefore many of the same timings. For some background information on stuff like banks, rows, and columns, this venerable article from Anandtech is a good overview of what SDRAM actually is and how it functions.
For this next section, we created a custom animation that can be found in our above-embedded video. That may assist in better understanding the below definitions. Activate : opens a row of a bank. A row must be active for reading and writing data. Precharge : closes the open row in one or all banks two separate commands , putting them into the idle state. Data is still stored in idle banks, but they must be activated again before reading or writing.
Read and Write : self explanatory. With these commands, an Auto Precharge flag can be set to automatically precharge the row when done. It can be a recurring command, but not frequently enough to make the related timings important to us. Refresh : refreshes the charge in memory cells by writing data back in place without changing it. All banks must be idle precharged before a refresh.
Timings are generally divided into three categories: Primary, Secondary, and Tertiary.
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