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DRAM Timing Control:

Takes us to the DRAM Timing sub-section:

Most of these settings can safely be left at Auto unless you wish to tune the system for optimal scoring in benchmarks. The primary timings will be set in accordance with the memory module SPD at a given frequency or fall back on ASUS defaults as memory bus frequency is increased.

ASUS Z77 UEFI Memory Timings

DRAM CAS Latency:

Column Address Strobe, defines the time it takes for data to be ready for burst after a read command is issued. As CAS factors in almost every read transaction, it is considered to be the most important timing in relation to memory read performance. To calculate the actual time period denoted by the number of clock cycles set for CAS we can use the following formula:

tCAS in Nano seconds=(CAS*2000)/Memory Frequency

This same formula can be applied to all memory timings that are set in DRAM clock cycles.

DRAM RAS TO CAS Latency:

Also known as tRCD. Defines the time it takes to complete a row access after an activate command is issued to a rank of memory. This timing is of secondary importance behind CAS as memory is divided into rows and columns (each row contains 1024 column addresses). Once a row has been accessed, multiple CAS requests can be sent to the row the read or write data. While a row is “open” it is referred to as an open page. Up to eight pages can be open at any one time on a rank (a rank is one side of a memory module) of memory.

DRAM RAS# PRE Time:

Also known as tRP. Defines the number of DRAM clock cycles it takes to Precharge a row after a page close command is issued in preparation for the next row access to the same physical bank. As multiple pages can be open on a rank before a page close command is issued the impact of tRP towards memory performance is not as prevalent as CAS or tRCD – although the impact does increase if multiple page open and close requests are sent to the same memory IC and to a lesser extent rank (there are 8 physical ICs per rank and only one page can be open per IC at a time, making up the total of 8 open pages per rank simultaneously).

DRAM RAS Active Time:

Also known as tRAS. This setting defines the number of DRAM cycles that elapse before a Precharge command can be issued. The minimum clock cycles tRAS should be set to is the sum of CAS+tRCD+tRTP.

DRAM Command Mode:

Also known as Command Rate. Specifies the number of DRAM clock cycles that elapse between issuing commands to the DIMMs after a chip select. The impact of Command Rate on performance can vary. For example, if most of the data requested by the CPU is in the same row, the impact of Command Rate becomes negligible. If however the banks in a rank have no open pages, and multiple banks need to be opened on that rank or across ranks, the impact of Command Rate increases.

Most DRAM module densities will operate fine with a 1N Command Rate. Memory modules containing older DRAM IC types may however need a 2N Command Rate.


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