[ The PC Guide | Systems and Components Reference Guide | System Memory | Memory Speed, Access and Timing ]

System Timing Settings

There are a number of settings that control the timing of your system memory. There are many different ways to set your system's memory timing, which depend on how the system and the BIOS are set up. These settings are important; they are discussed in full detail in the section on "Advanced Chipset Features" BIOS settings.

Some systems incorporate automatic timing settings, while others require manual adjustment of the individual parameters that control the timing level. It is normal for the BIOS to allow tweaking of the two main numbers that control system timing: the time for the initial access ("x" in the "x-y-y-y" notation) and the time for subsequent accesses ("y"). Being able to set the "x" and "y" independently gives more flexibility. Many BIOSes use different terms to refer to these numbers however. For example, some BIOSes refer to the time for the first access as "leadoff". Some use wait state notation instead of clock cycles.

Most systems now also have a type of automatic setting, which will set the system timing for you. These come in two flavors: one will actually autodetect the type and speed of memory installed in the PC and set the timing accordingly. The other will let you tell the PC what type and speed of DRAM you are using (in nanoseconds) and adjust the timing to maximize performance. Also, some implementations of SDRAM incorporate a technology called serial presence detect or SPD to allow the chipset to read the timing requirements of the SDRAM directly. See here fore more.

Next: Speculative Leadoff

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