Asynclat (Asynchronous Latency) – The Tech ARP BIOS Guide

Asynclat - The Tech ARP BIOS Guide

Asynclat

Common Options : 0 to 15 ns

 

Quick Review of Asynclat

Asynclat is an AMD processor-specific BIOS feature. It controls the amount of asynchronous latency, which depends on the time it takes for data to travel from the processor to the furthest DIMM on the motherboard and back. For your reference, AMD has a few conservative suggestions on setting the Asynclat BIOS feature.

Memory Type

Number Of
DIMM Slots

Memory Clock

200 MHz

166 MHz

133 MHz

100 MHz

Registered

8

8 ns

8 ns

9 ns

9 ns

Unbuffered

4

8 ns

8 ns

8 ns

8 ns

3 or 4

7 ns

7 ns

7 ns

7 ns

1 or 2

6 ns

6 ns

6 ns

6 ns

Do note that in this case, the distance of the furthest DIMM slot is considered analogous to the number of DIMM slots. The greater number of DIMM slots available on the motherboard, the further the final slot is from the memory controller.

Also, these values are rough and conservative recommendations that assume that the furthest DIMM slot is occupied by a module. If your motherboard has four slots and you choose to populate only the first two slots, you could use a shorter asynchronous latency.

Generally, it is recommended that you stick with the asynchronous latency recommended by AMD (see table above) or your memory module’s manufacturer. You can, of course, adjust the amount of asynchronous latency according to the situation. For example, if you are overclocking the memory modules, or if you populate the first two slots of the four available DIMM slots; you can get away with a lower asynchronous latency.

 

Details of Asynclat

Asynclat is an AMD processor-specific BIOS feature. It controls the amount of asynchronous latency, which depends on the time it takes for data to travel from the processor to the furthest DIMM on the motherboard and back.

The asynchronous latency is designed to account for variances in the trace length to the furthest DIMM on the motherboard, as well as the type of DIMM, number of chips in that DIMM and the memory bus frequency. For your reference, AMD has a few conservative suggestions on setting the Asynclat BIOS feature.

Memory Type

Number Of
DIMM Slots

Memory Clock

200 MHz

166 MHz

133 MHz

100 MHz

Registered

8

8 ns

8 ns

9 ns

9 ns

Unbuffered

4

8 ns

8 ns

8 ns

8 ns

3 or 4

7 ns

7 ns

7 ns

7 ns

1 or 2

6 ns

6 ns

6 ns

6 ns

Do note that in this case, the distance of the furthest DIMM slot is considered analogous to the number of DIMM slots. The greater number of DIMM slots available on the motherboard, the further the final slot is from the memory controller.

Also, these values are rough and conservative recommendations that assume that the furthest DIMM slot is occupied by a module. If your motherboard has four slots and you choose to populate only the first two slots, you could use a shorter asynchronous latency.

Naturally, the shorter the latency, the better the performance. However, if the latency is too short, it will not allow enough time for data to be returned from the furthest DIMM on the motherboard. This results in data corruption and system instability.

The optimal asynchronous latency varies from system to system. It depends on the motherboard design, where you install your DIMMs, the type of DIMM used and the memory bus speed selected. The only way to find the optimal asychronous latency is trial and error, by starting with a high value and working your way down.

Generally, it is recommended that you stick with the asynchronous latency recommended by AMD (see table above) or your memory module’s manufacturer. You can, of course, adjust the amount of asynchronous latency according to the situation. For example, if you are overclocking the memory modules, or if you populate the first two slots of the four available DIMM slots; you can get away with a lower asynchronous latency.

Go Back To > The Tech ARP BIOS Guide | Home

 

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