Digital Locked Loop (DLL) – The BIOS Optimization Guide

Digital Locked Loop (DLL) - The BIOS Optimization Guide

Digital Locked Loop (DLL)

Common Options : Enabled, Disabled

 

Quick Review

The Digital Locked Loop (DLL) BIOS option is a misnomer of the Delay-Locked Loop (DLL). It is a digital circuit that aligns the data strobe signal (DQS) with the data signal (DQ) to ensure proper data transfer of DDR, DDR2, DDR3 and DDR4 memory. However, it can be disabled to allow the memory chips to run beyond a fixed frequency range.

When enabled, the delay-locked loop (DLL) circuit will operate normally, aligning the DQS signal with the DQ signal to ensure proper data transfer. However, the memory chips should operate within the fixed frequency range supported by the DLL.

When disabled, the delay-locked loop (DLL) circuit will not align the DQS signal with the DQ signal. However, this allows you to run the memory chips beyond the fixed frequency range supported by the DLL.

It is recommended that you keep this BIOS feature enabled at all times. The digital locked loop circuit plays a key role in keeping the signals in sync to meet the tight timings required for double data-rate operations.

It should only be disabled if you absolutely must run the memory modules at clock speeds way below what they are rated for, and then only if you are unable to run the modules stably with this BIOS feature enabled. Although it is not a recommended step to take, running without an operational DLL is possible at low clock speeds due to the looser timing requirements.

It should never be disabled if you are having trouble running the memory modules at higher clock speeds. Timing requirements become stricter as the clock speed goes up. Disabling the DLL will almost certainly result in the improper operation of the memory chips.

 

Details

DDR, DDR2, DDR3 and DDR4 SDRAM deliver data on both rising and falling edges of the signal. This requires much tighter timings, necessitating the use of a data strobe signal (DQS) generated by differential clocks. This data strobe is then aligned to the data signal (DQ) using a delay-locked loop (DLL) circuit.

The DQS and DQ signals must be aligned with minimal skew to ensure proper data transfer. Otherwise, data transferred on the DQ signal will be read incorrectly, causing the memory contents to be corrupted and the system to malfunction.

However, the delay-locked loop circuit of every DDR, DDR2, DDR3 or DDR4 chip is tuned for a certain fixed frequency range. If you run the chip beyond that frequency rate, the DLL circuit may not work correctly. That’s why DDR, DDR2, DDR3 and DDR4 SDRAM chips can have problems running at clock speeds slower than what they are rated for.

If you encounter such a problem, it is possible to disable the DLL. Disabling the DLL will allow the chip to run beyond the frequency range for which the DLL is tuned for. This is where the Digital Locked Loop (DLL) BIOS feature comes in.

When enabled, the delay-locked loop (DLL) circuit will operate normally, aligning the DQS signal with the DQ signal to ensure proper data transfer. However, the memory chips should operate within the fixed frequency range supported by the DLL.

When disabled, the delay-locked loop (DLL) circuit will not align the DQS signal with the DQ signal. However, this allows you to run the memory chips beyond the fixed frequency range supported by the DLL.

Note : The Digital Locked Loop (DLL) BIOS option is a misnomer of the Delay-Locked Loop (DLL).

It is recommended that you keep this BIOS feature enabled at all times. The delay-locked loop circuit plays a key role in keeping the signals in sync to meet the tight timings required for double data-rate operations.

It should only be disabled if you absolutely must run the memory modules at clock speeds way below what they are rated for, and then only if you are unable to run the modules stably with this BIOS feature enabled. Although it is not a recommended step to take, running without an operational DLL is possible at low clock speeds due to the looser timing requirements.

It should never be disabled if you are having trouble running the memory modules at higher clock speeds. Timing requirements become stricter as the clock speed goes up. Disabling the DLL will almost certainly result in the improper operation of the memory chips.

 

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