Doc Overclock · 06-17-2002 · Category: Guides

System Timing and Memory Speed

It is important for you to understand the relationship between the two main aspects that control the actual speed that your system memory runs at.

Memory Timing Settings:

the timing that the system is told to use, often via settings in the BIOS setup program derives the memory's actual speed. These settings control how quickly the system will try to read or write to the memory.

DRAM Speed:

This is the minimum access time that the DRAM can physically run at and is rated in measurements of nanoseconds (ns). The speed of the DRAM sets the limits for how fast your memory's timing can be set. Sometimes the latest SDRAM modules are rated in MHz (frequency) instead of access time.

The connection between these two factors is as follows. The faster the physical DRAM is, the faster the systems memory timing can be set at. When you increase the system timing (by reducing the number of clock cycles required to access the memory using the appropriate BIOS settings) then the system will run faster.

The catch here is though if you set them too fast for the DRAM you are using it will result in system errors occurring. The speed of the DRAM does not straightforwardly control the speed of the memory system. What it does is set the maximum limit.

What this means to the user is that if you replace your system's 10ns SDRAM with 8ns SDRAM, the system will not run faster unless you also increase the system timing speed so that it tries to access the faster memory in a faster fashion. Conversely, replacing faster memory with slower memory won't cause the system to run any slower unless the system timing is decreased; however, if the new slower memory is too slow for the timing settings, memory errors (crashes, lockups, BSOD) will result.

Some systems will automatically set the memory timing based on the (SPD) speed of the memory, which is detected by the motherboard. This is the reason there is some confusion in this matter. Using faster memory with this type of system makes the faster DRAM automatically cause the system to run faster. However, one principle still holds true. The system timing is what is making the memory run faster. It's just that the system timing is being increased automatically and is therefore transparent to the user.

Contents

1. Introduction
2. SPD And CAS Latency Values
3. The Memory Bus
4. Bank Interleaving
5. System Timing and Memory Speed