Memory Frequency and FSB

Timing for memory is very important.

This is a short tutorial on RAM and FSB timing. Some of the concepts are not translatable from tech jargon in to everyday English. If you get stuck on a concept read the description again, remember that it is all timing and the timing is controlled by the frequency of the voltage as it is applied or refreshed in some cases.

Also remember that with Intel processors a high voltage means the binary digit of 1 (one) and the lack of voltage is the binary digit of 0 (zero).  (This creates less heat... Hummmm)

As you read through this tutorial try to keep in mind that all voltages are very small + or - 0.05 to 1.5 volts, higher voltage creates too much heat and will destroy the processor and the RAM. Always make changes to your FSB and processor multiplier in small increments, it may take some time to get where you want to be in the speed of your processor/RAM but in the long run it will not destroy the components.

If you mix different frequencies when installing RAM your computer will have a lot of problems if it starts at all.

There are three main components to memory timing:

• RAS - Row Address Select
• CAS - Column Address Select
• Frequency - The clock frequency of the memory bus or FSB (Front Side Bus)

In addition there are:

• WE - Write Enable
• DQ - Data In or Data Out
• Voltage - Applied or refresh

Operation of RAM timing:

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If it is a Read (Data Out) instruction the RAS is sent a low voltage signal, the low voltage signal does two things to the RAM location:

• It refreshes the voltage at the RAM location
• It reads the bits for their individual voltage such as a bit has Voltage Applied it is a 1, Voltage Absent then it is a 0.

Once the refresh has been accomplished the signal is returned to the MMC where it is parsed for CRC (Checksum Redundancy Check)  and then sent to the processor.

If the instruction is a write (Data In) to the memory address a WE signal is sent to the memory address to 'clear' that section of RAM then the appropriate Data In voltage is sent to each bit, Voltage Applied is a high voltage for 1 and Voltage Absent is low voltage for a 0, such as 1001001 that would be a high voltage, two low voltage, a high voltage, two low voltage, and then one high voltage signal.

This is where the frequency comes in, at a lower frequency these voltages take longer to accomplish, where as the higher the frequency then the faster these operations are accomplished.

Modern RAM frequencies are from 400 Mega Hertz (MHz) to 1600+ Mega Hertz (1.6+ Giga Hertz).

What I am trying to point out is that if you have 800 MHz RAM and add say 1200 MHz RAM the timing on the 1200 MHz will be degraded down to 800 MHz when this happens the RAS refresh low voltage has difficulty maintaining the refresh because the low voltage is almost the same value of voltage where the Voltage Absent is to maintain the value of 0 which could be mistaken for a Voltage Applied value of 1.

When the low voltage for refresh and the Voltage Absent are close to the same you will start having RAM errors.

Bottom line? Don't mix frequencies or FSB to maintain a stable RAM environment.

When you are considering a new computer or upgrading your existing motherboard take in to consideration the minimum and maximum frequency of the RAM. This is also called the FSB (Front Side Bus) frequency.

The timing of the RAM has a direct bearing on the speed of the processor.

That is the RAM frequency is part of the formula that is used to set the processor 'multiplier', the multiplier is what controls the clock frequency of the processor.

If the RAM frequency is say 200 MHz and the processor base clock frequency is say 1.5 GHz and you want the processor to run at 3 GHz the multiplier must be able to be set at 15. (This is not possible at 200 MHz, the processor would fry - this is an example only!) How did I arrive at 3 GHz from 1.5 GHz? A: 15 x 200MHz = 3 GHz

For more information on FSB, processor speed, and Overclocking see my memory tutorial or the Self Computer Repair Unleashed 2nd Edition Manual Chapter 10...

Update 02/17/20 - Don't think 2666 MHz (2.66 GHz) for memory isn't fast enough for you? Well I have read where the technology is coming to you at 3400+ MHz (3.4 GHz) memory, a couple of tech web sites indicate the major memory companies are experimenting with the technology, however as always this could or could not happen... Stay tuned as they used to say back in the radio only days...