Computer Repairs


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Choosing RAM

1/ Never mix and match RAM from different manufacturers, but if you do, match the specifications exactly then you MIGHT get away with it ? Always purchase RAM with the same exact specifications from the same manufacturer unless you know exactly what you're doing, and are prepared to take the risk. If you're using Kingston, then replace or add RAM from Kingston. If your using Crucial, then use Crucial, etc.

2/ You should NOT install RAM that has different specifications. For example, if you're using Corsair 667 MHz DDR2, then any RAM that you're adding to your system should have the exact same specifications as the RAM chips that are installed. In other words they must be 667 MHz DDR2 and they must use the same voltage, and timings etc. If you try to add 800 MHz RAM to a system that has currently 667 MHz  it might work but may also cause problems and should be avoided, even though people claim you can use 800 MHz and it will run at the slower RAM's speed it very rarely works without error. This mismatch means it is very likely your system won't even boot up and you'll get beeps at start up that indicates the RAM is incompatible. Always match your RAM.

3/ Value or generic RAM is a more risky prospect but can work perfectly ok. Value\generic RAM is often used by large manufacturers in order to keep their build costs down and will normally be very difficult if not impossible to match to in the future of the systems life.

If it gives no problems then Value\generic RAM performs just as well as Branded RAM. As an end user I would recommend it is always better to buy Branded RAM whenever possible, especially if your experiencing issues with Value RAM on your motherboard. The reason I say this becomes more obvious when you understand what Value\generic RAM means. Value\generic RAM either started life intended to be Branded RAM but subsequently failed the tolerance tests and couldn't be sold as Branded or was specifically built to order using the cheapest components available at the time, this creates two problems in it's use. The first is that it's very unlikely it will respond well under extreme stress such as high temperature conditions and overclocking. The second problem is that Value\generic RAM is very inconsistent in build quality where components are varying dependent on the cost of metals at the time it was manufactured.

This means same spec Value\generic RAM bought 6 months apart will most likely vary in component quality and produce different results performing differently and causing errors. If I ever build a system using Value\generic RAM I will buy ALL of the RAM I intend to have working on that system at the same time from the same supplier, I am also prepared for it to not work at all and know it can produce errors when the Operating system is first installed.

Kingston Value RAM appears to be the exception to this rule and is built with the typically high component quality and matching to specifications we have to come to expect from Kingston.

4/ You can use RAM chips that have the same specifications but are different sizes fitted in different channel slots, so you can put a 1 x 2 GB RAM chip in slot 0 and 1 x 4 GB RAM chip in slot 1. In other words each RAM slot is numbered 0 through 4 or 0 through 6, and in motherboards which utilize dual channel slot 0 and 1 may be paired or slot 0 and 2 may be paired (refer to motherboard manual). Most of the current CPUs run dual channel RAM with slot 0 and 2 being channel 0, and slot 1 and 4 being channel 1. If you only have to RAM chips, then you should insert them as noted in channel 0. If you have 4 RAM chips then you should insert them so that slot 0 and slot 2 have the same size and same specifications (i.e., 1 x 2 GB, 1 x 1 GB, 1 x 4 GB). The same applies to slot one and slot 4. This is what they mean by matching RAM in addition to making sure that all RAM chips are from the same manufacturer and have the same voltage and speed specifications.

5/ depending upon the number of RAM chips that you have you should always populate channel 0 (slot 0 and slot 2) first and then populate channel 1 (slot 1 and 3). Remember in computers all hardware designations start with 0, so if you have 4 RAM slots they are labeled 0 , 1 , 2 and 3, not 1, 2, 3, 4. Just remember populate channel 0 first and then populate channel 1.

You cannot check and research enough so to be safe I suggest do the following:

1. Check with your motherboard manufacturer regarding CPU and compatible RAM from their QVR (qualified Vendor list), specifically with regard to your motherboard and FSB (Front Side Bus) speed for your CPU.

2. Use the same manufacturer, although you can mix and match to a certain extent it will be at your own risk, and this really isn't a good idea for anyone who is a novice with regard to hardware. If you run into trouble you likely will not understand what's going on or how to remedy it.

3. Ideally You shouldn't mix RAM speeds. That is you should not mix 667 MHz with 800 MHz RAM chips.

4. You can't mix DDR2 with DDR3 RAM chips as they won't physically fit, and you can only use DDR3 when your motherboard and CPU support it.

5. try to buy all your RAM at the same time as component quality changes with metal prices so subtly changing Ram behaviour, although high spec branded Ram can be more consistent over it's production lifetime due to the stringent testing it is given to guarantee consistency.

6. You can rarely install RAM that is faster then your FSB (Front Side Bus) speed. If your CPU has a FSB (Front Side Bus) speed of 800 MHz, you can sometimes use 800 MHz RAM, but you can't use higher speed RAM unless the CPU & the motherboard support it, so you can't install 1066 MHz RAM on a system where the CPU only supports a FSB (Front Side Bus) speed of 800 MHz no matter what the motherboard specifications are, You are limited to RAM speed that is supported by the CPU.There are also occasions when even though the FSB (Front Side Bus) speed is 800 MHz due to a northbridge chipset limitation 800 MHz RAM chips may not work properly. If you get problems you are always safest by backing your RAM speed off to the next lowest level (i.e., CPU FSB (Front Side Bus) speed 800 MHz, RAM speed 667 MHz). If you're motherboard manufacturer says that the motherboard will support RAM speeds up to and including the CPU FSB (Front Side Bus) speed, then you can try that but if it doesn't work for what ever reason the most you can do is get back to your motherboard manufacturer and complain. Your only working option at this point is to exchange the RAM for the next lowest RAM speed.

7. If RAM that you install is incompatible or incorrectly installed, the BIOS Power-On Self Test (POST) will prompt you with four continuous beeps. If you get that when you start up your system, your RAM is either incompatible or incorrectly installed and you'll get no video and you won't even be able to get into your BIOS to make appropriate changes.

8. If you're a novice at computer hardware, I recommend you get someone who knows what they're doing to install your RAM. However if you do your homework and make sure that whatever RAM you purchase is compatible with your CPU (FSB (Front Side Bus)) and your motherboard and If necessary get your motherboard manufacturer on the phone, it is perfectly possible to get the correct RAM to make your hardware work without issue. It is normally fairly easy to research RAM online for compatibility, but DO NOT take risks with RAM if you're not sure what you're doing.

9. Laptops are a completely different issue and they must always use matched RAM chips. They can be different sizes, but otherwise they must match exactly.

to quote since windows 95 Microsoft have stated about memory testing programs "Defective memory chips may not be detected by memory checking tools. Some memory checking programs are not adequate tests because they do not test RAM in the same way that Windows uses RAM. Most memory checkers use read/write cycles when scanning memory. Since Windows is executing code from memory, it uses execute cycles. Execute cycles are different from read/write cycles and are more vulnerable to parity errors. It is possible for memory checking programs to find parity errors if the memory is extremely faulty."

To test memory I get consistent results by burning to CD (using an ISO burner) & running from boot memtest86+for at least 5 passes and moving the sticks between slots to verify motherboard ram slots work as well as the ram sticks.

for more detail on memtest86+ read this FAQ

ram explained at Super Talent