Member Avatar for NuGG

Is it possible to have 768MB RAM on a computer?(eg. one 512MB and one 256MB card).

I know its possible to use 256/512/1024MB.

I tried 768MB in my PC but it wont boot up. Im guessing i have to get another 512MB RAM.

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Mixing a 512MB and a 256MB DDR stick can work, but K8‑era boards vary a lot in how they initialize mismatched DIMMs. reports no POST; contributors , and already raised timing, slot and brand factors. Below are focused, practical checks and explanations that go beyond the usual “swap and see” tips.

Look at SPD and voltage first: read each module’s SPD/JEDEC profile (BIOS will show it or use a utility on a working OS). Note the rated clock, timings and required DRAM voltage. If one stick requires a higher VDIMM than the other, set the board’s DRAM voltage to the higher value and set the memory clock to the slower stick’s rating. Also confirm both modules are unbuffered, non‑ECC consumer parts; mixing registered/ECC with standard DIMMs will prevent startup.

Understand chip density and channel mapping: some 512MB DIMMs are built from higher‑density chips or different rank layouts that older chipsets cannot map correctly when paired with a 256MB module. If the BIOS has an “asymmetric/flex” or channel‑interleave option, enable it; if not, follow the manual’s recommended population order and place the larger stick in the primary channel as specified by the board maker.

Diagnostics and fallbacks: try a bootable memory tester (memtest86) to see whether the BIOS ever initializes DRAM, and consult POST beep codes or onboard debug LEDs for clues. A BIOS update can fix many mixed‑DIMM quirks. If none of the above works reliably, the sure fix is matched modules (same part number/manufacturer or a dual‑channel kit) for guaranteed compatibility and stability.

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Member Avatar for Coconut Monkey

It's possible. You might want to try one stick at a time to see if any are faulty. Also, make sure you're using relaxed RAM timings (i.e. higher, like 3-4-4-8 for starters), in case the new stick can't handle the timings of the old one. They are both rated to run at whatever speed you've set them to right?

Member Avatar for NuGG

I’ve tested it and it’s not faulty. I’ve checked the timings and every thing but it still won’t boot up. My motherboard supports dual channel memory up to 4GB so maybe it has something to do with which slots I put the memory in. I’ll have to experiment.

Member Avatar for nizzy1115

change your motherboard settings to disable duel channel support. that should fix it cuz you arent running duel channel

Member Avatar for Catweazle

What motherboard do you have? What make/model RAM modules do you have?

Member Avatar for NuGG

Its an Extreme K8 motherboard (i think) with DDR RAM

Member Avatar for Catweazle

If the modules aren't the same brand and model line, then it's most likely the two modules are conflicting with each other, and won't be usable together. But reset CMOS first and see if they work OK afterwards.

Member Avatar for NuGG

Yea they are different brands. Ill have a play around with the cmos tomorrow and see if i can get it working...

Cheers

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