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I just upgraded my laptop to 2 @8gb. I removed from it 2 @4gB which the RamExpert program said were DDR3 / PC3-12800.

I have an old laptop with 2 @ 2gB which RamExpert says are DDR3 / PC3-6400.

Can I replace that 2 @ 2gB with the old 2 @ 4gB? I am unsure what that 6400 and 12800 means and don't want to risk damaging even an old laptop.

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@Ramhound We know what the OP meant. It would be more helpful to suggest the edit. –  Jason C Jun 13 at 19:37

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Yes. It will run faster

The laptop had DDR3 and your new RAM is DDR3 and faster.

The higher the number 6400 12800 whatever, won't do any harm and can only potentially do good. It means the RAM is capable of more speed. But if the motherboard only supports up to a lower speed that's fine, it runs at the lower speed.

But, if the voltages are different or if the voltages don't match the motherboard, then i'd be cautious.

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@Mawg You have to get model numbers and hit google hard. Find out what voltage RAM the motherboard of your laptop requires.. Find out what voltage RAM the particular RAM part number is. So you google those model numbers and find out the voltages. Apparently they all sit around 1.5V anyway so it might not be an issue. –  barlop Jun 13 at 5:18
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@barlop All DDR3 memory PC3-* has nominal voltage 1.5V, maximum 1.975V. PC3L-* is 1.35V, PC3U-* is 1.25V. The latter two are additions to the standard and were introduced in June of 2010. –  Jason C Jun 13 at 10:14
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(No need for hard Googling either.) –  Jason C Jun 13 at 10:42
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@JasonC Two things then you'd have to address. Firstly there's the question of putting 1.5V RAM in a 1.25V/1.35V MBRD(e.g. perhaps an ultrabook) tomshardware.co.uk/answers/id-1859845/ddr3-ddr3l-slots.html (apparently worst case it might not boot -RAM not getting enough power BIOS not supporting that voltage level. Or might work giving full voltage to the RAM, though means laptop runs bit hotter than designed for) –  barlop Jun 13 at 11:15
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@JasonC And secondly the issue of putting a 1.25V/1.35V RAM in a 1.5V RAM MBRD. superuser.com/questions/564175/… (apparently ok because 1.35V RAM is actually dual voltage, can run at 1.35V or 5V) (maybe 1.25V is also dual voltage like 1.35V though that poster doesn't say.) –  barlop Jun 13 at 11:15

You mean PC3-12800 and PC3-6400. That number indirectly refers to the peak data rate of the memory (see Wikipedia for technical details), which is influenced by clock speed and other communication details.

You'll have to check the specifications for your computer to see if it will actually make it faster. Some machines support multiple clock rates but not always.

It should work though; but may not make a speed difference. If your motherboard does not support the faster clock rate it will usually clock it down to the rate it does support, which may just be the PC3-6400 rate.

There's no worry about voltage issues. All PC3-* memory has the same voltage requirements (1.5V nominal, 1.975V absolute max). The only other DDR3 standards are lower voltage (PC3L-* is 1.35V, PC3U*- is 1.25V, nominal), so if your laptop uses those instead (which according to you it doesn't) worst case is it doesn't provide enough power. And even if you accidentally went the other way they all have absolute maximums greater than 1.5V.

You could just try it. You won't damage either the machine or the memory; if it doesn't work it simply won't recognize the memory (or worst case won't boot, in which case you take it out again and all is well).

Also, in case you are wondering: Unless something happened in the last 5 or so years to change this, generally all modules in a given machine must be the same type and size (don't quote me on size), and of course must match the list of supported memory given in the PC's technical specifications. Damage won't occur from using the wrong type though; just failure to function properly.

Don't be surprised if your old laptop doesn't support the faster memory, though. Set your expectations low.

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1 Thanks. So long as you are sure that I can't damage the old laptop (what about that voltage comment from barlop?) then i will just stick it in & see if it gets recognized. –  Mawg Jun 13 at 4:28
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@Mawg All DDR3 memory that starts with PC3-* has the same voltage requirements (1.5V nominal, 1.575V max guaranteed stable, 1.95V absolute max before damage). All other DDR3 standards are newer and lower voltage; this means worst case is your laptop won't supply enough voltage if it uses PC3U- or PC3L- memory types, which according to you it doesn't, and which wouldn't hurt your laptop or memory anyways. You're not going to hurt the laptop (but do unplug it and take the battery out while changing). –  Jason C Jun 13 at 10:17
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And in general, for this kind of stuff, for the most part it's really hard to break things this way. Almost all peripheral devices that use the same connectors have similar voltage requirements with maximum voltages reasonably high enough to avoid issues. Incompatible devices simply don't work. Even for faulty devices, the vast majority of cases lead to bogus data from the device or failure to function rather than damage to other components. Computers these days are loaded with safeties for common issues too; e.g. CPU overheat protection, USB overcurrent protection, etc. –  Jason C Jun 13 at 10:24

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