800 MHz RAM instead of 667 MHz RAM on A1261 with Penryn CPU

[Michael.S]

So the RAM (2x 2 GB 667 MHz DDR2 SODIMM) in my A1261 4.1 MacBook Pro with Penryn CPU just died.

I need to relplace them and I have 2x 2GB 800 MHz lying around.

I am eager to try them out would have already done if it not been due to the possible incompatibility issues with Intel Penryn CPUs.

Would it kill the computer if I try it out or will it just not pass the mem check at start up?

Can someone bring some light into this?

 

[chrfr]

So the RAM (2x 2 GB 667 MHz DDR2 SODIMM) in my A1261 4.1 MacBook Pro with Penryn CPU just died.

I need to relplace them and I have 2x 2GB 800 MHz lying around.

I am eager to try them out would have already done if it not been due to the possible incompatibility issues with Intel Penryn CPUs.

Would it kill the computer if I try it out or will it just not pass the mem check at start up?

Can someone bring some light into this?

It'll most likely just work without any errors or differences. In any case, it will not damage the computer.

 

[Michael.S]

It'll most likely just work without any errors or differences. In any case, it will not damage the computer.

It somehow works although I am using 800 MHz RAM in only one slot and the other has 667 MHz.

 

[chrfr]

It somehow works although I am using 800 MHz RAM in only one slot and the other has 667 MHz.

The 800MHz RAM will happily run at lower speeds.

 

[jav6454]

So the RAM (2x 2 GB 667 MHz DDR2 SODIMM) in my A1261 4.1 MacBook Pro with Penryn CPU just died.

I need to relplace them and I have 2x 2GB 800 MHz lying around.

I am eager to try them out would have already done if it not been due to the possible incompatibility issues with Intel Penryn CPUs.

Would it kill the computer if I try it out or will it just not pass the mem check at start up?

Can someone bring some light into this?

You can put faster RAM modules into slower RAM modules as long as they are the same spec (DDR2). The faster modules will adjust to the speed of the bus. Also, this will also work if you have slow modules and fast bus. The bus will adapt to the modules.

No, you won't damage anything.

 

[EugW]

Depends on the model of machine and the specific memory modules, but on some machines if you put 800 MHz in 667 MHz slots, they may not work.

Why? Because the memory timings and speeds are encoded on the RAM modules. If the appropriate 667 MHz timings and speeds are correctly listed on those 800 MHz RAM modules, it will work. However, some 800 MHz RAM is missing the 667 MHz entries. In that case it may not work. It's not that the RAM is incapable. It's just that Macs are very strict. Often if the Mac doesn't see the correct specs listed, it just won't boot, even if the RAM is capable. (You can actually get around this sometimes by reprogramming the RAM module to display the right 667 MHz entry, but that isn't feasible in most cases.)

However, it won't damage anything. I would suggest just trying it. If it doesn't work, reseat the RAM and zap the pram or whatever and try again. And if it still doesn't work, then get the proper RAM.

It somehow works although I am using 800 MHz RAM in only one slot and the other has 667 MHz.

Again, it depends on the specific RAM module. If it has the proper 667 speed/timings entry, it should work. However, sometimes it will even work even if the entry is not there, if the other paired RAM module has the right 667 MHz entry. I believe this is because the Mac is only checking one of the two memory slots. In that case, if you reverse the location of the RAM modules, it may not work.

Ideally though you should be running paired RAM.

In summary, an 800 MHz RAM stick can be programmed to identify itself as just an 800 MHz stick, or can be programmed to identify itself as a 533/667/800 MHz stick, etc. The former may not work in a 667 MHz Mac, but the latter usually will (if it has the right listed specs).