What RAM for PC3 12800 AND 1333 (which is more important)

[cbay]

I just got this laptop and it only has 1 stick (2g) and i want another 2g sitting next to it. It is a lenovo b590 laptop with an i3 2328 chip with an hm77express mobo. I would like to keep everything compatible. But when searching ram it appears that all the ram for pc3 12800 is 1600mhz. The specs are 1333. What should i do?? Which is more important? I want the machine to perform the best it can.
Here is a brief look at specs.
2.2 GHz
Features: Hyper-Threading Technology , Integrated memory controller
Generation: 2
Manufacturer: Intel
Number of Cores: Dual-Core
Processor Number: I3-2328M
Type: Core i3
1 x 2 GB
Empty Slots: 1
Form Factor: SO DIMM 204-pin
Installed Size: 2 GB
Max Supported Size: 8 GB
Memory Specification Compliance: PC3-12800
Memory Speed: 1333 MHz
Slots Qty: 2
Technology: DDR3 SDRAM
Mainboard Chipset Type: Mobile Intel HM77 Express

 

[Goodeggray]

Not that much performance difference between 1333 and 1600 ram. Use what is compatible with your computer. Stability is more important that a small gain.

 

[Sakkura]

The motherboard/chipset is from the current generation, so it supports up to DDR3-1600 AKA PC3-12800. The CPU is from last generation, so it only supports up to DDR3-1333 AKA PC3-10600. You can actually buy either, if it's rated for 1600 it'll just run at 1333.

 

[ur6beersaway]

Very hard to find (I love a challenge) desktop. I found one kit for $209 and it was 16 gb. NO way. Sakkura ^ is right. Try this for options:http://www.tigerdirect.com/sectors/campaigns/memory-finder.asp#ABA

 

[cbay]

So if i'm getting this right, the transfer rate of the bus is 12800 on the mobo. The clock speed supported on the cpu only goes to 1333mhz. I can't find that combo in memory selection.
So,,,,, since the cpu is not compatible with 1600mhz ram, i look at the ram available at 1333mhz, and none of it has a transfer rate of 12800. So is it safe to use a lower transfer rate?????

 

[cbay]

Great. Thanks guys. I replied again before i saw your posts..
I always fear asking stupid questions on here but love to get understanding.

 

[cbay]

Oh, here i go again..... If i get the ram with the higher transfer rate (12800), will that transfer at that rate even though the clock speed is 1333mhz??

 

[ur6beersaway]

There are NO "stupid questions".

 

[Sakkura]

Oh, here i go again..... If i get the ram with the higher transfer rate (12800), will that transfer at that rate even though the clock speed is 1333mhz??

No. If you get the fast RAM (which is 12800 MB/s ~ 1600 MHz) it will run at the slow speed (10600 MB/s ~ 1333 MHz).

PC3-12800 is just another way of saying DDR3-1600, and likewise PC3-10600 and DDR3-1333.

 

[ur6beersaway]

Oh, here i go again..... If i get the ram with the higher transfer rate (12800), will that transfer at that rate even though the clock speed is 1333mhz??

OK, Get PC12800/1600. The motherboard will downclock it automatically to PC12800/1333.