Still struggling...RAM for i5-750

[rza]

**Warning** Noob trying to understand basic computing**Warning**

So I've been having the hardest time deciding which RAM I should go with for my build.

Current Build:
Case: CoolerMaster 690 Black (Basic)
CPU: i5-750 (Stock..for now)
MOBO: Asus P7P55D PRO
GPU: Sapphire Vapor-X 5770 1GB (CF soon)
PSU: Corsair 750tx
HDD: Samsung Spingpoint 500GB @7200rpm
OS: Win7 64bit

After diggin through forum after forum, I've come to understand that I should be looking for RAM with: 4GB (2x2GB) with a Cas Latency of 7 and a voltage of 1.5v... easier said then done.

I guess I am having a hard time understanding the speeds of RAM. These are the (2) models that the majority of folks are recommending; both from G.skill

$115 - Black
G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Desktop Memory Model F3-10666CL7D-4GBRH

$120 - Blue
G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL7D-4GBRM

Sorry I don't know how to make links or set photos on forums...don't hate!

Am I correct in saying that, I would have to OC my CPU in order to run DDR3 1600 RAM to its full potential?

If I'm going to OC, shouldn't I get 1600 RAM anyways?

Any insight on this matter would be greatly appreciated. Please feel free to make other suggestions as well. And if there is any other questions that you may have that would help in suggesting RAM, just let me know.

 

[Lmeow]

Well, might as well help you with explaining terms if you don't understand.

- Lower the latency the better, 7 is about as lowest as it goes for DDR3, some kits are CL6 although those are quiet rare.
- You are right getting a 2x2GB kit running in dual channel. A 3x2GB kit would be triple channel. Understand the connection? Although mind you, most of the time 4x2GB and 6x2GB is still dual channel and triple channel, only sometimes is it quad channel, and I haven't heard of hex-channel yet.
- As for voltage, lower is better, although faster kits tend to have higher voltage, 1.5V or below generally tend to be either value kits of Eco friendly kits.

[strike]You do not need to o/c your CPU to run your RAM at 1600MHz. Just set your memory multiplier to 12x or your FSB : DRAM ratio to 2:12. However, the point of high speed RAM is that your RAM won't hold you back when you're overclocking - the performance difference between 1066MHz and 1866MHz isn't noticeable in most applications.
[/strike]
If you have a BCLK of 150MHz for example, your RAM, if it's running at stock 8x/2:8 means it will be running at 150MHz x 8 will be running at 1200MHz. If you change your BCLK to 200MHz, then your RAM will be running at 200MHz x 8 = 1600MHz which is your target RAM speed. Now, you might be able to see the problem - if you try and push your BCLK further (BCLK x CPU multiplier = CPU speed, e.g. 133MHz x 20 = 2.66GHz, stock Core i5 750 setting IIRC), you will have to overclock the RAM past its designed speed, and may not run at any higher speeds, thus limiting your BCLK, and effectively, how far you can push your CPU. On my EVGA X58 SLI LE, the lowest memory ratio is 2:6 or 6x (the highest being over 2:16 or something), which means that I will start hitting BCLK limitations far less, I'm not sure if Core i7 800/Core i5 700 boards have similar memory multiplier/ratio.

I'd go for the $120 G.SKILL kit, might as well get faster RAM for $5.

If you want to know how to add links, it's not hard, just copy the link and then paste it into the textbox.

As for images, you need to have your image hosted on another site, or just have the image hosted on a site, and press the picture button in the textbox toolbar, and type in the link.

EDIT: Didn't know they only had a max memory multiplier 2:10.

 

[Nowa]

You are correct. To get your ram to work as 1600mhz you would have to overclock your computer. I have the same mobo and cpu and you cannot get higher memory clocks than 1333mhz without overclocking since the memory speed multiplier does not go any higher. The basic qpi clock would be 133mhz and the max memory multiplier is 2:10 (FSB/DRAM). So in order to get your memory work as 1600 Mhz you would have to raise the Bclock to 160mhz, effectively overclocking your cpu to 3,2Ghz. The CPU should clock easily to these speeds but you can always lower the cpu multiplier if you do not want to OC your cpu also.
To your other question.. if you plan to overclock you should definitely get the 1600mhz parts. With the same CAS latencies the 1600Mhz part is the faster one here. If you don't care about overclocking you might as well take the 1333Mhz part. All in all both of these memory kits would perform quite similarly.

 

[rza]

Thanks guys, that actually made sense and helps alot.

Nowa, what RAM are you useing?

Does it matter that the 1600mhz has a Voltage of 1.65? In one of the many forums it mentioned something along the lines of getting RAM with 1.5v for the i5xxx CPU. Does this matter?

 

[rza]

Best answer selected by rza.

 

[Nowa]

I am using G.Skill ram but not the ripjaw series.

4GB (2x2GB) Dual kit ECO, DDR3 1600, F3-12800CL7D-4GBECO, 7-8-7-24, 1.35V

1.65 is perfectly fine for 1600Mhz ram sticks. There are many that use lower voltages to achieve the same clock speeds and latencies though. Usually that means a higher quality part. 1.5-1.65 V is the usual range of memory voltages you will see with DDR3 memory modules 1.65V being the most common. Anything above 1.65 V is above the recommended voltage range.