RAM voltage and cas latency?

[d4m1r]

Hey guys, so I'd like to upgrade the RAM in my 13" MBP and know it takes DDR3 @ 1600MHz, but what about voltage and cas latency? Those things don't matter to me when I'm building desktops, but I know Apple is picky in terms of hardware....How anyone know what the stock RAM voltage and cas latency is? Does it matter if I get RAM not matching stock values?

I am hoping to get a 2x4GB Crucial set sometime over the holidays when I see one on sale....

 

[datapusher]

A lot of people on these forums recommend the CMSX16GX3M2A1600C10 for Macbook Pro. However, the latency doesn't match Apple's.

I'd be curious to hear what people say on this matter.

 

[d4m1r]

A lot of people on these forums recommend the CMSX16GX3M2A1600C10 for Macbook Pro. However, the latency doesn't match Apple's.

I'd be curious to hear what people say on this matter.

What is the stock latency?

 

[d4m1r]

Correct me if I'm wrong, but after doing a bit of research, it seems;

stock RAM cas latency = 9

and

stock RAM voltage = 1.5v

 

[hallux]

It looks like the latency on the stock memory from my July 2012 15" is 11, which means the Vengeance memory I have in it now is actually FASTER.

 

[ultra7k]

I've been using the 16GB kit from Corsair for the last month and have no problems whatsoever. In terms of latency and real world use, you probably won't see any noticeable gains.

 

[d4m1r]

It looks like the latency on the stock memory from my July 2012 15" is 11, which means the Vengeance memory I have in it now is actually FASTER.

Are you sure? After doing research, I am led to believe stock CAS latency on all mid 2012 MBP's is 9, meaning aftermarket RAM with a CAS of 11 would be slower....

Just ordered 2x4GB of GSkill 1.5v and 11 CAS RAM by the way from Newegg for under $60 shipped.

 

[IllmasterMath]

Latency scales up with frequency because higher latencies are negated by more cycles. RAM with CAS latency of 11 at 1600MHz is faster than RAM with CAS latency of 9 at 1333MHz.

 

[hallux]

Are you sure? After doing research, I am led to believe stock CAS latency on all mid 2012 MBP's is 9, meaning aftermarket RAM with a CAS of 11 would be slower....

Just ordered 2x4GB of GSkill 1.5v and 11 CAS RAM by the way from Newegg for under $60 shipped.

I'm fairly certain it was 11 in mine originally. I have the spec sheet downloaded on my Mac at home, all indications are that it's 11 though it's not listed specifically. I also deduced this by looking at the ratings on the sticker on the memory, there was an 11 in the spot where CAS latency normally resides in the string of specs. I'll post the string and photographic proof when I get home.

If yours originally shipped with 9 and you're installing 11 (with all other specs except size and latency the same) it will actually be a little SLOWER.

 

[d4m1r]

I'll post the string and photographic proof when I get home.

If yours originally shipped with 9 and you're installing 11 (with all other specs except size and latency the same) it will actually be a little SLOWER.

Please do. And yes, I realize that, but like a different poster already said, I could have gone with 1333Mhz @ 9 CAS but 1600Mhz @ 11 is still faster.

 

[richnyc]

Latency scales up with frequency because higher latencies are negated by more cycles. RAM with CAS latency of 11 at 1600MHz is faster than RAM with CAS latency of 9 at 1333MHz.

^^^Ditto. I would worry more about stability and reliability of the particular brand over any perceived speed improvements of the CAS latency optimization

 

[drambuie]

Please do. And yes, I realize that, but like a different poster already said, I could have gone with 1333Mhz @ 9 CAS but 1600Mhz @ 11 is still faster.

In terms of pure memory access times 1333MHz at 9 CAS is slightly faster with 6.75ns response, than 1600MHz at 11 CAS with 6.875ns response. Of course you are getting 20% more CAS requests per time period at 1600MHz than at 1333MHz, so in the end 1600MHz is slightly faster. Besides CAS and RAS, there is a whole sequential series of timings such as read, write, write verification, and settling times, all of which increase as frequency increases. If you can find 1600MHz at 9, that would be the clear winner.

RAM chip cells themselves aren't getting any faster, so the effort is in increasing the bandwidth of data to and from RAM. First there was dual data rate (DDR) which involves two accesses per clock cycle, then there was dual channel and triple channel, with the latest being quad channel.

 

[hallux]

According to the tech specs book I downloaded from Hynix based on the memory part number I searched on, my original memory, pictured below, will run CAS 9 if you run it at 1333 (PC3-10600). If you run it at 1600 (PC3-12800) you get CAS 11. With my Corsair Vengeance memory installed, my mid-2012 15" MBP reports that it's running at 1600 (PC3-12800).

 

[d4m1r]

Thanks for the confirmation and that is what I guessed, that the stock 1600Mhz RAM runs @ 11 CAS

Anyway, good to know that the GSkill RAM I got matches all stock values (1.5v and 11 CAS @ 1600Mhz). FYI, I did not see any 1600MHz RAM @ 9 CAS on Newegg when I bought my set the other day...

 

[w00t951]

Basically, the only things that matter are the timings and the speed. Speed comes in 1333, 1600, 1833 MHz. Higher is better, but I'm pretty sure the MacBooks only support up to 1600MHz. Timings are crucial - if you don't match the timings between your OEM RAM and your aftermarket RAM, you could end up with anything from slow performance to defunct RAM.