What is the difference between CAS 7 & CAS 9 of RAM

[Ekhattar]

I want to build an Intel Core i7 at my home and I am bit confused with the CAS timings of the ram due to which I am not able to choose the proper ram for this machine. Can you guys tell me that what is the major difference between the CAS 7 and CAS 9? I am looking forward to buy a Corsair 3GB DDR3 XMS3 PC3-10666C9 that has CAS of 9 and another one is OCZ 3GB DDR3 PC3-10666C7 which has a CAS of 7.

[Odalis]

CAS times refer to the number of clock cycles needed to perform the function indicated. So everything else being equal times more stringent (lower numbers) are better. That said, if it would be worth points in a artificial benchmark, I sincerely doubt anyone would be able to tell the difference between times and CAS9 CAS7 in actual use.

[Aandaleeb]

CAS is also related to frequency. Mostly, it falls on the roughly 10 ns. DDR, frequency 1600 MHz (DDR3 PC 12800) is infact the 800 MHz real latency for CAS 9 give: CAS latency = / frequency = 9 / 800 Mega = 9 / 0.9 Giga = 10 ns.

if it's 1333 MHz case 7, it gives:
CAS latency = / frequency = 7 / 667 = 7 Mega / Giga 0.667 = 10.5 ns. etc. ...

Afterwards, the frequency seems more important than the CAS, but the gain is not huge. For a real gain, it would kind of cases the 2000 MHz 7.

[Filiberto]

Case 7, who will be the most efficient level latencies: 7-7-7-15-21. Certified modules for 1.5 volts, 1333 MHz, CAS 9, they went pretty well, with 638 (1276 MHz) with 1.5 volts, to finish at 1340 MHz with 1.65 volts, so not so bad, with basic 1.65 volts you can boot in case 7 cons of case 9 announced.

CAS 8, which combines frequency and timings: 8-8-8-20-27. The timings 8 allow to obtain large frequencies, while minimizing losses latencies, a good compromise, here we start at 745 (1490 MHz), to jump to 790 just by mounting tension of 0.05 volts! (1580 MHz), almost the tensions of DDR3-1600.

CAS 9, which should help to achieve the best frequencies: 9-9-9-24-34. CAS 9 for its part, provides fair, normally, very high frequencies to compensate for latencies / timings, very wide. The barrier here is at 1.6 volts, you go from 770 (1440) to 900 MHz! (1800 MHZ DDR3), not bad at all.

[Mindstorm]

Corsair sign again of the modules to look nice, and we propose that both modules low voltage bright side of things, if you're not a big overclock, it will fit, it does well with 1.5 volts , it heats very little, it consumes little, short, fine. If instead you like big scores, it is necessary to forget, of course it goes up to 900 MHz (1800 MHz), with 1.6 volts cases9, but it stops there, every extra MHz will be hard to get, and CAS 9 is far from making gains on a super pi for example.

[samar69]

RAM time are measured in CAS, RCD, RP, and RAS. CAS is the number of clock cycles to reach the correct column of memory, RCD refers to the number of cycles between RAS to CAS, RP refers to the number of cycles needed to close a line and open the next line reading, and RAS refers to the smallest number of clock cycles a line should be actively consulted. To simplify this explanation, remember that times of RAM is measured in FSB clock cycles, so the lower number, the faster the system.