09-10-2014 10:22 PM
I have 2 x 4GB sticks of G.SKill F3-8500CL7D-8GBSQ DDR3-1066 PC3-8500 CL7-7-7-20 SO-DIMM.
They worked perfectly as the only memory sticks in a W500, but I'd like to install them in addition to the 2 x 4GB Lenovo memory sticks that came with the W520.
Is this going to work and be stable at all? After reading the W520 specs, I'm still uncertain about the memory speeds of the two different sets of sticks and if that is a real compatibility issue. I don't know enough about memory specs.
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09-10-2014 11:30 PM - edited 09-10-2014 11:30 PM
Very generally speaking, when you install different memory modules, they will all operate at the highest speed and timings commonly available to all installed memory modules. So, if the W520 hypothetically has PC3-8500 memory installed, it would operate at that speed, but if the installed memory has slower timings (say CL8-8-8-8-21), the G.Skill memory will likely be run with the slower timings those instead of its default faster ones.
In practice, you can check the memory timings of the instdalled RAM using something like CPU-Z, and then check with G.Skill to maker sure the F3-8500CL7D-8GBSQ kit will work with those timings, and then plug them in and you'll be good to go.
Even if the system boots up and works fine, I would still suggest running a program like MemTest86 overnight in order to test the RAM to make sure it is all working properly together.
09-11-2014 09:20 AM
Thanks for the advice, particularly re. CPU-Z and testing with Memtest-86! I installed CPU-Z, and the current RAM sticks have this configuration:
Memory type DDR3
Module format SO-DIMM
Manufacturer (ID) Samsung (CE00000000000000)
Size 4096 MBytes
Max bandwidth PC3-10700 (667 MHz)
Part number M471B5273DH0-CH9
Serial number 664F78D8
Manufacturing date Week 40/Year 11
Number of banks 8
Nominal Voltage 1.50 Volts
JEDEC timings table CL-tRCD-tRP-tRAS-tRC @ frequency
JEDEC #1 5.0-5-5-14-19 @ 380 MHz
JEDEC #2 6.0-6-6-17-23 @ 457 MHz
JEDEC #3 7.0-7-7-20-27 @ 533 MHz
JEDEC #4 8.0-8-8-22-30 @ 609 MHz
JEDEC #5 9.0-9-9-24-33 @ 666 MHz
and they are being run as follows:
Memory Type DDR3
Memory Size 8 GBytes
Memory Frequency 655.3 MHz (1:5)
CAS# latency (CL) 9.0
RAS# to CAS# delay (tRCD) 9
RAS# Precharge (tRP) 9
Cycle Time (tRAS) 24
Command Rate (CR) 1T
Am I right in thinking that after installing the slower G.Skill sticks, the whole memory system would run at the nominal JEDEC #3 rates, i.e. around 533 MHz and thus at 80% of the current rate? But in practice, would I ever notice a difference? Very few programs are exclusively memory bus speede limited.
I shall have to experiment.
09-11-2014 01:18 PM
09-18-2014 01:20 PM
Quite right, there's really no perceptible diffrence in performance.
I assigned the faster pair of sticks to slots A and the slower to slots B. I'm assuming that any memory access interleaving occurs across the pairs in either slot A or slot B, not between slot A and B.
In any case, the result is that the four sticks use the JEDEC #3 speed and timings, according to CPU-Z. Memory testing showed no sudden problems or crashes.
Thanks for all of your help on this matter!