My Mac (Mid 2009- MacBookPro5,5) laptop installing OS 10.8.2.

Currently, it is using 2 x 1GB (1066 Mhz).

My friend gave me 2 x 2GB (1600 Mhz) of his 2012 Mac.

After installing 2 x 2GB (1600 Mhz) on my Mac, it can not boot but can not start OS. This is the error that show on boot start up screen:

enter image description here

But it is possible to install 1x 1GB (1066) + 1x 2GB (1600). The system can down-clock it to both 1066 Mhz. But what i still have 1 x 1GB (1066) + 1x 2GB (1600) left!

3GB @ 1066 Mhz

My question is: Any better solution than using 1x 1GB (1066) + 1x 2GB (1600)?

More certainly, is there any way to install 2 x 1600 Mhz? (even down-clocking to 1066 is accepted). (currently, 2x1600 Mhz can not startup OS).

Edit 1: 4 RAM are healthy.

  • 2
  • Yep. A faster ram is always capable to speed down to lower frequences ... – Matthieu Riegler Jan 31 '13 at 0:50
  • @MatthieuRiegler: My question is: how to do it. I am very appreciate the answer about how to down-clock 2x1600 to 1066 on this system? Because currently, i can not start my system with 2x2GB. – BachT Jan 31 '13 at 6:53
  • It should do it automaticaly. It's not the ram it self who desides at which speed it runs. – Matthieu Riegler Jan 31 '13 at 10:44
  • I've posted an answer that is incorrect. But it should do it automatically, if not, it's problem with the module. – Shane Hsu Jan 31 '13 at 11:25

I recently ran in to a similar issue when trying to squeeze a little more life out of an old iMac. I could only get 800mhz DIMM's but the specs say it needs 667mhz. I can interchange 1x 667mhz DIMM with 1x800mhz DIMM but a single 800mhz DIMM or two 800mhz DIMMs result in a failure to boot.

My hunch was that the motherboard thinks it can run at 800mhz so doesn't downclock it to 667mhz unless there is a slow DIMM in one of the slots forcing it to.

I did some research, and discovered the timing information is set in the SPD data stored on an EEPROM on the DIMM. I booted an Ubuntu 16.10 liveUSB on the iMac, apt-get installed i2c-tools, modprobeed the i2c-i801 module to enable the SMBus (which talks to the DIMM EEPROM) and read out the SPD of a working and a too-fast DIMM with i2cget. After a lot more research, I merged the timing information from the working DIMM in to the SPD of the too-fast (but larger) DIMM. decode-dimms can calculate the correct CRC. I then wrote the modified data back to the fast DIMM with i2cset.

I can now pair that down-clocked DIMM with an unmodified 800mhz DIMM, and the system correctly downclocks the memory bus to 667mhz and boots.

FULL DISCLOSURE: After about a month the upgraded machine started hard-crashing and was replaced by a 2017 iMac ;)

  • Cool, I ended up going this route, and was able to get my DDR3-1333 operating at 1066. Of particular assistance was Wikipedia's table of SPD contents for DDR3 (en.wikipedia.org/wiki/Serial_presence_detect#DDR3_SDRAM). I was in a similar situation with my MacBook6,1 to the MacBookPro5,5, although with the B00 boot ROM it at least ran hot rather than crashing at boot. Obviously this is not an approach for everyone, as there are no easy second chances if you don't get the settings and the checksum updated properly the first time. – rakslice Sep 11 '17 at 2:18
  • Cool, now at least I know there was a solution to my problem. After a few years from my question, I bought a pair of 2x4GB RAM@1066 :) My mac is still usable until today for "light weighted" task, since it can not handle "simple" 1080p on Youtube :( – BachT Sep 12 '17 at 17:16

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