What exactly makes RAM "mac-compatible?"

Discussion in 'Buying Tips and Advice' started by Megatron, Nov 19, 2005.

  1. Megatron macrumors regular

    Nov 19, 2005
    Hi, I have a new ibook 1.33GHz 12", (my first mac) and I love it.

    I'd like to upgrade the RAM and i've done some searching through the forum, and everyone keeps stressing that we need to buy RAM from somewhere like Crucial or DataMem, etc.

    This seems to be b/c the RAM needs to be very particular in order to work - i'm wondering what specs exactly the ibook looks for to see if it will work?

    From the crucial memory checker I found that I need:

    DDR PC2700
    CL = 2.5
    128Meg x 64

    (for a 1GB stick)

    So what exactly is the critical value? The Cas-Latency (CL)? The error checking? (ECC)

    I'm just wondering if you get these specs somewhere else, will the memory be fine? Crucial's 1GB price is now close to $200, and Datamem is around $140.

    I've seen other places closer to $100.


    edit: also, I've read some things about the new ibooks taking DDR333 PC2700, but it's actually only running at PC2100 b/c of the motherboard - is that correct?
  2. Xephian macrumors 6502a


    May 2, 2005
    United States
    Just about any DDR PC-2700 RAM will work. Just don't get ECC RAM and try to stick to low latency.
  3. prostuff1 macrumors 65816


    Jul 29, 2005
    Don't step into the kawoosh...
    When i went and got my ram for my new iBook (same as yours) i just found the specs i need and whent to Newegg and found mine. I think i paid 115 shipped for mine.

    I just did a search and found this memory. Should work four what you need.

    My suggestion is to read through the comments and see if anyone has put the stuff in a Mac computer and how many have had success with it. I would not go to low in price. Usually Crucial, Kingston, and Crosair are good. I have this ram in my iBook and it works great. But mine was on sale when i bought so it was cheaper then the 'name brands'
  4. TheMonarch macrumors 65816


    May 6, 2005
    Bay Area
    Mac compatible just means that they'll go out of their way to make sure that that stick will work with your Mac. Even though its the same stick as the non-Mac.
  5. Sun Baked macrumors G5

    Sun Baked

    May 19, 2002
  6. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    What makes RAM Mac compatible (assuming the basics have been met - PC2700 SODIMM 2.5V etc.) are:

    1) the arrangement of rows and columns of the RAM banks and the chip density -- for example many Macs can't recognize high density chips, so an otherwise identical module with 8 high-density chips on it mightn't work, where one with 16 low-density chips would. Generally it is cheaper to make modules with fewer chips, so the cheapest modules tend not to work in certain Macs.


    2) the settings burned into the Serial Presence Detect Chip or SPD. Apple is much stricter about SPD values than PC makers. But you never get to compare what the SPD settings are because these are never advertised. That's why you need to rely on the seller to test the RAM and guarantee compatibility, or you can take your chances with generic RAM.

    From the Developer Notes: "Important: For a DIMM to be recognized by the startup software, the SPD feature must be programmed properly to indicate the timing modes supported by the DIMM."

    What you can get away with on one Mac doesn't necessarily mean it will work in another. PowerMac G5's pre Oct 19 were relatively tolerant, where iMac G5's and Minis are much fussier for compatibility on the nominally identical modules. Powerbook G4 1.5 GHz machines will take modules that the 1.0, 1.25 and 1.33 GHz 'books choke on.

    The problem with marginally compatible modules is that Apple can also change the compatibility picture with a Firmware update or a new OSX. Lots of RAM that just slipped under the wire and worked with OSX 10.3 failed when the machines were upgraded to OSX 10.4, just because Apple tightened the tests for adhering to standard.

    Latency is mostly a non-issue with Macs. Apple states that their machines run with a range of latency values... and very slow latency RAM will slow the machine down. In order to exploit lower latency, however, the motherboard must be able to change its timings, and there is no evidence from Apple that any Mac can take advantage of latencies faster than CL3 (CL4 on DDR-2).

    (it's the same in the PC world, the motherboard has to either have Intel's "PAT" or equivalent automatic latency adjustment built in, or you have to manually change it in the BIOS setup)

  7. Megatron thread starter macrumors regular

    Nov 19, 2005
    Guys thanks for the replies!

    Sun Baked, that is some really interesting stuff there on the developer pages. Guys, check this out:

    Apple Developer Site iBook RAM information

    It DOES say that the iBook uses PC2100 but can accomodate PC2700. Interesting.

    It also states 2.5V power supply and CAS latency of 2.5 or 3.

    Very cool site. I'll ceck out some of the links that you sent prostuff.

    Canada RAM - thanks - that is some really good info. How come they don't list the SPD values with the RAM? I didn't see that on the crucial site.
  8. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    I guess it's too much work, and would mean zilch to 99.9% of buyers. Plus, they use "compatible" vs "generic" to get more money for the ones that have gone through the Mac compatibility testing.

    Apple clearly states "The electrical design of the SDRAM DIMM is defined by the JEDEC specification JESD21-C, MODULES4_20_4, Release 11b". Most pc machines don't require 100% compliance, so the manufacturers don't bother to make sure that all SPD settings and other specifications are 100% to the JEDEC spec. and they get away with it most of the time. Except for the machines that need full compliance, of course.

    It's the same with anything: because it's cheaper not to comply, the cheapest RAM is a cr@pshoot whether it will comply 'enough' or not for a given model Mac.
  9. FFTT macrumors 68030


    Apr 17, 2004
    A Stoned Throw From Ground Zero
    I asked Crucial customer service about the difference between 2 sticks
    with identical "published" specs but with different Crucial part numbers.

    This was their reply:

    "Thank you for contacting Crucial Technology. The two parts that you reference have the same specifications. The only difference is price. The following link is to the kit that is guarenteed to be compatible with your Apple;



    So it seems that if you have the Crucial guaranteed Mac compatible specifications, any Crucial RAM with those specifications should work.

    There is no mention at all of SPD settings in their reply.
  10. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    Well of course, they're not going to say or tell you the SPDs. And as we discussed earlier you never get to see all the specifications. For example, the

    CT368079 DDR PC2700 • CL=2.5 • UNBUFFERED • NON-ECC • DDR333 • 2.5V • 128Meg x 64 $193
    is a different configuration of chip from

    CT464095 DDR PC2700 • CL=2.5 • UNBUFFERED • NON-ECC • DDR333 • 2.5V • 128Meg x 64 $185.26

    Although they nominally have the same specs CT464095 will not work in a Powerbook 15" 1.25 GHz, because Crucial had to come out with a specific build of module for the 1st gen AlBooks. I think your Crucial rep simply doesn't know and is playing the odds.

    I got that from them, their approach is "well if it doesn't work, just send it back" (this was on $3,600 worth of server RAM which they claimed one spec and shipped another. Twice. Turns out they don't even make that RAM, they were bringing it in from another vendor and didn't have a clue, they were just saying anything to get it out the door.)

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