RAM and PCIe

Discussion in 'MacBook Pro' started by AppleGoat, Feb 22, 2014.

  1. AppleGoat macrumors 6502a

    Oct 14, 2010
    Since the PCIe SSD storage is so quick in these new MacBook Pros, is there much risk to settling for 8GB of RAM which may potentially prove to be insufficient down the road? Would there be much of a performance drop off during memory paging with such fast storage? I have my eye on the base 15" model but it's a refurb so I don't have the option of upgrading the RAM from 8GB to 16GB.
  2. simon48 macrumors 65816


    Sep 1, 2010
    PCIe SSDs are really fast, but RAM is still way, way faster. I would not let the SSD influence your decision of how much RAM to get.
  3. yjchua95 macrumors 604

    Apr 23, 2011
    GVA, KUL, MEL (current), ZQN
    If you create a RAM disk and run Blackmagic tests on it, it's still way faster compared to paging from an SSD.

    My 21.5" iMac's 256GB SSD and RAM disk tests are shown below.

    Attached Files:

  4. simon48 macrumors 65816


    Sep 1, 2010
    Nice demo! ;)
  5. AppleGoat thread starter macrumors 6502a

    Oct 14, 2010
    Lol ...bit of a difference there. Thanks for the responses, though I was hoping to hear otherwise.
  6. dusk007 macrumors 68040


    Dec 5, 2009
    Of course RAM is still much faster but that doesn't mean the performance drop off is anywhere near what it used to be back in the day when paging really turned a omputer into crawling mode.

    Today there is just the sheer size of RAM. Yes you can fill 8GB of RAM but only few people can do it with the current working data set. Modern browsers need per tab anywhere from 20-100MB and they keep it in RAM and leave it to the OS to page that out. Some time ago browsers would have only held a handful of tabs in RAM and refreshed the rest if clicked on (which really takes about the time of a blink of an eye). Browsers do it because they can.
    It doesn't matter if all that stuff is paged out. Paging the necessary stuff back in takes no noticeable time with 150µs access time of an SSD and many hunderd MB/s max read speed.

    If you run one app that needs a ton of memory it matters but in all other cases the worst slow down you get from some paging is a split second of wait when switching to an app or tab you didn't use for a while.

    You are right with your assumption that with an SSD in the system having max RAM really isn't necessary and paging not a problem. Paging hurts battery life if it happens a lot but with 8GB you will barely ever hit the barrier.

    RAM is 10 times faster sequentially but the real difference isn't there. RAM access times are in 80ns and the SSD is still 150 000 ns. Also the CPU cannot work with the SSD directly it always needs to copy into RAM first. It really doesn't matter what sequential speed tests say, RAM is faster because it sits closer in is fast in random access patterns. Still for paging purposes an SSD is more than fast enough, you really need to low where to look for slow downs to notice the difference.
  7. Gav2k macrumors G3


    Jul 24, 2009
    If you think about it logically paging your ssd accelerates wear so you want the ram to do the work ;)
  8. MCAsan macrumors 601


    Jul 9, 2012
  9. PicnicTutorials macrumors 6502a


    Dec 29, 2013
    Considering you can't put more ram in after the fact I would go with 16 to be safe. Ram is like memory it seems to be doubling each couple years. Maybe not that much but you get eh idea.
  10. AppleGoat thread starter macrumors 6502a

    Oct 14, 2010
    I wish I could get one of those computers but they are both beyond my budget. It seems the base model is a good enough performer to last me for years but many are down on it. It's very appealing for those who initially set out to get a 13" rMBP then find a bit of wiggle room in their budget and step up to a bigger screen, faster CPU and faster integrated graphics.


    Thanks for the thorough response!

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