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.
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RAM and PCIe
- Thread starter AppleGoat
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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.
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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.
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.
If you get a 15" 2013 2.3 or 2.6 rMBP this is a mute question as 16GB is the default memory size. It is only the 2.0 rMBP that has 8GB standard. Always go with the 2.3 or 2.6 machine with 16GB and a dedicated GPU whenever possible.
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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.
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.
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Thanks for the thorough response!