Speeds of 128SSD v. 256SSD v 512SSD on i5

Discussion in 'MacBook Air' started by dizmonk, Oct 12, 2013.

  1. dizmonk macrumors regular

    Nov 26, 2010
    Hi.. Yes I've researched the forums.. but I still need some clarity on this. I just had a 4GB, 256GB refurbed i5 13" air. The SSD seems incredibly fast. I returned it due to the 4 GB.

    In its place I've got a i5, 8GB, 128GB 13". The SSD on this one seems much slower. When I run the Blackmagic speed test, I'm getting write speeds of 200+ MB and read speeds of 650+. On the 256 both speeds were upwards of 700MB.

    Is it fair to say that the 256GB is more than twice as fast as the 128GB? Does the 512GB get much faster than the 256?

  2. Weaselboy Moderator


    Staff Member

    Jan 23, 2005
    What you are seeing is normal and due to the difference in chip layout on the 256. You will see this with most any brand SSD going from 128 to 256. 512 and up are typically the same speed as 256.
  3. dizmonk thread starter macrumors regular

    Nov 26, 2010
    Hmm... This difference is leading me to return this one and likely get a i5 8GB with 256GB. It's interesting that the 512GB isn't faster than the 256GB?
  4. Boyd01 macrumors 601


    Feb 21, 2012
    New Jersey Pine Barrens
    FWIW... last time I tested, I got about 700 write and 730 read on my i7/8gb/512gb MBA.
  5. orangezorki macrumors 6502a

    Aug 30, 2006
    My understanding is that SSDs actually spread their data across all the chips available to enhance speed and wear-levelling. It's a bit like having RAID. The small and cheap SSDs don't have that many chips, but as you go for higher capacities, the number of chips increases, hence the bandwidth. I guess that the 512 has the same number as the 256, only higher density chips.

  6. drsox macrumors 65816


    Apr 29, 2011
    See this for an example of how the speeds track by size : http://www.tomshardware.com/reviews/m4-ssd-capacity-comparison,2957-2.html
    With this set of SSDs it's the Write rate that scales with capacity.
  7. mvmanolov macrumors 6502a

    Aug 27, 2013
    ok here is my scenario i have a 13" Haswell i7 8gig and a 128 (my wife doesnt need much space ) with about 75GB free FV2 is on and i'm only getting around 200 write and about 400 read does this make sense?
  8. robvas macrumors 68030

    Mar 29, 2009
    You will probably only notice it in benchmarks...
  9. foozipper macrumors member

    Oct 15, 2013
    Not twice but 256GB faster than 128GB, 512GB faster than 256GB.
    I want to add that Samsung SSD faster than SanDisk ;)
    Score of Speed

    Unit of MB/sec
  10. Enrico Pallazzo macrumors newbie

    Oct 16, 2013
    It's largely a matter of how many memory channels an SSD has. The more channels, the greater the bandwidth.

    Let's say that all three SSDs have the same type of memory chips. The 128gb disk has, say, 8 16gb chips while the others have 16 and 32 respectively. Each of those chips has its own maximum bandwidth so that the more chips you have on a disk the more bandwidth there is overall. The reason that larger SSDs are more expensive isn't just because there are more chips but because the higher number of chips also means that the underlying pathways tying them all together becomes more complex.

    Whether it makes for a noticeable difference is another matter. By and large, most people would never notice a difference because the main reason that SSDs are faster than conventional hard drives is due to their lower latency rather than higher bandwidth. The absolute vast majority of disk operations don't come anywhere near to using their theoretical maximums and one disk being twice faster in benchmarks doesn't mean that you will see a twofold decrease in time spent on disk operations. It's simply, if understandably, a faulty assumption.

    In other words, if you don't need the space then I wouldn't worry about it.

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