SSDs and RAM

Discussion in 'Mac Basics and Help' started by Thiol, May 19, 2009.

  1. Thiol macrumors 6502a


    Jan 26, 2008
    Hi all. So, I know that RAM amount is one of the first bottlenecks that any computer runs into. Running out of free RAM forces writing to a disk cache that is much slower. Here's my question, which I guess is sort of theoretical: Are page outs a problem with SSDs? If one has an SSD, that is almost certainly faster than a hard drive with most types of reads and writes (I know, but not all). I guess the connected question is: What type of reads and writes are involved in page outs? Are they small or large, random or sequential?
  2. Makosuke macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    The non-theoretical answer is "yes, they are still a problem." While an SSD is significantly faster than a spinning drive for most operations, it's nowhere near as fast as RAM, and so will still be a huge bottleneck if you're doing significant pageouts to disk. The exact behavior will vary depending on what the system is doing, but my not-particularly-educated guess is that pageouts do lean toward random medium-sized transactions.

    This would give SSDs a theoretical additional advantage over rotating storage, but on the other hand you could also get into issues where the heavy read-write cycles on the flash disk could cause performance degradation over time (due to the way flash memory deals with re-writes of used space). Either way, the SSD would still be a major bottleneck.

    Keep in mind that even if a SSD could saturate a SATAII bus you'd be looking at about 300MB/s throughput; that's in comparison to DDR3's 6.4-12.8GB/s--20-40 times faster. Even the slowest DDR1 can manage 1600MB/s, 5 times faster than the theoretical max of a current SSD (which nothing currently can hit).

Share This Page