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When RAM runs out on a computer, the swap file is used, and then the system can become quite slow. But if the notebook or desktop is using SSD nowadays, will it be less of a concern?

(Updated Oct 2014: For example, if we now buy a notebook computer with SSD, would it make sense to save some money not to buy more RAM, such as staying with 8 GB and not go for 16 GB, because SSD already make the swap file issue not a big issue?)

Peter Mortensen
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nonopolarity
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  • This just calls for speculation. Having no idea what the RAM size is, all one can answers is "well if it is 4GB of RAM, then your applications will swap X amount of data". But then that calls for speculations of what an "average application" will use and the "average" workload. What is the specific issue do you want to address?? – surfasb Dec 02 '11 at 13:23
  • or can you just give a common usage, such as 4GB and then the apps all together occupy 6GB? instead of negating the question by downvoting it – nonopolarity Dec 02 '11 at 13:43
  • Why the downvote? The question is reasonable to me, and if the answer has to be placed in terms of bounding cases like Paul did reasonable answers still exist. – Dan Is Fiddling By Firelight Dec 02 '11 at 13:56
  • possible duplicate of [Virtual Memory and SSD](http://superuser.com/questions/357357/virtual-memory-and-ssd) and [Should I keep my swap file on an SSD drive?](http://superuser.com/questions/51724/should-i-keep-my-swap-file-on-an-ssd-drive) – sblair Dec 02 '11 at 14:06
  • This question is entirely based on the misconception that swap files make systems slower. If that were true, why would anybody use them? in fact, swap files make systems faster by allowing them to get rarely used information out of main memory, making more space for things that improve performance like disk caches. – David Schwartz Oct 22 '14 at 07:27
  • @DanNeely yeah to me, this is a very valid question... swap file makes computer slow, but is it less of a concern when we have SSD now? – nonopolarity Oct 22 '14 at 11:43
  • @DavidSchwartz we can all agree that without a swap file being used, the system is running at its optimal speed. It is when RAM needs to be swapped out and swapped in (to and from the hard drive) that make the apps not running so smoothly – nonopolarity Oct 22 '14 at 11:53
  • @動靜能量 I don't agree with that at all. For example, without using a swap file, the system cannot eject dirty pages from physical RAM even where it would prefer to use that RAM as disk cache. Consider a service that dirties a bunch of memory at startup and is never used. Without using a swap file, that data must remain in precious physical RAM, shrinking the disk cache, even if it is literally *never* accessed. And that's just one of several reasons swap files make systems faster. That's the main reason we have them. The ability to have the working set exceed RAM is just one thing page files do. – David Schwartz Oct 22 '14 at 17:31

1 Answers1

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The best you'll get out of an HDD right now is 150 MB/s.

The maximum speed of transfer of an SSD is 600 MB/s, as that is the max speed of a SATA3 connection. They are usually slower than this though.

The maximum speed of transfer of DDR3-800 RAM is 6400 MB/s (so the slowest DDR3 RAM around)

These are all approximate and handwavy. However, while an SSD is quicker, HDD is 2% of RAM transfer rate, and SSD at its very best is 9% of RAM transfer rate.

So "it won't slow down the system so much", but whether you'll notice is another matter. More RAM is the answer to running out of RAM, not faster a hard disk.

Peter Mortensen
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Paul
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  • 6400MB/s... you mean all 6GB in 1 second? – nonopolarity Dec 02 '11 at 13:44
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    The performance penalty between an HDD and a SSD is probably larger than the bandwidth numbers imply since latency is one are that SSDs crush HDDs. Ram is still far faster though. – Dan Is Fiddling By Firelight Dec 02 '11 at 13:59
  • @動靜能量 Yes theoretically, see link. But you are never going to get that in real life, or any of the other cited speeds ("hand wavey"). So we can only use them for comparative purposes, as is the intent of the question in any case. – Paul Dec 02 '11 at 13:59
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    @動靜能量 yes, the slowest DDR3 can transfer over 6GB of data in 1 second. Now its been a couple of years DDR3-1600 is quite common and has a peak speed of 12800MB/s (yes over 12GB in 1 second). – BeowulfNode42 Jan 31 '14 at 07:33