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Usually when RAM runs out, and a swap file is used, then the system can become really slow. But if the notebook or desktop is using SSD already, will a swap file be such a bad idea any more?

Can someone who is familiar with RAM data speed, SDD speed, and 7200 or 5400 RPM hard drive speed give some insight as to how much SSD data rate is compared to RAM speed, so perhaps if it is already 1/2 or 1/3 of RAM speed, then swap file won't slow down the system so much?

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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 2 '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 –  動靜能量 Dec 2 '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 Neely Dec 2 '11 at 13:56
    
possible duplicate of Virtual Memory and SSD and Should I keep my swap file on an SSD drive? –  sblair Dec 2 '11 at 14:06
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1 Answer

up vote 2 down vote accepted

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

The maximum speed of transfer of an SSD is 600MB/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 6400MB/s (so the slowest DDR3 ram around)

These are all approximate and hand wavey. However, while an SSD is quicker, HDD is 2% of RAM transfer rate, and sdd 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 hard disk.

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6400MB/s... you mean all 6GB in 1 second? –  動靜能量 Dec 2 '11 at 13:44
    
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 Neely Dec 2 '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 2 '11 at 13:59
    
@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 at 7:33
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