Is it worth to spend money on a small capacity HDD (~5-20 GB, very cheap though) to use it as swapping area for the OS? I do believe it will increase the OS performance , or maybe SSD (still ~5-20 GB), that costs more, will give better performances?
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If you spend that memory on RAM, you won’t need swapping. Unless you are doing some crazy scientific calculation.– ChronialMay 4, 2013 at 15:04
The best performance you get if you prevent from swapping in the first place - by having enough RAM (and upgrading RAM could be also the cheapest way).
But if more RAM is not an option and your PC swaps a lot then new HDD or SSD will make things much faster. Also you should use all available physical drives for swapping (in windows), it should use them simultaneously so it will go even faster.
And one more thing, HDD reads and writes faster on it's beginning (when heads are near to edge of platter) so you should choose appropriate partition (usually the first one).
It would not be dramatic, unless you somehow had the combination of a fast drive interface (like on a modern system), and a serious lack of ram. You don't generally need swap except as a way to efficiently use ram (by swapping out less used blocks of memory), or as a way to handle not having enough ram (there's a third scenario, let me come to it). Swapping out less used memory shouldn't benefit significantly from faster storage. Swapping out memory to adjust for a lack of ram shouldn't happen on a well designed system, and more ram is generally a better investment than an SSD.
You may also use a pagefile to suspend - here, you may see a benefit from a fast page file.
In short, I don't see many scenarios where a small, separate drive will show benefits of any sort on a well designed system
short answer is yes.
long answer: as written in other answers, it is better to invest in RAM than SSD for a speed boost. However, if more RAM is not possible (due to hardware limitations) or irrelevant (your needs require physical disk read/writes to save permanent data) then an SSD is your best option or SSHD (Hybrid drives).
SSHD seems to be exactly what you are asking about - it is a physical disk that contains a small SSD/Flash buffer for quick IO access before the data is stored into the slow physical mechanism (giving your the speed boost of SSD and the data-retrieval recovery of a physical drive)
I know Seagate (the model is called Momentus) and Toshiba (the model is called MQ01ABDH Series Hybrid Drive) offers these products.
Edit: I forgot to mention, that the latest Linux Kernel (3.9) that was released just a couple of days ago added support for this exact thing (SSD to act as a buffer for slower devices) http://kernelnewbies.org/LinuxChanges#head-be292e4535097d186c2685e5173406880589dfe6