Wednesday, 27 February 2019

Why are computers slow to come back from hibernate?


Hibernation is supposed to write out RAM contents to disk, and coming back from hibernation is supposed to fill back RAM with saved contents. Why is coming back from hibernation slow, e.g. system is very unresponsive in general for quite some time?



Answer



The main cause is disk I/O. Reading and writing to a physical disk is much slower than from RAM. When your computer resumes from disk (hibernation) it also has to power up the components which may cause some slowdown. This is highly dependent on the computer. A SSD will have almost the same resume speed from disk as from RAM. Some computers let you move the mouse around before the ram has been completely filled up again, causing low response times.


Note: Assume you have 8GB of RAM and a SSD with 400MB/s throughput. It will still take 8*1024MB/400MB/s = 20.48s. This is not the same speed as resume from RAM.


Assuming a RAM throughput of 15,000MB/s, the resume time is 0.55 seconds.


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