[GLLUG] How can a VM be faster than raw hardware?

John Winters john at sinodun.org.uk
Sun Dec 9 17:24:32 UTC 2012

I've just noticed something odd which puzzles me.

For a while I've been developing a Rails application, using rspec to run 
the automated tests.  It's at an early stage, but to run the 212 
examples on my development machine currently takes about 38 seconds.

The machine has a Core i5 3570K (3.4GHz), 16G of RAM and an SSD 
providing the development area.

Because I need to play with it elsewhere, I just git cloned the source 
onto a Linux virtual machine running under VirtualBox on top of MacOS on 
a laptop.  The laptop is a much lower spec - 2.4 GHz Core 2 Duo, with 
only 1G of RAM available to the VM (4G in the machine in total), and a 
conventional spinning HDD.

I was concerned about how long the test suite would take on the laptop, 
but to my surprise it runs in only 29 seconds.

Anyone any idea why the lower spec machine would be so much faster?


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