On Facebook: I'm willing to bet a switch to binary from PHP is one magnitude less of processing power required, and an early switch would've cut their server requirements by 90%. Not sure which would've been cheaper, the C devs or all those extra servers burning electricity to interpret a language during runtime.
EDIT: And that's just an economic incentive. From an ecological perspective, it's borderline criminal for a website as massive as Facebook to be running PHP.
By switching to HipHop for PHP and later HHVM they saved lots of servers. 90% is a bit too much (consider: they went "services" first, where different tasks were done in different languages in independent services) And yes, for the ecological argument that is true (even more ecological it would be to shut down Facebook ... )
However using PHP allowed them to hire lots of staff quickly and adapt to changed requirements quickly. Which is economical valuable. Finding the right time for a switch is simpler in a retrospective though ;-)
(I have no insight to Facebook, but was heavily involved in the PHP project and talked to different Facebook engineers privately and professionally)
On Facebook: I'm willing to bet a switch to binary from PHP is one magnitude less of processing power required, and an early switch would've cut their server requirements by 90%. Not sure which would've been cheaper, the C devs or all those extra servers burning electricity to interpret a language during runtime.
EDIT: And that's just an economic incentive. From an ecological perspective, it's borderline criminal for a website as massive as Facebook to be running PHP.