How are Developer coordinating with each other in large Companies?

I have never actually worked in a project that requires more than 4 to 5 persons so please excuse my lack of knowledge on this -not rocket science- answer..

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So, how do large companies, with thousands of developers, coordinate with each other and not do the same job, let’s say, 10 developers at the same time? How do they know that the code they are editing or the bug that they are fixing isn’t being fixed at the same time by another developer? (resulting to a total waste of time for one of them)

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In general, how do they coordinate with that big ammount of Developers and Data?