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Big repository on Aix

Hello everyone,
We have source codes in many files of 20 years development. It's approx 800mb. There are many programs. Every has about 100-200 modules.
Company has 40 developers. They all works via terminal on aix.
At this time we have three folders for three versions. Everybody send changes to them via script blocking parallel work.
It's possible migrate to the Git version system. We are afraid of big local copies for every developer. We have not enough space for 40 x 800MB plus history etc. Exist some less dramatic way?
Thanks for your info.
Best Regards
Georg Black