Microsoft confirms Windows 10 Mobile requires 8 GB of Internal storage
This seems to be already an optimised situation already, as it uses 6 GB on a 16 GB device and 7 GB on a 32 GB device.
There is also the added implication that it would rather be difficult to force the OS onto a 4GB handset, suggesting 4GB handsets such as the Lumia 530 will probably never see the update.
See page can be seen at Microsoft here.
Via : Wmpu