[BetterRed]

Some file synch software has options to only sync the blocks that changed, the ones I use have that - rsync and goodsync, and no doubt many others do to. And some (all ?) of the cloud sync products have a similar option, Skydrive does, so does The Box.

But in that case its main purpose is to reduce network load, if during a normal business day you add/change a few accounts and transactions (3MB) to a 300GB MySql accounts payable database, then you probably wouldn't want to sync the whole enchilada every night to your disaster recover site.

BTW a .docx is a rebadged .zip just like a .epub. Any difference in speed is in the application. Word (33 years and who knows how many man decades) v Calibre Book Editor (33 weeks and probably fewer man weeks). BTW Word didn't come out of the blue, any more than Calibres Book Editor did; Word descends from Xerox Bravo, one of its developers was Charles Simonyi, who went to MS to write Word. First version of Word ran on Xenix.

BR