~44GB compressed. http://wiki.openstreetmap.org/wiki/Planet.osm

That was in reach of my Nokia N900 in 2009. 32GB internal storage with a 32GB SD card. We've gone backwards*

* Yes, it'd fit on any 128GB device, I guess.

But in a Postgres + PostGis it is more than 300GB, and you can add a tile cache or it will be too slow.

The offline maps like Osmand and whatnot elide a bunch of data and include indexes, and last I did the arithmetic, were in the vicinity of 50 GB. Numbers here:

http://download.osmand.net/rawindexes/

(Note that there are duplicated areas and wikipedia extracts in there, so a simple sum will be an overestimate)

Agree, that's uncompressed and with all of the required scaffolding. I would still argue that in the next few years, you'll be able to carry an entirely functional OSM system around with you, tile cache and all (Samsung is predicting 128TB SSDs by 2018).

Ah, the 29.3GB PBF might be better, I don't know about the CPU/RAM requirements of it though.