The teardown indicates that "K4X2" is written on the A4 chip and they believe this to be a Samsung DRAM part number. I Googled for it but found nothing helpful so am going to stab in the dark and guess 4 gigabits (a more common measurement on-the-chip for memory) * 2 == 512MB * 2 == 1 gigabyte. Of course, that's a total guess and I've not seen memory part numbers work quite that way before ;-)