While all the 3-inch disks were double-sided, the PCW 256's 3-inch drive and the PCW 8512's upper one were single-sided, while the 8512's lower one was double-sided and double-density. Hence there were two types of disk: single-density, which could store 180 KB of data per side, equivalent to about 70 pages of text each; and double density, which could store twice as much per side. The double-density drive could read single-density disks, but it was inadvisable to write to them using this drive. Users of single-sided drives had to flip the disks over to use the full capacity.