It has what was then a new -inch double-sided 800 KB floppy drive, offering double the capacity of floppy disks from previous Macs, along with backward compatibility. The then-new drive is controlled by the same IWM chip as in previous models, implementing variable speed GCR. The drive was still completely incompatible with PC drives. The 800 KB drive has two read/write heads, enabling it to simultaneously use both sides of the floppy disk and thereby double storage capacity. Like the 400 KB drive before it, a companion Macintosh 800K External Drive was an available option. However, with the increased disk storage capacity combined with 2-4x the available RAM, the external drive was less of a necessity than it had been with the 128K and 512K.