Although D in this question is probably the closest, the answer may have been transcribed incorrectly. CHS stands for Cylinder Head Sector, and S is not sides. Each side of a platter of a disk has its own head. A cylinder is an alignment of all tracks under one head position. So the answer is number of cylinders x number of heads x number of sectors (per track) x 512 bytes per sector (assuming that is the sector size as some disks may have larger sector sizes). The number of tracks per side of disk, or the number of tracks that a single head can access is equal to the number of cylinders.