 As hard disks grew larger, the MS-DOS and PC DOS implementations of FAT12 and FAT16 eventually lacked the means for taking advantage of extra capacity.Several manufacturers addressed this problem, however, by developing their own FAT variants within their OEM issued versions of MS-DOS.Some vendors (AST and NEC) supported eight, instead of the standard four, primary partition entries in their custom extended "Master Boot Record" ("MBR"), and they adapted MS-DOS to use more than a single primary partition.