The PCjx later had a BIOS upgrade chip, sold together with PC DOS 3.21, which could use the full 720 KB capacity of the diskette drives. Some popular options for the PCjx were a 5.25" 360 KB capacity diskette drive, a 10 MB external hard disk (both of these as stackable units the same size as the JX itself) and a joystick. IBM never released a 3270 emulation adapter for the PCjx, in order to steer enterprise customers to more-expensive IBM PCs and XTs.