Memory sizes range up to several gigabytes and the access speed can also vary considerably. Optical disks' capacities lie in the tens of gigabyte range and hard disk capacities in the hundreds of gigabyte range. Microcomputer displays are generally high-definition color monitors based on CRT and LCD technologies. LCD and plasma displays are used on laptops, notebooks, and other portable models. The flexibility of the hardware can be measured by the number and type of enhancements available. These might include extra memory, more disk drives, pointing devices, communications interfaces, and the ability to participate in networks. The operating system can be characterized by its use of memory, how much can be accessed and how well it is done, how many tasks can be run concurrently, and how it appears to the user.