The upper memory area (UMA) refers to the address space between 640 KiB and 1024 KiB (0xA0000–0xFFFFF). Three 128 KiB regions were defined in this area. The 128 KiB region between 0xA0000 and 0xBFFFF was reserved for video adapter screen memory. The 32 KiB region between 0xC0000 and 0xC7FFF was reserved for video adapter Video BIOS memory. The 160 KiB region between 0xC8000 and 0xEFFFF was reserved for device Option ROMs, and special RAM usually shared with physical devices (for example, shared memory for a network adapter). The IBM PC reserved the uppermost 64 KiB of the address space from 0xF0000 to 0xFFFFF for the BIOS and Cassette BASIC read-only memory (ROM).