The address range 640-1024 kilobytes on an IBM PC, reserved for BIOS, video cards, and add-on cards.
Depending on the configuration some of the address space may
be unused in which case it can be used by EMS or UMB.
Setting aside a portion of main memory for some purpose. All system and application programs reserve memory either at startup or during the course of operation. Memory is reserved for inputting data, additional software instructions or for the creation of control structures such as a stack. See dynamic memory allocation, memory allocation, buffer and stack.