In computing base and bounds refers to a simple form of virtual memory where access to computer memory is controlled by one or a small number of sets of processor registers called base and bounds registers.
[1] In its simplest form each user process is assigned a single contiguous segment of main memory.
The address is checked against the contents of the bounds register to prevent a process from accessing memory beyond its assigned segment.
The operating system is not constrained by the hardware and can access all of physical memory.
The user could also adjust this figure using the Get Info dialog, typically to increase the amount of memory for programs with large needs, like Photoshop.