Base-Bound Register (datum-limit register) Definition/Meaning:
Hardware used for virtual-memory
allocation. A base-bound register is associated with each segment of data or
code and defines the position in physical memory of word zero for that segment,
the so-called base or datum, and the number of words available to that segment,
the so-called bound or limit (or alternatively the physical memory address of
the next word after the end of the segment, in which case it is a bounds
register). Whenever a process attempts to access the memory segment, the
hardware of the system checks that the address of the word lies within the range
0 ≤ word address
≤ bound
and then adds the address to the value contained in the base register to give
the physical address. A restriction on this system is
that the storage for the segment must be allocated in a contiguous area of
memory (see best fit, first fit).
The base register, used in the construction of relative addresses, should not be
confused with the base of a base-bound system; the result of modifying an
address by a base register's contents is still an address within virtual memory
space of the process, and is not necessarily a physical address.
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