Base and bounds

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 operating system loads the physical address of this segment into a base register and its size into a bound register. Virtual addresses seen by the program are added to the contents of the base register to generate the physical address. 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.

This technique protects memory used by one process against access or modification by another. By itself it does not protect memory from erroneous access by the owning process. It also allows programs to be easily relocated in memory, since only the base and bounds registers have to be modified when the program is moved.

Some computer systems extended this mechanism to multiple segments, such as the i bank and d bank for instructions and data on the UNIVAC 1100 series computers or the separation of memory on the DEC PDP-10 system into a read/write "low" segment for the user process and a read-only "high" segment for sharable code.

Segmented virtual memory is a further generalization of this mechanism to a large number of segments. Usually the segment table is kept in memory rather than registers.

References

↑ Pfleeger, Charles P.; Pfleeger, Shari Lawrence (2013). Security in Computing. Prentice Hall Professional. p. 185. ISBN 0-13-035548-8.

Memory management

Memory management as a function of an operating system

Manual memory management	Static memory allocation C dynamic memory allocation new and delete (C++)

Virtual memory	Demand paging Page table Paging Virtual memory compression

Hardware	Memory management unit Translation lookaside buffer

Garbage collection	Boehm garbage collector Finalizer Garbage Mark-compact algorithm Reference counting Strong reference Weak reference

Memory segmentation	Protected mode Real mode Virtual 8086 mode x86 memory segmentation

Memory safety	Buffer overflow Buffer over-read Dangling pointer Stack overflow

Issues	Fragmentation Memory leak Unreachable memory

Other	Automatic variable International Symposium on Memory Management Region-based memory management

Operating systems

General

Kernel

Architectures	Exokernel Hybrid Microkernel Monolithic Rump kernel Unikernel

Components	Device driver Loadable kernel module Microkernel User space

Process management

Concepts	Context switch Interrupt IPC Process Process control block Thread Time-sharing

Scheduling algorithms	Computer multitasking Fixed-priority preemptive Multilevel feedback queue Preemptive Round-robin Shortest job next

Memory management and
resource protection

Storage access and
file systems

List

Miscellaneous concepts

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Base and bounds

See also

References