Process Address Space


Address space is an important concept in the operating system. It is the volume of memory which is allocated for all the potential addresses associated with a computational unit such as a file, a device, a networked computer system, or a server.

Address space may also denote a range of physical or virtual addresses which can be accessed by a processor. These addresses are also reserved for a process. Each address specifies an entity’s location as a unique identifier of single entities. Also, each computer device or the component is assigned an address space which is a part of the address space of the processor.

Components of a Process Address Space

The total amount of shared memory a system can allocate depends on several factors. The overall space may include sections such as stack space, program size required, memory mapped files, shared libraries, as well as memory allocated from the heap.

Memory allocation policies and address spaces used by the varied operating systems are complicated. They may also differ from one operating system to another. The figure below gives an overall layout of a generic process address space for a 32-bit operating system.

Each section in the given address space is dedicated to perform a specific task and is present to perform an explicit task. The most common areas are the Kernel, program and program data, stack value, heap value, and global data including shared libraries, shared memory, or Dynamic Link Libraries.

The magnitude of each section in the address space depends on the type and power of the operating system. These sizes also affect the size of allocated segments of the shared memory. In the case of a 64-bit operating system, most of the computational limits are theoretical and may change depending on the available hardware.

Address spaces can be further differentiated as either flat or segmented. In the case of flat address spaces, the addresses are expressed as incremental values which start from zero. In the case of segmented address spaces, the addresses are represented as distinct segments augmented by offsets. Offsets are values that are added to generate secondary addresses.

These address spaces can be transformed in some systems from one format to another following a process known as Thunking.

Addresses spaces have also been linked with the IP address spaces. It is said that the developers of IPv4 had not initially anticipated the exponential expansion of the internet. For this reason, the IPv4 address spaces were updated with the IPv6 address spaces with higher bandwidth and address storage capacity.