Address Space

What is Address Space?

An address space on the memory refers to the series of logical spaces where every data byte has its own address. In simple words, it signifies the total amount of memory that a computer system can address.

Technically, these address spaces are created by combining a lot of qualifiers that are uniquely identified.

This makes an address explicit within the space by partitioning it into different regions based on its mathematical structure.

Understanding Address Space

What is Address Space

The array of valid addresses that a program or a process can access is called an address space in memory. Ideally, an address space may refer to any one or both of the following:

For example, a 32-bit computer system may support a physical memory of a smaller capacity, say 4 GB, and a larger virtual memory, say 1 TB.

In the case of total order, such as in the memory addresses, the address spaces are usually simple chunks.

These chunks typically maintain a hierarchical design and usually may look like a directed ordered tree in specific nested domain hierarchies, such as:

As for the internet space, ranges of Internet Protocol (IP) addresses are assigned by the Internet Assigned Numbers Authority (IANA) to the different registries.

This allows each of them to manage their respective portions of the global Internet address space.

Used typically for carrying out instructions and storing data, in computing especially, an address space describes the set of separate addresses.

Each of these addresses may correspond to a different physical or logical entity such as:

There is an address space assigned to each and every device and process in a computer, and each of these spaces holds a specific portion of the address space of the processor.

However, this address space of the processor is normally limited to the following:

The address space, on the other hand, itself may be restricted by two specific limitations such as:

Typically, an address space is classified into specific groups, based on its design, such as:

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However, in some specific types of systems, the address space is also modified from one particular format to another by means of a process referred to as thunking.

It is the process where machine-generated, low-level codes called ‘Thunks’ are used to implement details of a software based virtual memory system to map them from virtual to physical addresses.

Address Space Example

As for a few examples of address spaces, they typically refer to the amount of memory assigned to all available addresses of any computational entity, such as a file, a device, a server, or a networked computer.

Ideally, these examples are based on the specific form of addresses and their varied uses. Some significant examples of these address spaces include, but are not limited to the following:

What is Address Space Size?

Ideally, the size of the address space depends on the architecture of the memory or a peripheral device as well as the operating system that supports it.

Every address space can be 16 exabytes in size, which is a bit more than a billion gigabytes, or a new address space may have 264 addresses, which is 8 billion times larger than a 2 GB address space that can logically hold 231 addresses.

Typically, before the 64-bit address space came into existence, there were two specific types of address spaces available, such as:

With reference to maintaining compatibility, two different Addressing Modes (AMODEs) were provided by the operating system. These are as follows:

When the size of the address spaces started to increase, newer terms were required to describe them.

Therefore, programs that use more than 2 GB address space of a virtual storage need to run in AMODE 64.

This eventually created an address space architecture of larger size that can provide 64-bit addresses.

However, the structure of the address spaces of less than 2 gigabytes remained unaltered. This means that all those programs that operated in AMODE 24 and AMODE 31 continued to run in the same way.

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Therefore, in some basic ways, it is the 64-bit address space that acts as the virtual line or the bar that marks the 2-gigabyte address. It separates the storage into two distinct parts, such as:

And, as for the 31-bit address space, a similar virtual line differentiates the 16-megabyte address in a different way as follows:

Ideally, there is no precise area above this specific bar that can be considered to be common to all available address spaces, and there are also no system control blocks that can occur above the bar.

Typically, the size of the address spaces can be altered to be more than the physical memory by means of a specific memory management tactic called virtual memory, also called a page file. This page file resides on the disk and performs in either of the two following ways:

What are the Types of Address Space?

There are basically three main types of address spaces, namely the ACB address space, the associated address space, and the session address space, to name a few. Each of these types comes with a diverse set of features and functionalities.

ACB address space

This specific type of address space opens the Access Method Control Block (ACB) for the applications and resides on the common storage to allow using multiple address spaces for the application program.

The ACB address space can be characterized as follows:

Associated address space

With respect to ACB, if an address space issues VTAM macroinstructions opened in a different address specifying an ACB, it is called an associated address space. It can be characterized as follows:

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Session address space

This is an address space designed for issuing VTAM macroinstructions for establishing OPNDST or OPNSEC sessions. These address spaces can be characterized as follows:

A couple of other types of address spaces are:

Virtual address space

This address space can be characterized as follows:

Logical address space

This is another specific type of address space that is produced by a computer system for a particular program. Ideally, these sets of logical address spaces, when mapped to their corresponding sets of physical addresses, create the physical address spaces.

Address Space Vs Memory

Where is the Address Space Located?

Usually, the address space is located on the secondary storage disk.

If it is virtual, the address space will be mapped to the physical or actual space by the operating system by maintaining an image of it in the secondary storage, which is why it is usually larger in size than the physical memory.

Ideally, it serves the requirements of different programs so that they can operate as they should when needed.


Therefore, after reading this article, you are now quite knowledgeable about the address space and how useful it is to the memory of a computer.

Typically, based on the design and functionalities, you can say that the address space on a memory of a computer is made up of both virtual memory and physical memory.