How to Program in Assembly Language for Mainframe Computers - ByteScout
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How to Program in Assembly Language for Mainframe Computers

Assembly language is known for low-level access to computers. As mainframes are all about performance and efficiency, assembly language is frequently used to program them.

In this article, we will learn how to program in assembly programming language for mainframe computers.

  1. Pre-Requisite To Get Started
  2. Getting Started With Assembly Language
  3. Examples!
  4. Assembler Source To Executable Module

So, let’s get started.

Program in Assembly programming language for mainframe

Pre-Requisite To Get Started

Assembly language is not for newbies. If you never coded or are very new to programming, then come back when you feel strongly about your programming or problem-solving skills.

Also, you need to set up the Assemble-Link JOB(JCL) before you get started. Each mainframe has its way of setting it up, and that’s why we recommend checking their documentation.

Also, different mainframes have different operating systems. For example, z/OS is used by IBM’s mainframe and if you want to get started with that, then you should also know about the OS as well.

In short, you need to know about the following:

  • Basic programming language experience
  • Excellent problem-solving skills
  • Understanding of computer organization
  • Know how hexadecimal and binary notation works
  • Understand the mainframe OS architecture and workflow
  • And, finally, how the main storage organization works.

Getting Started With Assembly Language

Assembly language or Assembler language is a low-level symbolic programming language that lets you write code instructions. It is very useful when you need to take control of the program you are writing. For instance, you want to control at the bit or byte level.

Just like other programming languages, assembly language also contains statements that are either used to showcase comments or instructions. The instructions can be further divided into three groups.

  • Machine instruction → Instructions set for the machine or architecture
  • Assembler instruction → Instructions that are aimed at the assembler so that it can do certain operations
  • Macro instructions → Macro instructions are those instructions that are pre-defined by a macro definition.

As memory is cheap and we have fast chips in our current generation mainframe, the programmer can customize their program to new levels. It is an established fact that no modern compiler can actually the efficiency of assembly language.

With assembly language for mainframe, the aim is to “programthe machine rather than write code as the programmer has total freedom when it comes to decision making.


Let’s check out some of the examples of assembly language.

  1. Moving Data from one register to another.


The above statement copies the 32-bit instruction from one register to another.

  1. Moving data without registers




There are other variants including XG, XR, XGR, and XC.


And many more!

The Assembly language is big! And, we recommend reading a book to get a proper understanding. You can also check online tutorials that cover assembly language in detail.

Assembler Source To Executable Module

In this section, we will learn how the assembler source is converted into an executable module.

Once you write down the instructions, the assembler then produces a program using the instructions that you put in. In simple words, it goes through the steps of the assembly process as it is a compiler for those assembly programs.

However, to make all of these work, it needs to make sure that the information interacts with the linker or binder before it can be run on the operating system. When the instructions are compiled, it is translated to object code. Now, the assembler needs to run the linkage-editing process so that it can resolve the address on which the data and instructions need to be run.

The binder creates a link map that is used to run the program. The binder also connects with the system libraries whenever needed.


This leads us to the end of our how to program in the assembly programming language for mainframe computers. As you can see, there is a lot of pre-requisite before you can start writing assembly code for the mainframe. We hope that you now have an idea of how to get started with assembly language for mainframe computers.


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