Introduction to Mainframe Basics for Security Professionals

1.1 Why Use a Mainframe?

Where do mainframes fit in? The mainframes we use today date back to April 7, 1964, with the announcement of the IBM System/360™. System/360 was a revolutionary step in the development of the computer for many reasons, including these:

• System/360 could do both numerically intensive scientific computing and input/output intensive commercial computing.
• System/360 was a line of upwardly compatible computers that allowed installations to move to more powerful computers without having to rewrite their programs.
• System/360 utilized dedicated computers that managed the input/output operations, which allowed the central processing unit to focus its resources on the application.

These systems were short on memory and did not run nearly as fast as modern computers. For example, some models of the System/360 were run with 32K (yes, K, as in 1,024 bytes) of RAM, which had to accommodate both the application and the operating system. Hardware and software had to be optimized to make the best use of limited resources.