Operating Systems
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Transient also refers to a module that, once loaded into main memory, is expected to remain in memory for a short time. Today, the term is rarely used, and may be obsolete. The term Overlay is commonly used instead, and refer to a program module that is brought to memory when it is needed by the running program and then replaced with another when it is no longer needed, so a program had lower memory requirements. Program modules were written to allow different modules to share the same memory region and the main program itself was responsible of exchanging modules between disk and memory as necessary.
In the mid-to-late 1960s, mainframe computers, such as the IBM System/360, had memory sizes from 8 KB to 512 KB. In order to conserve memory, transients were small modules that supported a specific task, and were swapped in and out of memory. The operating system for the 360 had two areas reserved for transients that supported input/output operations. These were referred to as the “logical transient area,” and the “physical transient area.” If an application program, for example, needed to use the printer, transients that supported printing were brought into the transient areas. If an application needed to use tape drives, transients that supported tape drive access were brought into the transient areas.
Read more about this topic: Transient (computer Programming)
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