RAMresident

RAMresident is a term used in computing to describe software that remains loaded in a computer’s main memory after its initial execution, in order to provide ongoing services or responses without requiring a reload. RAMresident programs allocate memory and install code that can be triggered later, effectively staying active in RAM until they are explicitly unloaded or the system shuts down.

Historically, RAMresident programs were common in MS-DOS environments and were commonly called terminate-and-stay-resident (TSR) programs. They typically hooked into interrupts and used the program’s PSP (program segment prefix) to declare themselves resident. TSRs could monitor keyboard input, respond to system events, or provide utilities such as hotkeys, memory managers, or clipboard helpers. To maximize available conventional memory, they often relocated to upper memory blocks or the high memory area when supported by memory managers like EMM386 or QEMM.

Limitations and risks accompany RAMresident software. Because they occupy memory for extended periods, they reduce the available RAM for other applications and can cause compatibility issues with other resident software or system components. Poorly designed TSRs could destabilize the system or conflict with memory managers. Some RAMresident programs were also used as a technique by malware to persist in memory.

Contemporary usage has shifted toward background services or daemons in modern operating systems, which remain resident in memory via OS-managed mechanisms rather than interrupt-hooking. The general concept of keeping functionality resident persists, but the term RAMresident is less common in current contexts.