tsrs

TSRs, short for Terminate and Stay Resident, are a class of programs from the era of DOS that continue to occupy a portion of memory after their initial execution. A TSR loads into conventional memory, requests a block of memory, and then terminates while leaving a portion of its code or data resident. This reserved fragment can be activated later, typically in response to a keyboard shortcut, a timer, or an interrupt, allowing the program to perform a task without full reloading.

Mechanism and operation

TSRs commonly install a small routine into the system’s interrupt handling path or hook into specific services provided by DOS. By intercepting events such as keystrokes or timer interrupts, a TSR can trigger its functionality on demand. Memory management was a key consideration for TSRs; they often sought to reside in upper memory blocks or the high memory area to preserve conventional memory for other programs, while carefully avoiding conflicts with other resident software.

Uses and examples

TSRs provided a wide range of utilities, including quick calculators, screen capture, clipboard helpers, hotkey launchers, system monitors, and search tools. They were popular because they offered convenient access to frequently used features without requiring a full program restart.

Limitations and legacy

Because TSRs occupy memory and may intercept system events, they could reduce available conventional memory and cause conflicts with other software or with system stability. With advances in memory management and the shift to protected, multitasking environments, TSRs became largely obsolete on modern systems. In DOS-compatible environments within Windows, they could still operate under special conditions, but their use declined as safer, more robust multitasking approaches emerged.

See also

Terminate and Stay Resident, DOS memory management, upper memory blocks, interrupt vector table.