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tech 2 May 2026

Why Are There Both TMP and TEMP Environment Variables?

Learn why your Windows system uses two environment variables for temporary files and which one is more appropriate.

Introduction

If you've ever explored the environment variables on your Windows system, you might have noticed both the TMP and TEMP variables. They appear to serve the same purpose: specifying the location of temporary files. So why are there two? And which one should you use?

A Bit of History

To understand the existence of both variables, we need to go back to the early 1980s. At that time, the CP/M operating system, used on microcomputers, did not have environment variables. Users had to manually configure programs to specify where to store temporary files. When MS-DOS arrived in 1981, it introduced the concept of environment variables, and that's where TEMP and TMP came into play.

TEMP vs TMP: What's the Difference?

At first glance, TEMP and TMP seem interchangeable, but there are nuances. Historically, some programs were coded to check TEMP, while others looked at TMP. To ensure maximum compatibility, Windows kept both. Today, most modern applications check TEMP, but some legacy applications may still use TMP.

A Concrete Example

Let's take a concrete example: you are using video editing software that creates large temporary files. The program might check TMP by default. If TMP points to a disk with limited space, it can cause performance issues. The solution? Check both variables and ensure they point to a location with enough space.

Impact on Performance

While you can set both variables to the same location, it's crucial to understand their potential impact on performance. An incorrect location can slow down applications or even cause errors.

TMP and TEMP Today

With the evolution of operating systems and applications, the importance of these variables has slightly diminished, but they remain essential for certain operations. For instance, during software installations or system updates, many temporary files are created.

Conclusion

The presence of TMP and TEMP is a legacy of the history of operating systems. Although they have similar origins, their usage can vary. Make sure to configure these variables correctly to avoid performance issues.

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TMP TEMP variables d'environnement fichiers temporaires performance système
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