What happens if I run a program to halt my computer?

Actually, your CPU already uses the HLT instruction during its standard operations to manage power. It doesn't crash your computer or anything drastic. It just tells the CPU to sleep until the next interrupt—like a timer or a keyboard input—happens, at which point everything continues as normal.

If HLT is executed while your program is running, it's typically just going to pause until the next hardware interrupt. On modern systems with multiple cores, you'd probably barely notice any effect at all since the OS keeps running in the background, handling other tasks. Essentially, it puts the CPU in a low-power state, waiting for the next event.

Privileged instructions like HLT just crash the program if run from user space. The OS will remain unaffected, so even if you somehow were to run it with kernel privileges, the usual outcome is very minimal—you're likely to just see a pause until the next interrupt.

Running the HLT instruction isn't as straightforward as it seems. In most operating systems, certain commands can only be executed from a specific privilege level. The HLT instruction should really only be callable from the kernel level, not just with administrative rights. So, if you try to run it from a regular application, it's likely to fail or crash that particular program without affecting the entire OS.

Honestly, this is all available with a quick Google search. Most of the info you need to understand how HLT works is out there, and it's not likely to brick anything.