Linux – How are signals implemented in Linux

Satō Katsura's comment answers my question adequately:

It's system-dependent whether signals are queued or not. There is no guarantee signals are delivered in a certain order. Signals of the same type may be delivered in the same order they are generated, but that also is system-dependent (f.i. it's true on Linux). Use pipes for command channels if you need to send more than one kind of command.

The short answer is yes. All practical approaches to preemption will use some sort of CPU interrupt to jump back into privileged mode, i.e. the linux kernel scheduler.

If you look at your /proc/interrupts you'll find the interrupts used in the system, including timers.

Note that linux has several different types of schedulers, and the classic periodic timer style, is seldom used - from the Completely Fair Scheduler (CFS) documentation:

CFS uses nanosecond granularity accounting and does not rely on any jiffies or other HZ detail. Thus the CFS scheduler has no notion of “timeslices” in the way the previous scheduler had, and has no heuristics whatsoever.

Also, when a program issues a system call (Usually by a software interrupt - "trap"), the kernel is also able to preempt the calling program, this is especially evident with system calls waiting for data from other processes.