A signal that is sent to a process "synchronously." This means that it is the direct result of
something that process did, such as dividing by zero. Should a program do a divide-by-
zero, the CPU will immediately trap into a kernel routine, which in turn will send a signal
to the process (cf. asynchronous signal).
system call
A function that sets up its arguments, then traps into the kernel in order to have the kernel
do something for it. This is the only means a user program has for communication with
the kernel.
time-sliced scheduling
An algorithm that allocates a set amount of time for a process (or LWP or thread) to run
before it is preempted from the CPU and another one is given time to run.
Trap
An instruction that causes the CPU to stop what it is doing and jump to a special routine
in the kernel (cf. system call).
user mode
An operating mode for a CPU in which certain instructions are not allowed. A user
program runs in user mode (cf. kernel mode).
user space
That area of memory devoted to user programs. The kernel sets up this space but
generally never looks inside (cf. kernel space).
virtual memory
The memory space that a program thinks it is using. It is mapped into physical memory
by the MMU. Virtual memory allows a program to behave as if it had 100 Mbytes, even
though the system has only 32 Mbytes.
Xview
A library of routines that draws and operates Openlook GUI components on a screen. It is
based on the SunViewTM library of the mid-1980s and has been superseded by CDE Motif.
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