A program that controls a physical device. The driver is always run as part of the kernel,
with full kernel permissions. Device drivers may be threaded, but they would use the
kernel threads library, not the library discussed in this topic.
dynamic library
A library of routines that a user program can load into core "dynamically." That is, the
library is not linked in as part of the user's executable image but is loaded only when the
user program is run.
errno
An integer variable that is defined for all ANSI C programs (PCs running DOS as well as
workstations running UNIX). It is the place where the operating system puts the return
status for system calls when they return error codes.
external cache
Cache memory that is not physically located on the same chip as the CPU. External cache
(a.k.a. "E$") is slower than internal cache (typically, around five cycles versus one) but
faster than main memory (upward of 100 cycles, depending upon architecture).
FIFO
An abbreviation for first in, first out--a kind of a queue. Contrast to last in, first out,
which is a stack.
file descriptor
An element in the process structure that describes the state of a file in use by that process.
The actual file descriptor is in kernel space, but the user program also has a file descriptor
that refers to this kernel structure.
fine-grained locking
The concept of putting lots of locks around tiny fragments of code. It's good because it
means that there's less contention for the individual locks. It's bad because it means that
the program must spend a lot of time obtaining locks. Coarse-grained locking is the
opposite concept and has exactly the opposite qualities.
green threads
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