CSE 80 -- Glossary of Terms

device file
An entry in the filesystem name space referring to a hardware device. In most Unix filesystems, the convention is that device files are all in the /dev directory, though Solaris uses /devices and /dev both. By making hardware devices appear as files, many standard utility programs may be used with hardware devices without special modification by I/O redirection or by using the device file names as parameters.
dollar expansion
Dollar expansion refers to the shell's expansion of shell and environment variables. Strings of alphanumeric characters preceeded by $ are interpreted as names of shell or environment variables, and the shell replaces that string (and the dollar sign) with the value of the variable.
Globbing refers to the expansion of shell metacharacters to complete file names. Shell globbing metacharacters are '*' and '?', which expands to a sequence of zero or more characters and exactly one character respectively.
Mounting refers to the attachment of a filesystem subtree (that is completely resident on a disk drive) to the currently accessible filesystem tree. The mount point, a directory in the currently accessible filesystem (typically an empty directory) becomes synonymous with the root directory of the subtree from the new drive, and the original contents of the mount point becomes invisible and inaccessible until the filesystem is dismounted.
mount point
See mount.
operating system
The operating system is the combination of the operating system kernel (or just `kernel' for short) and various system programs. These system programs are critical for the operation of the system but run above the kernel; examples of these are the programs (/etc/rc or /etc/init.d) that bring the system up for multi-user use, ones for system maintennence such as backing up the filesystem data (dump/restore), etc.
operating system kernel
The lowest level software responsible for managing the hardware. It is responsible for allocation of resources such as CPU time, available memory (in Unix and most other operating systems, as virtual memory), disk space (as a filesystem). Another purpose of the kernel is protection. Multiuser operating systems like Unix provide the user-id abstraction, so that programs run under one user-id can not erase or alter the files of another user without explicit permission, and one buggy program can not cause another independent program to crash.
(process ID) The process ID is a number that uniquely identifies a process.
A process is a running program.
process image
The memory contents of a process. The initial process image is described by the executable file, which contains the contents of the read-only text (instruction) portions and the contents of the mutable initialized data areas. Uninitialized data just has its location and size described so that the operating system can zero fill this when a process is created, saving space in the executable binary file.
system call
A system call is a request to the operating system kernel. These are accomplished using special instructions that forces a context switch to the kernel, which then figures out what the process wanted it to do.

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