Реферат: DOS And Unix Essay Research Paper Compare

when required (CIT). Process scheduling and management is also necessary, so

that all programs can be executed and run without conflict. Some programs might

need to be executed more frequently than others, for example, printing.

Conversely, some programs may need to be temporarily halted, then restarted

again, so this introduces the need for inter-program communication. In modern

operating systems, we speak more of a process (a portion of a program in some

stage of execution (CIT, 3)) than a program. This is because only a portion of

the program is loaded at any one time. The rest of the program sits waiting on

the disk until it is needed, thereby saving memory space. UNIX users speak of

the operating system as having three main parts: the kernel, the shell and the

file system. While DOS users tend not to use the term kernel and only sometimes

use the term shell, the terms remain relevant. The kernel, also known as the

?Real Time Executive?, is the low-level core of the OS and is loaded into

memory right after the loading of the BIOS whenever the system is started. The

kernel handles the transfer of data among the various parts of the system, such

as from hard disk to RAM to CPU. It also assigns memory to the various

system-level processes that occur whenever the computer does anything. The

kernel is also responsible for scheduling the CPU?s operations and for letting

the shell access the CPU (PC Mag, 1). The shell is the visible user interface to

the OS and is a program that loads on top of the operating system and offers

users commands that lets them access the OS. Strictly speaking, the shell is an

input utility that offers access to the operating system. Technically speaking,

the shell, being a separate program, is not a part of the OS at all. In the UNIX

world a number of shells are available, among them the Korn shell, the C-shell,

the Bourne shell and the Bourne Again shell (yes, really). In DOS, the standard

shell is COMMAND.COM, again nothing more than a program. As different versions

of command.com came with different versions of DOS, each added new commands and

new things that could be done by the user. For example, DOS 4?s COMMAND.COM

added the /P switch to DEL to verify each deletion, and DOS 5?s COMMAND.COM