DOS And Unix

Compare and Contrast Microsoft DOS with UNIX
is suggestive of its name, an operating system (OS) is a collection of programs
that operate the personal computer (PC). Its primary purpose is to support
programs that actually do the work one is interested in, and to allow competing
programs to share the resources of the computer. However, the OS also controls
the inner workings of the computer, acting as a traffic manager which controls
the flow of data through the system and initiates the starting and stopping
processes, and as a means through which software can access the hardware and
system software. In addition, it provides routines for device control, provides
for the management, scheduling and interaction of tasks, and maintains system
integrity. It also provides a facility called the user interface which issues
commands to the system software. Utilities are provided for managing files and
documents created by users, development of programs and software, communicating
between users with other computer systems and managing user requirements for
programs, storage space and priority. There are a number of different types of
operating systems with varying degrees of complexity. A system such as DOS can
be relatively simple and minimalistic, while others, like UNIX, can be somewhat
more complicated. Some systems run only a single process at a time (DOS), while
other systems run multiple processes at once (UNIX). In reality, it is not
possible for a single processor to run multiple processes simultaneously. The
processor of the computer runs one process for a short period of time, then is
switched to the next process and so on. As the processor executes millions of
instructions per second, this gives the appearance of many processes running at
once. User programs are usually stored on a hard disk and need to be loaded into
memory before being executed. This presents the need for memory management, as
the memory of the computer would need to be searched for a free area in which to
load a users program. When the user was finished running the program, the memory
consumed by it would need to be freed up and made available for another user
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 CPUs 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 came with different versions of DOS, each added new commands and
new things that could be done by the user. For example, DOS 4s COMMAND.COM
added the /P switch to DEL to verify each deletion, and DOS 5s COMMAND.COM
provided the ability to sort the output of the DIR command. HISTORY An acronym
for disk operating