DOS And Unix Essays - Software, Computer Architecture,

DOS And Unix Compare and Contrast Microsoft DOS with UNIX As 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 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 provided the ability to