Linux vs HP-UNIX Essay Example | Topics and Well Written Essays - 1000 words

Linux vs HP-UNIX - Essay Example "A single class of process is a feasible approach in Plan 9 because the kernel has an efficient system call interface and cheap process creation and scheduling." (Pike et al) Bell Labs: The kernel support for parallel programming in Plan 9 is a few hundred lines of portable code; a handful of simple primitives enable the problems to be handled cleanly at user level. Although the primitives work fine from C, they are particularly expressive from within Alef. The creation and management of slave I/O processes can be written in a few lines of Alef, providing the foundation for a consistent means of multiplexing data flows between arbitrary processes. (Pike et al) Bell Labs UNIX is a "multi-tasking OS, which means that there may be many programs and many programs and people using the same machine at the same time, by using the concept of a virtual machine". (Seth Noble, 2005) Linux's bottom half handlers were invented so that device drivers and other parts of the Linux kernel could queue work to be done later on. Figure 11.1 shows the kernel data structures associated with bottom half handling. Bottom Half Handling Figure 11.1: Bottom Half Handling Data Structures There can be up to 32 different bottom half handlers; bh_base is a vector of pointers to each of the kernel's bottom half handling routines. bh_active and bh_mask have their bits set according to what handlers have been installed and are active. If bit N of bh_mask is set then the Nth element of bh_base contains the address of a bottom half routine. If bit N of bh_active is set then the N'th bottom half handler routine should be called as soon as the scheduler deems reasonable. These indices are statically defined; the timer bottom half handler is the highest priority (index 0), the console bottom half handler is next in priority (index 1) and so on. Typically the bottom half handling routines have lists of tasks associated with them. For example, the immediate bottom half handler works its way through the immediate tasks queue (tq_immediate) which contains tasks that need to be performed immediately. (Rusling, David 1999) Shell The shell application inside the UNIX Plan9 system are set up for standard input and output connection to the editable text of the window with such features as its own private bitmap and multiplexed access to the keyboard, mouse and other graphical resources. The UNIX shell is commonly defined as the command line which provides the user interface for the actual operating system. By executing input commands, the shell will then execute those exact inputs. There are different shells that are available for Linux and is very much the same as UNIX in its description of how the shell application works. The following shells are available for Linux: Shell Name Developed by Where Remark BASH ( Bourne-Again SHell ) Brian Fox and Chet Ramey Free Software Foundation Most common shell in Linux.