| | | | | | have been incorporated into a fully functioning operating system and user environment. Chief among these is the GNU project, which has created a high-quality suite of POSIX compliant tools and utilities for program development, and general system support. Other software projects, such as the X Window System. the TeX document preparation system, the Apache web server, the Tcl/Tk and Perl scripting languages, sendmail, and others, combine to make Linux distributions fully functional environments. An increasing number of commercial software packages, such as the Java Development Kit, Adobe PDF viewers, and Netscape. are available free of charge for Linux. More recently, several high-profile commercial software firms have announced plans to support Linux versions of some of their products. Oracle, IBM, Informix, Sybase, Corel, and Computer Associates. among others are supporting their products on Linux. Some products are free of charge. while others have standard commercial licensing fees. | | | | | | | | | Linux is a full and complete Unix, developed with contributions from an international community. Linux, including every line of source code for the kernel and utilities, is available from many sources at little or no cost. There are no licensing fees to run Linux. It was originally restricted to the Intel x86 family of microprocessors, but has since been ported to many other architectures including the DEC Alpha, IBM PowerPC, Sun SPARC, Motorola 68k, and MIPS microprocessors. While other versions of Unix such as FreeBSD and Solaris have been successfully employed for Beowulf systems, the focus of this chapter is on Linux, its capabilities, interfaces, and installation. | | | | | | | | | Demand paging Linux provides complete support for virtual memory including transparent address translation and demand paging. Both the user virtual address space and the machine physical address space are organized into pages. These pages are contiguous blocks of memory, usually 4096 bytes in length. With some exceptions, a page of virtual memory may be mapped to any page of existing physical memory and the specific allocation is retained in a system directory table which is also stored in memory. The primary advantage of real virtual memory systems over more primitive systems that work directly in the physical space is that the virtual address space can be much larger than the actual number of pages provided by the physical installed memory of the system. This gives the user application an illusion of a very large amount of memory. This additional storage, if not in physical memory, has to exist somewhere, and the excess pages (those | | | | |
