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Dr. Dobb's Journal: Inside Debian Hurd

Nov 04, 2000, 13:03 (1 Talkback[s])
(Other stories by Jerry Epplin)

"For all its virtues as an open operating system, however, Linux -- or specifically the Linux kernel -- throws significant obstacles in the way of developers wishing to modify it. The first thing you encounter when studying it is its sheer size, consisting of thousands of source files. The amount of functionality included in the Linux kernel is impressive but daunting, with everything from the lowest level scheduling and memory management to higher level networking included in the kernel. Also, Linux kernel development is dominated by a hacker ethos, in which external documentation is held in contempt, and even code comments are viewed with suspicion."

"One possible approach to managing OS complexity is the use of an OS based on a "microkernel" architecture, of which the Hurd is a promising example. Originally a project of the Free Software Foundation, the Hurd has caught the interest of a number of other groups. (The Hurd is always referred to as "the Hurd," not just "Hurd." The word stands for "Hird of UNIX-replacing daemons." For more information about the genesis of the Hurd, see http://www.cs.pdx .edu/~trent/gnu/hurd/. "Hird," on the other hand, stands for "Hurd of interfaces representing depth.") Work began on the Hurd in 1990, just before Linux was started, with the goal of it becoming the centerpiece of the GNU operating system."

"The Hurd's attempt at modularity goes beyond using a microkernel with clean interfaces. It also organizes the extra kernel OS facilities into modules called "servers" (or daemons; these are the "UNIX-replacing daemons" referred to in the Hurd acronym). Each provides a fixed set of services to user applications. They communicate with each other, the kernel, and user processes by a set of clean interfaces."

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