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A monolithic kernel is an
A monolithic kernel is an operating system
An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ...
architecture
Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and construction, constructi ...
with the entire operating system running in kernel space
A modern computer operating system usually uses virtual memory to provide separate address spaces or regions of a single address space, called user space and kernel space. This separation primarily provides memory protection and hardware prote ...
. The monolithic model differs from other architectures such as the microkernel
In computer science, a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, ...
in that it alone defines a high-level virtual interface over computer hardware
Computer hardware includes the physical parts of a computer, such as the central processing unit (CPU), random-access memory (RAM), motherboard, computer data storage, graphics card, sound card, and computer case. It includes external devices ...
. A set of primitives or system call
In computing, a system call (syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, accessing a hard disk drive ...
s implement all operating system services such as process management, concurrency, and memory management
Memory management (also dynamic memory management, dynamic storage allocation, or dynamic memory allocation) is a form of Resource management (computing), resource management applied to computer memory. The essential requirement of memory manag ...
.
Device drivers can be added to the kernel as loadable kernel module
A loadable kernel module (LKM) is an executable library that extends the capabilities of a running kernel, or so-called ''base kernel'', of an operating system. LKMs are typically used to add support for new hardware (as device drivers) and/or ...
s.
Examples
*MostBSD
The Berkeley Software Distribution (BSD), also known as Berkeley Unix or BSD Unix, is a discontinued Unix operating system developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berkeley, beginni ...
kernels
**FreeBSD
FreeBSD is a free-software Unix-like operating system descended from the Berkeley Software Distribution (BSD). The first version was released in 1993 developed from 386BSD, one of the first fully functional and free Unix clones on affordable ...
**OpenBSD
OpenBSD is a security-focused operating system, security-focused, free software, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by fork (software development), forking NetBSD ...
**NetBSD
NetBSD is a free and open-source Unix-like operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was fork (software development), forked. It continues to ...
*Linux kernel
The Linux kernel is a Free and open-source software, free and open source Unix-like kernel (operating system), kernel that is used in many computer systems worldwide. The kernel was created by Linus Torvalds in 1991 and was soon adopted as the k ...
** Android
*Other Unix
Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...
/Unix-like
A Unix-like (sometimes referred to as UN*X, *nix or *NIX) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Uni ...
kernels
**AIX
Aix or AIX may refer to:
Computing
* AIX, a line of IBM computer operating systems
*Alternate index, for an IBM Virtual Storage Access Method key-sequenced data set
* Athens Internet Exchange, a European Internet exchange point
Places Belg ...
**Oracle Solaris
Oracle Solaris is a proprietary Unix operating system offered by Oracle for SPARC and x86-64 based workstations and servers. Originally developed by Sun Microsystems as Solaris, it superseded the company's earlier SunOS in 1993 and became kno ...
*MS-DOS
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few op ...
**Windows 9x
Windows 9x is a generic term referring to a line of discontinued Microsoft Windows operating systems released from 1995 to 2000 and supported until 2006, which were based on the kernel introduced in Windows 95 and modified in succeeding version ...
*OpenVMS
OpenVMS, often referred to as just VMS, is a multi-user, multiprocessing and virtual memory-based operating system. It is designed to support time-sharing, batch processing, transaction processing and workstation applications. Customers using Op ...
*Palm OS
Palm OS (also known as Garnet OS) is a discontinued mobile operating system initially developed by Palm, Inc., for personal digital assistants (PDAs) in 1996. Palm OS was designed for ease of use with a touchscreen-based graphical user interface. ...
(version ≤ 5.0)
Loadable modules
Modular operating systems such asOS-9
OS-9 is a family of real-time, process-based, multitasking, multi-user operating systems, developed in the 1980s, originally by Microware Systems Corporation for the Motorola 6809 microprocessor. It was purchased by Radisys Corp in 2001, a ...
and most modern monolithic-kernel operating systems such as OpenVMS
OpenVMS, often referred to as just VMS, is a multi-user, multiprocessing and virtual memory-based operating system. It is designed to support time-sharing, batch processing, transaction processing and workstation applications. Customers using Op ...
, Linux
Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...
, FreeBSD
FreeBSD is a free-software Unix-like operating system descended from the Berkeley Software Distribution (BSD). The first version was released in 1993 developed from 386BSD, one of the first fully functional and free Unix clones on affordable ...
, NetBSD
NetBSD is a free and open-source Unix-like operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was fork (software development), forked. It continues to ...
, DragonFly BSD
DragonFly BSD is a free and open-source Unix-like operating system forked from FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and FreeBSD developer between 1994 and 2003, began working on DragonFly BSD in ...
, Solaris
Solaris is the Latin word for sun.
It may refer to:
Arts and entertainment Literature, television and film
* ''Solaris'' (novel), a 1961 science fiction novel by Stanisław Lem
** ''Solaris'' (1968 film), directed by Boris Nirenburg
** ''Sol ...
, and AIX
Aix or AIX may refer to:
Computing
* AIX, a line of IBM computer operating systems
*Alternate index, for an IBM Virtual Storage Access Method key-sequenced data set
* Athens Internet Exchange, a European Internet exchange point
Places Belg ...
can dynamically load (and unload) executable kernel modules at runtime.
This modularity of the operating system is at the binary (image) level and not at the architecture level. Modular monolithic operating systems are not to be confused with the architectural level of modularity inherent in server-client operating systems (and its derivatives sometimes marketed as hybrid kernel
A hybrid kernel is an operating system Kernel (operating system), kernel whose architecture attempts to combine aspects and benefits of microkernel and monolithic kernel architectures used in operating systems.
Overview
The traditional kernel cat ...
) which use microkernels and servers (not to be mistaken for modules or daemons).
Practically speaking, dynamically loading modules is simply a more flexible way of handling the operating system image at runtime—as opposed to rebooting with a different operating system image. The modules allow easy extension of the operating systems' capabilities as required. Dynamically loadable modules incur a small overhead when compared to building the module into the operating system image.
However, in some cases, loading modules dynamically (as-needed) helps to keep the amount of code running in kernel space
A modern computer operating system usually uses virtual memory to provide separate address spaces or regions of a single address space, called user space and kernel space. This separation primarily provides memory protection and hardware prote ...
to a minimum; for example, to minimize operating system footprint for embedded devices or those with limited hardware resources. Namely, an unloaded module need not be stored in scarce random access memory
Random-access memory (RAM; ) is a form of electronic computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written ...
.
See also
*Exokernel
Exokernel is an operating system kernel developed by the MIT Parallel and Distributed Operating Systems group, and also a class of similar operating systems.
Operating systems generally present hardware resources to applications through high-le ...
*Hybrid kernel
A hybrid kernel is an operating system Kernel (operating system), kernel whose architecture attempts to combine aspects and benefits of microkernel and monolithic kernel architectures used in operating systems.
Overview
The traditional kernel cat ...
*Kernel (operating system)
A kernel is a computer program at the core of a computer's operating system that always has complete control over everything in the system. The kernel is also responsible for preventing and mitigating conflicts between different processes. It is ...
*Microkernel
In computer science, a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, ...
*Nanokernel
In computer science, a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, ...
*Tanenbaum–Torvalds debate
Starting in 1992, Andrew S. Tanenbaum and Linus Torvalds had a written debate over the Internet regarding the Linux kernel and kernel architecture in general. Tanenbaum, the creator of Minix, began the debate in Usenet discussion group , argu ...
References
{{Operating system Monolithic kernels