Terminate and Stay Resident
Encyclopedia
Terminate and Stay Resident (TSR) is a computer system call
in DOS
computer operating systems that returns control to the system as if the program has quit, but keeps the program in memory. Many software vendors use the call to create the appearance of multitasking
, by transferring control back to the terminated program on automatic or externally-generated events, such as pressing a certain key on the keyboard
. Some TSR programs are effectively device driver
s for hardware
not directly supported by the operating system, while others are small utility programs offering frequently-used functionality such as scheduling and contact directories.
operating system, only one program can be running at any given time, and when it wants to stop running, it relinquishes the control to DOS
's shell program, COMMAND.COM
, using the system call
INT 21H/4CH. The memory and system resources used by the program are marked as unused, effectively making it impossible to summon parts of it again without reloading it from scratch. However, if a program ends with the system call INT 27H or INT 21H/31H, the operating system does not reuse a certain specified part of the program's memory.
handlers pointing into itself, so that it can be called again. Installing a hardware interrupt vector allows such a program to react to hardware events. Installing a software interrupt vector allows it to be called by the currently running program. Installing a timer interrupt handler allows a TSR to run periodically (see ISA
and programmable interval timer
, especially the section "IBM PC compatible").
The typical method of utilizing an interrupt vector involves reading its present value (the address), storing it within the memory space of the TSR, and installing a pointer to its own code. The stored address is called after the TSR has received the interrupt and has finished its processing, in effect forming a singly linked list of interrupt handler
s, also called interrupt service routines, or ISRs. This procedure of installing ISRs is called chaining or hooking
an interrupt or an interrupt vector.
By chaining the interrupt vectors TSR programs could take complete control of the computer. A TSR could have one of two behaviors:
The 'terminate and stay resident' method was used by most MS-DOS viruses
which could either take control of the PC or stay in the background. Viruses would react to disk I/O or execution events by infecting executable (.EXE or .COM) files when they were run and data files when they were opened.
Parts of DOS itself, especially in DOS versions 5.0 and later, used this same technique to perform useful functions, such as the DOSKEY
command-line editor and various other installable utilities which were installed by running them at the command line (manually or from AUTOEXEC.BAT) rather than as drivers through CONFIG.SYS.
A TSR program can be loaded at any time; sometimes, they are loaded immediately after the operating system's boot, by being explicitly loaded in the AUTOEXEC.BAT
batch program, or alternatively at the user's request (for example, Borland
's SideKick
and Turbo Debugger or Quicken's QuickPay). These programs will, as 'TSR' implies, stay resident in memory while other programs are executing. Most of them do not have an option for unloading themselves from memory, so calling TSR means the program will remain in memory until a reboot. However unloading is possible externally, using utilities like the MARK.EXE/RELEASE.EXE combo by TurboPower Software or soft reboot TSRs which will catch a specific key combination and release all TSRs loaded after them. As the chain of ISRs is singly linked, there is no provision for discovering the previous handler's address, or to inform its predecessor that it needs to update its "next address to which to jump" not to point to the TSR which desires to remove itself. This gave rise to TSR cooperation frameworks such as TesSeRact and AMIS.
in a controlled manner. It is modeled after IBM's Interrupt Sharing Protocol, originally invented for sharing hardware interrupts of an x86 processor.
AMIS services are available via Int 2Dh http://www.ctyme.com/intr/int-2d.htm (see Ralf Brown's Interrupt List
).
The proposal never gained a widespread traction among programmers in its days. It existed alongside several other competing specifications of varying sophistication http://www.ctyme.com/intr/cat-042.htm.
's limitations, TSR programs had a reputation as troublemakers. Many of the programs effectively hijacked the operating system in varying, documented or undocumented ways, often causing systems to crash on their activation or deactivation when used with particular application programs or other TSRs. As explained above, some viruses
were coded as TSRs, and were deliberately troublesome. Additionally, all program code in DOS
systems, even those with large amounts of physical RAM, had to be loaded into the first 640 KB
of RAM (the conventional memory
). TSRs were no exception, and took chunks from that 640 KB that were thus unavailable to application programs. This meant that writing a TSR was a challenge of achieving the smallest possible size for it, and checking it for compatibility with a lot of software products from different vendors—often a very frustrating task.
In the late 1980s and early 1990s, many video games on the PC platform pushed up against this limit and left less and less space for TSRs—even essential ones like CD-ROM
drivers—and arranging things so that there was enough free RAM to run the games, while keeping the necessary TSRs present, became a black art. Many gamers had several boot disk
s with different configurations for different games. In latter versions of MS-DOS "boot menu" scripts allowed various configurations to be selectable via a single "boot disk". In the mid- to later 1990s, while many games were still written for DOS, the 640K limit was eventually overcome by putting parts of the game's data and/or program code above the first 1 MB of memory and using the code below 640K to access the extended memory (using extra-DOSian methods), with code being swapped into the lowest 1 MB of RAM as overlays
. Because programming with many overlays is a challenge in and of itself, once the program was too big to fit entirely into about 512 KB, use of extended memory was almost always done using a third-party DOS extender implementing VCPI or DPMI, because it becomes much easier and faster to access memory above the 1 MB boundary, and possible to run code in that area, when the x86 processor is switched from real mode
to protected mode
. However, since DOS and all DOS programs run in real mode (VCPI or DPMI makes a protected mode program look like a real mode program to DOS and the rest of the system by switching back and forth between the two modes), DOS TSRs and device drivers also run in real mode, and so any time one gets control, the "DOS extender
" has to switch back to real mode until it relinquishes control, incurring a time penalty.
boards and especially of Intel 80386
processors in the second half of the 1980s, it became possible to use memory above 640 KB to load TSRs. This required complex software solutions, named expanded memory managers, but provided some additional breathing room for several years. Famous memory managers are QRAM and QEMM
by Quarterdeck
, 386Max
by Qualitas, CEMM
by Compaq
and later EMM386
by Microsoft
. The memory areas usable for loading TSRs above 640 KB are called "upper memory blocks
" (UMBs) and loading programs into them is called loading high. Later, memory managers started including programs which would try to automatically determine how to best allocate TSRs between low and high memory (Quarterdeck's Optimize or Microsoft's MemMaker) in order to try to maximize the available space in the first 640 KB.
s (a notable early example was Doom) which bypassed the 640 KB barrier, many of the issues relating to TSRs disappeared, and with the widespread adoption of Microsoft Windows
and especially Windows 95
(followed by Windows 98
) — which rendered most TSRs unnecessary and some TSRs incompatible — the TSR faded into the obsolescence, though Win16 applications could do TSR-like tricks such as patching the IDT
because real-mode Windows allowed it. The TSR has now almost disappeared completely, as multitasking operating systems such as Windows XP
, Windows Vista
, Mac OS X
, and Linux
provide the facilities for multiple programs and device drivers to run simultaneously without the need for special programming tricks, and the modern notion of protected memory makes the kernel and its modules exclusively responsible for modifying an interrupt
table.
System call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
in DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
computer operating systems that returns control to the system as if the program has quit, but keeps the program in memory. Many software vendors use the call to create the appearance of multitasking
Computer multitasking
In computing, multitasking is a method where multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for...
, by transferring control back to the terminated program on automatic or externally-generated events, such as pressing a certain key on the keyboard
Keyboard (computing)
In computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches...
. Some TSR programs are effectively device driver
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
s for hardware
Computer hardware
Personal computer hardware are component devices which are typically installed into or peripheral to a computer case to create a personal computer upon which system software is installed including a firmware interface such as a BIOS and an operating system which supports application software that...
not directly supported by the operating system, while others are small utility programs offering frequently-used functionality such as scheduling and contact directories.
Brief history
Normally in the MS-DOSMS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
operating system, only one program can be running at any given time, and when it wants to stop running, it relinquishes the control to DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
's shell program, COMMAND.COM
COMMAND.COM
COMMAND.COM is the filename of the default operating system shell for DOS operating systems and the default command line interpreter on Windows 95, Windows 98 and Windows Me...
, using the system call
System call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
INT 21H/4CH. The memory and system resources used by the program are marked as unused, effectively making it impossible to summon parts of it again without reloading it from scratch. However, if a program ends with the system call INT 27H or INT 21H/31H, the operating system does not reuse a certain specified part of the program's memory.
Using TSR
The original call, INT 27H, is called 'terminate but stay resident', hence the name 'TSR'. Using this call, a program can make up to 64KB of its memory resident. MS-DOS version 2.0 introduced an improved call, INT 21H/function 31H ('Keep Process'), which removed this limitation and let the program return an exit code. Before making this call, the program can install one or several interruptInterrupt
In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....
handlers pointing into itself, so that it can be called again. Installing a hardware interrupt vector allows such a program to react to hardware events. Installing a software interrupt vector allows it to be called by the currently running program. Installing a timer interrupt handler allows a TSR to run periodically (see ISA
Industry Standard Architecture
Industry Standard Architecture is a computer bus standard for IBM PC compatible computers introduced with the IBM Personal Computer to support its Intel 8088 microprocessor's 8-bit external data bus and extended to 16 bits for the IBM Personal Computer/AT's Intel 80286 processor...
and programmable interval timer
Programmable Interval Timer
In computing and in embedded systems, a programmable interval timer is a counter which triggers an interrupt when it reaches the programmed count.- Common features :...
, especially the section "IBM PC compatible").
The typical method of utilizing an interrupt vector involves reading its present value (the address), storing it within the memory space of the TSR, and installing a pointer to its own code. The stored address is called after the TSR has received the interrupt and has finished its processing, in effect forming a singly linked list of interrupt handler
Interrupt handler
An interrupt handler, also known as an interrupt service routine , is a callback subroutine in microcontroller firmware, operating system or device driver whose execution is triggered by the reception of an interrupt...
s, also called interrupt service routines, or ISRs. This procedure of installing ISRs is called chaining or hooking
Hooking
In computer programming, the term hooking covers a range of techniques used to alter or augment the behavior of an operating system, of applications, or of other software components by intercepting function calls or messages or events passed between software components...
an interrupt or an interrupt vector.
By chaining the interrupt vectors TSR programs could take complete control of the computer. A TSR could have one of two behaviors:
- Take complete control of an interrupt by not calling other TSRs that had previously altered the same interrupt vector.
- Cascade with other TSRs by calling the old interrupt vector. This could be done before or after they executed their actual code. This way TSRs could form a chain of programs where each one calls the next one.
The 'terminate and stay resident' method was used by most MS-DOS viruses
Computer virus
A computer virus is a computer program that can replicate itself and spread from one computer to another. The term "virus" is also commonly but erroneously used to refer to other types of malware, including but not limited to adware and spyware programs that do not have the reproductive ability...
which could either take control of the PC or stay in the background. Viruses would react to disk I/O or execution events by infecting executable (.EXE or .COM) files when they were run and data files when they were opened.
Parts of DOS itself, especially in DOS versions 5.0 and later, used this same technique to perform useful functions, such as the DOSKEY
DOSKey
DOSKey is a utility for MS-DOS and Microsoft Windows that adds command history, macro functionality, and improved editing features to the command line interpreters COMMAND.COM and cmd.exe...
command-line editor and various other installable utilities which were installed by running them at the command line (manually or from AUTOEXEC.BAT) rather than as drivers through CONFIG.SYS.
A TSR program can be loaded at any time; sometimes, they are loaded immediately after the operating system's boot, by being explicitly loaded in the AUTOEXEC.BAT
AUTOEXEC.BAT
AUTOEXEC.BAT is a system file found originally on DOS-type operating systems. It is a plain-text batch file that is located in the root directory of the boot device...
batch program, or alternatively at the user's request (for example, Borland
Borland
Borland Software Corporation is a software company first headquartered in Scotts Valley, California, Cupertino, California and finally Austin, Texas. It is now a Micro Focus subsidiary. It was founded in 1983 by Niels Jensen, Ole Henriksen, Mogens Glad and Philippe Kahn.-The 1980s:...
's SideKick
SideKick
SideKick was an early Personal Information Manager software application by Borland launched in 1983 under Philippe Kahn's leadership. It was notable for being a Terminate and Stay Resident program, which enabled it to load into memory then return the computer to the DOS command prompt, allowing...
and Turbo Debugger or Quicken's QuickPay). These programs will, as 'TSR' implies, stay resident in memory while other programs are executing. Most of them do not have an option for unloading themselves from memory, so calling TSR means the program will remain in memory until a reboot. However unloading is possible externally, using utilities like the MARK.EXE/RELEASE.EXE combo by TurboPower Software or soft reboot TSRs which will catch a specific key combination and release all TSRs loaded after them. As the chain of ISRs is singly linked, there is no provision for discovering the previous handler's address, or to inform its predecessor that it needs to update its "next address to which to jump" not to point to the TSR which desires to remove itself. This gave rise to TSR cooperation frameworks such as TesSeRact and AMIS.
Interrupts sharing
To manage problems with many TSR programs sharing the same interrupt, a method called Alternate Multiplex Interrupt Specification (AMIS) was proposed by Ralf Brown as an improvement over previously used services offered via INT 2Fh. AMIS provides ways to share software interruptsINT (x86 instruction)
INT is an assembly language instruction for x86 processors that generates a software interrupt. It takes the interrupt number formatted as a byte value.When written in assembly language, the instruction is written like this:...
in a controlled manner. It is modeled after IBM's Interrupt Sharing Protocol, originally invented for sharing hardware interrupts of an x86 processor.
AMIS services are available via Int 2Dh http://www.ctyme.com/intr/int-2d.htm (see Ralf Brown's Interrupt List
Ralf Brown's Interrupt List
Ralf Brown's Interrupt List or RBIL is a comprehensive list of interrupts, calls, hooks, interfaces, data structures, memory and port addresses, and processor opcodes for x86 for machines from the very start of the PC era in 1981 up into the year 2000, most of it still applying to PCs today as well...
).
The proposal never gained a widespread traction among programmers in its days. It existed alongside several other competing specifications of varying sophistication http://www.ctyme.com/intr/cat-042.htm.
Faults
While very useful, or even essential to overcome DOSDOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
's limitations, TSR programs had a reputation as troublemakers. Many of the programs effectively hijacked the operating system in varying, documented or undocumented ways, often causing systems to crash on their activation or deactivation when used with particular application programs or other TSRs. As explained above, some viruses
Computer virus
A computer virus is a computer program that can replicate itself and spread from one computer to another. The term "virus" is also commonly but erroneously used to refer to other types of malware, including but not limited to adware and spyware programs that do not have the reproductive ability...
were coded as TSRs, and were deliberately troublesome. Additionally, all program code in DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
systems, even those with large amounts of physical RAM, had to be loaded into the first 640 KB
Kilobyte
The kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
of RAM (the conventional memory
Conventional memory
In DOS memory management, conventional memory, also called base memory, is the first 640 kilobytes of the memory on IBM PC or compatible systems. It is the read-write memory usable by the operating system and application programs...
). TSRs were no exception, and took chunks from that 640 KB that were thus unavailable to application programs. This meant that writing a TSR was a challenge of achieving the smallest possible size for it, and checking it for compatibility with a lot of software products from different vendors—often a very frustrating task.
In the late 1980s and early 1990s, many video games on the PC platform pushed up against this limit and left less and less space for TSRs—even essential ones like CD-ROM
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....
drivers—and arranging things so that there was enough free RAM to run the games, while keeping the necessary TSRs present, became a black art. Many gamers had several boot disk
Boot disk
A boot disk is a removable digital data storage medium from which a computer can load and run an operating system or utility program. The computer must have a built-in program which will load and execute a program from a boot disk meeting certain standards.Boot disks are used for:* Operating...
s with different configurations for different games. In latter versions of MS-DOS "boot menu" scripts allowed various configurations to be selectable via a single "boot disk". In the mid- to later 1990s, while many games were still written for DOS, the 640K limit was eventually overcome by putting parts of the game's data and/or program code above the first 1 MB of memory and using the code below 640K to access the extended memory (using extra-DOSian methods), with code being swapped into the lowest 1 MB of RAM as overlays
Overlay (programming)
In a general computing sense, overlaying means "replacement of a block of stored instructions or data with another" Overlaying is a programming method that allows programs to be larger than the computer's main memory...
. Because programming with many overlays is a challenge in and of itself, once the program was too big to fit entirely into about 512 KB, use of extended memory was almost always done using a third-party DOS extender implementing VCPI or DPMI, because it becomes much easier and faster to access memory above the 1 MB boundary, and possible to run code in that area, when the x86 processor is switched from real mode
Real mode
Real mode, also called real address mode, is an operating mode of 80286 and later x86-compatible CPUs. Real mode is characterized by a 20 bit segmented memory address space and unlimited direct software access to all memory, I/O addresses and peripheral hardware...
to protected mode
Protected mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units...
. However, since DOS and all DOS programs run in real mode (VCPI or DPMI makes a protected mode program look like a real mode program to DOS and the rest of the system by switching back and forth between the two modes), DOS TSRs and device drivers also run in real mode, and so any time one gets control, the "DOS extender
DOS extender
A DOS extender is a computer software program which enables software to run under a protected mode environment even though the host operating system is only capable of operating in real mode....
" has to switch back to real mode until it relinquishes control, incurring a time penalty.
Return
With the arrival of expanded memoryExpanded memory
In DOS memory management, expanded memory is a system of bank switching introduced April 24, 1985 that provided additional memory to DOS programs beyond the limit of conventional memory. Expanded memory uses parts of the address space normally dedicated to communication with peripherals for program...
boards and especially of Intel 80386
Intel 80386
The Intel 80386, also known as the i386, or just 386, was a 32-bit microprocessor introduced by Intel in 1985. The first versions had 275,000 transistors and were used as the central processing unit of many workstations and high-end personal computers of the time...
processors in the second half of the 1980s, it became possible to use memory above 640 KB to load TSRs. This required complex software solutions, named expanded memory managers, but provided some additional breathing room for several years. Famous memory managers are QRAM and QEMM
QEMM
Quarterdeck Expanded Memory Manager , was a memory manager produced by Quarterdeck Office Systems in the late 1980s through late 1990s. It was the most popular memory manager for the MS-DOS and other DOS operating systems.-QEMM product ranges:QRAM: A memory manager for 286 or higher CPU. It...
by Quarterdeck
Quarterdeck Office Systems
Quarterdeck Office Systems, later Quarterdeck Corporation , was an American computer software company. It was founded by Therese Myers and Gary Pope in 1981and incorporated in 1982...
, 386Max
386MAX
386MAX was a computer memory manager for DOS-based personal computers. It competed with Quarterdeck's QEMM memory manager. It was manufactured by Qualitas....
by Qualitas, CEMM
CEMM
CEMM, for Compaq Expanded Memory Manager was the first so-called PC "memory manager" for Intel 80386 CPUs, able to transform "XMS" extended memory into "EMS" expanded memory by using the virtual memory features and the virtual 8086 mode of the CPU....
by Compaq
Compaq
Compaq Computer Corporation is a personal computer company founded in 1982. Once the largest supplier of personal computing systems in the world, Compaq existed as an independent corporation until 2002, when it was acquired for US$25 billion by Hewlett-Packard....
and later EMM386
EMM386
The name EMM386 was used for the expanded memory managers of both Microsoft's MS-DOS and Digital Research's DR-DOS, which created expanded memory using extended memory on Intel 80386 CPUs. There also is an EMM386.EXE available in FreeDOS....
by Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
. The memory areas usable for loading TSRs above 640 KB are called "upper memory blocks
Upper Memory Area
In DOS memory management, the upper memory area refers to memory between the addresses of 640 KB and 1024 KB in an IBM PC or compatible. IBM reserved the uppermost 384 KB of the 8088 CPU's 1024 KB address space for ROM, RAM on peripherals, and memory-mapped input/output...
" (UMBs) and loading programs into them is called loading high. Later, memory managers started including programs which would try to automatically determine how to best allocate TSRs between low and high memory (Quarterdeck's Optimize or Microsoft's MemMaker) in order to try to maximize the available space in the first 640 KB.
Decline
With the development of games using DOS extenderDOS extender
A DOS extender is a computer software program which enables software to run under a protected mode environment even though the host operating system is only capable of operating in real mode....
s (a notable early example was Doom) which bypassed the 640 KB barrier, many of the issues relating to TSRs disappeared, and with the widespread adoption of Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
and especially Windows 95
Windows 95
Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products...
(followed by Windows 98
Windows 98
Windows 98 is a graphical operating system by Microsoft. It is the second major release in the Windows 9x line of operating systems. It was released to manufacturing on 15 May 1998 and to retail on 25 June 1998. Windows 98 is the successor to Windows 95. Like its predecessor, it is a hybrid...
) — which rendered most TSRs unnecessary and some TSRs incompatible — the TSR faded into the obsolescence, though Win16 applications could do TSR-like tricks such as patching the IDT
Interrupt descriptor table
The Interrupt Descriptor Table is a data structure used by the x86 architecture to implement an interrupt vector table. The IDT is used by the processor to determine the correct response to interrupts and exceptions....
because real-mode Windows allowed it. The TSR has now almost disappeared completely, as multitasking operating systems such as Windows XP
Windows XP
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
, Windows Vista
Windows Vista
Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
, Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
, and Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
provide the facilities for multiple programs and device drivers to run simultaneously without the need for special programming tricks, and the modern notion of protected memory makes the kernel and its modules exclusively responsible for modifying an interrupt
Interrupt
In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....
table.
See also
- DaemonDaemon (computer software)In Unix and other multitasking computer operating systems, a daemon is a computer program that runs as a background process, rather than being under the direct control of an interactive user...
(Unix) - Windows serviceWindows ServiceOn Microsoft Windows operating systems, a Windows service is a long-running executable that performs specific functions and which is designed not to require user intervention. Windows services can be configured to start when the operating system is booted and run in the background as long as...
- Computer multitaskingComputer multitaskingIn computing, multitasking is a method where multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for...
- MacOS INITExtension (Mac OS)On the Apple Macintosh operating system prior to Mac OS X, extensions were small pieces of code that extended the system's functionality. They were run initially at start-up time, and operated by a variety of mechanisms, including trap patching and other code modifying techniques. Initially an...
- DOS Protected Mode ServicesDOS Protected Mode ServicesDOS Protected Mode Services is a set of extended DOS memory management services to allow DPMS-enabled DOS drivers to load and execute in extended memory and protected mode....
(DPMS)
External links
- An early TSR
- comp.os.msdos.programmer FAQ - How can I write a TSR (Terminate-and-Stay-Resident) utility?
- The Alternate Multiplex Interrupt Specification (AMIS), v.3.5
- AMISLIB - a function library to write self-highloading, removable TSRs in assembler
- A to Z of C; a free book on DOS programming in C; Chapter 27 -
- IBM's Interrupt-Sharing Protocol, zip archive, 6.5 KB (SimtelSimtelSimtel is an Internet-based archive of shareware for various operating systems, particularly Microsoft Windows and MS-DOS. The Simtel archive has been available on the public Internet since 1993, when its older ARPANET host was shut down....
)