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Encyclopedia > Terminate and Stay Resident

Terminate and Stay Resident (TSR) is a system call in DOS operating systems that returned control to the system as if the program had quit, but kept 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. Some TSR programs are effectively device drivers for hardware not directly supported by MS-DOS, whilst others are small utility programs offering frequently-used functionality such as scheduling and contact directories. In computing, a system call is the mechanism used by an application program to request service from the operating system. ... Instructions on how to use the directory command. ... In computing, multitasking is a method by which 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... Windows XP loading drivers during a Safe Mode bootup A device driver, or a software driver is a specific type of computer software, typically developed to allow interaction with hardware devices. ... Computer hardware is the physical part of a computer, including the digital circuitry, as distinguished from the computer software that executes within the hardware. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ...

Contents

Brief history

Normally, in the DOS operating system, only one program can be running at any given time, and when it wants to stop running, it relinquished 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. However, if a program ended with the system call INT 21H/31H, the operating system does not reuse a certain, specified, part of the program's memory. Instructions on how to use the directory command. ... Instructions on how to use the directory command. ... COMMAND.COM is the name for the default operating system shell (or command line interpreter) for DOS and 16/32bits versions of Windows (95/98/98 SE/Me). ... In computing, a system call is the mechanism used by an application program to request service from the operating system. ...


Using TSR

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By chaining the interrupt vectors TSR programs could take complete control of the computer. A TSR could have one of two behaviours:

  • 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 which could either take control of the PC or stay at the background. Viruses would react on disk I/O or execution events by infecting executable (.EXE or .COM) files when they were run and data files when they were opened. A computer virus is a computer program that can copy itself and infect a computer without permission or knowledge of the user. ...


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 either the AUTOEXEC.BAT or CONFIG.SYS scripts, or alternatively at the user's request (for example, Borland's SideKick and Turbo Debugger). These programs will, as 'TSR' implies, stay resident in memory whilst 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. AUTOEXEC.BAT is the name of a system file found originally on the MS-DOS operating system. ... CONFIG.SYS is the primary configuration file for the MS-DOS and OS/2 operating systems. ... Borland Software Corporation is a software company headquartered in California. ... Don Quixote and Sancho Panza unsuccessfully confront windmills. ...


Faults

Whilst very useful, or even essential to overcome DOS's limitations, TSR programs had a reputation as troublemakers. 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. Some viruses were coded as TSRs, and were deliberately troublesome. Additionally, all program code in MS-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. Instructions on how to use the directory command. ... A computer virus is a computer program that can copy itself and infect a computer without permission or knowledge of the user. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. ... A kilobyte (derived from the SI prefix kilo-, meaning 1000) is a unit of information or computer storage equal to the decimal 1024 bytes (2 to the 10th power, or 1,024 bytes based in the binary system). ... Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...


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 disks with different configurations for different games. Namcos Pac-Man was a hit, and became a universal phenomenon. ... The CD-ROM (an abbreviation for Compact Disc Read-Only Memory (ROM)) is a non-volatile optical data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. ... Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. ... A boot disk is a removable media, normally read-only, that can boot an operating system or utility. ...


Return

With the arrival of expanded memory 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 is 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 and maximize the available space in the first 640 KB. Expanded Memory was a trick invented around 1984 that provided more memory to byte-hungry, business-oriented MS-DOS programs. ... The Intel 80386 is a microprocessor which was used as the central processing unit (CPU) of many personal computers from 1986 until 1994 and later. ... The 1980s refers to the years from 1980 to 1989. ... QEMM, the Quarterdeck Expanded Memory Manager by Quarterdeck, was a popular memory manager for the DOS operating system. ... QEMM (sometimes pronounced IPA: , though not by those who developed it), the Quarterdeck Expanded Memory Manager by Quarterdeck, was the most popular third party memory manager for the DOS operating system. ... Quarterdeck Office Systems, later Quarterdeck Corporation, was an American computer software company. ... 386MAX (written as 386MAX, pronounced 386-to-the-max) was a computer memory manager for DOS-based personal computers. ... CEMM, for Compaq Expanded Memory Manager was probably the first so-called PC memory manager for Intel 80386 CPUs, able to transform extended memory into EMS expanded memory by using the virtual memory features and the virtual 8086 mode of the CPU. It was present in Compaq DOS 3. ... Compaq Computer Corporation is an American personal computer company founded in 1982, and now a brand name of Hewlett-Packard. ... EMM386 was Microsofts expanded memory manager, which created expanded memory using extended memory on Intel 80386 CPUs. ... Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... The Upper Memory Area (UMA) is a feature of the design of IBM PC-compatible x86 computers. ... A partial list of the most common commands for Microsofts MS-DOS operating system follows. ...


Decay

With the development of games using DOS extenders (a notable early example was Wolfenstein 3D) 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 - which rendered TSRs unnecessary and some TSRs incompatible - the TSR faded into the background, though Win16 applications could do TSR-like tricks such as patching the IDT because real-mode Windows allowed it. Windows Me discontinued support for all TSRs. The TSR has now almost disappeared completely, as multitasking operating systems such as Windows XP, Mac OS, 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. DOS extender is the name invented in the 1980s for a technology to allow programs started from MS-DOS, which ran in Real mode, to actually run in protected mode. ... Wolfenstein 3D (commonly abbreviated to Wolf 3D) is the computer game that started the first person shooter genre on the PC. It was created by id Software and published by Apogee Software on May 5, 1992. ... Microsoft Windows is the name of several families of proprietary software operating systems by Microsoft. ... Windows Millennium Edition, or Windows Me (IPA pronunciation: [miː], [ɛm iː]), is a hybrid 16-bit/32-bit graphical operating system released on September 14, 2000 by Microsoft. ... Windows XP is a line of proprietary operating systems developed by Microsoft for use on general-purpose computer systems, including home and business desktops, notebook computers, and media centers. ... This article or section does not adequately cite its references or sources. ... It has been suggested that Criticism of Linux be merged into this article or section. ... Memory protection is a system that prevents one process from corrupting the memory of another process running on the same computer at the same time. ... A kernel connects the application software to the hardware of a computer. ... In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ...


See also

THIS IS RUBISH In Unix and other computer multitasking operating systems, a daemon is a computer program that runs in the background, rather than under the direct control of a user; they are usually instantiated as processes. ... A Windows service is an application that starts when Windows is booted and runs in the background as long as Windows is running. ...


  Results from FactBites:
 
TSR - Terminate and Stay Resident (719 words)
Terminate and Stay Resident Refers to a program that remains in memory when the user exits it in order that it be immediately available at the press of a hotkey.
TSR viruses usually design a method by which they are put into memory when the computer is booted, and then run until the computer is shut down.
Terminate and Stay Resident, a term used for programs that run and then stay in memory for instant use later, a Mouse driver or a Network driver are examples
  More results at FactBites »

 
 

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