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- In computing, a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point. This allows multiple processes to share a single central processing unit (CPU), and is an essential feature of a multitasking operating system. The precise meaning of the phrase 'context switch' varies.
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- The 17.5 release of Advanced Installer is a free update for customers with a valid Maintenance Plan through September 22nd, 2020.You can check your Maintenance Plan expiration date in the Customer Information section.
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Windows Installer can install a package on a computer into two installation contexts: per-machine and per-user. A per-machine installation of the package is required to enable all users of the computer to access and use the application. Because a per-machine installation makes changes to the system that affect all users, standard users having limited privileges may be prevented from installing a package into the per-machine context without first obtaining permission.
You can specify installation context by authoring the package for per-user or per-machine installation and using the ALLUSERS and MSIINSTALLPERUSER properties. Based on these properties, Windows Installer automatically redirects the values of folder properties and registrations to locations for the per-user or per-machine context.
Note
The MSIINSTALLPERUSER property, available beginning with Windows Installer 5.0 and Windows Server 2008 R2 and Windows 7, can facilitate the development of a single package capable of being installed in either the per-machine or per-user context. For information about developing a dual-purpose package that gives the user the capability to choose the installation context at installation time, see Single Package Authoring. Windows Installer ignores the MSIINSTALLPERUSER property if the value of ALLUSERS is not 2. Windows Installer always resets the value of ALLUSERS to 1 when it installs in the per-machine context and resets the value of ALLUSERS to an empty string (') when it installs in the per-user context.
Shortcut Redirection
The following table compares the locations of shortcuts for per-machine and per-user installation contexts.
Per-Machine Installation Context (ALLUSERS=1) | Per-User Installation Context (ALLUSERS=') |
---|---|
Applications appear under Add/Remove Programs on Control Panel for all users of the computer. | Applications appear only under Add/Remove Programs on Control Panel for users that have installed the applications. |
Shortcuts are installed to the All Users profile. | Shortcuts are installed only to that user's profile. |
Icons and transforms are stored in %WINDOWS%Installer{ProductCode}. | Icons and transforms are stored in %USERPROFILE%Application DataMicrosoftInstaller{ProductCode GUID} |
Registry Redirection
The following table compares the locations of registry entries for the per-machine and per-user installation contexts.
Per-Machine Installation Context (ALLUSERS=1) | Per-User Installation Context (ALLUSERS=') |
---|---|
Windows Installer writes or removes registry values entered in the Registry table and RemoveRegistry table, with the value -1 in the Root column, under HKEY_LOCAL_MACHINE. | Windows Installer writes or removes registry values entered in the Registry table and RemoveRegistry table, with the value -1 in the Root column, under HKEY_CURRENT_USER. |
Windows Installer writes or removes registry values entered in the Registry table and RemoveRegistry table, with the value msidbRegistryRootClassesRoot (0) in the Root column, under HKLMSoftwareClasses. | Windows Installer writes or removes registry values entered in the Registry table and RemoveRegistry table, with the value msidbRegistryRootClassesRoot (0) in the Root column, under HKCUSoftwareClasses. |
COM registration is written to HKLMSoftwareClasses. | COM registration is written to HKCUSoftwareClasses. |
Folder Redirection
Windows Installer sets the values of the folder properties to the full path of the respective folder for the installation context.
Note
Folders are identified by their KNOWNFOLDERID and CSIDL constants. Beginning with Windows Vista, applications should use the SHGetKnownFolderPath function and the KNOWNFOLDERID to determine the full path to the special folders. Existing applications that use the SHGetFolderPath function and constant special item IDs (CSIDL) will continue to work.
The following table compares the locations of folders that are used when Windows Installer installs the package in the per-machine or per-user installation contexts. Dropshelf 1 3 1 download free.
Per-Machine Installation Context (ALLUSERS=1) | Per-User Installation Context (ALLUSERS=') |
---|---|
DesktopFolderThe full path of the Desktop folder for all users. FOLDERID_PublicDesktop (CSIDL_COMMON_DESKTOPDIRECTORY) | DesktopFolderThe full path of the Desktop folder for the current user. FOLDERID_Desktop (CSIDL_DESKTOP, CSIDL_DESKTOPDIRECTORY) |
ProgramMenuFolderThe full path of the Program Menu folder for all users. FOLDERID_CommonPrograms (CSIDL_COMMON_PROGRAMS) | ProgramMenuFolderThe full path of the Program Menu folder for the current user. FOLDERID_Programs (CSIDL_PROGRAMS) |
StartMenuFolderThe full path of the Start Menu folder for the all users. FOLDERID_CommonStartMenu (CSIDL_COMMON_STARTMENU) | StartMenuFolderThe full path of the Start Menu folder for the current user. FOLDERID_StartMenu (CSIDL_STARTMENU) |
StartUpFolderThe full path of the Start Up folder for all users. FOLDERID_CommonStartup (CSIDL_COMMON_STARTUP) | StartUpFolderThe full path of the Start Up folder for the current user. FOLDERID_Startup (CSIDL_STARTUP) |
TemplateFolderThe full path of the Templates folder for all users. FOLDERID_CommonTemplates (CSIDL_COMMON_TEMPLATES) | TemplateFolderThe full path of the Templates folder for the current user. FOLDERID_Templates (CSIDL_TEMPLATES) |
AdminToolsFolderThe full path of the Admin Tools folder for all users. FOLDERID_CommonAdminTools (CSIDL_COMMON_ADMINTOOLS) | AdminToolsFolderThe full path of the Admin Tools folder for the current user. FOLDERID_AdminTools (CSIDL_ADMINTOOLS) |
AppDataFolderThe full path of the Program Menu folder. Windows Vista and later: The full path of the Roaming folder. FOLDERID_RoamingAppData (CSIDL_APPDATA) | AppDataFolderThe full path of the Program Menu folder. Windows Vista and later: The full path of the Roaming folder. FOLDERID_RoamingAppData (CSIDL_APPDATA) |
CommonAppDataFolderThe full path of the folder that contains application data for all users. FOLDERID_ProgramData (CSIDL_COMMON_APPDATA) | CommonAppDataFolderThe full path of the folder that contains application data for all users. FOLDERID_ProgramData (CSIDL_COMMON_APPDATA) |
FavoritesFolderThe full path of the Favorites folder for the current user. FOLDERID_Favorites (CSIDL_FAVORITES) | FavoritesFolderThe full path of the Favorites folder for the current user. FOLDERID_Favorites (CSIDL_FAVORITES) |
PersonalFolderThe full path of the My Documents folder or Personal folder for the current user. Windows Vista and later: The full path of the Documents folder for the current user. FOLDERID_Documents (CSIDL_PERSONAL) | PersonalFolderThe full path of the My Documents folder or Personal folder for the current user. Windows Vista and later: The full path of the Documents folder for the current user. FOLDERID_Documents (CSIDL_PERSONAL) |
SendToFolderThe full path of the SendTo folder. FOLDERID_SendTo (CSIDL_SENDTO) | SendToFolderThe full path of the SendTo folder. FOLDERID_SendTo (CSIDL_SENDTO) |
FontsFolderThe full path of the System Fonts folder. FOLDERID_Fonts (CSIDL_FONTS) | FontsFolderThe full path of the System Fonts folder. FOLDERID_Fonts (CSIDL_FONTS) |
ProgramFilesFolder32-bit version of Windows: The property value is the full path to the Program Files folder for all users (for example, %ProgramFiles%.) The identifier for this folder is FOLDERID_ProgramFiles (CSIDL_PROGRAM_FILES.) The identifiers FOLDERID_ProgramFiles and FOLDERID_ProgramFilesX86 represent the same folder. Files in this folder can be accessed by all users. 64-bit version of Windows: The property value is the full path to the Program Files (x86) folder for all users (for example, %ProgramFiles(x86)%.) The identifier for this folder is FOLDERID_ProgramFilesX86 (CSIDL_PROGRAM_FILESX86.) Files in this folder can be accessed by all users. | ProgramFilesFolderWindows Server 2008 R2 and Windows 7: The property value is the full path of the Programs folder for the current user (for example, %LocalAppData%Programs.) The identifier for this folder is FOLDERID_UserProgramFiles on 32-bit and 64-bit systems. There is no equivalent CSIDL identifier for FOLDERID_UserProgramFiles. Files in this folder can be accessed only by the user that installed this folder. Windows Server 2008 and earlier, and Windows Vista and earlier: No per-user capable folder is available. The path is the same as for the per-machine context (for example, %ProgramFiles% or %ProgramFiles(x86)%.) Files in this folder can be accessed by all users. |
CommonFilesFolder32-bit version of Windows: The property value is the full path to the Common Files folder for all users (for example, %ProgramFiles%Common Files.) The identifier for this folder is FOLDERID_ProgramFilesCommon (CSIDL_PROGRAM_FILES_COMMON.) The identifiers FOLDERID_ProgramFilesCommon and FOLDERID_ProgramFilesCommonX86 represent the same folder. Files in this folder can be accessed by all users. 64-bit version of Windows: The property value is the full path to the Common Files folder for all users (for example, %ProgramFiles(x86)%Common Files.) The identifier for this folder is FOLDERID_ProgramFilesCommonX86 (CSIDL_PROGRAM_FILES_COMMONX86.) Files in this folder can be accessed by all users. | CommonFilesFolderWindows Server 2008 R2 and Windows 7: The property value is the full path of the Common folder for the current user (for example, %LocalAppData%ProgramsCommon.) The identifier for this folder is FOLDERID_UserProgramFilesCommon on 32-bit and 64-bit systems. There is no equivalent CSIDL identifier for FOLDERID_UserProgramFilesCommon. Files in this folder can be accessed only by the user that installed this folder. Windows Server 2008 and earlier, and Windows Vista and earlier: No per-user capable folder is available. The path is the same as in the per-machine context (for example, %ProgramFiles%Common Files or %ProgramFiles(x86)%Common Files.) Files in this folder can be accessed by all users. |
ProgramFiles64FolderThe property value is the full path to the Program Files folder for all users (for example, %ProgramFiles%.) The identifier for this folder is FOLDERID_ProgramFilesX64. There is no equivalent CSIDL identifier to FOLDERID_ProgramFilesX64. This is the pre-defined folder for 64-bit components and applies to 64-bit systems. Files in this folder can be accessed by all users. | ProgramFiles64FolderWindows Server 2008 R2 and Windows 7: The property value is the full path of the Programs folder for the current user (for example, %LocalAppData%Programs.) The identifier for this folder is FOLDERID_UserProgramFiles. There is no equivalent CSIDL identifier for FOLDERID_UserProgramFiles. Files in this folder can be accessed only by the user that installed this folder. Windows Server 2008 and earlier, and Windows Vista and earlier: No per-user capable folder is available. The path is the same as for the per-machine context (for example, %ProgramFiles%.) Files in this folder can be accessed by all users. |
CommonFiles64FolderThe property value is the full path to the Common Files folder for all users (for example, %ProgramFiles%Common Files.) This is the pre-defined folder for 64-bit components and applies to 64-bit systems. The identifier for this folder is FOLDERID_ProgramFilesCommonX64. There is no equivalent CSIDL identifier to FOLDERID_ProgramFilesCommonX64. Files in this folder can be accessed by all users. | CommonFiles64FolderWindows Server 2008 R2 and Windows 7: The property value is the full path of the Common folder for the current user (for example, %LocalAppData%ProgramsCommon.) The identifier for this folder is FOLDERID_UserProgramFilesCommon. There is no equivalent CSIDL identifier for FOLDERID_UserProgramFilesCommon. Files in this folder can be accessed only by the user that installed this folder. Windows Server 2008 and earlier, and Windows Vista and earlier: No per-user capable folder is available. The path is the same as for the per-machine context (for example, %ProgramFiles%Common Files.) Files in this folder can be accessed by all users. |
WindowsFolderThe full path of the Windows folder. FOLDERID_Windows (CSIDL_WINDOWS) | WindowsFolderThe full path of the Windows folder. FOLDERID_Windows (CSIDL_WINDOWS) |
SystemFolderThe full path of the System folder. FOLDERID_SystemX86 (CSIDL_SYSTEMX86) | SystemFolderThe full path of the System folder. FOLDERID_SystemX86 (CSIDL_SYSTEMX86) |
LocalAppDataFolderThe full path of the folder that contains local (nonroaming) applications. FOLDERID_LocalAppData (CSIDL_LOCAL_APPDATA) | LocalAppDataFolderThe full path of the folder that contains local (nonroaming) applications. FOLDERID_LocalAppData (CSIDL_LOCAL_APPDATA) |
MyPicturesFolderThe full path of the Pictures or My Pictures folder. FOLDERID_Pictures (CSIDL_MYPICTURES) | MyPicturesFolderThe full path of the Pictures or My Pictures folder. FOLDERID_Pictures (CSIDL_MYPICTURES) |
PrintHoodFolderThe full path of the PrintHood folder. FOLDERID_PrintHood (CSIDL_PRINTHOOD) | PrintHoodFolderThe full path of the PrintHood folder. FOLDERID_PrintHood (CSIDL_PRINTHOOD) |
NetHoodFolderThe full path of the NetHood folder. FOLDERID_NetHood (CSIDL_NETHOOD) | NetHoodFolderThe full path of the NetHood folder. FOLDERID_NetHood (CSIDL_NETHOOD) |
RecentFolderThe full path of the Recent folder. FOLDERID_Recent (CSIDL_RECENT) | RecentFolderThe full path of the Recent folder. FOLDERID_Recent (CSIDL_RECENT) |
Note
An application can call the MsiEnumProducts or MsiEnumProductsEx functions to enumerate all the products installed on the system. The application can then retrieve information about the installation context of these products by calling the MsiGetProductInfoEx or MsiGetProductInfo functions. For information see Determining Installation Context.
In computing, a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point. This allows multiple processes to share a single central processing unit (CPU), and is an essential feature of a multitasking operating system.
The precise meaning of the phrase 'context switch' varies. In a multitasking context, it refers to the process of storing the system state for one task, so that task can be paused and another task resumed. A context switch can also occur as the result of an interrupt, such as when a task needs to access disk storage, freeing up CPU time for other tasks. Some operating systems also require a context switch to move between user mode and kernel mode tasks. The process of context switching can have a negative impact on system performance.[1]:28
Cost[edit]
Context switches are usually computationally intensive, and much of the design of operating systems is to optimize the use of context switches. Switching from one process to another requires a certain amount of time for doing the administration – saving and loading registers and memory maps, updating various tables and lists, etc. What is actually involved in a context switch depends on the architectures, operating systems, and the number of resources shared (threads that belong to the same process share many resources whether compared to unrelated non-cooperating processes. For example, in the Linux kernel, context switching involves switching registers, stack pointer (it's typical stack-pointer register), program counter, flushing the translation lookaside buffer (TLB) and loading the page table of the next process to run (unless the old process shares the memory with the new).[2][3] Furthermore, analogous context switching happens between user threads, notably green threads, and is often very lightweight, saving and restoring minimal context. In extreme cases, such as switching between goroutines in Go, a context switch is equivalent to a coroutine yield, which is only marginally more expensive than a subroutine call.
Switching cases[edit]
There are three potential triggers for a context switch:
Multitasking[edit]
Most commonly, within some scheduling scheme, one process must be switched out of the CPU so another process can run. This context switch can be triggered by the process making itself unrunnable, such as by waiting for an I/O or synchronization operation to complete. On a pre-emptive multitasking system, the scheduler may also switch out processes that are still runnable. To prevent other processes from being starved of CPU time, preemptive schedulers often configure a timer interrupt to fire when a process exceeds its time slice. This interrupt ensures that the scheduler will gain control to perform a context switch.
Interrupt handling[edit]
Modern architectures are interrupt driven. This means that if the CPU requests data from a disk, for example, it does not need to busy-wait until the read is over; it can issue the request (to the I/O device) and continue with some other task. When the read is over, the CPU can be interrupted (by a hardware in this case, which sends interrupt request to PIC) and presented with the read. Checkbook 2 6 3 – manage personal checking accounts payable. For interrupts, a program called an interrupt handler is installed, and it is the interrupt handler that handles the interrupt from the disk.
When an interrupt occurs, the hardware automatically switches a part of the context (at least enough to allow the handler to return to the interrupted code). The handler may save additional context, depending on details of the particular hardware and software designs. Often only a minimal part of the context is changed in order to minimize the amount of time spent handling the interrupt. The kernel does not spawn or schedule a special process to handle interrupts, but instead the handler executes in the (often partial) context established at the beginning of interrupt handling. Once interrupt servicing is complete, the context in effect before the interrupt occurred is restored so that the interrupted process can resume execution in its proper state.
User and kernel mode switching[edit]
When the system transitions between user mode and kernel mode, a context switch is not necessary; a mode transition is not by itself a context switch. However, depending on the operating system, a context switch may also take place at this time.
Steps[edit]
Liquibid video exposure and effects 1 0 65. In a switch, the state of the process currently executing must be saved somehow, so that when it is rescheduled, this state can be restored.
Per-Machine Installation Context (ALLUSERS=1) | Per-User Installation Context (ALLUSERS=') |
---|---|
DesktopFolderThe full path of the Desktop folder for all users. FOLDERID_PublicDesktop (CSIDL_COMMON_DESKTOPDIRECTORY) | DesktopFolderThe full path of the Desktop folder for the current user. FOLDERID_Desktop (CSIDL_DESKTOP, CSIDL_DESKTOPDIRECTORY) |
ProgramMenuFolderThe full path of the Program Menu folder for all users. FOLDERID_CommonPrograms (CSIDL_COMMON_PROGRAMS) | ProgramMenuFolderThe full path of the Program Menu folder for the current user. FOLDERID_Programs (CSIDL_PROGRAMS) |
StartMenuFolderThe full path of the Start Menu folder for the all users. FOLDERID_CommonStartMenu (CSIDL_COMMON_STARTMENU) | StartMenuFolderThe full path of the Start Menu folder for the current user. FOLDERID_StartMenu (CSIDL_STARTMENU) |
StartUpFolderThe full path of the Start Up folder for all users. FOLDERID_CommonStartup (CSIDL_COMMON_STARTUP) | StartUpFolderThe full path of the Start Up folder for the current user. FOLDERID_Startup (CSIDL_STARTUP) |
TemplateFolderThe full path of the Templates folder for all users. FOLDERID_CommonTemplates (CSIDL_COMMON_TEMPLATES) | TemplateFolderThe full path of the Templates folder for the current user. FOLDERID_Templates (CSIDL_TEMPLATES) |
AdminToolsFolderThe full path of the Admin Tools folder for all users. FOLDERID_CommonAdminTools (CSIDL_COMMON_ADMINTOOLS) | AdminToolsFolderThe full path of the Admin Tools folder for the current user. FOLDERID_AdminTools (CSIDL_ADMINTOOLS) |
AppDataFolderThe full path of the Program Menu folder. Windows Vista and later: The full path of the Roaming folder. FOLDERID_RoamingAppData (CSIDL_APPDATA) | AppDataFolderThe full path of the Program Menu folder. Windows Vista and later: The full path of the Roaming folder. FOLDERID_RoamingAppData (CSIDL_APPDATA) |
CommonAppDataFolderThe full path of the folder that contains application data for all users. FOLDERID_ProgramData (CSIDL_COMMON_APPDATA) | CommonAppDataFolderThe full path of the folder that contains application data for all users. FOLDERID_ProgramData (CSIDL_COMMON_APPDATA) |
FavoritesFolderThe full path of the Favorites folder for the current user. FOLDERID_Favorites (CSIDL_FAVORITES) | FavoritesFolderThe full path of the Favorites folder for the current user. FOLDERID_Favorites (CSIDL_FAVORITES) |
PersonalFolderThe full path of the My Documents folder or Personal folder for the current user. Windows Vista and later: The full path of the Documents folder for the current user. FOLDERID_Documents (CSIDL_PERSONAL) | PersonalFolderThe full path of the My Documents folder or Personal folder for the current user. Windows Vista and later: The full path of the Documents folder for the current user. FOLDERID_Documents (CSIDL_PERSONAL) |
SendToFolderThe full path of the SendTo folder. FOLDERID_SendTo (CSIDL_SENDTO) | SendToFolderThe full path of the SendTo folder. FOLDERID_SendTo (CSIDL_SENDTO) |
FontsFolderThe full path of the System Fonts folder. FOLDERID_Fonts (CSIDL_FONTS) | FontsFolderThe full path of the System Fonts folder. FOLDERID_Fonts (CSIDL_FONTS) |
ProgramFilesFolder32-bit version of Windows: The property value is the full path to the Program Files folder for all users (for example, %ProgramFiles%.) The identifier for this folder is FOLDERID_ProgramFiles (CSIDL_PROGRAM_FILES.) The identifiers FOLDERID_ProgramFiles and FOLDERID_ProgramFilesX86 represent the same folder. Files in this folder can be accessed by all users. 64-bit version of Windows: The property value is the full path to the Program Files (x86) folder for all users (for example, %ProgramFiles(x86)%.) The identifier for this folder is FOLDERID_ProgramFilesX86 (CSIDL_PROGRAM_FILESX86.) Files in this folder can be accessed by all users. | ProgramFilesFolderWindows Server 2008 R2 and Windows 7: The property value is the full path of the Programs folder for the current user (for example, %LocalAppData%Programs.) The identifier for this folder is FOLDERID_UserProgramFiles on 32-bit and 64-bit systems. There is no equivalent CSIDL identifier for FOLDERID_UserProgramFiles. Files in this folder can be accessed only by the user that installed this folder. Windows Server 2008 and earlier, and Windows Vista and earlier: No per-user capable folder is available. The path is the same as for the per-machine context (for example, %ProgramFiles% or %ProgramFiles(x86)%.) Files in this folder can be accessed by all users. |
CommonFilesFolder32-bit version of Windows: The property value is the full path to the Common Files folder for all users (for example, %ProgramFiles%Common Files.) The identifier for this folder is FOLDERID_ProgramFilesCommon (CSIDL_PROGRAM_FILES_COMMON.) The identifiers FOLDERID_ProgramFilesCommon and FOLDERID_ProgramFilesCommonX86 represent the same folder. Files in this folder can be accessed by all users. 64-bit version of Windows: The property value is the full path to the Common Files folder for all users (for example, %ProgramFiles(x86)%Common Files.) The identifier for this folder is FOLDERID_ProgramFilesCommonX86 (CSIDL_PROGRAM_FILES_COMMONX86.) Files in this folder can be accessed by all users. | CommonFilesFolderWindows Server 2008 R2 and Windows 7: The property value is the full path of the Common folder for the current user (for example, %LocalAppData%ProgramsCommon.) The identifier for this folder is FOLDERID_UserProgramFilesCommon on 32-bit and 64-bit systems. There is no equivalent CSIDL identifier for FOLDERID_UserProgramFilesCommon. Files in this folder can be accessed only by the user that installed this folder. Windows Server 2008 and earlier, and Windows Vista and earlier: No per-user capable folder is available. The path is the same as in the per-machine context (for example, %ProgramFiles%Common Files or %ProgramFiles(x86)%Common Files.) Files in this folder can be accessed by all users. |
ProgramFiles64FolderThe property value is the full path to the Program Files folder for all users (for example, %ProgramFiles%.) The identifier for this folder is FOLDERID_ProgramFilesX64. There is no equivalent CSIDL identifier to FOLDERID_ProgramFilesX64. This is the pre-defined folder for 64-bit components and applies to 64-bit systems. Files in this folder can be accessed by all users. | ProgramFiles64FolderWindows Server 2008 R2 and Windows 7: The property value is the full path of the Programs folder for the current user (for example, %LocalAppData%Programs.) The identifier for this folder is FOLDERID_UserProgramFiles. There is no equivalent CSIDL identifier for FOLDERID_UserProgramFiles. Files in this folder can be accessed only by the user that installed this folder. Windows Server 2008 and earlier, and Windows Vista and earlier: No per-user capable folder is available. The path is the same as for the per-machine context (for example, %ProgramFiles%.) Files in this folder can be accessed by all users. |
CommonFiles64FolderThe property value is the full path to the Common Files folder for all users (for example, %ProgramFiles%Common Files.) This is the pre-defined folder for 64-bit components and applies to 64-bit systems. The identifier for this folder is FOLDERID_ProgramFilesCommonX64. There is no equivalent CSIDL identifier to FOLDERID_ProgramFilesCommonX64. Files in this folder can be accessed by all users. | CommonFiles64FolderWindows Server 2008 R2 and Windows 7: The property value is the full path of the Common folder for the current user (for example, %LocalAppData%ProgramsCommon.) The identifier for this folder is FOLDERID_UserProgramFilesCommon. There is no equivalent CSIDL identifier for FOLDERID_UserProgramFilesCommon. Files in this folder can be accessed only by the user that installed this folder. Windows Server 2008 and earlier, and Windows Vista and earlier: No per-user capable folder is available. The path is the same as for the per-machine context (for example, %ProgramFiles%Common Files.) Files in this folder can be accessed by all users. |
WindowsFolderThe full path of the Windows folder. FOLDERID_Windows (CSIDL_WINDOWS) | WindowsFolderThe full path of the Windows folder. FOLDERID_Windows (CSIDL_WINDOWS) |
SystemFolderThe full path of the System folder. FOLDERID_SystemX86 (CSIDL_SYSTEMX86) | SystemFolderThe full path of the System folder. FOLDERID_SystemX86 (CSIDL_SYSTEMX86) |
LocalAppDataFolderThe full path of the folder that contains local (nonroaming) applications. FOLDERID_LocalAppData (CSIDL_LOCAL_APPDATA) | LocalAppDataFolderThe full path of the folder that contains local (nonroaming) applications. FOLDERID_LocalAppData (CSIDL_LOCAL_APPDATA) |
MyPicturesFolderThe full path of the Pictures or My Pictures folder. FOLDERID_Pictures (CSIDL_MYPICTURES) | MyPicturesFolderThe full path of the Pictures or My Pictures folder. FOLDERID_Pictures (CSIDL_MYPICTURES) |
PrintHoodFolderThe full path of the PrintHood folder. FOLDERID_PrintHood (CSIDL_PRINTHOOD) | PrintHoodFolderThe full path of the PrintHood folder. FOLDERID_PrintHood (CSIDL_PRINTHOOD) |
NetHoodFolderThe full path of the NetHood folder. FOLDERID_NetHood (CSIDL_NETHOOD) | NetHoodFolderThe full path of the NetHood folder. FOLDERID_NetHood (CSIDL_NETHOOD) |
RecentFolderThe full path of the Recent folder. FOLDERID_Recent (CSIDL_RECENT) | RecentFolderThe full path of the Recent folder. FOLDERID_Recent (CSIDL_RECENT) |
Note
An application can call the MsiEnumProducts or MsiEnumProductsEx functions to enumerate all the products installed on the system. The application can then retrieve information about the installation context of these products by calling the MsiGetProductInfoEx or MsiGetProductInfo functions. For information see Determining Installation Context.
In computing, a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point. This allows multiple processes to share a single central processing unit (CPU), and is an essential feature of a multitasking operating system.
The precise meaning of the phrase 'context switch' varies. In a multitasking context, it refers to the process of storing the system state for one task, so that task can be paused and another task resumed. A context switch can also occur as the result of an interrupt, such as when a task needs to access disk storage, freeing up CPU time for other tasks. Some operating systems also require a context switch to move between user mode and kernel mode tasks. The process of context switching can have a negative impact on system performance.[1]:28
Cost[edit]
Context switches are usually computationally intensive, and much of the design of operating systems is to optimize the use of context switches. Switching from one process to another requires a certain amount of time for doing the administration – saving and loading registers and memory maps, updating various tables and lists, etc. What is actually involved in a context switch depends on the architectures, operating systems, and the number of resources shared (threads that belong to the same process share many resources whether compared to unrelated non-cooperating processes. For example, in the Linux kernel, context switching involves switching registers, stack pointer (it's typical stack-pointer register), program counter, flushing the translation lookaside buffer (TLB) and loading the page table of the next process to run (unless the old process shares the memory with the new).[2][3] Furthermore, analogous context switching happens between user threads, notably green threads, and is often very lightweight, saving and restoring minimal context. In extreme cases, such as switching between goroutines in Go, a context switch is equivalent to a coroutine yield, which is only marginally more expensive than a subroutine call.
Switching cases[edit]
There are three potential triggers for a context switch:
Multitasking[edit]
Most commonly, within some scheduling scheme, one process must be switched out of the CPU so another process can run. This context switch can be triggered by the process making itself unrunnable, such as by waiting for an I/O or synchronization operation to complete. On a pre-emptive multitasking system, the scheduler may also switch out processes that are still runnable. To prevent other processes from being starved of CPU time, preemptive schedulers often configure a timer interrupt to fire when a process exceeds its time slice. This interrupt ensures that the scheduler will gain control to perform a context switch.
Interrupt handling[edit]
Modern architectures are interrupt driven. This means that if the CPU requests data from a disk, for example, it does not need to busy-wait until the read is over; it can issue the request (to the I/O device) and continue with some other task. When the read is over, the CPU can be interrupted (by a hardware in this case, which sends interrupt request to PIC) and presented with the read. Checkbook 2 6 3 – manage personal checking accounts payable. For interrupts, a program called an interrupt handler is installed, and it is the interrupt handler that handles the interrupt from the disk.
When an interrupt occurs, the hardware automatically switches a part of the context (at least enough to allow the handler to return to the interrupted code). The handler may save additional context, depending on details of the particular hardware and software designs. Often only a minimal part of the context is changed in order to minimize the amount of time spent handling the interrupt. The kernel does not spawn or schedule a special process to handle interrupts, but instead the handler executes in the (often partial) context established at the beginning of interrupt handling. Once interrupt servicing is complete, the context in effect before the interrupt occurred is restored so that the interrupted process can resume execution in its proper state.
User and kernel mode switching[edit]
When the system transitions between user mode and kernel mode, a context switch is not necessary; a mode transition is not by itself a context switch. However, depending on the operating system, a context switch may also take place at this time.
Steps[edit]
Liquibid video exposure and effects 1 0 65. In a switch, the state of the process currently executing must be saved somehow, so that when it is rescheduled, this state can be restored.
The process state includes all the registers that the process may be using, especially the program counter, plus any other operating system specific data that may be necessary. This is usually stored in a data structure called a process control block (PCB) or switchframe.
The PCB might be stored on a per-process stack in kernel memory (as opposed to the user-mode call stack), or there may be some specific operating system-defined data structure for this information. A handle to the PCB is added to a queue of processes that are ready to run, often called the ready queue.
Since the operating system has effectively suspended the execution of one process, it can then switch context by choosing a process from the ready queue and restoring its PCB. In doing so, the program counter from the PCB is loaded, and thus execution can continue in the chosen process. Process and thread priority can influence which process is chosen from the ready queue (i.e., it may be a priority queue).
Example[edit]
Considering a general arithmetic addition operation A = B+1. The instruction is stored in the instruction register and the program counter is incremented. A and B are read from memory and are stored in registers R1, R2 respectively. In this case, B+1 is calculated and written in R1 as the final answer. This operation only requires reads and writes that happen in a sequence/order and there are no function calls used, hence no context switch/wait takes place in this case.
However, certain special instructions require system calls that require context switch to wait/sleep processes. A system call handler is used for context switch to kernel mode. A display(data) function may require data from disk and a device driver in kernel mode, hence the display() function goes to sleep and waits on the 'read data' operation for the system call to wake it up when the 'data' is received from the disk. i.e It waits for the function call to be released. After the 'data' is received, the display(data) function is re-executed with the new value in order to prevent inconsistencies.
Performance[edit]
Context switching itself has a cost in performance, due to running the task scheduler, TLB flushes, and indirectly due to sharing the CPU cache between multiple tasks.[4] Switching between threads of a single process can be faster than between two separate processes, because threads share the same virtual memory maps, so a TLB flush is not necessary.[5]
Hardware vs. software[edit]
Context switching can be performed primarily by software or hardware. Some processors, like the Intel 80386 and its successors,[6] have hardware support for context switches, by making use of a special data segment designated the task state segment (TSS). A task switch can be explicitly triggered with a CALL or JMP instruction targeted at a TSS descriptor in the global descriptor table. It can occur implicitly when an interrupt or exception is triggered if there's a task gate in the interrupt descriptor table (IDT). When a task switch occurs the CPU can automatically load the new state from the TSS.
As with other tasks performed in hardware, one would expect this to be rather fast; however, mainstream operating systems, including Windows and Linux,[7] do not use this feature. This is mainly due to two reasons:
- Hardware context switching does not save all the registers (only general-purpose registers, not floating point registers — although the
TS
bit is automatically turned on in theCR0
control register, resulting in a fault when executing floating-point instructions and giving the OS the opportunity to save and restore the floating-point state as needed). - Associated performance issues, e.g., software context switching can be selective and store only those registers that need storing, whereas hardware context switching stores nearly all registers whether they are required or not.
Contexts 3 5 1 – Fast Window Switcher Installer Free
See also[edit]
References[edit]
Contexts 3 5 1 – Fast Window Switcher Installers
- ^Tanenbaum, Andrew S.; Bos, Herbert (March 20, 2014). Modern Operating Systems (4th ed.). Pearson. ISBN978-0133591620.
- ^IA-64 Linux Kernel: Design and Implementation, 4.7 Switching Address Spaces
- ^Operating Systems, 5.6 The Context Switch, p. 118
- ^Chuanpeng Li; Chen Ding; Kai Shen. 'Quantifying The Cost of Context Switch'(PDF).Cite journal requires
|journal=
(help) - ^Ulrich Drepper (9 October 2014). 'Memory part 3: Virtual Memory'. LWN.net.
- ^'Context Switch definition'. Linfo.org. Archived from the original on 2010-02-18. Retrieved 2013-09-08.
- ^Bovet, Daniel Pierre; Cesati, Marco (2006). Understanding the Linux Kernel, Third Edition. O'Reilly Media. p. 104. ISBN978-0-596-00565-8. Retrieved 2009-11-23.
External links[edit]
- Context Switching at OSDev.org
- Context Switch Definition by The Linux Information Project (LINFO)
- Context Switches from the Microsoft Developer Network (MSDN)
- General Architecture and Design -Interrupt Handling at FreeBSD.org