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Load Task Register
The LTR x86 instruction stands for load task register and is used in operating systems that support multitasking. LTR is supported only in protected mode and long mode, not in real mode Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. The mode gets its name from the fact that addresses in real mode always correspond to real locations in memory. Real mode is characterized by a 20-bit seg ... or virtual 8086 mode. It must be executed when the Current Privilege Level (CPL) is 0, and therefore cannot be used by application programs. LTR loads the special x86 task register with a segment selector that points to a task state segment (TSS). After executing the LTR instruction, the TSS pointed to by the argument is marked busy, but no hardware task switch occurs. The opposite of the LTR instruction is the STR instruction, which means store task register and copies the value of the task register to the specified location. Note that the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Operating Systems
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer from cellular phones and video game consoles to web servers and supercomputers. The dominant general-purpose personal computer operating system is Microsoft Windows with a market share of around 74.99%. macOS by Apple Inc. is in second place (14.84%), and th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Multitasking
In computing, multitasking is the concurrent execution of multiple tasks (also known as processes) over a certain period of time. New tasks can interrupt already started ones before they finish, instead of waiting for them to end. As a result, a computer executes segments of multiple tasks in an interleaved manner, while the tasks share common processing resources such as central processing units (CPUs) and main memory. Multitasking automatically interrupts the running program, saving its state (partial results, memory contents and computer register contents) and loading the saved state of another program and transferring control to it. This " context switch" may be initiated at fixed time intervals (pre-emptive multitasking), or the running program may be coded to signal to the supervisory software when it can be interrupted (cooperative multitasking). Multitasking does not require parallel execution of multiple tasks at exactly the same time; instead, it allows more than o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protected Mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking designed to increase an operating system's control over application software. When a processor that supports x86 protected mode is powered on, it begins executing instructions in real mode, in order to maintain backward compatibility with earlier x86 processors. Protected mode may only be entered after the system software sets up one descriptor table and enables the Protection Enable (PE) bit in the control register 0 (CR0). Protected mode was first added to the x86 architecture in 1982, with the release of Intel's 80286 (286) processor, and later extended with the release of the 80386 (386) in 1985. Due to the enhancements added by protected mode, it has become widely adopted and has become the foundation for all subsequent enhancements ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Long Mode
In the x86-64 computer architecture, long mode is the mode where a 64-bit operating system can access 64-bit instructions and registers. 64-bit programs are run in a sub-mode called 64-bit mode, while 32-bit programs and 16-bit protected mode programs are executed in a sub-mode called compatibility mode. Real mode or virtual 8086 mode programs cannot be natively run in long mode. Overview An x86-64 processor acts identically as an IA-32 processor when running in real mode or protected mode, which are supported sub-modes when the processor is ''not'' in long mode. A bit in the CPUID extended attributes field informs programs in real or protected modes if the processor can go to long mode, which allows a program to detect an x86-64 processor. This is similar to the CPUID attributes bit that Intel IA-64 processors use to allow programs to detect if they are running under IA-32 emulation. With a computer running legacy BIOS, the BIOS and the boot loader is running in Real mode, th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Real Mode
Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. The mode gets its name from the fact that addresses in real mode always correspond to real locations in memory. Real mode is characterized by a 20-bit segmented memory address space (giving 1 MB of addressable memory) and unlimited direct software access to all addressable memory, I/O addresses and peripheral hardware. Real mode provides no support for memory protection, multitasking, or code privilege levels. Before the release of the 80286, which introduced protected mode, real mode was the only available mode for x86 CPUs; and for backward compatibility, all x86 CPUs start in real mode when reset, though it is possible to emulate real mode on other systems when starting on other modes. History The 286 architecture introduced protected mode, allowing for (among other things) hardware-level memory protection. Using these new features, however, required a new operating system that was ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virtual 8086 Mode
In the 80386 microprocessor and later, virtual 8086 mode (also called virtual real mode, V86-mode, or VM86) allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running a protected mode operating system. It is a hardware virtualization technique that allowed multiple 8086 processors to be emulated by the 386 chip. It emerged from the painful experiences with the 80286 protected mode, which by itself was not suitable to run concurrent real-mode applications well. John Crawford developed the Virtual Mode bit at the register set, paving the way to this environment. VM86 mode uses a segmentation scheme identical to that of real mode (for compatibility reasons), which creates 20-bit linear addresses in the same manner as 20-bit physical addresses are created in real mode, but are subject to protected mode's memory paging mechanism. Overview The virtual 8086 mode is a mode for a protected-mode task. Cons ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Current Privilege Level
In computer science, hierarchical protection domains, often called protection rings, are mechanisms to protect data and functionality from faults (by improving fault tolerance) and malicious behavior (by providing computer security). Computer operating systems provide different levels of access to resources. A protection ring is one of two or more hierarchical ''levels'' or ''layers'' of privilege within the architecture of a computer system. This is generally hardware-enforced by some CPU architectures that provide different CPU modes at the hardware or microcode level. Rings are arranged in a hierarchy from most privileged (most trusted, usually numbered zero) to least privileged (least trusted, usually with the highest ring number). Ring 0 is the level with the most privileges and allows direct interaction with the physical hardware such as certain CPU functionality and chips on the motherboard. Special call gates between rings are provided to allow an outer ring to acces ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Task State Segment
The task state segment (TSS) is a structure on x86-based computers which holds information about a task. It is used by the operating system kernel for task management. Specifically, the following information is stored in the TSS: * Processor register state * I/O port permissions * Inner-level stack pointers * Previous TSS link All this information should be stored at specific locations within the TSS as specified in the IA-32 manuals. Location of the TSS The TSS may reside anywhere in memory. A segment register called the task register (TR) holds a segment selector that points to a valid TSS segment descriptor which resides in the GDT (a TSS descriptor may not reside in the LDT). Therefore, to use a TSS the following must be done by the operating system kernel: # Create a TSS descriptor entry in the GDT # Load the TR with the segment selector for that segment # Add information to the TSS in memory as needed For security purposes, the TSS should be placed in memory that is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Store Task Register
Store may refer to: Enterprises * Retail store, a shop where merchandise is sold, usually products and usually on a retail basis, and where wares are often kept ** App store, an online retail store where apps are sold, included in many mobile operating systems ** Department store, a retail store offering a wide range of consumer goods ** Warehouse club (or wholesale club), a no-frills retail store, usually selling a wide variety of merchandise, in which customers may buy large, wholesale quantities at low prices * Warehouse, a location where items are stored, e.g., a ship's paint store, and sometimes sold, e.g., Costco Warehouse Club Arts, entertainment, and media * The Store (ITV), a British shopping television programming on ITV1 * ''The Store'' (novel), a 1932 novel by Thomas Sigismund Stribling * "Store", a song by Carly Rae Jepsen from the EP '' Emotion: Side B'' Other uses * Data store, a repository for persistently storing and managing collections of data * Štore, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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