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X86 Instructions
The x86 instruction set refers to the set of instructions that x86-compatible microprocessors support. The instructions are usually part of an executable program, often stored as a computer file and executed on the processor. The x86 instruction set has been extended several times, introducing wider registers and datatypes as well as new functionality. x86 integer instructions Below is the full 8086/ 8088 instruction set of Intel (81 instructions total). These instructions are also available in 32-bit mode, in which they operate on 32-bit registers (eax, ebx, etc.) and values instead of their 16-bit (ax, bx, etc.) counterparts. The updated instruction set is grouped according to architecture ( i186, i286, i386, i486, i586/ i686) and is referred to as (32-bit) x86 and (64-bit) x86-64 (also known as AMD64). Original 8086/8088 instructions This is the original instruction set. In the 'Notes' column, ''r'' means ''register'', ''m'' means ''memory address'' and ''imm'' mean ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Instruction Set
In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ''implementation'' of that ISA. In general, an ISA defines the supported Machine code, instructions, data types, Register (computer), registers, the hardware support for managing Computer memory, main memory, fundamental features (such as the memory consistency, addressing modes, virtual memory), and the input/output model of implementations of the ISA. An ISA specifies the behavior of machine code running on implementations of that ISA in a fashion that does not depend on the characteristics of that implementation, providing binary compatibility between implementations. This enables multiple implementations of an ISA that differ in characteristics such as Computer performance, performa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Opcode
In computing, an opcode (abbreviated from operation code) is an enumerated value that specifies the operation to be performed. Opcodes are employed in hardware devices such as arithmetic logic units (ALUs), central processing units (CPUs), and software instruction sets. In ALUs, the opcode is directly applied to circuitry via an input signal bus. In contrast, in CPUs, the opcode is the portion of a machine language instruction that specifies the operation to be performed. CPUs Opcodes are found in the machine language instructions of CPUs as well as in some abstract computing machines. In CPUs, an opcode may be referred to as an instruction machine code, instruction code, instruction syllable, instruction parcel, or opstring. For any particular processor (which may be a general CPU or a more specialized processing unit), the opcodes are defined by the processor's instruction set architecture (ISA). They can be described using an opcode table. The types of operations may in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Branch (computer Science)
A branch, jump or transfer is an instruction in a computer program that can cause a computer to begin executing a different instruction sequence and thus deviate from its default behavior of executing instructions in order. ''Branch'' (or ''branching'', ''branched'') may also refer to the act of switching execution to a different instruction sequence as a result of executing a branch instruction. Branch instructions are used to implement control flow in program loops and conditionals (i.e., executing a particular sequence of instructions only if certain conditions are satisfied). A branch instruction can be either an ''unconditional branch'', which always results in branching, or a ''conditional branch'', which may or may not cause branching depending on some condition. Also, depending on how it specifies the address of the new instruction sequence (the "target" address), a branch instruction is generally classified as ''direct'', ''indirect'' or ''relative'', meaning that the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interrupt
In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted, the processor will suspend its current activities, save its state, and execute a function called an '' interrupt handler'' (or an ''interrupt service routine'', ISR) to deal with the event. This interruption is often temporary, allowing the software to resume normal activities after the interrupt handler finishes, although the interrupt could instead indicate a fatal error. Interrupts are commonly used by hardware devices to indicate electronic or physical state changes that require time-sensitive attention. Interrupts are also commonly used to implement computer multitasking and system calls, especially in real-time computing. Systems that use interrupts in these ways are said to be interrupt-driven. History Hardware interrupts wer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
INT (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: :INT ''X'' where ''X'' is the ''software interrupt'' that should be generated (0-255). As is customary with machine binary arithmetic, interrupt numbers are often written in hexadecimal form, which can be indicated with a prefix ''0x'' or with the suffix ''h''. For example, INT 13H will generate the 20th ''software interrupt'' (0x13 is nineteen (19) in hexadecimal notation, and the count starts at 0), causing the function pointed to by the 20th vector in the interrupt table to be executed. INT is widely used in real mode. In protected mode, INT is a privileged instruction. Real mode When generating a ''software interrupt'', the processor calls one of the 256 functions pointed to by the interrupt address table, which is located in the first 1024 by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HLT (x86 Instruction)
In the x86 computer architecture, HLT (halt) is an assembly language instruction which halts the central processing unit (CPU) until the next external interrupt is fired. Interrupts are signals sent by hardware devices to the CPU alerting it that an event occurred to which it should react. For example, hardware timers send interrupts to the CPU at regular intervals. Most operating systems execute a HLT instruction when there is no immediate work to be done, putting the processor into an idle state. In Windows NT, for example, this instruction is run in the " System Idle Process". On x86 processors, the opcode of HLT is 0xF4. On ARM processors, the similar instructions are WFI (Wait For Interrupt) and WFE (Wait For Event). History on x86 All x86 processors from the 8086 onward had the HLT instruction, but it was not used by MS-DOS prior to 6.0 and was not specifically designed to reduce power consumption until the release of the Intel DX4 processor in 1994. MS-DOS 6.0 provided a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Floating-point Unit
A floating-point unit (FPU), numeric processing unit (NPU), colloquially math coprocessor, is a part of a computer system specially designed to carry out operations on floating-point numbers. Typical operations are addition, subtraction, multiplication, division, and square root. Modern designs generally include a fused multiply-add instruction, which was found to be very common in real-world code. Some FPUs can also perform various transcendental functions such as exponential or trigonometric calculations, but the accuracy can be low, so some systems prefer to compute these functions in software. Floating-point operations were originally handled in software in early computers. Over time, manufacturers began to provide standardized floating-point libraries as part of their software collections. Some machines, those dedicated to scientific processing, would include specialized hardware to perform some of these tasks with much greater speed. The introduction of microcode in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Signed Number Representations
In computing, signed number representations are required to encode negative numbers in binary number systems. In mathematics, negative numbers in any base are represented by prefixing them with a minus sign ("−"). However, in RAM or CPU registers, numbers are represented only as sequences of bits, without extra symbols. The four best-known methods of extending the binary numeral system to represent signed numbers are: sign–magnitude, ones' complement, two's complement, and offset binary. Some of the alternative methods use implicit instead of explicit signs, such as negative binary, using the base −2. Corresponding methods can be devised for other bases, whether positive, negative, fractional, or other elaborations on such themes. There is no definitive criterion by which any of the representations is universally superior. For integers, the representation used in most current computing devices is two's complement, although the Unisys ClearPath Dorado series mainf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IF (x86 Flag)
The Interrupt flag (IF) is a flag bit in the CPU's FLAGS register, which determines whether or not the (CPU) will respond immediately to maskable hardware interrupts. If the flag is set to 1 maskable interrupts are enabled. If reset (set to 0) such interrupts will be disabled until interrupts are enabled. The Interrupt flag does not affect the handling of non-maskable interrupts (NMIs) or software interrupts generated by the INT instruction. Setting and clearing In a system using x86 architecture, the instructions CLI (Clear Interrupt) and STI (Set Interrupt). The POPF (Pop Flags) removes a word from the stack into the FLAGS register, which may result in the Interrupt flag being set or cleared based on the bit in the FLAGS register from the top of the stack. Privilege level In systems that support privileged mode, only privileged applications (usually the OS kernel) may modify the Interrupt flag. In an x86 system this only applies to protected mode code (Real mode code ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Direction Flag
The direction flag is a flag that controls the ''left-to-right'' or ''right-to-left'' direction of string processing, stored in the FLAGS register on all x86-compatible CPUs. at It is bit number 10. This flag is used to determine the direction ('forward' or 'backward') in which several bytes of data will be copied from one place in the , to another. The direction is important mainly when the original data position in memory and the target data position overlap. * If it is set to 0 (using the clear-dir ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carry Flag
In computer processors, the carry flag (usually indicated as the C flag) is a single bit in a system status register A status register, flag register, or condition code register (CCR) is a collection of status Flag (computing), flag bits for a Central processing unit, processor. Examples of such registers include FLAGS register (computing), FLAGS register in the .../flag register used to indicate when an arithmetic carry (arithmetic), carry or borrow has been generated out of the most significant bit, most significant arithmetic logic unit (ALU) bit position. The carry flag enables numbers larger than a single ALU width to be added/subtracted by carrying (adding) a binary digit from a partial addition/subtraction to the least significant bit position of a more significant word. This is typically programmed by the user of the processor on the assembly or machine code level, but can also happen internally in certain processors, via digital logic or microcode, where some processors ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
