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A model-specific register (MSR) is any of various control registers in the x86 system architecture used for debugging, program execution tracing, computer performance monitoring, and toggling certain CPU features.
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A model-specific register (MSR) is any of various control registers in the x86 system architecture used for debugging, program execution tracing, computer performance monitoring, and toggling certain CPU features.
With the introduction of the 80386 processor, Intel began introducing "experimental" features that would not necessarily be present in future versions of the processor. The first of these were two "test registers" (TR6 and TR7) that enabled testing of the processor's translation lookaside buffer (TLB); a special variant of the MOV instruction allowed moving to and from the test registers. [1] Three additional test registers followed in the 80486 (TR3–TR5) that enabled testing of the processor's caches for code and data. [2] None of these five registers were implemented in the subsequent Pentium processor; the special variant of MOV generated an invalid opcode exception. [3] [4]
With the introduction of the Pentium processor, Intel provided a pair of instructions (RDMSR and WRMSR) to access current and future "model-specific registers", as well as the CPUID instruction to determine which features are present on a particular model. Many of these registers have proven useful enough to be retained. Intel has classified these as architectural model-specific registers and has committed to their inclusion in future product lines. [5]
Reading and writing to these registers is handled by the rdmsr and wrmsr instructions, respectively. As these are privileged instructions, they can be executed only by the operating system. Use of the Linux msr kernel module creates a pseudo file "/dev/cpu/x/msr" (with a unique x for each processor or processor core). A user with permissions to read and/or write to this file can use the file I/O API to access these registers. The msr-tools [6] package provides a reference implementation.
Documentation regarding which MSRs a certain processor implementation supports is usually found in the processor documentation of the CPU vendor. Examples for rather well-known MSRs are the memory type range registers (MTRRs) and the address-range registers (ARRs).
IA-32 is the 32-bit version of the x86 instruction set architecture, designed by Intel and first implemented in the 80386 microprocessor in 1985. IA-32 is the first incarnation of x86 that supports 32-bit computing; as a result, the "IA-32" term may be used as a metonym to refer to all x86 versions that support 32-bit computing.
The Pentium is a microprocessor introduced by Intel on March 22, 1993. It is the first CPU using the Pentium brand. Considered the fifth generation in the x86 (8086) compatible line of processors, succeeding the i486, its implementation and microarchitecture was internally called P5.
x86 is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel, based on the 8086 microprocessor and its 8-bit-external-bus variant, the 8088. The 8086 was introduced in 1978 as a fully 16-bit extension of 8-bit Intel's 8080 microprocessor, with memory segmentation as a solution for addressing more memory than can be covered by a plain 16-bit address. The term "x86" came into being because the names of several successors to Intel's 8086 processor end in "86", including the 80186, 80286, 80386 and 80486. Colloquially, their names were "186", "286", "386" and "486".
In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit central processing units (CPU) and arithmetic logic units (ALU) are those that are based on processor registers, address buses, or data buses of that size. A computer that uses such a processor is a 64-bit computer.
The Intel x86 computer instruction set architecture has supported memory segmentation since the original Intel 8086 in 1978. It allows programs to address more than 64 KB (65,536 bytes) of memory, the limit in earlier 80xx processors. In 1982, the Intel 80286 added support for virtual memory and memory protection; the original mode was renamed real mode, and the new version was named protected mode. The x86-64 architecture, introduced in 2003, has largely dropped support for segmentation in 64-bit 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 segmentation, virtual memory, paging and safe multi-tasking designed to increase an operating system's control over application software.
x86 assembly language is a family of low-level programming languages that are used to produce object code for the x86 class of processors. These languages provide backward compatibility with CPUs dating back to the Intel 8008 microprocessor, introduced in April 1972. As assembly languages, they are closely tied to the architecture's machine code instructions, allowing for precise control over hardware.
x86-64 is a 64-bit extension of the x86 instruction set architecture first announced in 1999. It introduces two new operating modes: 64-bit mode and compatibility mode, along with a new four-level paging mechanism.
A processor register is a quickly accessible location available to a computer's processor. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only. In computer architecture, registers are typically addressed by mechanisms other than main memory, but may in some cases be assigned a memory address e.g. DEC PDP-10, ICT 1900.
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.
In the 80386 microprocessor and later, virtual 8086 mode 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.
In computing, the x86 memory models are a set of six different memory models of the x86 CPU operating in real mode which control how the segment registers are used and the default size of pointers.
In the x86 architecture, the CPUID instruction is a processor supplementary instruction allowing software to discover details of the processor. It was introduced by Intel in 1993 with the launch of the Pentium and SL-enhanced 486 processors.
The Time Stamp Counter (TSC) is a 64-bit register present on all x86 processors since the Pentium. It counts the number of CPU cycles since its reset. The instruction RDTSC returns the TSC in EDX:EAX. In x86-64 mode, RDTSC also clears the upper 32 bits of RAX and RDX. Its opcode is 0F 31. Pentium competitors such as the Cyrix 6x86 did not always have a TSC and may consider RDTSC an illegal instruction. Cyrix included a Time Stamp Counter in their MII.
A control register is a processor register that changes or controls the general behavior of a CPU or other digital device. Common tasks performed by control registers include interrupt control, switching the addressing mode, paging control, and coprocessor control.
A test register, in the Intel 80386 and Intel 80486 processor, was a register used by the processor, usually to do a self-test. Most of these registers were undocumented, and used by specialized software. The test registers were named TR3 to TR7. Regular programs don't usually require these registers to work. With the Pentium, the test registers were replaced by a variety of model-specific registers (MSRs).
On the x86 architecture, a debug register is a register used by a processor for program debugging. There are six debug registers, named DR0...DR7, with DR4 and DR5 as obsolete synonyms for DR6 and DR7. The debug registers allow programmers to selectively enable various debug conditions associated with a set of four debug addresses. Two of these registers are used to control debug features. These registers are accessed by variants of the MOV instruction. A debug register may be either the source operand or destination operand. The debug registers are privileged resources; the MOV instructions that access them can only be executed at privilege level zero. An attempt to read or write the debug registers when executing at any other privilege level causes a general protection fault.
Memory type range registers (MTRRs) are a set of processor supplementary capability control registers that provide system software with control of how accesses to memory ranges by the CPU are cached. It uses a set of programmable model-specific registers (MSRs) which are special registers provided by most modern CPUs. Possible access modes to memory ranges can be uncached, write-through, write-combining, write-protect, and write-back. In write-back mode, writes are written to the CPU's cache and the cache is marked dirty, so that its contents are written to memory later.
In computing, Machine Check Architecture (MCA) is an Intel and AMD mechanism in which the CPU reports hardware errors to the operating system.
Transactional Synchronization Extensions (TSX), also called Transactional Synchronization Extensions New Instructions (TSX-NI), is an extension to the x86 instruction set architecture (ISA) that adds hardware transactional memory support, speeding up execution of multi-threaded software through lock elision. According to different benchmarks, TSX/TSX-NI can provide around 40% faster applications execution in specific workloads, and 4–5 times more database transactions per second (TPS).