Central Processing Unit Technologies
Reviews | Category: Misc
The central processing unit (CPU) is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. CPUs are composed of thin layers of thousands of transistors, i.e. semi-conductors resisting or conducting electrical flow depending on the voltage. The transistors' ability to transform from a non-conducting to a conducting state allow them to convert electrical input signals into a new output signal. When one or more of the inputs receive electricity, the combined charge changes the state of the transistor internally and produces an output which may serve as new input for a transistor. This simple effect of the transistor is what makes it possible for the computer to count and perform logical operations, all of which we call processing. The speed of processing depends on the CPU's ability to create electrical currents serving as input for the transistors. These currents are generated by an electrical voltage which changes from low to high and back again at regular intervals. The resulting signal is a wave of which the alternating rate (frequency) is measured in Hertz. For instance, a CPU of 3 gigahertz can produce 3,000,000,000 voltage cycles per second. Note that the speed of processing is merely a projection (and not a reflection) of CPU performance. Modern CPUs are integrated chips, which means that they combine several types of components into a single piece of silicon. These components typically consist of one or more execution cores, arithmetic unit (ALU), logic unit, registers, instruction memory, cache memory and the input/output controller (bus controller). CPU manufacturers engineer new ways to do processing that requires some significant re-engineering of the current chip design. When they create this new design that changes the number of bits the chip can handle, or some other major way in which the chip performs its job, they are creating a new generation of processors.
This page provides information about CPU flags. These flags indicate the technologies a processor supports, and can be retrieved in Ubuntu by typing grep --color=always -i flags /proc/cpuinfo in the console. On Windows systems, the command-line utility Coreinfo can be used for the same purpose.
Intel-defined CPU features (x86)
The common architecture behind all Intel microprocessors is known as the x86 architecture. Until the late 80s, Intel was essentially the only producer of PC microprocessors. Nowadays, however, several manufacturers (including AMD) produce chips supporting the Intel instruction set. A detailed overview of the Intel 64 instruction set can be found here.
- fpu Onboard FPU. A floating-point unit (FPU, colloquially a math coprocessor) is a part of a computer system specially designed to carry out operations on floating point numbers. With the Intel family of processors up until the 80486DX the floating point unit was an external unit (commonly called a math coprocessor), subsequent processors such as the Pentium have the FPU built in. The evolution of Internet has considerably increased the employability of a FPU, which is now commonly used by numerous video and audio applications.
- vme Virtual Mode Extensions. This extension 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. Examples are the execution of DOS programs in Windows/386, Windows 3.x, Windows 9x/Me and OS/2 2.x.
- de The Debugging Extensions consist of several scan chains around the processor, and some additional signals that are used to control the behavior of the processor for debug purposes.
- pse The Page Size Extensions allow increased memory allocations to avoid cluttering of the TLB cache. This may considerably improve performance, but also increase the risk of fragmentation.
- tse The Time Stamp Counter is a register that stores the number of CPU cycles since the last reset. It is used as a low-overhead (but rather inaccurate) technique of getting CPU timing information.
- msr Model-Specific Registers are control registers used for performance monitoring, debugging, testability and program execution tracing. They often also allow enabling or disabling certain model-specific features of the processor implementation.
- pae The Physical Address Extensions is a feature to increase the maximal physical memory size (including random access memory and memory mapped devices) of (32-bit) x86 processors from 4 GB to 64 GB. To use PAE, operating system support is required. An example is the installation of a new linux kernel.
- mce The Machine Check Exception allows tracking of hardware errors that occurs when the CPU detects a hardware problem. In Windows, these errors usually lead to a Blue Screen Of Death (BSOD).
- cx8 CMPXCHG8 instruction
- apic Onboard APIC. The Advanced Programmable Interrupt Controller allows the implementation of priority models and Advanced Interrupt Requests. For this purpose, it contains a timer and a mechanism for generating and accepting interrupts. The APICs are essential in a multiprocessor system and provide interprocessor communication. More information.
- sep The SYSENTER/SYSEXIT instructions aim to optimize programs' service requests from an operating system's kernel. In essence, they reduce the necessary memory reads to identify the target of system calls by relying on the Model-Specific Registers.
- mtrr The Memory Type Range Registers are a set of processor supplementary capabilities control registers that provide system software with control of how accesses to memory ranges by the CPU are cached. Hereto, it uses a set of programmable Model-Specific Registers.
- pge Page Global Enable is a flag in the CR4 control register to allow sharing of address translations (PDE or PTE records) between address spaces.
- mca Machine Check Architecture is a mechanism in which the CPU reports hardware errors to the operating system. Typical errors are system bus errors, ECC errors, parity errors, cache errors, and translation lookaside buffer errors.
- cmov Conditional Move (CMOV) instructions are combined instructions that increase code density and improve performance for for unpredictable branches. An example is the following line of C code that has a condition dependent upon one of the constants: X = (A < B) ? CONST1 : CONST2;. This code conditionally compares two variables, A and B. If the condition is true, X is set to CONST1; otherwise it is set to CONST2. An assembly code sequence equivalent to the aforementioned C code can contain unpredictable branches if the variables A and B are independent. Note: Linus Torvald is clearly not a proponent of CMOV. He argues that the performance gain is not worth the effort, and that its use is only advantageous under fairly limited circumstances.
- pat Page Attribute Table is a processor supplementary capability extension to the page table format to allow fine-grained control over how areas of memory are cached. This greatly increases an operating system's ability to select the most efficient behavior for any given task.
- pse36 The 36-bit Page Size Extensions (PSE) is a simpler alternative to PAE for extending the physical memory addressing capabilities from 32 bits to 36 bits.
- pn This flag indicates whether there is a CPUID instruction to obtain a 96-bit Processor Serial number. The processor serial number creates a software accessible identity for an individual processor, and can be used for user identification when combined with other qualifiers. In addition, it provides information about the features supported by and implemented on the Intel processor.
- clflsh The Cache Line Flush instruction flushes a Cache Line from all levels of cache. It is a useful instruction to remove stale data from the CPU cache.
#define X86_FEATURE_DS (0*32+21) /* "dts" Debug Store */
#define X86_FEATURE_ACPI (0*32+22) /* ACPI via MSR */
#define X86_FEATURE_MMX (0*32+23) /* Multimedia Extensions */
#define X86_FEATURE_FXSR (0*32+24) /* FXSAVE/FXRSTOR, CR4.OSFXSR */
#define X86_FEATURE_XMM (0*32+25) /* "sse" */
#define X86_FEATURE_XMM2 (0*32+26) /* "sse2" */
#define X86_FEATURE_SELFSNOOP (0*32+27) /* "ss" CPU self snoop */
#define X86_FEATURE_HT (0*32+28) /* Hyper-Threading */
#define X86_FEATURE_ACC (0*32+29) /* "tm" Automatic clock control */
#define X86_FEATURE_IA64 (0*32+30) /* IA-64 processor */
#define X86_FEATURE_PBE (0*32+31) /* Pending Break Enable */
/* AMD-defined CPU features, CPUID level 0x80000001, word 1 */
/* Don't duplicate feature flags which are redundant with Intel! */
#define X86_FEATURE_SYSCALL (1*32+11) /* SYSCALL/SYSRET */
#define X86_FEATURE_MP (1*32+19) /* MP Capable. */
#define X86_FEATURE_NX (1*32+20) /* Execute Disable */
#define X86_FEATURE_MMXEXT (1*32+22) /* AMD MMX extensions */
#define X86_FEATURE_FXSR_OPT (1*32+25) /* FXSAVE/FXRSTOR optimizations */
#define X86_FEATURE_GBPAGES (1*32+26) /* "pdpe1gb" GB pages */
#define X86_FEATURE_RDTSCP (1*32+27) /* RDTSCP */
#define X86_FEATURE_LM (1*32+29) /* Long Mode (x86-64) */
#define X86_FEATURE_3DNOWEXT (1*32+30) /* AMD 3DNow! extensions */
#define X86_FEATURE_3DNOW (1*32+31) /* 3DNow! */
/* Transmeta-defined CPU features, CPUID level 0x80860001, word 2 */
#define X86_FEATURE_RECOVERY (2*32+ 0) /* CPU in recovery mode */
#define X86_FEATURE_LONGRUN (2*32+ 1) /* Longrun power control */
#define X86_FEATURE_LRTI (2*32+ 3) /* LongRun table interface */
/* Other features, Linux-defined mapping, word 3 */
/* This range is used for feature bits which conflict or are synthesized */
#define X86_FEATURE_CXMMX (3*32+ 0) /* Cyrix MMX extensions */
#define X86_FEATURE_K6_MTRR (3*32+ 1) /* AMD K6 nonstandard MTRRs */
#define X86_FEATURE_CYRIX_ARR (3*32+ 2) /* Cyrix ARRs (= MTRRs) */
#define X86_FEATURE_CENTAUR_MCR (3*32+ 3) /* Centaur MCRs (= MTRRs) */
/* cpu types for specific tunings: */
#define X86_FEATURE_K8 (3*32+ 4) /* "" Opteron, Athlon64 */
#define X86_FEATURE_K7 (3*32+ 5) /* "" Athlon */
#define X86_FEATURE_P3 (3*32+ 6) /* "" P3 */
#define X86_FEATURE_P4 (3*32+ 7) /* "" P4 */
#define X86_FEATURE_CONSTANT_TSC (3*32+ 8) /* TSC ticks at a constant rate */
#define X86_FEATURE_UP (3*32+ 9) /* smp kernel running on up */
#define X86_FEATURE_FXSAVE_LEAK (3*32+10) /* "" FXSAVE leaks FOP/FIP/FOP */
#define X86_FEATURE_ARCH_PERFMON (3*32+11) /* Intel Architectural PerfMon */
#define X86_FEATURE_PEBS (3*32+12) /* Precise-Event Based Sampling */
#define X86_FEATURE_BTS (3*32+13) /* Branch Trace Store */
#define X86_FEATURE_SYSCALL32 (3*32+14) /* "" syscall in ia32 userspace */
#define X86_FEATURE_SYSENTER32 (3*32+15) /* "" sysenter in ia32 userspace */
#define X86_FEATURE_REP_GOOD (3*32+16) /* rep microcode works well */
#define X86_FEATURE_MFENCE_RDTSC (3*32+17) /* "" Mfence synchronizes RDTSC */
#define X86_FEATURE_LFENCE_RDTSC (3*32+18) /* "" Lfence synchronizes RDTSC */
#define X86_FEATURE_11AP (3*32+19) /* "" Bad local APIC aka 11AP */
#define X86_FEATURE_NOPL (3*32+20) /* The NOPL (0F 1F) instructions */
/* 21 available, was AMD_C1E */
#define X86_FEATURE_XTOPOLOGY (3*32+22) /* cpu topology enum extensions */
#define X86_FEATURE_TSC_RELIABLE (3*32+23) /* TSC is known to be reliable */
#define X86_FEATURE_NONSTOP_TSC (3*32+24) /* TSC does not stop in C states */
#define X86_FEATURE_CLFLUSH_MONITOR (3*32+25) /* "" clflush reqd with monitor */
#define X86_FEATURE_EXTD_APICID (3*32+26) /* has extended APICID (8 bits) */
#define X86_FEATURE_AMD_DCM (3*32+27) /* multi-node processor */
#define X86_FEATURE_APERFMPERF (3*32+28) /* APERFMPERF */
/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
#define X86_FEATURE_XMM3 (4*32+ 0) /* "pni" SSE-3 */
#define X86_FEATURE_PCLMULQDQ (4*32+ 1) /* PCLMULQDQ instruction */
#define X86_FEATURE_DTES64 (4*32+ 2) /* 64-bit Debug Store */
#define X86_FEATURE_MWAIT (4*32+ 3) /* "monitor" Monitor/Mwait support */
#define X86_FEATURE_DSCPL (4*32+ 4) /* "ds_cpl" CPL Qual. Debug Store */
#define X86_FEATURE_VMX (4*32+ 5) /* Hardware virtualization */
#define X86_FEATURE_SMX (4*32+ 6) /* Safer mode */
#define X86_FEATURE_EST (4*32+ 7) /* Enhanced SpeedStep */
#define X86_FEATURE_TM2 (4*32+ 8) /* Thermal Monitor 2 */
#define X86_FEATURE_SSSE3 (4*32+ 9) /* Supplemental SSE-3 */
#define X86_FEATURE_CID (4*32+10) /* Context ID */
#define X86_FEATURE_FMA (4*32+12) /* Fused multiply-add */
#define X86_FEATURE_CX16 (4*32+13) /* CMPXCHG16B */
#define X86_FEATURE_XTPR (4*32+14) /* Send Task Priority Messages */
#define X86_FEATURE_PDCM (4*32+15) /* Performance Capabilities */
#define X86_FEATURE_PCID (4*32+17) /* Process Context Identifiers */
#define X86_FEATURE_DCA (4*32+18) /* Direct Cache Access */
#define X86_FEATURE_XMM4_1 (4*32+19) /* "sse4_1" SSE-4.1 */
#define X86_FEATURE_XMM4_2 (4*32+20) /* "sse4_2" SSE-4.2 */
#define X86_FEATURE_X2APIC (4*32+21) /* x2APIC */
#define X86_FEATURE_MOVBE (4*32+22) /* MOVBE instruction */
#define X86_FEATURE_POPCNT (4*32+23) /* POPCNT instruction */
#define X86_FEATURE_TSC_DEADLINE_TIMER (4*32+24) /* Tsc deadline timer */
#define X86_FEATURE_AES (4*32+25) /* AES instructions */
#define X86_FEATURE_XSAVE (4*32+26) /* XSAVE/XRSTOR/XSETBV/XGETBV */
#define X86_FEATURE_OSXSAVE (4*32+27) /* "" XSAVE enabled in the OS */
#define X86_FEATURE_AVX (4*32+28) /* Advanced Vector Extensions */
#define X86_FEATURE_F16C (4*32+29) /* 16-bit fp conversions */
#define X86_FEATURE_RDRAND (4*32+30) /* The RDRAND instruction */
#define X86_FEATURE_HYPERVISOR (4*32+31) /* Running on a hypervisor */
/* VIA/Cyrix/Centaur-defined CPU features, CPUID level 0xC0000001, word 5 */
#define X86_FEATURE_XSTORE (5*32+ 2) /* "rng" RNG present (xstore) */
#define X86_FEATURE_XSTORE_EN (5*32+ 3) /* "rng_en" RNG enabled */
#define X86_FEATURE_XCRYPT (5*32+ 6) /* "ace" on-CPU crypto (xcrypt) */
#define X86_FEATURE_XCRYPT_EN (5*32+ 7) /* "ace_en" on-CPU crypto enabled */
#define X86_FEATURE_ACE2 (5*32+ 8) /* Advanced Cryptography Engine v2 */
#define X86_FEATURE_ACE2_EN (5*32+ 9) /* ACE v2 enabled */
#define X86_FEATURE_PHE (5*32+10) /* PadLock Hash Engine */
#define X86_FEATURE_PHE_EN (5*32+11) /* PHE enabled */
#define X86_FEATURE_PMM (5*32+12) /* PadLock Montgomery Multiplier */
#define X86_FEATURE_PMM_EN (5*32+13) /* PMM enabled */
/* More extended AMD flags: CPUID level 0x80000001, ecx, word 6 */
#define X86_FEATURE_LAHF_LM (6*32+ 0) /* LAHF/SAHF in long mode */
#define X86_FEATURE_CMP_LEGACY (6*32+ 1) /* If yes HyperThreading not valid */
#define X86_FEATURE_SVM (6*32+ 2) /* Secure virtual machine */
#define X86_FEATURE_EXTAPIC (6*32+ 3) /* Extended APIC space */
#define X86_FEATURE_CR8_LEGACY (6*32+ 4) /* CR8 in 32-bit mode */
#define X86_FEATURE_ABM (6*32+ 5) /* Advanced bit manipulation */
#define X86_FEATURE_SSE4A (6*32+ 6) /* SSE-4A */
#define X86_FEATURE_MISALIGNSSE (6*32+ 7) /* Misaligned SSE mode */
#define X86_FEATURE_3DNOWPREFETCH (6*32+ 8) /* 3DNow prefetch instructions */
#define X86_FEATURE_OSVW (6*32+ 9) /* OS Visible Workaround */
#define X86_FEATURE_IBS (6*32+10) /* Instruction Based Sampling */
#define X86_FEATURE_XOP (6*32+11) /* extended AVX instructions */
#define X86_FEATURE_SKINIT (6*32+12) /* SKINIT/STGI instructions */
#define X86_FEATURE_WDT (6*32+13) /* Watchdog timer */
#define X86_FEATURE_LWP (6*32+15) /* Light Weight Profiling */
#define X86_FEATURE_FMA4 (6*32+16) /* 4 operands MAC instructions */
#define X86_FEATURE_NODEID_MSR (6*32+19) /* NodeId MSR */
#define X86_FEATURE_TBM (6*32+21) /* trailing bit manipulations */
#define X86_FEATURE_TOPOEXT (6*32+22) /* topology extensions CPUID leafs */
#define X86_FEATURE_PERFCTR_CORE (6*32+23) /* core performance counter extensions */
/*
* Auxiliary flags: Linux defined - For features scattered in various
* CPUID levels like 0x6, 0xA etc, word 7
*/
#define X86_FEATURE_IDA (7*32+ 0) /* Intel Dynamic Acceleration */
#define X86_FEATURE_ARAT (7*32+ 1) /* Always Running APIC Timer */
#define X86_FEATURE_CPB (7*32+ 2) /* AMD Core Performance Boost */
#define X86_FEATURE_EPB (7*32+ 3) /* IA32_ENERGY_PERF_BIAS support */
#define X86_FEATURE_XSAVEOPT (7*32+ 4) /* Optimized Xsave */
#define X86_FEATURE_PLN (7*32+ 5) /* Intel Power Limit Notification */
#define X86_FEATURE_PTS (7*32+ 6) /* Intel Package Thermal Status */
#define X86_FEATURE_DTS (7*32+ 7) /* Digital Thermal Sensor */
/* Virtualization flags: Linux defined, word 8 */
#define X86_FEATURE_TPR_SHADOW (8*32+ 0) /* Intel TPR Shadow */
#define X86_FEATURE_VNMI (8*32+ 1) /* Intel Virtual NMI */
#define X86_FEATURE_FLEXPRIORITY (8*32+ 2) /* Intel FlexPriority */
#define X86_FEATURE_EPT (8*32+ 3) /* Intel Extended Page Table */
#define X86_FEATURE_VPID (8*32+ 4) /* Intel Virtual Processor ID */
#define X86_FEATURE_NPT (8*32+ 5) /* AMD Nested Page Table support */
#define X86_FEATURE_LBRV (8*32+ 6) /* AMD LBR Virtualization support */
#define X86_FEATURE_SVML (8*32+ 7) /* "svm_lock" AMD SVM locking MSR */
#define X86_FEATURE_NRIPS (8*32+ 8) /* "nrip_save" AMD SVM next_rip save */
#define X86_FEATURE_TSCRATEMSR (8*32+ 9) /* "tsc_scale" AMD TSC scaling support */
#define X86_FEATURE_VMCBCLEAN (8*32+10) /* "vmcb_clean" AMD VMCB clean bits support */
#define X86_FEATURE_FLUSHBYASID (8*32+11) /* AMD flush-by-ASID support */
#define X86_FEATURE_DECODEASSISTS (8*32+12) /* AMD Decode Assists support */
#define X86_FEATURE_PAUSEFILTER (8*32+13) /* AMD filtered pause intercept */
#define X86_FEATURE_PFTHRESHOLD (8*32+14) /* AMD pause filter threshold */
/* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */
#define X86_FEATURE_FSGSBASE (9*32+ 0) /* {RD/WR}{FS/GS}BASE instructions*/
#define X86_FEATURE_SMEP (9*32+ 7) /* Supervisor Mode Execution Protection */
#define X86_FEATURE_ERMS (9*32+ 9) /* Enhanced REP MOVSB/STOSB */