You know everything about the features of your beloved CPU – its frequency, bus speed, voltage, production process and more. But what about on the inside?
Every CPU comes with a host of features some of which, over time, have been inherited from previous architectures. With the right tools you can view the flags (also called caps) associated with your CPU, but while many programs will display the list of flags reported by your CPU, not many will explain what they actually mean.
If you've already browsed the feature set of your CPU before, you'll know there's a lot of them. We don't have space to cover them all here, but we'll cover the most common or interesting flags you're likely to find.
And who knows, you might learn something you didn't know about your CPU!
3DNOW3DNOWEXT - AMD's 3DNow! multimedia extensions added to its processors starting from 1998, and the answer to Intel's MMX which appeared in 1997. 3DNOWEXT refers to extra instructions later added and unofficially called Extended 3DNow! or Enhanced 3DNow!, and first appeared in Athlon processors.
ACPI - Advanced Configuration and Power Interface, the open standard for device configuration and power management. ACPI support in the CPU signifies it can use and report on low-power states.
APIC - Indicates support for Local APIC in the Advanced Programmable Interrupt Controller standard. Local APIC resides on the CPU and manages all external interrupts that involve the CPU, communicating with system buses that use I/O APICs. It's a core component of modern CPUs and motherboards, and necessary for SMP or multi-core systems.
CX8 - CX8 is worth mentioning for historical reasons. The flag actually represents the CMPXCHG8B instruction, which is used to compare and exchange eight bytes, a function useful for preventing collisions with SMP (or multi-core) systems accessing the same memory location. Unfortunately for Intel, when combined with a lock command in the original Pentium would cause the CPU to reset itself (and Windows to display a blue-screen). This achieved fame as the f00f bug (as actual instruction is [code]f0 0f c7 c8[/code]) and was first reported by Linux developers who found it an amusing bug. Later, both Windows and Linux implemented workarounds until Intel fixed the issue in subsequent CPUs.
CX16 - We've mentioned CX8 so we might as well cover CX16. The CMPXCHG16B instruction, as with CMPXCHG8B, is useful on multi-processor systems and allows for ensuring synchronicity between multiple processors using 128-bit double quad-word data types and high resolution timers. Yeah, that's cryptic but that's all we have space for.
EST - Intel's Enhanced SpeedStep support for dynamically adjusting CPU frequency on the fly to reduce power usage, especially in notebooks.
FPU - On board x87 Floating Point Unit to handle floating point maths, which has been built into CPUs since the 80486. Prior to this, the optional 80387 maths co-processor could be socketed next to an 80386 CPU on appropriate motherboards to add floating-point processing. To give you an idea of timescale, the 80386 (at a blistering 12Mhz) was the Core i7 of 1986. Yeah, awesome music and CPUs back then.
FXSR - Short for FXSAVE/FXRSTOR, aka Fast Save and Restore, this flag represents the FXSAVE instruction that can be used to write the state of the FPU, MMX and SSE control, data, and status registers to a memory location, where FXRSTOR can then restore it. The function is used to reduce the overhead when an operating system needs to perform a context switch (a core function of any multitasking operating system).
HT - Hyperthreading Technology support on Intel CPUs. Originally and ostensibly developed to provide pesudo-SMP functionality on a single-core CPU and, while it did help some tasks, it could slow down others and was generally seen as more of a stunt to one-up AMD than a useful feature. HT isn't used in the dual- and quad- Core Duo range from Intel, but has made a comeback with Core i7. Confusingly, the HT flag can also be found on AMD CPUs where, naturally, it represents the Hyper Transport capability.
LM - Long Mode represents 64-bit capability, for both Intel and AMD CPUs. See last month's X-Ray for more on the 64-bit capabilities of CPUs.
MCA - Machine Check Architecture is a feature of the CPU to be able to report non-critical hardware errors to an operating system.
MCE - Machine Check Exception provides for the CPU to report an unrecoverable problem. You'll see MCE errors in Windows with BSODs. Although it's reported as a hardware error, it can result from the CPU being stressed, such as with overclocking. BSODs with MCEs are a good indication you're pushing your CPU too far.
Issue: 107 | December, 2009