Processor Types and Specifications - Upgrading and Repairing PCs - page 157

If you unlock these cores using a method such as enabling the Advanced Clock Cal-
ibration (ACC) feature in the system BIOS (see http://www.tomshardware.com/reviews/
unlock-phenom-ii,2273-5.html for details), one of the following results can take place:
• The unlocked core may function perfectly. This is the result if a core were disabled
strictly to enable the chip to be sold as an X3 rather than an X4.
• Your system boots and runs normally, but the 'unlocked' core can't be detected or
used. A core disabled because of moderate problems would result in this problem.
• Your system might not boot or might not be able to run Windows until you reset the
ACCsettinginyoursystemBIOStoitsdefaultmode.Moreseriouscorestabilityprob-
lems would cause this result.
• You could destroy your processor or motherboard. This would be the result if the core
were disabled because it contained a short.
To be able to try unlocking disabled cores, you need a motherboard that has an adjustable
ACC setting in the system BIOS (many motherboards using the AMD750 South Bridge
[SB] feature this option) and a motherboard BIOS that does not include AMD-provided
microcode to prevent unlocking via the ACC adjustment routine.
Although the AMD850 South Bridge used on the latest motherboards does not include
an ACC option, motherboard vendors such as ASUS and Gigabyte have added an ACC
chip to their motherboards and added core unlocking capabilities to their BIOS setups.
MSIalsooffersunlocking,butisusingapurelyBIOS-basedunlockroutineforitsmother-
boards with the SB850 processor.
If you do unlock an additional core or two, you might enjoy faster performance and better
multithreaded and multitasking operating for free, or you might find your system to be
unstable or unable to start. Before you assume that a system that runs with an unlocked
core is truly stable, use some of the tests I recommend in Chapter 20 , “ PC Diagnostics,
Testing, and Maintenance .”
Bus Speeds and Multipliers
Modernprocessorsrunatamultipleofthemotherboardspeed,andtheselectedmultipleis
usually locked within the processor; therefore, all you can do to change speeds is change
the processor bus speed settings. The processor bus is also called the CPU bus , FSB, or
processor side bus (PSB), all of which are interchangeable terms.
For example, I built a system that uses an Intel Pentium 4 3.2E processor, which typically
runs at 3,200MHz on an 800MHz CPU bus. Thus, the processor is locked to run at four
times the speed of the CPU bus. I was able to increase the CPU bus speed from 800MHz
to 832MHz, which meant the processor speed increased from 3,200MHz to 3,328MHz,