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Processor Update Feature

All processors can contain design defects or errors. Many times, the effects of any given bug can be avoided by implementing hardware or software workarounds. Intel documents these bugs and workarounds well for its processors in its processor Specification Update manuals; this manual is available from Intel's Web site. Most of the other processor manufacturers also have bulletins or tips on their Web sites listing any problems or special fixes or patches for their chips.

Previously, the only way to fix a processor bug was to work around it or replace the chip with one that had the bug fixed. Now, a new feature built into the Intel P6 processors, including the Pentium Pro and Pentium II, can allow many bugs to be fixed by altering the microcode in the processor. Microcode is essentially a set of instructions and tables in the processor that control how the processor operates. These processors incorporate a new feature called reprogrammable microcode, which allows certain types of bugs to be worked around via microcode updates. The microcode updates reside in the system ROM BIOS and are loaded into the processor by the system BIOS during the power on self test (POST). Each time the system is rebooted, the fix code is reloaded, ensuring that it will have the bug fix installed anytime the processor is operating.

The easiest method for checking the microcode update is to use the Pentium Pro and Pentium II processor update utility, which is developed and supplied by Intel. This utility can verify whether the correct update is present for all Pentium Pro processor-based motherboards. The utility displays the processor stepping and version of the microcode update. A stepping is the processor hardware equivalent of a new version. In software, we refer to minor version changes as 1.0, 1.1, 1.2, and so on, while in processors we call these minor revisions steppings.

To install a new microcode update, however, the motherboard BIOS must contain the routines to support the microcode update, which virtually all Pentium Pro and Pentium II BIOSes do have. The Intel processor update utility determines whether the code is present in the BIOS, compares the processor stepping with the microcode update currently loaded, and installs the new update, if needed. Use of this utility with motherboards containing the BIOS microcode update routine allows just the microcode update data to be changed; the rest of the BIOS is unchanged. A version of the update utility is provided with all Intel boxed processors. The term boxed processors refers to processors packaged for use by system integrators—that is, people who build systems. If you want the most current version of this utility, you have to contact an Intel processor dealer to download it, because Intel only supplies it to its dealers.

Note that if the BIOS in your motherboard does not include the processor microcode update routine, you should get a complete system BIOS upgrade from the motherboard vendor.

When you are building a system with a Pentium Pro, Celeron, or Pentium II/III processor, you must use the processor update utility to check that the system BIOS contains microcode updates that are specific to particular silicon stepping of the processor you are installing. In other words, you must ensure that the update matches the processor stepping being used.

Table 3.18 contains the current microcode update revision for each processor stepping. These update revisions are contained in the microcode update database file that comes with the Pentium Pro processor and Pentium II processor update utility. Processor steppings are listed in the sections on the Pentium, Pentium Pro, and Pentium II processors later in this chapter.

Table 3.18 Processor Steppings (Revisions) and Microcode Update Revisions Supported by the Update Database File PEP6.PDB

Processor

Stepping

Stepping Signature

Microcode Update Revision Required

Pentium Pro

C0

0x612

0xC6

Pentium Pro

sA0

0x616

0xC6

Pentium Pro

sA1

0x617

0xC6

Pentium Pro

sB1

0x619

0xD1

Pentium II

C0

0x633

0x32

Pentium II

C1

0x634

0x33

Pentium II

dA0

0x650

0x15


Using the processor update utility (CHECKUP3.EXE) available from Intel, a system builder can easily verify that the correct microcode update is present in all systems based on the P6 (Pentium Pro, Celeron, Pentium II/III, and Xeon) processors. For example, if a system contains a processor with stepping C1 and stepping signature 0x634, the BIOS should contain the microcode update revision 0x33. The processor update utility identifies the processor stepping, signature, and microcode update revision that is currently in use.

If a new microcode update needs to be installed in the system BIOS, the system BIOS must contain the Intel-defined processor update routines so the processor update utility can permanently install the latest update. Otherwise, a complete system BIOS upgrade is required from the motherboard manufacturer. It is recommended that the processor update utility be run after upgrading a motherboard BIOS and before installing the operating system when building a system based on any P6 processor. The utility is easy to use and executes in just a few seconds. Because the update utility may need to load new code into your BIOS, ensure that any jumper settings on the motherboard are placed in the "enable flash upgrade" position. This enables writing to the flash memory.

After running the utility, turn off power to the system and reboot—do not warm boot—to ensure that the new update is correctly initialized in the processor. Also ensure that all jumpers, such as any flash upgrade jumpers, and so on, are returned to their normal position.

Both Intel and AMD have a number of useful utilities available for downloading from their Web sites, utilities which can be very useful for somebody who is building a system. These include utilities which will identify exactly which processor you have, the speed the processor is running at, in some cases whether it has been overclocked, and even useful information like processor temperature, steppings, and more.

In addition to software utilities, both Intel and AMD have extensive technical documentation libraries online, all free for downloading. These documents range from the actual processor and chipset data books to motherboard schematics, design guides, and even information about cooling and thermal requirements.

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