Processor Microcode Explained: Updates, Fixes, and Performance Impact

Processor microcode is a set of low-level control instructions that help the CPU perform certain operations. Thanks to microcode updates, manufacturers like Intel and AMD can fix some bugs and vulnerabilities in already released processors, without changing their physical design.

However, microcode does not replace regular software or turn an old processor into a new one. It adjusts specific chip mechanisms, and updates can be delivered via BIOS/UEFI or through the operating system.

What Is Processor Microcode?

Microcode is an internal control mechanism within the processor, used to implement certain machine instructions and operations. It defines the sequence of low-level actions required to execute them.

A modern CPU consists of many hardware blocks: execution units, registers, cache memory, and control logic. Some instructions are processed directly by hardware circuits, while more complex operations may utilize microcode.

Unlike regular software, microcode operates inside the processor and is not directly accessible to applications. Users cannot arbitrarily modify it or run it as a standalone program.

It's important to distinguish between microcode and BIOS/UEFI. BIOS/UEFI is the motherboard firmware responsible for initial hardware setup and system boot. It may contain a microcode update that loads into the processor when the computer starts.

In summary, microcode is part of the CPU's internal control logic, while BIOS/UEFI is one way to deliver its updates.

How Processor Microcode Works

When a program executes a command, the processor receives a machine instruction, decodes it, and sends it to internal execution units. Simple instructions may be handled directly by hardware, while more complex ones are managed via microcode.

In modern x86 processors, microcode helps translate certain complex instructions into sequences of internal micro-operations. These micro-operations are executed by the CPU's computational blocks.

For example, a single machine instruction might require several actions: reading data from memory, performing calculations, and storing the result. Microcode manages the sequence of these operations, as dictated by the processor's architecture.

How Microcode Loads

The base version of microcode is embedded in the processor during manufacturing. However, some CPUs support loading fixes that alter the behavior of certain internal mechanisms.

The update process usually works as follows:

1. When the computer powers on, the processor starts with its built-in microcode.
2. BIOS/UEFI detects the CPU's model and revision.
3. If a suitable update is available, it is loaded into the CPU.
4. The processor applies the fixes and continues normal operation.

The operating system can also load microcode updates if both the CPU and OS support this feature.

A key point: loaded microcode updates are typically stored in the processor's volatile memory. They are lost when power is removed, so updates must be reapplied at every startup.

Microcode cannot change the physical construction of the chip, add cores, or increase cache size. Its capabilities are limited to mechanisms provided by the manufacturer.

For more about how a processor executes instructions and which characteristics determine its performance, read the article Why IPC Matters More Than GHz: Understanding Modern CPU Performance.

What Issues Do Microcode Updates Fix?

Microcode updates allow Intel and AMD to correct certain processor bugs discovered after release. These fixes can improve system stability, patch vulnerabilities, and adjust CPU internal mechanisms.

Main reasons for issuing updates include:

• Computation errors: Correcting improper execution of specific instructions and rare hardware faults.
• System instability: Fixing causes of freezes, crashes, and unexpected reboots.
• Security vulnerabilities: Changing processor behavior to reduce the risk of attacks exploiting microarchitecture features.
• Processor management bugs: Adjusting algorithms related to power consumption, voltage, and other CPU operating modes.

Examples of Intel and AMD Updates

One well-known case involved stability problems in Intel Core 13th and 14th generation desktop CPUs. In 2024, Intel released microcode updates to limit incorrect high-voltage requests, which could contribute to processor degradation.

The company has continued releasing fixes. Intel recommends affected users install the latest BIOS with microcode 0x12F or newer. Note that updates do not repair physical chip damage that has already occurred.

For AMD processors, microcode is also used to patch vulnerabilities. For instance, Zenbleed fixes for affected Zen 2 CPUs were aimed at preventing data leaks through instruction execution quirks.

Can Microcode Updates Reduce Performance?

Yes, some microcode updates can affect processor performance. This is especially true for fixes addressing vulnerabilities related to speculative execution and other acceleration mechanisms.

The performance impact depends on the specific fix and workload. In everyday applications, the difference may be negligible, while certain server tasks could see more noticeable slowdowns.

However, a microcode update does not always reduce CPU speed. Many fixes have little to no effect on performance, and resolving instability can make your computer more reliable.

How to Update Processor Microcode

Updating CPU microcode usually doesn't require separate installation. Manufacturers distribute fixes via motherboard BIOS/UEFI updates or through operating system updates.

Updating via BIOS/UEFI

This is one of the main ways to update microcode. The motherboard manufacturer includes Intel or AMD fixes in a new BIOS version, which is then loaded into the processor at boot.

Update steps:

1. Identify your exact motherboard model.
2. Visit the official website of your motherboard manufacturer.
3. Find the BIOS section in the downloads list.
4. Check the new version's description for microcode updates or CPU stability fixes.
5. Install the update following the manufacturer's instructions.

Important: Only update the BIOS for your specific motherboard model and revision. Do not interrupt the flashing process, and if possible, ensure stable power during the update.

For more on the differences between computer boot systems, see the article UEFI vs BIOS: Key Differences and How Modern PCs Boot.

Updating via Windows and Linux

On Windows, microcode fixes are sometimes distributed via Windows Update. For supported CPUs, Microsoft releases special updates that allow microcode fixes to be loaded without reflashing the BIOS.

On Linux, Intel and AMD microcode is typically supplied in intel-microcode and amd64-microcode packages or similar packages in your distribution. With proper setup, fixes load early in the OS boot process.

Both methods let you update microcode without physically altering the processor.

Do You Need to Update Microcode Manually?

Most users only need to keep their BIOS/UEFI and operating system up to date. Manual microcode installation is rarely required.

Not every BIOS update contains new microcode, and OS updates do not always replace the need for motherboard firmware updates. If a serious vulnerability or stability issue is discovered, check the recommendations from your processor's manufacturer.

How to Check Processor Microcode Version and Whether You Need to Update

The microcode version shows which fixes are applied to your CPU. You can check it using your operating system or specialized tools.

How to Check the Microcode Version

On Windows, one of the easiest ways is to use HWiNFO. This tool displays your processor's technical specs, including microcode ID and version, if available for your system.

On Linux, check the loaded version in the terminal:

grep microcode /proc/cpuinfo

This command outputs the microcode version for logical CPUs. If the update loaded successfully, you'll usually see the new version applied.

To determine if your microcode is current, compare the version number with information from your CPU or motherboard manufacturer. Be sure to consider your exact CPU model and revision: identical version numbers for different processors might not mean identical fixes.

When Is an Update Needed?

Check for updates in these cases:

• The manufacturer has reported a critical CPU vulnerability.
• Your computer experiences freezes or instability for which a fix has been released.
• The new BIOS version description lists fixes for your CPU.
• The manufacturer recommends updating for your installed CPU model.

If your computer is stable and there are no critical fixes for your CPU, urgent microcode updates are usually unnecessary. Still, regularly installing vetted security updates is a good practice.

Don't rely solely on the version number. It's more important to understand what the update fixes, whether it applies to your CPU, and if it's recommended by the manufacturer.

Conclusion

Processor microcode allows Intel and AMD to fix some CPU bugs and vulnerabilities without replacing the chip itself. As a result, even older processors can receive updates that improve security and stability.

Most users do not need to update microcode manually. Keeping BIOS/UEFI and the operating system up to date is usually sufficient. Pay special attention to critical vulnerability and stability fixes that affect your specific CPU model.

Remember, microcode cannot repair physical damage or hardware defects. Its capabilities are limited to what the manufacturer designed into the chip.