Internal Cache Test Failed – Cache is Disabled

Internal Cache Test Failed – Cache is Disabled

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Explanation: The BIOS has tested the processors internal cache and has determined that it is not functioning correctly, and has disabled it. Although we discuss the processor cache in greater detail elsewhere on our Web site, a brief explanation might be helpful.

Primary (Level 1) Cache and Cache Controller
All modern processors incorporate a small, high-speed cache built right onto the chip. This is designed to hold recently-used data and instructions received from memory. A computer science principle called locality of reference states that if the processor recently referred to a location in memory, it is likely that it will refer to it again in the near future. Using a cache to hold recently used memory values saves the processor from going to memory each time to reload them, thus making the system faster. This provides a significant performance boost, because main memory is much slower than the processor’s cache.

The cache on the processor is called primary (or level 1) because it is the cache closest to the processor. Each time the processor requests information from memory, the cache controller on the chip uses special circuitry to first check if the memory data is already in the cache. If it is, then the system is spared a time consuming access to the main memory. Most computers also use a secondary or level 2 cache, to some of this recently used data that doesn’t fit in the smaller primary cache.

A full explanation of cache principles, the different levels of caching in a PC and caching protocols and technologies, can be found in our Performance Center under processors. The principles of operation of the primary and secondary caches are similar, however the actual technology used for primary and secondary caches is of course different, as are their sizes and speeds.

The typical processor primary cache ranges in size from 8 KB to 256 KB, with larger amounts on the newer processors reaching 2 gigabytes. Older processors (386 class and earlier) have no primary cache at all. The majority of these caches are very fast because they run at the full speed of the processor and are integrated into it.

Processors can organize their primary cache in two different ways. Some processors have a single cache with which to handle both command instructions and program data, which is referred to as a unified cache. Some processors have separate data and instruction caches. In some cases the capabilities of the data and instruction caches may be slightly different, as in the Pentium processor. The Pentium data cache can use the write-back write policy, whereas the instruction cache is write-through only. The overall performance difference between integrated and separate primary caches is not significant.

You may find that a unified cache is also referred to as an integrated cache, however it is not to be confused with the integrated secondary cache of the Pentium Pro and later Pentium II, III and Pentium IV processors. Integrated, in the context of these later processors means that the secondary cache is in the same package as the chip itself.

Diagnosis: It is very unusual for the internal cache to be nonfunctional while the rest of the processor is. This is likely a processor or motherboard problem.

Recommendation:

  • Troubleshoot the processor by testing it in a known good motherboard. If it functions in another motherboard, then you have narrowed the issue to the socket on the motherboard or the motherboard itself.
  • Troubleshooting the motherboard can be difficult at best. If your testing narrows the issue to the motherboard only, replace it.

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