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Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →A system-level cache is a cache that operates at or below the operating-system layer, keeping data or metadata so later access can be served more efficiently. It is an umbrella term, not the standard name for one specific component. The precise meaning depends on the layer: it may refer to cached file data, storage-device data, or hardware information such as address translations.
What does “system-level cache” mean?
A cache retains information that may be needed again, allowing a later request to use the retained copy instead of repeating a more costly operation. In the system-level examples covered here, the cache improves access to data or metadata while the backing file or storage device remains the source of the data.
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Because the term is not a uniquely standardized component name, check the context in which it appears. A discussion of memory and files may mean the operating system’s page cache; storage configuration may mean a block-device cache; processor documentation may mean a CPU cache or translation lookaside buffer (TLB). These caches retain different kinds of information.
What are the main cache layers?
Operating-system page cache
The page cache holds file data in physical memory. Linux kernel documentation calls it “the primary way that the user and the rest of the kernel interact with filesystems.” Ordinary file reads, writes, and memory mappings generally use it; O_DIRECT is an example of a path that can bypass it. See the Linux 6.9 Page Cache documentation.
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When Linux reads file data from storage, it places that data in the page cache so a later read can avoid another storage access. Writes also enter the cache. A page that has been changed but not yet written to its backing storage is marked dirty, so data being “in the cache” does not by itself mean the write has reached the storage device. The kernel describes this read and write behavior in its Page Cache documentation.
CPU cache and TLB
A CPU cache is a hardware cache close to the processor. A TLB is more specific: Linux describes it as a CPU cache of virtual-to-physical address translations derived from software page tables. It caches address-translation information, not file contents. The Linux kernel explains the distinction in its page-table documentation.
Storage or block-device cache
A block-device cache can keep data from a larger, slower origin device on a smaller, faster cache device. Linux’s dm-cache supports writeback, writethrough, and passthrough modes, which differ in where writes go and when they are considered complete. These are storage configuration choices, not alternate names for the page cache. Details are in the Linux device-mapper cache documentation.
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Filesystem caching framework
Some operating systems also provide a framework through which filesystems can use cache backends, including for network filesystems. Linux documentation covers cache interfaces, invalidation, and management in its filesystem caching documentation.
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Does cached data use memory permanently?
Not necessarily. Linux can reclaim page-cache memory when it is needed for other uses because cached file data can be read from storage again. Memory reported as cache is therefore not automatically unavailable to applications. This behavior describes Linux page-cache memory; it is not a guarantee that every system cache is harmless, instantly reclaimable, or safe to clear. Dirty pages and other cache types can have different consequences.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How do the Linux dm-cache write modes differ?
| Mode | Write behavior |
|---|---|
| Writeback | Writes can be deferred to the origin device. |
| Writethrough | Writes wait to reach both the cache and origin devices. |
| Passthrough | Reads are served from the origin device, and writes are forwarded there. |
These mode descriptions apply to Linux dm-cache. They do not describe every system-level cache. For an actual configuration, the origin and cache devices, block size, policy, and write mode all matter; consult the current kernel documentation and the system’s configuration before changing storage behavior.
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What should you check when you see the term?
- Identify the layer: Is the context about files and memory, storage devices, processor hardware, or address translation?
- Ask what is retained: File contents, storage blocks, or address mappings imply different cache behavior.
- Check write behavior: A cached write may still be waiting to reach backing storage.
- Check the operating system or product: The Linux page-cache and
dm-cacheexamples are Linux-specific; the broad phrase alone does not establish how another system works.
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