A complete file system software stack providing support for a variety of media through a uniform, easy-to-use programming interface.

Allows for interoperability, fail-safety, and high performance, all at once.



Interoperable: Cs/FS implements the ubiquitous FAT12/16/32 file system allowing for unrivaled data sharing possibilities. Includes long filename support as well as UTF-8 character encoding.

Reliable: Cs/FS' journaling module guarantees that the file system's internal state will remain consistent in the case of untimely power failures.

Low footprint: with a minimal requirement of one buffer, Cs/FS can run with as little as 1kB of available RAM.

Flash memory support: Cs/FS provides support for NOR and NAND flash memory through a highly configurable Flash Translation Layer (FTL). In addition to providing a uniform block device abstraction on top of heterogeneous flash technologies, the FTL optimizes flash memory lifetime thanks to its built-in wear-leveling mechanisms.

Removable media support: Cs/FS provides support for SD cards, Multimedia Memory Cards (MMC) and MSC devices, including asynchronous insertion/removal notification to the application and stale files access protection.

Performance: Cs/FS offers high performance without sacrificing reliability. This is thanks to a sophisticated write-back caching mechanism that is journaling-compatible. Moreover, its advanced locking scheme ensures thread safety while allowing a high degree of concurrency.

Easy to use: Cs/FS offers unprecedented ease of use through both its native and POSIX compliant APIs.

Customizable: The memory footprint (both RAM and ROM) of μC/OS-FS can be adjusted at compile-time based on the required features



Memory Footprint


Minimal (block device only): 7 Kbytes

Typical: 65 Kbytes


Minimal (bare-metal, file API, and SD driver): 1 Kbytes

Typical: 5 Kbytes


 Key Specifications

Memory allocation

Static and dynamic mode supported
File operations Read, write, truncate, rename, copy, query
Kernel Required No
POSIX compliant Yes
File buffers supported Yes
Supported file systems FAT12/16/32
Raw block device interface Yes

Preemptive file read operations

Preemptive file write operations on different volumes

Fail-safe Yes (with optional journaling module)
Write back caching Yes (can be used along with journaling)
Partition support Yes (DOS-style partitions)
Unicode support Yes
Storage media technology support NAND, NOR, SD (card mode + SPI), SCSI, RAM
Bare metal support Yes


Storage Device Support

SD/MMC SD, SDHC, and SDXC cards, as well as MMC cards and e-MMC chips. Card mode and SPI implementations are available. SD Specification v2.00 or later supported.
NAND SLC and MLC memories with a parallel bus. Both small page and large page devices are supported. Fast ECC (error correction codes) are provided for 1-bit correction per codeword using Hamming codes. Hardware ECC is supported (either on the memory device or as a CPU peripheral).
NOR Support for a wide variety of serial SPI/QSPI and parallel NOR.
MSC All MSC compatible USB drives.



Commercial License

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Technical Support

Technical Support Plan

Technical support services for any of the Cs/ software is readily available to all customers currently using or interested in the Cs/ family of RTOS components.

If you are currently without technical support for the Cs/OS software don’t go at it alone. Please contact us to learn how our Cs/OS product experts, with years of embedded software experience, can save you valuable engineering time and money.

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Consulting Services

Specialized Engineering Services

Do you need specialized assistance with your Cesium-based embedded project? Do you need real-time embedded software expertise for your mission critical application? For these or any other embedded software projects, help is available via our Consulting Services that are tailored to your unique needs. Please contact us with your requirements to learn how we can quickly deliver our expertise to your team.

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Cesium software includes comprehensive documentation, full source code, powerful debugging features, and support for a huge range of CPU architectures.


Cesium software offers unprecedented ease-of-use, a small memory footprint, remarkable energy efficiency, and all with a full suite of protocol stacks.


Engineers across the world building industrial controls, medical devices, and aerospace systems know they can rely on Cesium software for the foundation of exceptional products.