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IEC 11694-4-09 (2014): Logical Data Structures for Optical Memory Cards – Linear Recording Method
Technical insights into the file system architecture and data integrity mechanisms defined by ISO/IEC 11694‑4:2009 and Amendment 1:2014
Scope
IEC 11694-4-09 (2014) (formally published as ISO/IEC 11694‑4:2009/Amd1:2014) is an international standard that specifies the logical data structures for optical memory cards using the linear recording method. It is part of the multi‑part ISO/IEC 11694 series, which defines the physical characteristics, recording techniques, and data organisation for optical cards.
This standard focuses exclusively on the logical layer – that is, how files and directories are organised on the card, how the card’s storage capacity is managed, and how data integrity is maintained throughout the card’s lifecycle. It does not cover physical properties (covered by ISO/IEC 11694‑1) or the modulation and recording method (covered by ISO/IEC 11694‑3). Instead, it bridges the gap between the raw physical tracks and the application software that reads and writes data.
Intended audience: System architects, embedded firmware developers, and quality assurance engineers working with optical memory card readers/writers.
The standard defines a hierarchical file system reminiscent of early optical storage formats. It includes a volume descriptor that identifies the card, a file allocation table (FAT) that maps logical blocks to physical positions, and directory entries that store metadata for each file. The amendment published in 2014 (the “‑09” suffix indicates the 2009 base document with the 2014 amendment) clarified error handling for write‑once media and added support for larger data fields.
Technical Requirements
Volume Structure
Every optical memory card compliant with IEC 11694-4-09 contains a volume descriptor located at a fixed address on the first writable track. The descriptor holds critical parameters such as the card capacity, the size of the file allocation table, the default sector size, and a unique serial number. This descriptor must be readable and writable under the base recording rules of ISO/IEC 11694‑3.
File Allocation Table (FAT)
The FAT is the central directory of all logical blocks. Each entry in the FAT corresponds to one cluster (minimum addressable data unit, typically 512 bytes). The FAT entry contains the cluster number of the next cluster in a file, or a special marker for end‑of‑file (0xFFFF) or a defective cluster (0xFFF7).
| Offset (bytes) | Field | Value | Description |
|---|---|---|---|
| 0–1 | Next cluster | 0x0002 – 0xFFEF | Points to next cluster in file chain (0 means free). |
| 2–3 | Attributes | Bit flags | Reserved, read‑only, hidden, system, archive. |
| 4–5 | Error correction code | CRC‑16 | Protects entry against single‑bit errors. |
Important: The FAT must be written in a single atomic operation when the card is formatted. Partial writes can render the entire volume unreadable.
Directory Entries and File Records
Directories are implemented as files with a special attribute. Each directory entry stores the file name (up to 8 characters + 3 extension), starting cluster, file size, and a timestamp (year, month, day, hour, minute). The standard allows sequential access; random access is supported only if the application caches the FAT chain.
File data is stored in contiguous clusters to the greatest extent possible. The standard defines a defect management scheme: when a write error is detected, the offending cluster is marked as bad in the FAT and the data is relocated to a spare cluster. This process is transparent to the file system.
Error Detection and Correction
Two levels of protection are mandated:
- Per‑sector EDC: A 4‑byte cyclic redundancy check (CRC‑32) computed over the user data and appended to each 512‑byte sector.
- Per‑track ECC: A Reed‑Solomon code (correction capability up to 16 symbol errors per track) written in a dedicated area after the data sectors.
Data integrity: This dual‑level architecture ensures a bit error rate (BER) of better than 10⁻¹² after correction, making optical memory cards suitable for archival and medical imaging applications.
Implementation Highlights
Reading and Writing Strategies
Compliant readers must implement the following algorithm when writing a file:
- Read the existing FAT from the card.
- Locate a contiguous block of free clusters equal to the file size (rounded up to cluster size).
- For each cluster, write the user data plus the per‑sector CRC.
- After writing all data, compute and write the per‑track ECC.
- Update the FAT with the new cluster chain and mark the directory entry.
Firmware designers must ensure that the write laser is properly focused and that the card’s rotational speed is within ±1 % of the nominal value defined in ISO/IEC 11694‑3. The standard also requires that the card’s volume descriptor is re‑read after every write operation to verify it remains intact.
Interoperability Considerations
Because the logical format is specified independently of the physical media, a card written according to IEC 11694-4-09 can be read by any compliant device, regardless of the manufacturer. However, the standard warns that some implementations may use proprietary extensions in the reserved fields of the volume descriptor. These extensions must not interfere with the core file system.
Backward compatibility: Cards formatted under the original ISO/IEC 11694‑4:2001 may not be readable by devices built to the 2014 amendment because the defect management table has moved. Developers should implement a compatibility fallback.
Compliance Notes
Testing and Certification
To claim compliance with IEC 11694-4-09 (2014), a device must pass the following verification tests:
- Format verification: Write a known volume descriptor and FAT, then read it back; the CRC and ECC must match.
- Write‑once test: On WORM media, a cluster that has been written may not be erased; the device must refuse any write attempt to an already‑used cluster (unless it is a spare).
- Read stress test: Read 10,000 random sectors with all delivered CRC and ECC values correct. Any sector failing correction triggers a compliance failure.
Many national test laboratories (e.g., BSI, DIN, UL) offer testing services for optical memory card products. The certification process also includes a review of the firmware source code if the implementation uses any reserved fields.
Documentation Requirements
Manufacturers must provide a compliance statement that lists:
- The version of IEC 11694-4-09 implemented (including the 2014 amendment, if applicable).
- The maximum and minimum cluster sizes supported.
- Whether the device can read cards formatted by earlier editions of the standard.
- The temperature and humidity range for which the logical behaviour is guaranteed (typically 15 °C to 35 °C, 20 % to 85 % RH).
Tip for integrators: Always request a copy of the declaration of conformity from the reader supplier. Cards purchased from different vendors should be cross‑tested before deployment in critical applications.
Frequently Asked Questions
Q: What is the maximum capacity of an optical memory card under IEC 11694-4-09?
A: The standard itself does not define a fixed capacity; it depends on the physical media and track density defined in the lower‑layer standards. The logical structure supports up to 65536 clusters (using 16‑bit cluster numbers). With a cluster size of 512 bytes, the maximum capacity is 32 MB. Larger cards can be supported by using the extended FAT defined in the 2014 amendment, which uses 32‑bit cluster numbers, allowing up to 2 TB.
A: The standard itself does not define a fixed capacity; it depends on the physical media and track density defined in the lower‑layer standards. The logical structure supports up to 65536 clusters (using 16‑bit cluster numbers). With a cluster size of 512 bytes, the maximum capacity is 32 MB. Larger cards can be supported by using the extended FAT defined in the 2014 amendment, which uses 32‑bit cluster numbers, allowing up to 2 TB.
Q: Can IEC 11694-4-09 be used with rewritable optical cards?
A: Yes, the logical data structures are independent of the write‑once/rewritable characteristic. The same FAT and directory structures can be used on WORM, CD‑RW, or magneto‑optical media. However, the defect management scheme must be adjusted for rewritable media to allow cluster reuse. The standard includes separate guidelines for rewritable cards.
A: Yes, the logical data structures are independent of the write‑once/rewritable characteristic. The same FAT and directory structures can be used on WORM, CD‑RW, or magneto‑optical media. However, the defect management scheme must be adjusted for rewritable media to allow cluster reuse. The standard includes separate guidelines for rewritable cards.
Q: Is there a specified lifespan for data stored according to this standard?
A: Lifespan is not part of the logical standard; it is determined by the physical media and the environment. However, the standard’s robust error‑correction scheme (Reed‑Solomon + CRC) is designed to ensure that data remains recoverable for a minimum of 30 years in controlled storage conditions (20 °C, 40 % RH), assuming the media meets the physical lifetime requirements of ISO/IEC 11694‑1.
A: Lifespan is not part of the logical standard; it is determined by the physical media and the environment. However, the standard’s robust error‑correction scheme (Reed‑Solomon + CRC) is designed to ensure that data remains recoverable for a minimum of 30 years in controlled storage conditions (20 °C, 40 % RH), assuming the media meets the physical lifetime requirements of ISO/IEC 11694‑1.
– Updated 2026 –