ISO 9660

A disc holds many files.

It uses a special rule. This rule helps computers find things. It works on many machines. This helps us share our work.

This rule is called ISO 9660. It was made by a group of experts. They met at a hotel in Nevada. They wanted all discs to work the same way.

The rule keeps files in a neat order. It uses a list to find them. This makes it fast to find a file.

Do you like using discs?

A disc holds many files. To find them, it uses a set of rules. This set of rules is called ISO 9660. It is a file system. A file system is a way to organize data. This helps different computers read the same disc.

Experts first met at a hotel in Nevada. They were part of the High Sierra Group. They wanted to make a standard. Before this, every maker used their own way. This made it hard to share files. The group made the High Sierra Format. This later became ISO 9660.

The disc has many parts. The first 16 sectors are empty. They are kept for other uses. The rest starts with a volume descriptor set. This is a header block. It describes how the disc is laid out. It tells the computer the name of the disc. It also says who made it.

Next, the disc uses path tables. These tables act like a map. They show where each directory is. A directory is a folder for files.

There are also special ways to add more. One way is called Joliet. It helps use different kinds of writing. This lets people use many languages.

ISO 9660 is a special set of rules for optical discs. It is known as a file system. A file system is a way to organize data on a disc. This helps different kinds of computers read the same disc easily. It is an international standard from the International Organization for Standardization. This makes it a very important tool for sharing digital information.

This system works by organizing data in a very specific order. The first 16 sectors on the disc are left empty. These are reserved for other uses, like making a disc bootable. After that, the disc starts with a volume descriptor set. This set acts like a header for the whole disc. It tells the computer the name of the volume and who created it. It also shows where the root directory is located.

In the past, making discs was a bit messy. In 1983, the Yellow Book defined the format for CD-ROMs. However, it did not explain how to organize files. This meant every maker used their own different method. To fix this, experts met at the High Sierra Hotel in Nevada. This group became known as the High Sierra Group. They included people from companies like Apple, Microsoft, and Sony. They released a proposal in May 1986 called the High Sierra Format.

This High Sierra Format eventually became the ISO 9660 standard. The ISO published the official version in 1988. Since then, there have been many updates to the rules. New versions were published in 2013, 2017, 2019, and 2020. Some extensions help the system do even more things. For example, Joliet allows the use of many different languages. Rock Ridge lets users use longer names for files. El Torito helps a disc start up a computer.

You can think of ISO 9660 like a library. The disc is the building, and the files are the books. The path tables act like a map of the library aisles. They show exactly where each folder and file is kept. This structure ensures that no matter which computer you use, you can find your data. It turns a spinning disc into a neat and tidy digital filing cabinet.

ISO 9660 is an international standard for an optical disc file system. A file system is a method for organizing data on a storage medium. This specific standard ensures that different computers can read the same disc. It is managed by the International Organization for Standardization (ISO). Because the technical specifications are public, many different operating systems use it. This makes it a vital tool for cross-platform data sharing.

The mechanism of ISO 9660 relies on a very strict data layout. The first 16 sectors of the disc are kept empty. Each sector is 2,048 bytes, so this reserved area is 32,768 bytes. This space is used for special tasks, like making a disc bootable. After this area, the data begins with a volume descriptor set. This set acts as a header for the entire disc. It describes the layout of everything that follows. The set must end with a specific volume descriptor set terminator. This marker tells the computer that the header information is finished.

Within this set, the primary volume descriptor is essential. It contains metadata, which is data that describes other data. This includes the volume name and the creator of the disc. It also stores the size and number of logical blocks used. The primary volume descriptor tells the computer where the root directory is located. A disc must have at least one primary volume descriptor to be compliant. Some discs also use supplementary volume descriptors. These provide extra support, such as additional code page support for different languages.

To find specific files, the system uses path tables. A path table acts like a map for the directory hierarchy. For every directory, the table provides a directory identifier. It also lists the location of the data extent. An extent is a sequential series of sectors where the data lives. The table also includes the length of any extended attributes. Finally, it provides an index for the parent directory. This parent directory number is a 16-bit value. This limits the number of parent entries to 65,535.

The history of this standard began with the "Yellow Book" in 1983. This specification defined the format for CD-ROMs. However, it did not define how to organize files into logical units. This caused many manufacturers to create incompatible formats. To solve this, the National Information Standards Organization (NISO) formed a committee in 1985. In November 1985, representatives met at the High Sierra Hotel in Nevada. This group, called the High Sierra Group (HSG), included experts from Apple, Microsoft, and Sony. They released the High Sierra Format in May 1986. This proposal eventually became the ISO 9660 standard in 1988.

Over time, several extensions were created to relax the original rules. Rock Ridge allows for Unix-style permissions and longer file names. Joliet is an extension that uses Unicode. This allows for non-Latin scripts, such as different alphabets, to be used. El Torito is another extension that enables discs to be bootable. There are also Apple ISO 9660 Extensions for Mac-specific features. In 2013, Amendment 1 was released to harmonize ISO 9660 with the Joliet specification. Further updates were published in 2017, 2019, and 2020 to refine the standard.

The standard handles data using different byte orders. It uses little-endian, big-endian, and a unique "both-byte" order. Both-byte order is required for certain fields in volume descriptors. This ensures that different types of computer processors can interpret the numbers correctly. ISO 9660 also manages complex character sets. It uses ISO 2022 and ISO 2375 to identify specific code pages. This allows the system to support many international languages. While the standard provides the framework, the specific code tables depend on the disc creator.

ISO 9660 connects to many other areas of computing. It relates to how operating systems manage files and directories. It also connects to the history of hardware development involving companies like Philips and Sony. By providing a universal language for discs, it allows for mass archival storage. This means large amounts of data can be saved and read for many years. It remains a foundational concept in how we think about digital organization and interoperability.