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5. File I/O: Further Details > I/O on Large Files

I/O on Large Files

The off_t data type used to hold a file offset is typically implemented as a signed long integer. (A signed data type is required because the value -1 is used for representing error conditions.) On 32-bit architectures (such as x86-32) this would limit the size of files to 231–1 bytes (i.e., 2 GB).

However, the capacity of disk drives long ago exceeded this limit, and thus the need arose for 32-bit UNIX implementations to handle files larger than this size. Since this is a problem common to many implementations, a consortium of UNIX vendors cooperated on the Large File Summit (LFS), to enhance the SUSv2 specification with the extra functionality required to access large files. We outline the LFS enhancements in this section. (The complete LFS specification, finalized in 1996, can be found at http://opengroup.org/platform/lfs.html.)


  

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