CentOS-4

CentOS-4 is a freely distributable OS built from the source at:

ftp://ftp.redhat.com/pub/redhat/linux/enterprise/4/en/os/i386/SRPMS

Before building the OS, non-free packages are altered. Non-free packages would include those encumbered with a non-redistributable copyright or trademark.

CentOS-4 supports x86 (i586 and i686), x86_64 (AMD64 and Intel EMT64), ia64, ppc, alpha, sparc, s390, and s390x architectures (The ppc and sparc architectures are currently BETA). Updates are distributed via YUM repositories (i386 only updates are also available via apt).
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그러니까.. 레드햇4 Enterprise Edition의 SRPMS가져다가 만든 배포판인듯