Thursday, June 14, 2012

File system of CD

 HFS (Hierarchical File Structure)

It is a CD file system for MAC machine. It is also developed from ISO-9660. CD of ISO-9660 standard can not store special information of HFS such as icon, icon position on desktop, data files, and relations between data files and executive files. But the information stored on the second layer can not be read by computers except MAC. 

UDF (Universal Disc Format)

UDF is the abbreviation of Universal Disc Format; it is compatible with the ISO 9660 format. It uses a standard technology package to write; users can modify and delete files on a CD-ROM. 

While burning with UDF format, the CD burning software will packet the data and establish a special but temporary file directory table in the memory, at the same time, it will take over the access to CD. Deleted files or modified files are still in CD-R partially. The revised part of data will be written in CD separately. In the directory table in memory, data can be restructured by setting permission to access special links. All this can make the system have no access to old data, and the new data will take the place of old data. So the old data shall be deleted. After the operation of users, this will help them to rewrite the new directory into CD and record the operation content. The above process will make it convenient for the read in and data recovery of CD.

While using UDF, users can burn CD through a drag operation like operations on hard disk under Windows Explorer.

At present, all software with UDF can support the burning of CE-RW. But there are some subtle differences. The deleted files are really deleted, and it is not the way like above said. The only shortcoming of UDF is that it reduces the valid storage space, moreover, a format to CD-R/CD-RW is required, but the format will reduce the CD-RW by 100 MB or so. In the lower version of Windows Systems, the read of CD-RW disc with UDF format needs the support of software.

CD-RF(CD-Recordable File System)
It is a file system defined by SONY Company that likes UDF.

EI Torito(Bootable CD-ROM)
Bootable CD-ROM is a CD-ROM that burns wit information from the boot area on hard disk or floppy disk, this CD-ROM can be used to boot computer.

This is a kind of mixed CD. This CD has two or more than two data sessions. Each session contains complete file record and information. Two data session can adopt different file format of different operating systems. (Four types at present: DOS/Windows, HFS, Unix, and OS/2). The usually used Hybrid disc is DOS and MAC file format (DOS adopts ISO-9660 file system, MAC adopts HFS file system).

Shared Hybrid
The shared Hybrid CD can be used on two and more than two operating systems, different system can read out the same data on CD-ROM. This type of CD has only one data area, all related data and files used by system are stored in the same data session. However, users can only check DOS files on DOS system, and MAC files can be seen on MAC system.

The following image shows the relations between format and file systems.

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