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Beginners Guides: Optical Drives & Recording Formats
Beginners Guides: Optical Drives & Recording Formats - PCSTATS
Everything from the differing optical media recording standards, read/record speeds to selecting the best recordable DVD format is covered.
Filed under: Beginners Guides Published:  Author: 
External Mfg. Website: PCSTATS Dec 08 2003   M. Dowler  
Home > Reviews > Beginners Guides > PCSTATS

UDF/Packet Writing

The one major disadvantage of the standard ISO 9660 format for creating CDs is that it requires a lot of overhead. If you wish to copy several small sets of data to a CD-R or CD-RW over a certain time period, making daily backups for example, the system will need to create a separate session for each set of data.

As each session requires its own lead-in which contains the table of contents and data needed to synchronize the reader for the data to follow, and lead-out space, the overhead for creating a session equates to 13MB of wasted space. The UDF file system is an alternative method of storage, created to allow small files to be efficiently added to CD media without wasting space.

In effect, the CD will appear as a form of removable media like a floppy disk, once formatted with the UDF file system.

This method does have some drawbacks of its own though; any information written to the disk has a minimum size of 32KB, meaning that files smaller than this will take up a 32K block of space regardless, resulting in a fair bit of wasted space. Originally, the UDF file system required that the whole CD be erased before space created by deleting files could be used again, but newer revisions of the format allow for random deleting. This modification allows individual sectors of the disk to be erased and reused on the fly.

UDF disks still require formatting before use, which can take a long time. Also, compatibility can be a real issue, as older CD-ROMs and early CD-R drives will not read CDs created using packet writing, and so software must be installed to create the disks. Newer packet writing technologies such as the Mount Rainier standard provide faster formatting and less wasted space, but still need additional software to read the created CDs. More on Mt. Rainier in a moment.

Understanding CD-R/RW media Read and Write speeds

There are a variety of types of CD-R and RW media on the market, and it can be bewildering at times, though concerns about the physical makeup of CD-R disks have become somewhat marginalized as the technology has become commonplace and the price of individual disks has plummeted.

There are some things that the buyer should look out for still, the most important of these being the rated speed of the disks.

As you will have noticed, CD burners are rated for the speed in which they can create and read CDs. These speeds are generally listed in the format (CD-R write speed)/(CD-RW write speed)/(CD read speed); for example 48x/24x/48x. The speed is calculated by taking the 150KB per second transfer rate of a 1X CD-ROM drive and multiplying it. The trouble is that the media you use may or may not be able to keep up with the burner, depending on the process used to manufacture it.

Using a CD-R disk made a few years ago on a modern 48X or above CD-RW drive, for example, is just not likely to work well, resulting in errors or outright failure unless you reduce the write speed of the drive considerably. Modern CD-R media is produced to take the higher write speeds into account, so the best practice is to make sure the advertised acceptable speed of the disks you are buying matches the speed of your burner.

Note that this is not a hard and fast rule.... media that is not advertised as 48X compatible may in fact work at that speed, it's just not guaranteed to, so proceed at the risk of making lovely drink coasters. Using higher speed rated media on a lower rated burner will work fine, of course.

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Contents of Article: PCSTATS
 Pg 1.  Beginners Guides: Optical Drives & Recording Formats
 Pg 2.  How CD-Rs store data
 Pg 3.  Reading CDs and DVDs
 Pg 4.  — UDF/Packet Writing
 Pg 5.  Understanding CD-R/RW media
 Pg 6.  Other DVD Recordable Standards
 Pg 7.  DVD-Dual and DVD-Multi formats

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