Data files are written on a CD by fitting the data into the recording blocks originally intended to be used for audio recording. The resulting ‘track’ then has to be organized to be seen by the computer as files in a File System. This is done in one of two fundamentally different ways: the ISO file system, or the UDF file system.
ISO (with the ‘Joliet’ extensions to support Windows-style long file names) is the original method, and the one used in “pressed” CD-ROMs, such as the Windows XP CD-ROM. In this system, all the files to be written are selected, then written to the disk as continuous tracks, together with a Table of Contents (TOC) which defines where the data of a file is to be found in the track. Together, these files and TOC form a session. If the disk has not been filled, it can be put back into the writer, and a further session written. The TOC for the new session will link back to the previous TOC, so that all the files on the disk appear as being on a single CD.
Because of this method of writing, the files cannot be individually changed or deleted. If on a CD-RW disk, they can only be erased as a whole. The ISO file system is mostly used, therefore, with CD-R media.
Every session has an overhead of about 14 MB, so this is a very wasteful method if used to write files individually rather than in batches.
The resulting burned disk can be read in any PC CD-ROM drive (except, perhaps, some very obsolete ones) using only the normal software of any version of Windows.
This is a quite different approach, in which a CD-RW disk is first formatted into packets which then behave very much like the sectors of a hard disk. While the file system can be used in disks organized in tracks, as with the ISO system, and is also used on DVD disks, the term “UDF” will be used here in the sense of it using this packet writing base on CD-RW disks. Files can be written to a series of packets as an individual operation, and, later, those of a file can be selectively erased or updated. Therefore, such a CD is described as behaving as a “giant floppy” (or very slow, small hard disk). When UDF is implemented, files can be dragged and dropped to and from the CD in Windows Explorer, just as to and from a hard disk; or, to give another example, the CD can be selected as the drive to use in a “Save As” dialog in a program. The UDF file system was often used in earlier versions of Windows through third party packages such as Direct CD.
Reading such disks needs special software in earlier versions of Windows, and may not be possible with all CD drives, even when that software is present.
While there is a variant of the UDF method that can be used to write to CD-R media, it is rarely used.
Windows XP’s inbuilt CD-burning software allows you to select files and apparently write them to the disk immediately, by dragging and dropping them to the CD drive’s icon, or by right-clicking them, taking Send To, and selecting CD Drive x: as the destination. This gives the impression that the files are being written to the disk right then, as in a UDF system. But this is not the case. Doing this simply stashes up copies of these files on the hard disk, in a “staging area” (which, by default, is in your Documents and Settings folder).
They are only written to the CD when you take an explicit action. This may be:
This burning method is strictly for CD media only. There is no support at all in the inbuilt burning for burning DVD media.
When you put such a disk back in the drive, it will be opened in an Explorer window, which will show the existing files, under a heading “Files Currently on the CD,” and may also have a section at the top entitled “Files Ready to be Written to the CD.” This will show any files you have setup for writing since last a session was written, and is a place you can add more files to by dragging and dropping. If you thus add a file whose name matches one already on the CD, only the new one will be seen subsequently. This appears to be a means of replacing a file; though the space occupied by the original is not released, so the disk fills up.
So the Windows XP inbuilt software is really a system most suitable for preparing straightforward data CDs on CD-R. It is not one which allows a CD-RW to be used as a backing store on which individual files can be updated, and it will not work as an output destination for backup programs and other software that simply attempts to write to it directly as if it were a hard disk. Nor will it make a direct copy of a CD. And, because of the overhead for a TOC in each session, it is not suitable for updating a small volume of files on a regular basis.
Note that this software also allows you to select a “Playlist” of audio files, such as MP3 or WMA files, in Windows Media Player, and will then convert them to an audio format and record the disk as an audio CD. This has to be of the complete content of the audio CD in one operation; you cannot put the disk back and add more tracks to it, because most audio players would not recognize the result. CAVEAT: Do not try to mix these audio files with data files for this purpose!
XP’s Windows Explorer does have some support for UDF disks, which will allow you to read those produced by some third party software, such as Direct CD — but not all such software, and not even those from every version of Direct CD. Please note, however, that this is strictly a read-only matter. There is no way to write to an UDF disk in XP: you cannot add files to one, nor can you delete individual files from an existing disk, nor update any single file. All you can do is erase the entire disk.
If you have any third party CD-writing software installed on a system you are going to upgrade to Windows XP, it will be disabled in the process of the upgrade. A lot of difficulties can be avoided by always uninstalling such software completely in advance of the XP upgrade, then re-installing XP-compatible versions after the upgrade. In doing so, uninstall any related programs that make use of CD writing — especially the TakeTwo program from Adaptec (now Roxio). In this matter you may want to review the “Homework Before You Install” section of the article on Upgrading to Windows XP, written by MS-MVP Gary Woodruff.
For this you must install a third party UDF package. These usually come as part of a complete suite of programs, including a “mastering” program to write ISO sessions. Ensure that you have a version that supports Windows XP. The major packages that do so are:
Any of the “mastering” programs in these suites also will create Audio CDs from simple WAV files and from compressed MP3 files. NOTE: None of these packages now make use of an “ASPI layer,” and you should not attempt to install one in XP for their benefit.
If you install any of these packages, the inbuilt burning software probably will be disabled, and you should use the associated “mastering” program instead. If the native software is not disabled automatically, you should disable it manually. (See Section 6 immediately below.)
Service Pack 1 for Windows XP introduced some support for the new “Mount Rainier” format, a new method of handling the lower level packet writing used with the UDF File system. At present, Windows XP SP1 will read such disks directly in a CD writer that has the necessary firmware, or in most drives using the reader program EasyWriteReader obtainable from www.nero.com. Formatting and writing a Mount Rainier disk requires a writer with appropriate firmware. These are now becoming available, and third party software — such as InCD version 3.28 or later, Drag to Disk, or Write CD-RW 3.5 (see above) — support it on CD-RW disks.
In My Computer, right-click on the CD-drive, then click Properties. There should be:
It is recommended that you manually choose a speed in the provided box, especially if you do choose to use the technique with CD-RW media, for which the drive will usually not be capable of the speed assumed (the faster one, for CD-R writing).
In addition to these settings, you also can change the location of the “staging area” for files awaiting burning by using TweakUI for Windows XP (part of the Windows XP PowerToys). In its My Computer | Special Folders section is an entry for the CD Burning folder. Set it to whatever location you like. (If the location is on an NTFS partition, its Security must be set to provide ’Full Control’ for Administrators, Creator Owner, and SYSTEM.)
There is no inbuilt check in the writing software to confirm that the files you have selected actually will fit onto the CD. Although a CD is described as 74 minutes or 650 MB (or 80 minutes, 720 MB), by the time you have allowed for the overhead of even one session, 640 and 695 MB may be nearer the mark; and each additional session loses about 14 MB to these overheads. Also, the laying out of files into the track behaves like a hard disk with 16K clusters, so you have to allow for the wastage (“slack space”) which that causes as well. So play safe!
There appear to be quite a lot of drives whose performance is, for one reason or another, incompatible with the methods used by the Windows XP inbuilt software. If these are detected then it will be disabled. The drive will, in all probability, work well with one of the packages mentioned in Section 5 above.
It may be that the “hotfix” from Microsoft’s Windows Update for Application compatibility (Update for CD Burners, referred to in Microsoft Knowledge Base article 320174), will help with such a problem — but it also has been known to introduce it, in which case the update should be un-installed.
This happens quite often if one of the third-party packages has been uninstalled. They add references in the Registry for modules which they use, and these references fail to be removed, leaving Windows unable to find the files apparently needed for CD devices at the next boot. There is a simple Registry patch to correct this (download it here). Before using the patch, be sure to back up the Registry. After using the patch and rebooting, the drives should reappear. Any third party package that is still required will then need to be re-installed.
This problem also may arise if there is underlying trouble with the Input-Output system of the machine: for example, interactions with controllers like Promise or Highpoint, or with special drivers. It may be worth trying a change in the DMA settings for the device in Control Panel | System | Hardware | Device Manager. Under IDE controllers, double click on the Primary or Secondary IDE Channel concerned, then click the tab for the Advanced Settings page.
Microsoft has acknowledged various problems with the inbuilt software that can result in files (or sometimes whole disks) being unreadable when they have been burned with the inbuilt software. See MSKB 320174. They have posted a patch on the Microsoft Download Center, which may resolve the issue. (Click here to go directly to the patch download page.) It is recommended, though, that you only apply this patch if you are actually suffering from trouble, not just “because it is there.”
There appears to be a bug in Windows Explorer, such that when you put in a disk that contains multiple ISO Sessions, Properties shows the size of the files in the last session only, which may be very misleading. This applies to multi-session disks burned with third party software, as well as the native Win XP system.
Microsoft’s Knowledge Base now includes a useful troubleshooting page for other problems with the inbuilt burning of Windows XP. See How to Troubleshoot Issues That Occur When You Write Data to a CD-R or CD-RW Optical Disc in Windows XP (MSKB 324129).
Two excellent sources for details of the way CD recording works in general, with technical detail, are: