Under the Hood

This article describes how the advanced features of WinISO work under the hood.

Quick Save

With quick save enabled, WinISO tries to minimize data writes to reduce the time required for saving changes. This feature is ideal for updating small files within a large disc image file, especially on slow storage devices such as HDDs.

However, useless data may be left in the image file. To eliminate them, use "Save As" to rebuild a new copy.

This feature is enabled by default. It can be configured in the Save tab in the Configurations dialog box. If this feature is disabled, the entire image is rebuilt on each save, and additional space is required for the rebuilding.

The example below shows how it works for common tasks.

When a file is deleted, only the file system data is updated, while the file content is not overwritten. The space occupied by deleted files is considered free space.

File SystemFile 1File 2File 3Delete File 2File SystemFile 1File 2File 3

The free space is used for storing newly added files.

File SystemFile 1File 3Add File 4File SystemFile 1File 4File 3

If the free space is insufficient, new files will be appended to the end of the image file, increasing the image file size.

File SystemFile 1File 4File 3Add File 5File SystemFile 1File 4File 3File 5

By saving a new copy or disabling the quick save feature, the entire image is rebuilt. The image file size may be reduced since all data in the free space is discarded.

File SystemFile 1File 4File 3File 5RebuildFile SystemFile 1File 4File 3File 5

File Deduplication

With file deduplication enabled, WinISO looks for all files with the same content during the save process, and makes them share the same data block. It may reduce the size of the image file, but it takes more time to find duplicate files.

This feature is not enabled by default. It can be configured in the Save tab in the Configurations dialog box.

In the example below, assuming that the content of File A, File B, and File 1 are the same, file deduplication results in a smaller image file.

ISO FSUDF FSFile AFile BFile CFile 1File 2ISO FSUDF FSFile A / B / 1File CFile 2

Bridged and Non-Bridged Modes

An optical disc may contain multiple file systems, typically ISO 9660 and UDF. WinISO offers two authoring modes: bridged mode and non-bridged mode.

  • In bridged mode, the contents of each file system are the same.

    For example, almost all DVD-Video discs use a combination of UDF and ISO 9660 file systems to provide backwards compatibility for operating systems that support only ISO 9660.

  • In non-bridged mode, the contents of each file system are independent.

    For example, the Windows 7 installer disc stores installation files in the UDF file system and a plain text file in the ISO 9660 file system. On operating systems that support only ISO 9660, the plain text file appears instead of the installation files, stating that your operating system does not support UDF.

The example below shows how the two modes differ.

  • In bridged mode, adding a file affects both file systems.
ISO FSUDF FSFile AFile BFile CISO FSUDF FSFile AFile BFile CFile D
  • In non-bridged mode, adding a file to one file system does not affect another file system.
ISO FSUDF FSFile AFile BFile CISO FSUDF FSFile AFile BFile CFile D

UDF Meta Partition

UDF Revision 2.50 adds the Metadata Partition facilitating metadata clustering, easier crash recovery, and optional duplication of file system information. All metadata like nodes and directory contents are written on a separate partition which can optionally be mirrored. This format is used by some versions of Blu-ray discs.

WinISO places the metadata before the file data and mirrored metadata after the file data. The two metadata partitions are placed as far apart as possible to avoid loss of all data.

UDF FSMetadataFile AFile BFile CMirrored MetadataUDF FSMetadataFile AFile BFile CMirrored MetadataDamaged

However, some disc authoring tools place the two metadata partitions next to each other. In this case, both metadata partitions are still vulnerable to damage, resulting in the loss of all data.

UDF FSMetadataMirrored MetadataFile AFile BFile CUDF FSMetadataMirrored MetadataFile AFile BFile CDamaged

Multi-Boot Image File (.bifx) Format

According to the El Torito specification, a bootable CD-ROM can be configured with multiple boot images. But usually, a boot image file (.bif or .img) represents only a single boot image.

In WinISO v6.4, a new file format (.bifx) was introduced for storing the entire boot information. The .bifx file format is fairly simple.

  • It consists of the Boot Catalog sectors followed by the Boot Image sectors.
  • The Load RBA (bytes 8–12) of the Boot Entry is the starting block address of the boot image, relative to the beginning of the file.
System DataBoot RecordBoot CatalogDefault EntryBoot EntryBoot EntryBoot Image #1Boot Image #2Boot Image #3File Data.iso FileBoot Image #1.bif or .img FileBoot CatalogDefault EntryBoot EntryBoot EntryBoot Image #1Boot Image #2Boot Image #3.bifx File