INTRODUCTION

This is wimlib version 1.7.1-BETA (June 2014). wimlib is a C library for creating, modifying, extracting, and mounting files in the Windows Imaging Format (WIM files). These files are normally created using the ImageX (imagex.exe) or Dism (Dism.exe) utilities on Windows, but wimlib is distributed with a free implementation of ImageX called "wimlib-imagex" for both UNIX-like systems and Windows.

                              INSTALLATION

To install wimlib and wimlib-imagex on Windows you simply need to download and extract the ZIP file containing the latest binaries from the SourceForge page (http://sourceforge.net/projects/wimlib/), which you may have already done.

To install wimlib and wimlib-imagex on UNIX-like systems (with Linux being the primary supported and tested platform), you must compile the source code, which is also available at http://sourceforge.net/projects/wimlib/. Alternatively, check if a package has been prepared for your Linux distribution. Example files for Debian and RPM packaging are in the debian/ and rpm/ directories.

                                WIM FILES

A Windows Imaging (WIM) file is an archive designed primarily for archiving Windows filesystems. However, it can be used on other platforms as well, with some limitations. Like some other archive formats such as ZIP, files in WIM archives may be compressed. WIM files support multiple compression formats, including LZX, XPRESS, and LZMS. All these formats are supported by wimlib.

A WIM file consists of one or more "images". Each image is an independent top-level directory structure and is logically separate from all other images in the WIM. Each image has a name as well as a 1-based index in the WIM file. To save space, WIM archives automatically combine all duplicate files across all images.

A WIM file may be either stand-alone or split into multiple parts. Split WIMs are read-only and cannot be modified.

Since version 1.6.0, wimlib also supports ESD (.esd) files, except when encrypted. These are still WIM files but they use a newer version of the file format.

                         IMAGEX IMPLEMENTATION

wimlib itself is a C library, and it provides a documented public API (See: http://wimlib.sourceforge.net) for other programs to use. However, it is also distributed with a command-line program called "wimlib-imagex" that uses this library to implement an imaging tool similar to Microsoft's ImageX. wimlib-imagex supports almost all the capabilities of Microsoft's ImageX as well as additional capabilities. wimlib-imagex works on both UNIX-like systems and Windows, although some features differ between the platforms.

Run `wimlib-imagex' with no arguments to see an overview of the available commands and their syntax. For additional documentation:

• If you have installed wimlib-imagex on a UNIX-like system, you will find further documentation in the man pages; run `man wimlib-imagex' to get started.

• If you have downloaded the Windows binary distribution, you will find the documentation for wimlib-imagex in PDF format in the "doc" directory, ready for viewing with any PDF viewer. Please note that although the PDF files are converted from UNIX-style "man pages", they do document Windows-specific behavior when appropriate.

                          COMPRESSION RATIO
  

wimlib (and wimlib-imagex) can create XPRESS, LZX, or LZMS compressed WIM files. wimlib includes its own compression codecs and does not use the compression API available on some versions of Windows.

I have gradually been improving the compression codecs in wimlib. For XPRESS and LZX, they now usually outperform and outcompress the equivalent Microsoft implementations. Although results will vary depending on the data being compressed, in the table below I present the results for a common use case: compressing an x86 Windows PE image. Each row displays the compression type, the size of the resulting WIM file in bytes, and how many seconds it took to create the file. When applicable, the results with the equivalent Microsoft implementation in WIMGAPI is included.

============================================================================= | Compression || wimlib (v1.7.1) | WIMGAPI (Windows 8.1) |

| None [1] || 361,182,560 in 3.7s | 361,183,674 in 4.4s | | XPRESS [2] || 138,349,798 in 5.8s | 140,416,657 in 6.8s | | XPRESS (slow) [3] || 135,234,072 in 19.5s | N/A | | LZX (quick) [4] || 131,816,279 in 6.7s | N/A | | LZX (normal) [5] || 126,808,347 in 28.3s | 127,259,566 in 31.4s | | LZX (slow) [6] || 126,199,523 in 61.4s | N/A | | LZMS (non-solid) [7] || 122,083,126 in 30.4s | N/A | | LZMS (solid) [8] || 93,752,206 in 84.3s | 88,742,238 in 156.1s | | "WIMBoot" [9] || 167,039,787 in 7.6s | 169,051,718 in 14.9s | | "WIMBoot" (slow) [10] || 165,141,503 in 15.8s | N/A |

Notes: [1] '--compress=none' for wimlib-imagex; '/compress:none' for DISM.

[2] '--compress=XPRESS' for wimlib-imagex; '/compress:fast' for DISM. Compression chunk size defaults to 32768 bytes in both cases.

[3] '--compress=XPRESS:80' for wimlib-imagex; no known equivalent for DISM. Compression chunk size defaults to 32768 bytes.

[4] '--compress=LZX:20' for wimlib-imagex; no known equivalent for DISM. Compression chunk size defaults to 32768 bytes.

[5] '--compress=LZX' or '--compress=LZX:50' or no option for wimlib-imagex; '/compress:maximum' for DISM. Compression chunk size defaults to 32768 bytes in both cases.

[6] '--compress=LZX:100' for wimlib-imagex; no known equivalent for DISM. Compression chunk size defaults to 32768 bytes.

[7] '--compress=LZMS' for wimlib-imagex; no known equivalent for DISM. Compression chunk size defaults to 131072 bytes.

[8] '--solid' for wimlib-imagex. Should be '/compress:recovery' for DISM, but only works for /Export-Image, not /Capture-Image. Compression chunk size in solid blocks defaults to 33554432 for wimlib, 67108864 for DISM.

[9] '--wimboot' for wimlib-imagex; '/wimboot' for DISM. This is really XPRESS compression with 4096 byte chunks, so the same as '--compress=XPRESS --chunk-size=4096'.

[10] '--wimboot --compress=XPRESS:80' for wimlib-imagex; no known equivalent for DISM. Same format as [9], but trying harder to get a good compression ratio.

Note: wimlib-imagex's --compress option also accepts the "fast", "maximum", and "recovery" aliases for XPRESS, LZX, and LZMS, respectively.

Testing environment:

- 64 bit binaries
- Windows 8.1 virtual machine running on Linux with VT-x
- 2 CPUs and 2 GiB memory given to virtual machine
- SSD-backed virtual disk
- All tests done with page cache warmed

The compression ratio provided by wimlib is also competitive with commonly used archive formats. Below are file sizes that result when the Canterbury corpus is compressed with wimlib (v1.7.0), WIMGAPI (Windows 8), and some other formats/programs:

 =================================================
 | Format                         | Size (bytes) |
 =================================================
 | tar                            | 2,826,240    |
 | WIM (WIMGAPI, None)            | 2,814,278    |
 | WIM (wimlib, None)             | 2,813,856    |
 | WIM (WIMGAPI, XPRESS)          | 825,410      |
 | WIM (wimlib, XPRESS)           | 792,024      |
 | tar.gz (gzip, default)         | 738,796      |
 | ZIP (Info-ZIP, default)        | 735,334      |
 | tar.gz (gzip, -9)              | 733,971      |
 | ZIP (Info-ZIP, -9)             | 732,297      |
 | WIM (wimlib, LZX quick)        | 722,196      |
 | WIM (WIMGAPI, LZX)             | 651,766      |
 | WIM (wimlib, LZX normal)       | 649,204      |
 | WIM (wimlib, LZX slow)         | 639,618      |
 | WIM (wimlib, LZMS non-solid)   | 592,136      |
 | tar.bz2 (bzip, default)        | 565,008      |
 | tar.bz2 (bzip, -9)             | 565,008      |
 | WIM (wimlib, LZMS solid)       | 525,270      |
 | WIM (wimlib, LZMS solid, slow) | 521,700      |
 | WIM (WIMGAPI, LZMS solid)      | 521,232      |
 | tar.xz (xz, default)           | 486,916      |
 | tar.xz (xz, -9)                | 486,904      |
 | 7z  (7-zip, default)           | 484,700      |
 | 7z  (7-zip, -9)                | 483,239      |
 =================================================

Note: WIM does even better on directory trees containing duplicate files, which the Canterbury corpus doesn't have.

                              NTFS SUPPORT

WIM images may contain data, such as alternate data streams and compression/encryption flags, that are best represented on the NTFS filesystem used on Windows. Also, WIM images may contain security descriptors which are specific to Windows and cannot be represented on other operating systems. wimlib handles this NTFS-specific or Windows-specific data in a platform-dependent way:

• In the Windows version of wimlib and wimlib-imagex, NTFS-specific and Windows-specific data are supported natively.

• In the UNIX version of wimlib and wimlib-imagex, NTFS-specific and Windows-specific data are ordinarily ignored; however, there is also special support for capturing and extracting images directly to/from unmounted NTFS volumes. This was made possible with the help of libntfs-3g from the NTFS-3g project.

For both platform