-wimlib (and wimlib-imagex) can create XPRESS or LZX compressed WIM archives.
-Currently, the XPRESS compression ratio is slightly better than that provided by
-Microsoft's software, while by default the LZX compression ratio is approaching
-that of Microsoft's software but is not quite there yet. Running time is as
-good as or better than Microsoft's software, especially with multithreaded
-compression, available in wimlib v1.1.0 and later.
-
-The following tables compare the compression ratio and performance for creating
-a compressed x86_64 Windows PE image. Note: these timings were done on Windows
-7 so that the times would be fully comparable; however, wimlib-imagex may have
-even better performance on Linux.
-
- Table 1. WIM size
-
- XPRESS Compression LZX Compression
- wimlib-imagex (v1.4.0): 165,301,379 bytes 155,254,385 bytes
- Microsoft imagex.exe: 167,212,939 bytes 149,973,212 bytes
-
- Table 2. Time to create WIM
-
- XPRESS Compression LZX Compression
- wimlib-imagex (v1.4.0, 2 threads): 18 sec 51 sec
- Microsoft imagex.exe: 25 sec 93 sec
-
-The above LZX values are using the default LZX compressor. wimlib v1.5.2
-introduced a new experimental LZX compressor which can be enabled by passing
-'--compress-slow' to `wimlib-imagex capture' or `wimlib-imagex optimize'. This
-compressor is much slower but compresses the data slightly more --- currently
-usually to within a fraction of a percent of the results from imagex.exe.
+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 (v1.7.4) | WIMGAPI (Windows 8.1) |
+ =============================================================================
+ | None [1] || 361,314,224 in 2.4s | 361,315,338 in 4.5s |
+ | XPRESS [2] || 138,218,750 in 3.0s | 140,457,436 in 6.0s |
+ | XPRESS (slow) [3] || 135,173,511 in 8.9s | N/A |
+ | LZX (quick) [4] || 130,332,007 in 4.1s | N/A |
+ | LZX (normal) [5] || 126,714,807 in 12.5s | 127,293,240 in 19.2s |
+ | LZX (slow) [6] || 126,150,743 in 20.5s | N/A |
+ | LZMS (non-solid) [7] || 121,909,792 in 11.9s | N/A |
+ | LZMS (solid) [8] || 93,650,936 in 45.0s | 88,771,192 in 109.2 |
+ | "WIMBoot" [9] || 167,023,719 in 3.5s | 169,109,211 in 10.4s |
+ | "WIMBoot" (slow) [10] || 165,027,583 in 7.9s | 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
+ - 4 CPUs and 4 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 (v1.7.2), WIMGAPI (Windows 8.1), and some other
+formats/programs:
+
+ =====================================================
+ | Format | Size (bytes) |
+ =====================================================
+ | tar | 2,826,240 |
+ | WIM (WIMGAPI, None) | 2,814,254 |
+ | WIM (wimlib, None) | 2,814,216 |
+ | WIM (WIMGAPI, XPRESS) | 825,536 |
+ | WIM (wimlib, XPRESS) | 790,016 |
+ | 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) | 704,006 |
+ | WIM (WIMGAPI, LZX) | 651,866 |
+ | WIM (wimlib, LZX normal) | 632,614 |
+ | WIM (wimlib, LZX slow) | 625,050 |
+ | WIM (wimlib, LZMS non-solid) | 581,960 |
+ | tar.bz2 (bzip, default) | 565,008 |
+ | tar.bz2 (bzip, -9) | 565,008 |
+ | WIM (wimlib, LZX solid) | 532,700 |
+ | WIM (wimlib, LZMS solid) | 525,990 |
+ | WIM (wimlib, LZX solid, slow) | 525,140 |
+ | WIM (wimlib, LZMS solid, slow) | 523,728 |
+ | WIM (WIMGAPI, LZMS solid) | 521,366 |
+ | WIM (wimlib, LZX solid, very slow) | 520,832 |
+ | 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.