- 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 all three
-codecs, 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 (v1.8.0) | 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] || 130,207,195 in 3.8s | N/A |
- | LZX (normal) [5] || 126,522,539 in 10.4s | 127,293,240 in 19.2s |
- | LZX (slow) [6] || 126,042,313 in 17.3s | N/A |
- | LZMS (non-solid) [7] || 116,150,682 in 25.3s | N/A |
- | LZMS (solid) [8] || 88,107,484 in 61.7s | 88,769,830 in 102.3s |
- | "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 resources defaults to 67108864 bytes in both cases.
-
- [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 (v1.8.0), 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) | 789,296 |
- | 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) | 690,110 |
- | WIM (WIMGAPI, LZX) | 651,866 |
- | WIM (wimlib, LZX normal) | 624,634 |
- | WIM (wimlib, LZX slow) | 620,728 |
- | WIM (wimlib, LZMS non-solid) | 581,046 |
- | tar.bz2 (bzip, default) | 565,008 |
- | tar.bz2 (bzip, -9) | 565,008 |
- | WIM (WIMGAPI, LZMS solid) | 521,366 |
- | WIM (wimlib, LZMS solid) | 515,800 |
- | 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.