- 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.