- 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, and in some
-cases they now 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 type || wimlib (v1.7.0) | WIMGAPI (Windows 8.1) |
- =============================================================================
- | None [1] || 361,182,560 in 7.6s | 361,183,674 in 11.9s |
- | XPRESS [2] || 138,992,007 in 11.5s | 140,416,657 in 13.9s |
- | LZX (quick) [3] || 131,428,113 in 15.2s | N/A |
- | LZX (normal) [4] || 126,807,853 in 58.9s | 127,259,566 in 55.2s |
- | LZX (slow) [5] || 126,085,971 in 125s | N/A |
- | LZMS (non-solid) [6] || 122,082,982 in 59.8s | N/A |
- | LZMS (solid) [7] || 92,171,126 in 260s | 88,742,356 in 556s |
- =============================================================================
-
-Notes:
- [1] '--compress=none' for wimlib-imagex;
- '/compress:none' for DISM.
-
- [2] '--compress=fast' or '--compress=XPRESS' for wimlib-imagex;
- '/compress:fast' for DISM.
- Compression chunk size is 32768 bytes, the default for XPRESS.
-
- [3] No compression option specified to wimlib-imagex;
- no known equivalent for DISM.
- Compression chunk size is 32768 bytes, the default for LZX.
-
- [4] '--compress=maximum' or '--compress=LZX' for wimlib-imagex;
- '/compress:maximum' for DISM.
- Compression chunk size is 32768 bytes, the default for LZX.
-
- [5] '--compress=maximum --compress-slow' for wimlib-imagex;
- no known equivalent for DISM.
- Compression chunk size is 32768 bytes, the default for LZX.
-
- [6] '--compress=recovery' or '--compress=LZMS' for wimlib-imagex;
- no known equivalent for DISM.
- Compression chunk size is 131072 bytes, the default for LZMS.
-
- [7] '--compress=recovery --solid' or '--compress=LZMS --solid' for
- wimlib-imagex. Should be '/compress:recovery' for DISM, but it doesn't
- work; I called WIMGAPI directly instead.
- Compression chunk size in solid blocks is 67108864 bytes in both cases.
-
-I did the timings on Windows 8.1 running in a virtual machine so that
-side-by-side comparisons with the Microsoft implementation would be possible.
-However, do note that wimlib may have even better performance on other operating
-systems such as Linux. I used the 64-bit builds of both programs.
-
-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.