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Let the facts speak for themselves: The new disk image format that Apple is using for DiskCopy 6.1.2 is now used natively by ShirnkWrap. However, ShrinkWrap uses the faster and smaller StuffIt compression technology to compress NDIF images instead of Apple's new proprietary codec. Compression TestTested using Apprentice CD
Explanation: Elapsed Time: The elapsed time indicates the time required to verify the entire CD (for original) or convert it to a compressed NDIF image. (Yes, the DiskCopy 6.1 time is right, it *really* took 2 1/2 hours to create the image.) Norton Scan: Time required to scan the mounted volume for bad blocks and damaged files using Norton Disk Doctor 3.2.4. This a good "real world" test for the driver decompression performance, since it includes large sequential reads during the media verification and then quasi-random reads during the file verification. Cache: Size of internal cache buffer maintained by the driver to decompress chunks of the disk image. The larger the chunk cache, the better compression ratio and the more likely the desired block is already decompressed in the cache ready to use. However, larger caches take up more RAM from your system. The ShrinkWrap rule of thumb is to use 16 times the allocation block size or 16K, whichever is larger. DiskCopy appears to use 16K for small volumes and 200K for large volumes.
Conversion TestTested using Disk Tools DiskCopy 4.2 image file and converting to a compressed NDIF image.
Explanation: The DiskCopy 4.2 image actually performs worse than both the DiskCopy 6.1 and ShrinkWrap 3.0 images even though it's not compressed. This is due to the fact that the DiskCopy 4.2 image is offset by an 84 byte header that screws up the block alignment. Consequently, the driver has to read two blocks for every one that is requested. To write, the driver takes 4 times as long, reading the blocks on both sides of the block boundary, changing the appropriate bytes, and then writing them both back to disk. The Disk Tools disk is a tough compression task, since much of what's on there is already compressed with resource compression. It's interesting to note for comparison that the StuffIt Engine compresses the same DiskCopy 4.2 image down to a 1,142,226 byte file in 9.52 secs.
For both tests: Test config: PM 8500/120, 600i CD-ROM, System 7.6, default configurations. This testing data and explanation is courtesy of Chad Magendanz author of ShrinkWrap.
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Copyright 1997, 1998 Aladdin Systems, Inc. Questions? Send us a note. Modified 3/12/98 FxD Webworks |
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