In general, the HIRO will not create a single zip file larger than 1.5 GB in size because files of that size can often cause problems when you attempt to open them (particularly with older or 32-bit operating systems). However, it is not uncommon for users to request image data in amounts that would exceed this size even with the best compression software available. As a result, the HIRO takes advantage of a zip feature known as "volumes" (also known as a split or spanned archive).

When zipping large amounts of data, the HIRO will use its archiving software to split the large zip file into several volumes. Each volume has the same maximum size; once that size is reached for the first volume file a new volume file is created. This process continues until all of the data has been compressed. For example, assume you have requested a large number of scans and when compressed your data shrinks to 4.75 GB in size. If the HIRO were to provide you with a single 4.75 GB zip file, you might encounter problems when you attempted to open or unzip it (in fact, zip files of this size are impossible to open on 32-bit systems). Splitting the zip file into 1 GB volumes would circumvent this issue, and would look like this:

Although zipping in this manner splits the zip file into smaller files, it is still technically a single zip archive (that is, it is not five individual zip files). To successfully unzip the archive, you will need all the files, and you should only attempt to unzip the first volume (the file ending in .zip.001). Your zip program will automatically recombine the volumes and unzip everything at once. Zipping data in this manner is still considered lossless compression, so all of your data will be intact in its original form.

Unzipping a Split Archive Under Microsoft Windows

Unfortunately, the zip utility that is built into Windows cannot unzip split archives. To unzip split archives under Windows, the HIRO recommends the 7-Zip Utility. This free utility is relatively simple to use and can compress and uncompress files in a wide variety of formats. To unzip the example above, you can right-click on the MyImageData.zip.001 file (after you've installed 7-Zip), select the 7-Zip menu, and then choose one of the "extract" options.

Unzipping a Split Archive Under Mac OS X

Unfortunately, the zip utility that is built into OS X cannot unzip split archives. To unzip split archives under OS X, the HIRO recommends the Keka File Archiver Utility. This free utility is relatively simple to use and can uncompress files in several formats. To unzip the example above, double-click on the MyImageData.zip.001 file after you've installed Keka. The Linux p7zip command line program is also available for OS X. The HIRO is only able to provide limited support for Macs.

Unzipping a Split Archive Under Linux

To unzip split archives under Linux, the HIRO recommends the p7zip utility. This command line utility is included by default in many flavors of Linux, and is available as an RPM package. To unzip the example above, you would use the following command:

user[at]localhost ~ $ 7za x MyImageData.zip.001

The 'x' option will extract the archive while maintaining full paths. To learn more about the 7za command, the HIRO recommends you review the 7za man page as well as the shared documentation installed by the package. It's quite extensive.

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