Features For Archiving
There are a few variables to consider when selecting the right archiving tool.
Application and Compatibility
What do you need to compress or archive? For small files that need to be emailed, you might not need high compression ratios per se, but it might make sense to put multiple files into one convenient archive. Commercial applications, in particular, offer a high level of OS integration, giving you access to advanced features with a right-click in Windows Explorer. Focus on ZIP or RAR if you want to forward data to people you don’t know well. Most readers can open and extract a ZIP file, but you take your chances with other formats.
The situation is different if you’re solely focused on reducing file sizes. In this case, it makes sense to look for a more powerful (but perhaps less popular) tool. With that said, look at the tool’s history and make sure it has been receiving regular updates and that updates will still be available if you switch to a new operating system. It also doesn’t hurt to pick an archiving app that employs a container that can be read and decompressed by other tools.
Compression vs. Speed vs. Data Types
Higher compression helps reduce file sizes, but it can take much longer. Modern applications typically are thread-optimized, meaning that they take advantage of multi-core processors. However, there are a few solutions that still operate only on a single processing core. This is perhaps one of the biggest reasons we wanted to write this piece. After years of relying on WinZip as a staple benchmark, we as testers and you as readers think it's silly to pay $30 for a piece of software that is less feature-complete than free alternatives.
It’s important to know that file types like documents can be compressed quite a lot, while others should only be stored or compressed with a minimum compression ratio in order to speed up the process. JPEG images, software installation files, and similar data are already compressed, so you shouldn’t expect to see more than a cosmetic decrease in their file sizes after additional compression.
Processing speed is probably a passing thought if you're merely wrapping up a handful of files that have to be emailed; they're probably less than a few megabytes and nearly instantaneous to archive. However, performance becomes more important if you need to compress large amounts of data into a backup.
As a simple example, 50GB worth of information can be packed into a single file almost as quickly as a standard copy if you're using minimal compression. But it can take hours if you're trying to realize the smallest file sizes possible.
Due to the nature of storage media and email account settings, it's sometimes necessary to limit the size of files or backup sets. Email accounts are often limited to 10MB or 20MB per message, and media (like CDs, DVDs, and even Blu-ray discs) has limited capacities. In these cases, it may be necessary to create a multi-part archive in which you define the file size per part. These “multi-volume” archives are supported by many modern archiving software titles, though not all of them. If this is a feature that's important to you, bear in mind that you'll need to keep an eye out for it.
Passwords and Encryption
The best way to ensure that archives are protected from unauthorized access is to apply a password, along with encryption of the contents. This will cause the compression and encryption process to take even longer, but this combination represents much more effective protection. Most archiving tools support AES encryption, and some (7-Zip and WinZip) already take advantage of additional hardware-based processor instructions that Intel started to deploy on its Core i5 dual-core processors. As a result, encryption will have a less-noticeable impact on archive processing time in the future, as long as your archiving software supports the AES-NI capability. For owners of AMD-based platforms, it's only a matter of time until a similar instruction set appears.
There are a few limitations, particularly for large file sizes and older containers. The ZIP 2.0 specification only supported individual file and archive sizes of up to 2GB. Your hard drive partition might be an issue as well, since FAT32 on older Windows systems maxes at 4GB. Larger archives will require NTFS. Finally, modern archiving tools may consume a large amount of memory, since large dictionaries (where patterns are looked up) typically have to be handled in main memory. Therefore, best performance can only be achieved if you don’t impose a memory capacity bottleneck.