Written in Java, Jalatext is capable of opening very large (1 gig+) files almost instantly. Rather than churn madly trying to fit as much of the file as possible into RAM, it loads a small portion at a time, keeping performance swift. The user can adjust the size of the loaded segments, in accordance with their available RAM.
Once Jalatext is loaded, you can navigate by segment. If you tell it to load 10,000 lines at a time, each click of the appropriate control will move to the next/prior 10,000 lines. Or by scrolling within a segment. You can also rapidly go to the beginning/end of a file.
This points out one of the problems with Jalatext, namely, it's not easy to tell your relative position in a file.
Jalatext's status bar tells you the byte range being displayed, but not the line number, which is far more useful for many purposes. The scroll bar tells you the relative position of what you're seeing within the loaded segment, which is good, but there's little to provide a quick, intuitive, sense of your position within the file itself. If you know the area you're interested in is, say, line 234,500 out of 1 million lines, there is no "go to this line" function or command.
One thing that can mitigate this is the use of bookmarks.
Jalatext allows you to mark positions in a file, and rapidly move between them. You can also export all of the text between bookmarks, which is handy when trying to extract a large segment of data. When combined with the regex (Regular Expression, and if you need a program like Jalatext, you either know what these are, or you need to learn) enabled search functionality, this can enable a lot of navigation shortcuts.
However, I've had freezes with Jalatext when doing searches in large files. I've worked around this by reducing the size of the file segment I chose to use.
Jalatext also has the ability to save the file in a different encoding, a boon when moving huge files from one OS to another, or making them readable by newer or older programs than the ones that output them, a common occurrence.
On the negative side, Jalatext does not have any capacity to identify delimited files and to display the data in an easier-to-read format. Delimited (often comma or tab delimited) files are one of the most common types of huge files, and this would be a good feature for future expansion.
Jalatext does a specialized job and does it well, but it's a little bare-bones for the $30 price. The 30-day trial has no functionality restrictions, so that's ample time for anyone to test it out and draw their own conclusions.
The "Try it for free" button on the Product Information page takes you to the vendor's site, where you can download the latest version of the software appropriate to your system.