TransMagic has a rule of thumb regarding RAM. We call this the 10x4 rule: When translating a file (assembly) TransMagic will typically consume 10x the file size in RAM (either physical or swap). So in the case of a 100 MB file, this means that TransMagic would likely consume around 1.0 GB of RAM to read this file into TransMagic. Once in TransMagic, meaning post-translation, RAM will fall to about 4x the file size. So, 400 MB. So the best thing you can do for TransMagic is have plenty of RAM when dealing with large files.
For extremely large files, we recommend you look into the TransMagic MagicBatch Add-On. The advantage of the TransMagic MagicBatch addon is that you do not visualize the part. You simply select the input file(s), the output format, where to save the output file and click "Go." MagicBatch processes the file until complete. You could start one file or a collection of files before you leave the office and have the output files sitting in the output folder when you get back to the office the next day. This unattended process also saves you time and frees up your system resources while you're working during the day.