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In Java, a software package can specify its memory limitations, or it can use the default ones provided by the JVM (Java environment) installed.
In case of x86 Oracle JVM, default max memory usage is 1GB.
In case of x64 Oracle JVM, default max memory usage is 4GB.
The philosophy of Java is that if all the stuff you need is in memory, the application is faster (or course, at the expense of memory usage). This basically means that the garbage collector is not executed by the JVM until memory consumption of the application gets close to the limit, or until system memory starts running out.
If you limit how much RAM an application can claim, there is of course a trade-off. The less RAM an application has assigned, the more often the garbage collector will need to run, which will increase the CPU utilization. If you assign too little memory, the application can crash with "not enough memory" errors.
So the actual RAM utilization of Unimus will depend on how many devices you have, how often you run backups, etc. - basically on how utilized the software is.
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