The dispute is over Sun's Java Virtual Machine (JVM), a piece of software that is needed for a computer to run software written in Java. The language, developed by Sun in 1995, is popular for internet-based applications.
However, its future was threatened by Microsoft's decision to drop Sun's JVM from its flagship operating system, Windows XP, because Microsoft has its own competing language and virtual machine.
Seeking damages, Sun accuses Microsoft of using its dominant position in the market for operating systems to sidetrack Java, in breach of antitrust laws. Sun also alleges that Microsoft views Java as a threat in the new markets for mobile phones and handheld devices.
In a hearing that started on Tuesday and it is expected to conclude today, Sun has asked US District Judge J. Frederick Motz to issue an order requiring Microsoft to distribute its JVM with Windows until the case is resolved.