The talk is about the speaker's experience of developing an emulator in Java for the ZX Spectrum and Sega Master System. The speaker discusses the challenges and decisions they made during development, including the use of different APIs in Java, such as graphics rendering and audio output. They also touch on topics such as timing and concurrency, data manipulation, and checking for JIT compiler optimizations. The speaker concludes by mentioning that their emulator is able to run most software for the ZX Spectrum and Sega Master System, and they plan to continue improving it.