Standard Windows audio drivers cause noticeable delay when you press keys on a MIDI keyboard.
Cubase 5 was one of the first DAWs to offer native 64-bit support. This architecture allows the software to utilize more than 4 Gigabytes (GB) of System RAM. Why 64-Bit Architecture Matters Breaks the 4GB memory limit of 32-bit systems. Cubase 5 Download 64 Bit