True you can load samples into RAM in Halion Sonic SE. Sadly that's a small amount though.
If only you could load whole sessions into RAM
Well, if that is of great concern to you, consider upgrading to Halion's full version.
Desktop: i7 3770k, 32 GB RAM, nVidia GTX770 + GT640-DCSL fanless, 3 monitors (30" 2560x1600 + 2x 27" 1920x1080), 256 GB SSD (OS), 2 TB SATA III (audio), 3 TB SATA III (sample libraries), 3x 3 TB USB 3.0 (backup/archives), RME UFX, Win 8.1 Pro x64, Cubase 7.5, Sonar X3, Vienna Ensemble Pro 5.
Slaves: 2x i7 2700k, 16 GB RAM, 256 GB SSD, 3 TB SATA III, Win 8.1 Pro x64, Vienna Ensemble Pro 5.
Laptop: 17" HP EliteBook 8770w (i7 3820QM 2.7 Ghz/3.7 Ghz max OC, 16 GB RAM, 256 GB SSD, 1 TB SATA III), RME Babyface, Win 7 Pro x64, Vienna Ensemble Pro 5, Cubase 7.5, Sonar X3.