The Alienware Aurora R4 system uses a combination of SSD and HDD to combine speedy start up with plenty of storage capacity. This is an ideal way to set up a high performance gaming system.
Alienware and Dell use last generation Samsung Solid State Drives, so they are limited to SATA 2 transfer speeds. The Solid State Drive is significantly faster than the 1TB mechanical drive (as would be hope for), although 120MB/s sequential read/write is as fast as we could expect.
The ATTO Bench benchmark records similar results as seen with the CrystalDiskMark test. Decent performance from both drives.