1. Dell put in a 128 hard drive was hoping I was getting the 250 memory hard drive for windows 10 operating system.
3. I know that the Alienware 17 R4 is a newer system with the newer GPU gtx10 series. Yet 16 GBs is showing to be too little memory to be able to use this laptop and not experience drag time.
1. You get the sized HDD/SSD that you custom-build the computer with.
While a computer will run fine with 120gb drive ... by the time Dell and Windows-10 drops some Recovery Partitions on it, Windows-10 install, and some Apps (not even large games), virtual memory swap-file, and leave 10 gigs free work space on it, you are cutting it pretty close. But I have seen it work for "mom and pop" or business computer.
Still, minimum SSD I install as C: boot is 240gb these days. SSDs are cheap now. If you want a bigger one, you can upgrade it.
To try to survive with 120gb C: drive as a gamer (read ... large game installs) ... be sure your games, Steam, Origin, etc. are setup to use D: instead.
Also, you will probably have to do this:
3. 16gb of ram memory should be fine. This is not causing gaming lag.