Alienware Aurora R3 vs. Alienware X51
Comparison and Differences
Differences between Alienware Aurora R3 and Alienware X51
Both computers, the Alienware Aurora R3 and the Alienware X51, were released during the same year - 2011.
If you are looking for the smaller form factor the Alienware X51 is the right one for you. It is smaller than the Alienware Aurora R3 and will fit more easily under your desk.
Processor
Usually the newer the generation of the CPU, the better the performance and efficiency is. If your budget allows it, you should go with the Alienware X51 as it is running a newer generation CPU. This is not to say that Alienware Aurora R3 is bad - it can still run some powerful CPUs, albeit being an older generation.
Memory
The Alienware Aurora R3 has 4 RAM slots while the Alienware X51 has only 2 slot(s). This is not something to worry about. Just make sure you take it into consideration when planning how much RAM you are going to use.
The Alienware Aurora R3 is using the faster 1866 MT/s RAM. The Alienware X51 is slower by supporting RAM speeds of up to 1333 MT/s. Additionally, if you will be needing a lot of RAM, better go for the Alienware Aurora R3 as it has the ability to run 32 GB of RAM. The Alienware X51 can do a bit less at max 8 GB. Most of the times, this should be sufficient for the majority of users.
Ports
In total the Alienware Aurora R3 has 13 USB ports. The Alienware X51 is inferior in this regard and packs 8 USB ports. In any case, if you miss USB ports, you can always purchase a USB hub. None of the desktop models has a USB 3.1 port (10Gb/s), so if you need a fast connection to your peripherals, like external Solid State Drive, you will need to look elsewhere.
Nowadays, almost every new computer comes equipped with a DisplayPort. However, none of the devices being compared here has one. Don't worry though, DisplayPort adapters are very cheap and you can get virtually any combination of conversion types.
The Alienware X51 comes with an HDMI port, while the Alienware Aurora R3 does not support the interface. Of course missing HDMI port is something that can be easily fixed with a good adapter (e.g. DisplayPort to HDMI).
SATA slots are located on the motherboard and it is where SSD, HDD and Optical Disk Drives are connected. Each of the two models being compared have 4 SATA slot(s). Keep in mind that having too few SATA slots might limit your options for connecting additional memory drives.
M.2 SSD interface allows you to transfer data with higher speeds compared to the old SATA interface. Unfortunately, neither the Alienware Aurora R3, nor the Alienware X51 has one. However, you can still use a SATA SSD drive which should give you satisfactory performance.
Make sure that the available M.2 slot supports the PCIe (also called NVMe) interface. This is important as there are M.2 slots which support only the inferior SATA III interface. For comparison, the SATA III interface has max speeds of 6Gb/s, while the PCIe 3.0 x4 will support speeds up to 32Gb/s!
Power Supply
Having a Power Supply Unit with high power rating is important, if you are going to use components which require extra power. The Alienware X51 comes with a decent 330 Watt PSU, but the Alienware Aurora R3 has a more powerful one rated at 875 Watts. Choosing either one depends on your specific requirements and use case. Also don't forget that some models might have more than one PSU option - try to always get the most powerful one, especially if you plan to upgrade to a powerful GPU.
Motherboard
