Alienware X51 R3 vs. Dell OptiPlex 390 MT
Comparison and Differences
Differences between Alienware X51 R3 and Dell OptiPlex 390 MT
If you are looking for a more modern desktop, then you should go with the Alienware X51 R3 which was released in 2015. The Dell OptiPlex 390 MT is older and entered production in 2011.
If you are looking for the smaller form factor the Alienware X51 R3 is the right one for you. It is smaller than the Dell OptiPlex 390 MT 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 R3 as it is running a newer generation CPU. This is not to say that Dell OptiPlex 390 MT is bad - it can still run some powerful CPUs, albeit being an older generation.
Memory
Both models have have equal amount of ram slots (2 RAM). Usually two RAM slots are more than enough for most cases. However, the count should be taken into account when planning how much and what combination of RAM you are going to need for your system.
The Alienware X51 R3 is using the faster 2133 MT/s RAM. The Dell OptiPlex 390 MT 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 X51 R3 as it has the ability to run 32 GB of RAM. The Dell OptiPlex 390 MT can do a bit less at max 8 GB. Most of the times, this should be sufficient for the majority of users.
Ports
Both models have the same amount of USB ports for total count of 8. If this is not enough, using a USB hub is always a viable option. What is nice about the Alienware X51 R3, is that it has 2 USB 3.1 port(s) which allows transfer of up to 10Gb/s. Unfortunately, the Dell OptiPlex 390 MT has no such port, thus restricting your transfer speeds significantly. For people who want to use external drives on regular basis, this might be an issue.
Unfortunately, only the Alienware X51 R3 has a DisplayPort. The Dell OptiPlex 390 MT does not have one? Don't worry though, nowadays video adapters are cheap and you can get almost any combination of conversion types.
The Dell OptiPlex 390 MT comes with an HDMI port, while the Alienware X51 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 ports are placed on the system board and it is where you connect your HDD, SSD and Optical Disk Drives. More SATA slots will allow you to have more drives running at the same time. In this regard the Dell OptiPlex 390 MT is better equipped as it comes with 4 SATA slot(s), while the Alienware X51 R3 has 3 slot(s).
M.2 SSD interface allows you to transfer data with higher speeds compared to the old SATA interface. Unfortunately, neither the Dell OptiPlex 390 MT, nor the Alienware X51 R3 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 Dell OptiPlex 390 MT comes with a decent 265 Watt PSU, but the Alienware X51 R3 has a more powerful one rated at 330 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
