Alienware X51 R2 vs. Dell OptiPlex 990 DT
Comparison and Differences
Differences between Alienware X51 R2 and Dell OptiPlex 990 DT
If you are looking for a more modern desktop, then you should go with the Alienware X51 R2 which was released in 2013. The Dell OptiPlex 990 DT is older and entered production in 2011.
If you are looking for the smaller form factor the Alienware X51 R2 is the right one for you. It is smaller than the Dell OptiPlex 990 DT 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 R2 as it is running a newer generation CPU. This is not to say that Dell OptiPlex 990 DT is bad - it can still run some powerful CPUs, albeit being an older generation.
Memory
The Dell OptiPlex 990 DT has 4 RAM slots while the Alienware X51 R2 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 X51 R2 is using the faster 1600 MT/s RAM. The Dell OptiPlex 990 DT is slower by supporting RAM speeds of up to 1333 MT/s. In addition, you will be able to install the same amount of RAM in both models, and most probably 16 GB of RAM will be enough for most people. However, if you will be needing more RAM, make sure to check other desktop models too.
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. 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.
The DisplayPort is usually the more popular video port used with desktops and laptops, while the HDMI is used predominantly in consumer electronics. That's why, it is good to see that both of the models come with a DisplayPort.
None of the models has an HDMI port. If your monitor supports only the HDMI interface, you will need to buy an adapter. Such adapters are cheap so nothing to worry about.
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 3 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 Dell OptiPlex 990 DT, nor the Alienware X51 R2 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 990 DT comes with a decent 250 Watt PSU, but the Alienware X51 R2 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
