Dell OptiPlex 990 SFF vs. Dell Vostro 3650
Comparison and Differences
Differences between Dell OptiPlex 990 SFF and Dell Vostro 3650
If you are looking for a more modern desktop, then you should go with the Dell Vostro 3650 which was released in 2016. The Dell OptiPlex 990 SFF is older and entered production in 2011.
If you are looking for the smaller form factor the Dell OptiPlex 990 SFF is the right one for you. It is smaller than the Dell Vostro 3650 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 Dell Vostro 3650 as it is running a newer generation CPU. This is not to say that Dell OptiPlex 990 SFF is bad - it can still run some powerful CPUs, albeit being an older generation.
Memory
The Dell OptiPlex 990 SFF has 4 RAM slots while the Dell Vostro 3650 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 Dell Vostro 3650 is using the faster 1600 MT/s RAM. The Dell OptiPlex 990 SFF 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
In total the Dell OptiPlex 990 SFF has 10 USB ports. The Dell Vostro 3650 is inferior in this regard and packs 6 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.
Unfortunately, only the Dell OptiPlex 990 SFF has a DisplayPort. The Dell Vostro 3650 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 Vostro 3650 comes with an HDMI port, while the Dell OptiPlex 990 SFF 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 Vostro 3650 is better equipped as it comes with 4 SATA slot(s), while the Dell OptiPlex 990 SFF 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 990 SFF, nor the Dell Vostro 3650 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
Looking at the Power Supply Unit (PSU) of the two models we don't see any differences. For either of them you get a maximum power of 240 Watts. However be careful, many models have more than one power supply option. When buying your computer, it is a good idea to get a version with the most powerful PSU. This will potentially allow you to upgrade to a more powerful GPU for example.
Motherboard
