Dell Vostro 3900 vs. HP EliteDesk 800 G3 Tower
Comparison and Differences
Differences between Dell Vostro 3900 and HP EliteDesk 800 G3 Tower
Both models have the same form factor, meaning reoughtly they have the same phiysical size and form.
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 HP EliteDesk 800 G3 Tower as it is running a newer generation CPU. This is not to say that Dell Vostro 3900 is bad - it can still run some powerful CPUs, albeit being an older generation.
The HP EliteDesk 800 G3 Tower has 4 RAM slots while the Dell Vostro 3900 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 HP EliteDesk 800 G3 Tower is using the faster 2400 MT/s RAM. The Dell Vostro 3900 is slower by supporting RAM speeds of up to 1600 MT/s. Additionally, if you will be needing a lot of RAM, better go for the HP EliteDesk 800 G3 Tower as it has the ability to run 64 GB of RAM. The Dell Vostro 3900 can do a bit less at max 16 GB. Most of the times, this should be sufficient for the majority of users.
In total the HP EliteDesk 800 G3 Tower has 10 USB ports. The Dell Vostro 3900 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.
Unfortunately, only the HP EliteDesk 800 G3 Tower has a DisplayPort. The Dell Vostro 3900 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 3900 comes with an HDMI port, while the HP EliteDesk 800 G3 Tower 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 HP EliteDesk 800 G3 Tower is better equipped as it comes with 5 SATA slot(s), while the Dell Vostro 3900 has 4 slot(s).
If you want the fastest transfer speeds for your SSD, an M.2 interface is crucial. Thus, if the M.2 SSD slot is a mandatory requirement for you, go with the HP EliteDesk 800 G3 Tower. Sadly, the Dell Vostro 3900 has no such slot, and you will be forced to use the SATA interface instead.
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!
Having a Power Supply Unit with high power rating is important, if you are going to use components which require extra power. The Dell Vostro 3900 comes with a decent 300 Watt PSU, but the HP EliteDesk 800 G3 Tower has a more powerful one rated at 500 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.