Dell OptiPlex 7040 SFF vs. HP ProDesk 400 G6 SFF
Comparison and Differences
Differences between Dell OptiPlex 7040 SFF and HP ProDesk 400 G6 SFF
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 ProDesk 400 G6 SFF as it is running a newer generation CPU. This is not to say that Dell OptiPlex 7040 SFF is bad - it can still run some powerful CPUs, albeit being an older generation.
The Dell OptiPlex 7040 SFF has 4 RAM slots while the HP ProDesk 400 G6 SFF 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 ProDesk 400 G6 SFF is using the faster 2666 MT/s RAM. The Dell OptiPlex 7040 SFF is slower by supporting RAM speeds of up to 2133 MT/s. In addition, you will be able to install the same amount of RAM in both models, and most probably 64 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.
In total the Dell OptiPlex 7040 SFF has 10 USB ports. The HP ProDesk 400 G6 SFF 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.
DisplayPort is crucial for any desktop machine. It is good to see that both models are featuring DisplayPorts. However, the Dell OptiPlex 7040 SFF comes with 2 ports, while the HP ProDesk 400 G6 SFF has only 1. If you are planning to use multiple monitors, the Dell OptiPlex 7040 SFF is the better choice.
The Dell OptiPlex 7040 SFF comes with an HDMI port, while the HP ProDesk 400 G6 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 OptiPlex 7040 SFF is better equipped as it comes with 3 SATA slot(s), while the HP ProDesk 400 G6 SFF has 2 slot(s).
When your goal is to have the fastest SSD transfer speeds, an M.2 interface is crucial. Thus, it is good that both models have M.2 SSD slots. Today M.2 SSDs are not much more expensive than the average SATA drives, so it really does not make sense to invest in SATA drives anymore.
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!
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 180 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.