Dell OptiPlex 980 MT vs. HP ProDesk 400 G3 Microtower
Comparison and Differences
Differences between Dell OptiPlex 980 MT and HP ProDesk 400 G3 Microtower
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 G3 Microtower as it is running a newer generation CPU. This is not to say that Dell OptiPlex 980 MT is bad - it can still run some powerful CPUs, albeit being an older generation.
The Dell OptiPlex 980 MT has 4 RAM slots while the HP ProDesk 400 G3 Microtower 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 G3 Microtower is using the faster 2133 MT/s RAM. The Dell OptiPlex 980 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 HP ProDesk 400 G3 Microtower as it has the ability to run 32 GB of RAM. The Dell OptiPlex 980 MT 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 Dell OptiPlex 980 MT has 10 USB ports. The HP ProDesk 400 G3 Microtower 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.
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 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 980 MT is better equipped as it comes with 4 SATA slot(s), while the HP ProDesk 400 G3 Microtower 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 980 MT, nor the HP ProDesk 400 G3 Microtower 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!
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 980 MT comes with a decent 255 Watt PSU, but the HP ProDesk 400 G3 Microtower has a more powerful one rated at 300 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.