Dell OptiPlex 990 USFF vs. Lenovo ThinkCentre M900 Tiny
Comparison and Differences
Differences between Dell OptiPlex 990 USFF and Lenovo ThinkCentre M900 Tiny
If you are looking for a more modern desktop, then you should go with the Lenovo ThinkCentre M900 Tiny which was released in 2015. The Dell OptiPlex 990 USFF is older and entered production in 2011.
If you are looking for the smaller form factor the Lenovo ThinkCentre M900 Tiny is the right one for you. It is smaller than the Dell OptiPlex 990 USFF 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 Lenovo ThinkCentre M900 Tiny as it is running a newer generation CPU. This is not to say that Dell OptiPlex 990 USFF is bad - it can still run some powerful CPUs, albeit being an older generation.
Memory
Both models have have equal amount of ram slots (2 RAM). Usually two RAM slots are more than enough for most cases. However, the count should be taken into account when planning how much and what combination of RAM you are going to need for your system.
The Lenovo ThinkCentre M900 Tiny is using the faster 2133 MT/s RAM. The Dell OptiPlex 990 USFF 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 Lenovo ThinkCentre M900 Tiny as it has the ability to run 32 GB of RAM. The Dell OptiPlex 990 USFF can do a bit less at max 8 GB. Most of the times, this should be sufficient for the majority of users.
Ports
In total the Dell OptiPlex 990 USFF has 7 USB ports. The Lenovo ThinkCentre M900 Tiny 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.
DisplayPort is crucial for any desktop machine. It is good to see that both models are featuring DisplayPorts. However, the Lenovo ThinkCentre M900 Tiny comes with 2 ports, while the Dell OptiPlex 990 USFF has only 1. If you are planning to use multiple monitors, the Lenovo ThinkCentre M900 Tiny is the better choice.
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 990 USFF is better equipped as it comes with 2 SATA slot(s), while the Lenovo ThinkCentre M900 Tiny has 1 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 Lenovo ThinkCentre M900 Tiny. Sadly, the Dell OptiPlex 990 USFF 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!
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 Lenovo ThinkCentre M900 Tiny comes with a decent 65 Watt PSU, but the Dell OptiPlex 990 USFF has a more powerful one rated at 200 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
