PC-O5S Internal Design
Getting inside the PC-O5S is very easy: remove the glass panel and half the job is done. This grants you access to most of the internals, while the removable panel on the back provides access to the rest of the case.
With the large glass panel removed users are presented with a very unusual looking case. High up on the list of unusual items is the vertically mounted PCIe x16 riser card to the far left which is connected to a very long ribbon cable.
There isn't any obvious location to install the power supply and there certainly isn't an external bracket. The riser card means that GPUs are mounted flat in the PC-O5S which will look very cool.
This design allows the PC-O5S case to be much thinner than it would be otherwise. Since Mini-ITX cases only support single GPUs this design makes perfect sense. It is a similar concept to what we saw in the Asrock M8 or the Silverstone RVZ01.
With the hard drive cage installed, the PC-O5S' graphics card support is limited to cards no longer than 190mm. This limits your options somewhat, though new high-end graphics cards such as the Gigabyte N970IXOC-4GD (GTX 970) measure just 170mm long and therefore will fit nicely.
Unlike most compact computer cases removing the hard drive cage doesn't remove 3.5" drive support from the PC-O5S entirely. Therefore I suggest doing away with it as this enables graphics cards as long as 310mm to fit snug inside. Moreover, massive triple slot cards such as the Gainward GTX 980 Phantom will fit without a problem.
Although support for larger graphics cards comes at the cost of the hard drive cage which does support three 3.5" drives it is possible to still squeeze one 3.5" drive into the PC-O5S. This is done by accessing the rear side of the motherboard tray where there is room for two storage devices which includes either one 3.5" and one 2.5" drive or two 2.5" drives.
Alternatively, if you are not interested in installing a discrete GPU and would rather focus on storage, then the PC-O5S can accommodate a total of eight drives with a maximum of five 3.5" drives.
A potential limitation of the PC-O5S is its 85mm sealing height for CPU coolers, you can forget tower coolers then. There are a number of very good low-profile coolers available, but even better, the PC-O5S supports all-in-one liquid coolers.
In addition to the two top mounted 120mm fans that come included, the PC-O5S supports an optional 140mm rear fan.
Moving air though the PC-O5S is important as key components such as the power supply are embedded within the case with no means of drawing in fresh air. The case uses the smaller SFX power supply form factor, which translates into a 140mm PSU length limitation.
This could be viewed as a weakness, though I don't have a problem with it. There are some very powerful SFX units getting around now that offer fully modular designs such as the 600w Silverstone SX600-G or the super quiet SX500-LG which boasts a 120mm fan.
These SFX power supplies are capable of powering GPUs such as the GeForce GTX 980, so this doesn't limit the capabilities of PC-O5S.