New images of the Xbox Series X's casing have appeared online, giving us our strongest indication yet of what kind of input and output ports are found on the rear of the machine. The legacy HDMI input from the TVTVTVTV era is gone, replaced with a rather more mundane arrangement of USB ports, Toslink, Ethernet and a curious non-identified mystery port.

The images first surfaced on NeoGAF, with acknowledgement that this is the real deal coming via Thurrott's Brad Samms - a site and an author well known for deeply embedded sources within Microsoft. Adding a little extra weight to the validity of this source is that a Twitter user - amusingly - claimed the machine on his Microsoft accont via the clearly visible serial number.

With all of this in mind, the likelihood is that this is a genuine look at an Xbox Series X casing from new angles as opposed to an elaborately fake render or 3D printing. We see further air intakes (though not quite as large as I imagined) along with a standard figure-eight power input, Ethernet input and dual USB 'SuperSpeed' ports, Toslink audio and an HDMI 2.1 output. There's also a Kensington lock too, for the security-conscious amongst us.

The two leaked image, which first appeared on NeoGAF, courtesy of user Curry Panda.

However, the nature of the port to the left of the HDMI output that remains a mystery. Brad Samms suggests that it's some kind of diagnostic port that may not appear on final hardware (this unit is clearly marked as a prototype). However, although purely speculation on our behalf, we wouldn't be surprised at all if this eventually turns out to be an expandable storage bay for NVMe PCI Express drives, perhaps encased in some kind of stick-like cartridge configuration - an idea mooted by our very own John Linneman when the Series X was first unveiled.

The dimensions look right and it would provide an easy plug 'n' play solution to a serious challenge posed by the move to ultra-fast solid-state storage: in a world where games are now frequently over 100GB in size, how do you deliver a cost effective console that's still capable of housing a substantial game collection? This may well be the next-gen iteration of the slot-in hard drive idea we saw Microsoft explore with Xbox 360.

With prototype Xbox Series X hardware now leaking like this, hopefully we'll get to see something more official from Microsoft soon.