Sony is hosting a special PlayStation event on Wednesday 7 September where it is expected to announce not one but two new versions of its PlayStation 4 console. The first will be a slimmer, thinner machine with a few improvements over the current model, the second a much more powerful games machine to take the brand forward.

These are dubbed the PS4 Slim and PS4 Neo (AKA PS4.5 or PS4K) and are likely to come out in 2016 and 2017 respectively.

We suspect they will both completely replace the existing machine, of which Sony has sold more than 40 million units to date, but if you already have one it is unlikely you'll be forced to upgrade any time soon.

There are some that might consider doing so, however, so here are the differences between all three models based on the rumours, leaks and speculation we have so far. It might help you decide whether to save up for a replacement.

Although there is considerable debate on how effective the PS4 Neo will be at playing games in a 4K resolution, with leaked specifications taken into account, Sony boss Andrew House has gone on record to say the machine will support the format. At the very least its higher spec'ed graphics processing and CPU will be capable of running games at smoother frame rates and in Full HD - maybe even 120fps as some have hinted.

We'll keep an open mind on this one, as 4K gaming is something Xbox is discussing for its Project Scorpio machine out next year. It would be madness if the PS4 Neo couldn't match those ambitions.

Neither the PS4 Slim nor the original PS4 can play 4K games. It is even highly unlikely that the former will be upscale existing titles to 4K, considering every indication to date points to it having the same inner gubbins as the current model.

Some were surprised when the original PlayStation 4 was released without HDMI 2.0 connectivity or HDCP 2.2 copy protection. Those are mandatory for 4K Blu-ray playback and thus the PS4 will never be upgraded to work with Ultra HD discs. There's also the matter of the disc drive, which is of Blu-ray, but not UHD BD standard.

From what we've heard of the PS4 Slim so far, the same will be true of the slimmer machine. Even though consoles have reportedly made it into some customers hands, allegedly through a retailer in the United Arab Emirates, there hasn't been a single report of them doubling as 4K Ultra HD Blu-ray players.

The PS4 Neo, on the other hand, will be capable of playing 4K Blu-rays. That's almost guaranteed. What's more, it will support HDR picture tech for a wider colour gamut and better contrast on compatible TVs.

There is a direct parallel between each of the machines Blu-ray compatibility and 4K video, from services such as Netflix and Amazon. Neither the PS4 nor PS4 Slim are expected to carry the 4K versions of streaming services and, in the case of the latter, likely to have the necessary connectivity for video or copy protection.

However, the PS4 Neo will almost certainly be able to play back 4K content from a growing number of online services.

A while back a leaked document appeared online, detailing some of the headline specs of Sony's premium PS4 Neo. It might be fully representative - we'll only find out that on 7 September - but it's something to go on now.

It stated that the Neo will have 4.14 teraflops of GPU power and GDDR5 memory rynning at 218GB/s. It will also reportedly run on a 2.1GHz octa-core processor.

That clearly beats the AMD Jaguar CPU on the PS4 and 1.84 teraflops of graphucs processor found on the PS4 and, it is said, the PS4 Slim.

Performance wise, that means it is considerably faster and capable of much more intensive work.

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We currently have no idea what the PS4 Neo will look like, and might not even find out on 7 September either, if the original PS4 unveiling was anything to go by (which only featured the DualShock gamepad design, rather than the console).

However, thanks to plenty of PS4 Slim leaks, each featuring the same build and design we can safely say that it will be smaller and thinner than its predecessor. The new DualShock is also slightly redesigned, with a clear LED lit strip now running along the top of the touchpad.

If we're being honest, we actually prefer the current PS4 design to the Slim version we've seen in leaked photos. Although it would be great if the new one is quieter. Our current console sounds like an industrial leaf blower at times.

While backwards compatibility on the PS4 is restricted to PlayStation Now - which features cloud-playable versions of PS3 games - and downloadable, converted releases, the PlayStation 4 family will benefit from all PS4 games being playable on across the consoles.

Andrew House confirmed that releases with better graphics, HDR and other bells and whistles for PS4 Neo will also run, in a lower resolution or graphical detail, on the other PS4 machines around the globe. There will be no games that are exclusive to the premium machine, he promised.

Pocket-lintBatman PS VR-1

As far as we know, PlayStation VR headsets - which come out on 13 October - will be compatible with all PS4 consoles, regardless of their spec. We wonder though if the PS4 Neo will be able to run titles at 120 frames per second to match the headset's top capabilities.

At present, existing PS4 consoles run them at 60fps and the PS VR media box upscales (frame doubles) the video.

There have been quite a lot of suggestions floating around about price. At present, you can get a 500GB PS4 for around £280 including a game. The 1TB version costs anywhere from £320 with a game.

Strangely, the one UK PS4 Slim leak suggested it will cost £380. Unless it comes with a 2TB hard drive, that doesn't make sense to us. Surely it should be cheaper than the existing model rather than more expensive, especially if size and an LED strip on the controller are the only major changes?

That price also doesn't sit well with pricing suggestions for the PS4 Neo. Several sources claim it'll be around $399 (£349) at launch. Again, that can't be dramatically cheaper than the PS4 Slim.

We wouldn't actually be surprised if Neo ended up around the $499 mark at launch.

The standard, current PS4 has been around for three years and is readily stocked everywhere. It is tipped that the PS4 Slim replacement model will hit shops from 14 September - a week after the launch event - and considering alleged devices have made it onto the marketplace already, that makes sense.

The PS4 Neo, however, is unlikely to come out in 2016. Instead, we expect it to majorly rival Xbox's Project Scorpio for Christmas 2017. 

A conclusion about which of the consoles to buy is actually quite easy, even at this stage where final details are not known. If you are looking for a games console right now, and PlayStation shades it for you over Xbox, it's worth holding on for another week or two for the PS4 Slim.

That said, if there are few hardware improvements, only aesthetic ones and an extra light bar on the controller, you might want to check out the pricing of existing PlayStation 4 variants. There's plenty of stock still out there and they are bound to be reduced in price when the Slim arrives.

Those who are happy to wait should do so, however. The PS4 Neo will undoubtedly be the king of the family and therefore the machine to aspire to.