This Sunday, 25 February, Samsung will unveil its two latest flagship smartphones; the Galaxy S9 and Galaxy S9+.

They will be announced on stage at a Samsung Unpacked event at Mobile World Congress and the world will be watching the livestream to get a glimpse of the new designs and see the entire spec list.

However, thanks to multiple leaks, we already have a pretty good idea of what to expect from Samsung come launch day, from its design right down to the features of the new dual-lens camera. This year's Galaxy S flagship doesn't stray too far away from the design of the S8, but it will still be an important update for Samsung nonetheless.

That's why we've put together a chronological round-up of all the major Samsung Galaxy S smartphones from the first to the two expected to launch this week. We've ignored variants - the Neo, Plus, Mini, etc - and stuck to the major phones from each line.

So scan the phones below and see how Samsung has changed its design philosophy as the technology has improved.

Samsung Galaxy S

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First released in June 2010, the Samsung Galaxy S ran on Android 2.1 and had an 800 x 480 Super AMOLED display.

It also had a single-core 1GHz processor and 0.5GB of RAM.

The rear camera was 5-megapixels, while front was just 0.3-megapixels.

Samsung Galaxy S2

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Also known as the Samsung Galaxy S II, the refreshed phone was released in April 2011 and sported a similar 800 x 480 screen as its predecessor.

The processor got a bump up to dual-core and 1.2GHz, and there was 0.75GB of RAM.

The rear camera was 8-megapixels this time, with a 2-megapixel front-facing cam.

Samsung Galaxy S3

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Again sticking with the Roman numerals, so therefore technically known as the Samsung Galaxy S III, this model came out in May 2012 and was the first in the series to have a HD screen.

Its resolution of 1280 x 720 was pretty revolutionary at the time. It also sported Android 4.0 Ice Cream Sandwich.

There was a 1.4GHz quad-core processor with 1GB of RAM on launch, although Samsung stuck with an 8-megapixel rear camera.

Samsung Galaxy S4

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Released in April 2013 and ditching the Roman numerals that nobody used when referring to Galaxy phones on the internet anyway, the S4 had a 5-inch Full HD display.

It also upped the processing power to a 1.9GHz quad-core chip, with 2GB of RAM.

The rear camera had a jump too, up to 13-megapixels.

Samsung Galaxy S5

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Coming in April 2014, the S5 also had a Full HD screen but it was slightly bigger, measuring 5.1-inches (an LTE-A model eventually upped that to 2560 x 1440).

There was a 2.5GHz quad-core processor on board, with 2GB of RAM. And the rear camera was once again improved, to a 16-megapixel module.

Samsung Galaxy S6

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April 2015's Galaxy S line was the first to offer two separate devices at the same time.

The more standard Galaxy S6 featured a flat 2560 x 1440 Quad HD Super AMOLED display, measuring 5.1-inches.

It ran on a Samsung-made octa-core processor, had 3GB of RAM and a 16-megapixel rear camera capable of recording Ultra HD footage. A 5-megapixel camera was adopted for the front.

Samsung Galaxy S6 edge

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Like its stablemate also released in April 2015, the Galaxy S6 edge had a 5.1-inch Quad HD screen, octa-core processor, 3GB of RAM, 16-megapixel rear camera and 5-megapixel front-facing cam.

Where it differed is that the sides of the display are curved and wrap around to give the illusion of no bezel - a radical alternative at the time.

Samsung Galaxy S7

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The Galaxy S7 was announced in February 2016 and came with a 5.1-inch QHD display (2560 x 1440).

Like the S6 before it, it was the flat-screen version of two handsets, but added a dual-pixel 12-megapixel camera for better low light photography and faster octa-core processor.

Samsung Pay was enabled on the phone, which could work through NFC and magnetic strip systems.

Samsung Galaxy S7 edge

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The Galaxy S7 edge was (and even now it's two years old, still is) a true flagship phone in every respect. It too was announced in February 2016 and its 5.5-inch dual edge QHD display was simply superb.

All of the same features as the S7 were on board and the design was a touch rounder than the S6 edge that preceded it.

Samsung Galaxy S8

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The Samsung Galaxy S8 was the first to introduce the Infinity Display, that referred to the fact it had an edge-to-edge display with virtually no bezels. The front-mounted home button was moved to the back too, albeit in a slightly awkward position - something Samsung should correct with the S9.

While there was also a second variant in the Plus, the standard Galaxy S8 came with curved edges as standards. 

Samsung Galaxy S8+

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The Samsung Galaxy S8+ is exactly the same as its smaller S8 sibling in almost every respect, save from a larger, 6.2-inch display and a 3,500mAh battery compared to a 3,000mAh cell on the S8. While a 6.2-inch screen may sound huge, thanks to the Infinity Display design, the S8 Plus wasn't much bigger than an iPhone 7 Plus.

The extra screen real estate made it an absolute joy to watch movies on and the battery kept it going for hours on end. We loved the S8+ so much we considered to the one of the, if not the best Android phone of 2017.

Samsung Galaxy S9

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On the surface the S9 looks very similar to the S8 from 2017. The phone still offers that curved edge design and comes with a 5.8-inch OLED screen size and will be, once again, waterproof. 

The Galaxy S9 will offer AR emoji, where the phone will create a 3D avatar by scanning your face and create a range of custom emoji for you. These can be used when chatting in WhatsApp or Facebook Messenger, for example, rather than using basic emoji. Social. 

Samsung Galaxy S9+

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Externally, the new Galaxy S9+ looks like the 2017 S8+, but this year there's more than just a size difference between these two handsets, with the larger Galaxy S9+ model getting an secondary camera for 2x optical zoom.

The camera is the main focus point for the Galaxy S9 models, with both handsets offering a new dual aperture main camera. This integrates a mechanical aperture, giving you f/1.5 for low light and f/2.4 for brighter conditions.