The iPhone 4S is here - read our iPhone 4S review - so we've taken an in-depth look at the key specs and seen how it compares to its year-older sibling, the iPhone 4 and two-year old iPhone 3GS (read our iPhone 3GS review) – still going and now the budget handset of the pack.

You can check out our iPhone 4S video preview, complete with a look at the new voice controlled Siri software.

Processor and memory

The iPhone 4S boasts the same dual-core processor as the iPad 2 – the Apple A5 which is based on the ARM Cortex-A9 microarchitecture. Apple says it has twice the speed of the Apple A4 chip in the iPhone 4. The 3GS had an ARM Cortex A8-based processor running at 600MHz.

System memory

The 4S now has 1GB of system memory, double that of the iPhone 4. The 3GS has 256MB.

Storage

The iPhone 4 is still available at capacities of 16 and 32GB, but the 4S ups the ante here with a 64GB model. As of summer 2010 the iPhone 3GS regressed – from being available with 16 and 32GB, models produced from then on had just 8GB of memory, as befitting the budget handset of the range.

Size and weight

iPhone 4S uses the same chassis as the iPhone 4 - 24 per cent thinner than the iPhone 3GS at 9.3mm instead of 12.3mm. It's also ever so slightly wider by 3.5mm. In terms of weight, the 140g 4S is slightly heavier than the 137g iPhone 4, which in turn is slightly heavier than the 135g iPhone 3GS.

Voice control

Both the 3GS and iPhone 4 support basic voice control, but the 4S ups the ante with Siri, a voice assistant that means you can compose messages, set reminders and ask questions. You can also dictate to your handset. We're not sure how useful it would be, but we'd love to try it out. Sadly it's not part of the iOS 5 update for the older handsets.

Camera(s)

The iPhone 4 was quite limited in its photography. Still, against the 3GS it seemed positively brilliant, with 5 megapixels instead of 3 megapixels and the addition of an LED flash (which can also be used for the video) as well as a front-facing cam for video chat. Apple would like to think you would use FaceTime for this, but who does? However, Apple knew the camera was becoming a really weak point of the iPhone line, so it has given it some serious beefing up in the latest model.

There's a five element lens in the 4S instead of the four element in the 4, face detection and an 8-megapixel sensor. There's 60 per cent more pixels, a larger f/2.4 aperture and an advanced hybrid IR filter that produces sharper and brighter images. The Camera app has also been improved and the shot to shot capability is twice as fast according to Apple.

Video

Instead of the 3GS's VGA quality video recording and the iPhone 4's 720p HD, the 4S is capable of Full HD 1080p video, while there's also video stabilisation built-in too. You can also mirror the display to an HD TV using AirPlay.

Display

The 3GS 480 x 320 display now looks completely outdated – the iPhone 4 and 4S have the same high-resolution retina display with 960 x 640 resolution and a pixel density of 326ppi. Compare that to the 163ppi of the iPhone 3GS. While the screens aren't OLED as with some other smartphones, Apple says its IPS display tech is better

Wireless and data

In terms of Wi-Fi, iPhone 4S and 4 have 802.11n Wi-Fi, while the 3GS is stuck with the older 802.11b and g standards. This won't matter unless you connect it to an 802.11n router, of course. iPhone 4S has an upgraded version of Bluetooth – 4.0 instead of 2.1 in the other handsets. The 4S also boasts both GSM and CDMA capability, meaning it can be used on virtually any network across the globe. Data speeds have also been improved in the new handset, with 14.4Mbps downloads now possible.

Power and battery

The iPhone 4S has a slightly better battery life than the iPhone 4: up from 7 hours talk time on 3G to 8 hours - and much better than the 5 hours on the 3GS. Standby time is a cited 300 hours for the iPhone 4 and 3GS but strangely this is 100 hours more than the 4S. Is Apple being more realistic, or is it due to the notification strain in iOS 5?

Location and hardware

All three handsets boast accelerometer, aGPS and compass while the 4 and 4S have a six-axis gyro for greater accuracy of movement with apps and games.

Colours

The 3GS remains only available in black (the while model was discontinued in 2010), while iPhone 4 and 4S both have black and white variants.

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Liked this? Then check out Hands on: Phone 4S review

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