iPhone is a smartphone designed by Apple, sold in many countries and on many mobile carriers. What makes iPhone special from past mobile phones is its minimalist design and heavily reliance on a touch screen instead of buttons. iPhone sports many features that make it attractive as not only a phone, but a general purpose computing device. More importantly, iPhone has recently gained a massive foothold in the handheld gaming market through the App Store, allowing users to easily download apps from the device itself. With iPhone's massive popularity and considered by many to be their primary gaming platform, major publishers such as Gameloft, EA, Epic Games and Sega have all released games for iPhone.
The iPhone is a very capable platform in terms of processing power. It has a 620 MHz ARM 1176 underclocked to 400 MHz processor, 128 MB eDRAM as well as a PowerVR MBX graphics processing unit. This allows it to run 3D and sprite-based games which put most phones' graphical capabilities to shame. Graphics are run through OpenGL, however it is the less-powerful Embedded System version. The iPhone 3GS has a 833 MHz ARM Cortex-A8 underclocked to 600 MHz, 256 MB eDRAM, and a PowerVR SGX GPU.
The iPhone 4 has the ARM Cortex-A8CPU integrated with a PowerVR SGX 535 GPU and 515 MB eDRAM.
There are some issues for running games on the iPhone, the main one being a lack of a tactile input. The iPhone is controlled via a combination of a touch screen, which can recognize multiple points of contact, as well as an accelerometer, which can sense movement of the device. These methods of input can work well for many genres, including racing, puzzle, and adventure games. However the lack of physical button-based input can inhibit more traditional action-based games, platformers, etc. due to the finger needing to obscure the screen. Virtual buttons may be used instead, but that takes up space on the rather small screen and lacks tactile feedback and the ability to be pressure sensitive. Unlike the Nintendo DS, the iPhone's screen is not sensitive to physical pressure, but only disturbances through bioelectric contact such as skin -- the former being known as resistive and the latter capacitive. This is why using a plastic stylus or most inorganic objects will not register input.
Since the original iPhone release, Apple have upgraded the model year over year in a tick-tock fashion, adding new features one year and a complete redesign the next. The iPhone 3G boasted a new streamlined design, replacing the aluminum backing for a more suited black plastic. It also introduced 3G to the iPhone, which was a feature that many critics complained about the original not having, considering it was a smartphone and a GPS. The iPhone 3GS released in 2009 claimed to be "twice as fast" as the 3G (the S is for Speed), it also has a 3.0 megapixel camera that takes stills and video, compared to the iPhone and the 3G's fixed focus 2.0 megapixel camera, which could not record video. Additionally, the 3GS added a digital compass.
In June 2010, the iPhone 4 was released. The iPhone was vastly improved now, with a faster CPU, a higher resolution "retina" display, noise suppressing dual microphones, a 5.0 megapixel camera and a newly added front-facing camera, longer battery life, and a design change which made it distinct from older models.
On October 4 2011, Apple announced the iPhone 4S. Changes include a new 8MP camera,1080p video recording, an improved antenna, Apple's A5 dual core processor and Siri, a voice controlled assistant. It released on October 14, 2011.
The iPhone 5 was released on September 21, 2012. The phone is slimmer, lighter, and also introduced the first 4" screen. It was also the first iPhone to support LTE. Apple put a their new A6 processor, and added 1GB of RAM.
iPhone 5s and 5c
The iPhone 5s and 5c were announced on September 10, 2013 and launched on September 20, 2013. The iPhone 5s uses a 64-bit A7 processor, while the lower-end iPhone 5c uses the A6 processor previously used in the iPhone 5. The iPhone 5s also adds a fingerprint scanner, which is not present on the iPhone 5c. Fingerprint data is stored within a "secure enclave" on the A7 chip.
iPhone 6 and 6 Plus
On September 19th, 2014, Apple announced it's 5th major redesign of the iPhone, the iPhone 6, with a 4.7" screen. In addition, Apple unprecedentedly release two different models, with the iPhone 6 Plus having a 5.5" screen. These models improved on the previous generations with the A8 SoC and M8 coprocessor, and expanded LTE connectivity.
iPhone 6s and 6s Plus
The newest models were released on September 25th, 2015 with identical physical design of the previous generation. This "S" variation introduced some very significant internal improvements, however, with a vastly superior Touch ID sensor and the introduction of 3D Touch. As with other releases, the new generation also included updated chips with the A9 and M9 processors.
Jailbreaking is a process that allows the iPhone and iPod Touch to run unsigned code on, bypassing Apple's official distribution platform, the App Store. Once jailbroken, iPhone users are able to download many applications previously unavailable through the App Store due to Apple's rules.
Jailbreaking is heavily discouraged by Apple, and according to the Terms of Service, technically voids the warranty. Apple's official stance is that they "may deny service" for any device with unauthorized software installed, so in most cases removing the unauthorized software will bring the device back under the warranty guidelines.
The iPod Touch
The iPod Touch looks a lot like the iPhone, but there are a few key differences between the two. The most notable of these differences is the fact that the iPod touch does not have a GSM radio built into it, and therefore cannot use a cellular network with which to make phone calls or access the internet, though it does include Wi-Fi. The first generations did not have a built-in camera or microphone, but the second generation (2G, 2008) of the hardware does include an internal speaker and adds support for an external microphone. The fourth generation (4G, 2010) now includes a built-in microphone and also a camera which can record both images and video. Like the iPhone, the iPod touch runs iPhone OS. The iPhone OS 3.0 on the iPod touch unlocks Bluetooth (for 2G touch), landscape keyboard in more apps, peer-to-peer gameplay, and several other new features. The iPod Touch functions much like the iPhone, but is slightly smaller, lighter, and can be purchased without a phone contract.
Game Center is Apple's gaming platform for the iPod Touch, iPhone and iPad, which was announced as part of the iPhone OS 4.0 on April 8, 2010. The new platform will work as a social gaming network, with the ability to track friends and invite them to games, matchmaking, leaderboards and achievements. Game Center will replace other gaming networks on the iPhone such as OpenFeint, and allow for a more wholesome experience. The network was supposed to launch as part of iPhone OS 4.0 in June 2010, but was delayed to September 2010.