Apple’s A4 CPU – The processing power behind the ipad

Posted: March 2, 2010 in General Area, Google, Hack, Subscribe
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As we move further from the press release of the iPad, and move further into getting the actual details, and some of us get hands on with the iPad, we all begin to see where Apple is going with the iPad. Today I’ll talk about the CPU specifically, the mystical A4. Not to far back, I called the A4, “a glorified SPARC processor”, and some of the younger, or less techie readers probably wondered what I was talking about. SPARC processors by Sun Microsystems was first introduced to the public in 1987, and are actually still manufactured today, albeit with some upgrades.  ”

The original SPARC processor contained as many as 128 gpr’s (general purpose registers), you can think of this as a prehistoric version of floating point calculations. At any point, only 32 of them are immediately visible to software – 8 are global registers (one of which, gO, is hard-wired to zero, so only 7 of them are usable as registers) and the other 24 are from the stack of registers. These 24 registers formed what is called a register window, and at function call/return, que a command, it returns a response,  this window is moved up and down the register stack. Each window has 8 local registers and shares 8 registers with each of the adjacent windows. The shared registers are used for passing function parameters and returning values, and the local registers are used for retaining local values across function calls.

Ok I get it, your most likely not tracking, and you may be wondering what the outdated architecture of the SPARC has to do with the iPad and it’s A4. Just wait my young paddawans, I’m getting there.

The iPad is said to run up to 10 hours of battery life. This is achieved by have the CPU only run processes that are absolutely needed, like an iPhone on airplane mode. The A4 accomplishes this by using (well not using but by being) SoC technology. System-on-a-chip (SoC) technology is the packaging of all the necessary electronic circuits and parts for a “system” (such as the not included iPad camera or the included USB ) on a single integrated circuit ( IC ). For example, a system-on-a-chip for the iPad  includes an audio receiver (to record sound), an analog-to-digital converter ( ADC ) (to process the audio signals), necessary memory , and the  input controller (touchscreen keyboard) control for a user – all on a single microchip. How this begins to make sense, is that when all circuits are on a single chip, only a single chip requires power, and then it filters the power to the departments that need it only when needed.

As John Stokes wrote this last Sunday, “the chip really isn’t anything more than an ARM Cortex A8 that has been stripped of much of its I/O functionality. The ARM Cortex A8, running at 600 MHz, is the SoC that powers the iPhone 3Gs The [“new”] A4 is a 1GHz custom SoC with a single Cortex A8 core and a PowerVR SGX GPU (Graphics processing unit). Common Cortex A8-based SoCs often have more onboard functions than are really required by mobile phones so that manufacturers don’t need to design a special chip. The usual Cortex A8-based SoC has infrared, RS232 serial, USB, keypad controller, and camera blocks to handle multiple input and output devices. The iPad, of course, will only need one USB port and one serial UART, both wired to the 30-pin connector at the bottom of the device.”

To sum that up, you have an iPhone 3Gs processor, with an added graphics processor which was needed in order to run the higher resolution and play movies at a higher resolution, however keep in mind, this was only meeting standards, NOT exceeding them as Apple has a reputation for.

Ok, so the A4 is not a glorified SPARC processor from 1987, it’s more like an ULTRASPARC III Cu from 2000 combined with an awesome mobile OS from Apple. The facts at the end of the day is that the OS is making more advancements and improvements that the hardware behind it. I think that within 6-8 months of the actual release of the iPad we will see a faster more equipped iPad, possibly the iPad Pro?

  1. Every time I come to there is another interesting article up. One of my friends was telling me about this topic a couple weeks ago, so I think I will send them the link here and see what they say.

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