Wednesday, October 5, 2011


Jack Dikian
October 2011

Today, like many others, I couldn’t but resist having a look at the new iPhone 4S with all the expected hype and media frenzy. I was particularly interested in its specifications, and more specifically the new processor chipset it is using.

According to reports the new iPhone is using the A5 chip, which is also used by the iPad 2. This is a dual-core Cortex A9 processor which is said to be up to twice the speed of its predecessor. Also, the PowerVR SGX543MP GPU embedded graphics accelerator is up to seven times faster than the GPU found inside the previous chipset. The A5 contains a rendition of chip based upon the dual-core ARM Cortex-A9 MPCore CPU manufactured by Samsung.

Now the chips’ manufacture claim that the performance optimized dual-core Cortex A9 can do 10,000 DMIPS (Dhrystone MIPS) at clock speeds of 2000 MHz. Remember that CPU performance is generally about the number of instructions it can execute in a time period (say a second) and the amount of actual work it can do in that period.

The first is controlled by CPU architecture, memory speed, etc while the second has those as variables, as well as the effectiveness of its instruction set at doing the sort of typical application it is used in. The Cortex A9 processor runs the Dhrystone benchmark at about 2.50 DMIPS/MHz per core – an extremely efficient architecture at the sort of application the Dhrystone measures.

The reason I’m taking an interested in this architecture isn’t so much about how Apple is using these processors as enablers in there consumer products, not that I’m complaining as I am and have been an Apple fan from the day I first used the Apple Lisa at university. More so, because I was recently reminded of the very first computer I built when I was a teenager. At the time, anyone that was half-interested in electronics either built a micro-computer or an Amplifier of sort. My friends and I were more interested in wire-wraps, logic gates, LEDs, and nasty RF-modulators. The very slow and erratic cassette tape interface came much later thanks to Radio Shack and the TRS-80.

So as high school kids, my friends and I would catch the train from North Sydney to an electronics hobby store in Hornsby where we got to see an “expert” demonstrate his Mini-Scamp microcomputer and us using what little money we had to buy the components so that we can each build our own.

The Mini-Scamp micro-computer was, I think, a Dick Smith Electronics kit the design of which was published in "Electronics Australia". The Mini-Scamp was based on the SC/MP CPU from National Semiconductors and boasted a [massive] 256 bytes of RAM. Yes, that’s all the memory it had. Just as a simple comparison my current iPhone 4 has 3,435,9738,368 bytes of memory.

This nifty computer didn’t come with ROM so the idea of accessing an interpreter or a compiler was still, for us, years away. So we would load binary into RAM by requesting the data byte and address in binary using toggle switches. Pressing the deposit button stored the byte in memory. The LEDs showed the current contents of the memory location. After the program was entered this way a switch was flipped from DMA to Run mode and the micro did the rest.

These days I sometimes have a little chuckle to myself when an IT helpdesk puts me on hold while trying to rectify a trivial password glitch – and wonder how they would cope if all they have to work with is a soldering iron, a bit of copper printed circuit board, and if really lucky a second hand CRO.

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