Everything you need to know about your PC's processor

Light a candle and bake a cake, then pop down to the shop to pick up a hilarious card – your CPU has just turned 30! While its best years aren't behind it quite yet, it could do with cheering up.

In 1978, Intel released its first 16-bit microprocessor, the 8086. Although it was the cheaper, cut down 8-bit version – the 8088 – that made it into the IBM PC and quite literally changed the world as we know it, today's Core 2 and Phenom chips are designed to run code based on what's still called the x86 instruction set. In fact, they still share some important common core characteristics with the venerable 8086.

Quite why it should have been the x86 family is a different story for another time. Intel's chips were far from the most advanced, cleverest or cheapest available at the end of the 1970s, and had some fairly serious design bugs, which had to be replaced by IBM free of charge some years later. In the annals of our times, though, that will be deemed irrelevant: this was the general purpose processor that drove the desktop revolution.

Curiously, one of its competitors – the Zilog Z80 which powered Sinclair's home computer of (almost) the same name – is actually still manufactured and used today. The 8086, however, has been consigned to history.

Why do we bring these curious factoids up? Because later this month also sees the launch of Intel's seventh generation of x86 CPUs, the Core i7 (Nehalem). Intel is touting it as the biggest architectural change in the company's history; and for once we're actually prepared to believe it.

Core i7: Your essential guide to Intel's new processor

The success of x86 is, of course, backwards compatibility. Somewhere in the Core i7's infinitely more complex design are the same 116 instructions that the 8086 could execute, albeit substantially enhanced with later additions, and the same is true of the AMD Phenom. These are the basic arithmetic and logic commands – like ADD, MUL, OR and XOR – along with a few more specific instructions for which bit of data belongs in which block of memory or system register.

In reality, of course, the things couldn't be more different today if they tried. The 8086 ran at 4MHz, had a total transistor count of less than 30,000 and was packaged in a 40-pin dual in-line chip: physically, it was one of those long black things with the legs sticking out from the sides like an evil metal spider. The Core i7, by contrast, is a two-, four- or eight-core beast, with up to 1.4 billion transistors in its largest variety.

At launch, it will be clocked at well over the 3GHz mark. It has 1567 pin outs, and comes in the flat FCLGA (flip chip land grid array) packaging that will be familiar from the Core 2 line. That means that balls of solder meet the circuit board head on, and end in simple pads which are then laid on to of pins in the motherboard socket.

We've come a long way, clearly. The CPUs of the seventies look like single-celled organisms in primordial processor sludge by comparison to the staggering complexity of today's chips. It takes teams of hundreds of people several years to design a new CPU, and it's unlikely that any individual could completely navigate the finished silicon topography by hand.

Inside the shell

We can, however, do our bit to improve general understanding by looking at certain core principles of CPU design. Technically speaking, a CPU is any processor that can execute programmable code, but for the purposes of our sanity, we'll stick to a discussion of modern day x86 chips here.

Though the layout of today's chips bear as much resemblance to the original 8086s as a dog does to its jellyfish ancestors, nevertheless the core operational procedure follows the same cycle. The CPU's task is broken into four stages: fetch, decode, execute and write back.

Instructions are called from a memory store to the registers. These are then interpreted, processed and a result is written back. This result can be output to, say, a graphics card or hard drive, or called back into the CPU for processing again. However intricate a processor is, these basic four steps are a good way to understand how they work and why they are designed the way they are.

That cycle can be sped up, of course, by increasing the clockspeed of the CPU and the number of cycles it performs per second. Intel learnt the hard way that the key to building a really fast processor isn't just about raw gigahertz. If a single cycle requires a certain amount of electricity to be performed, more cycles per second means increasing the power consumed and – importantly – the heat produced.