Just a quick note: Intel has four different processor lines -- or four different "microarchitectures". All Intel processors support the x86 instruction set externally, but have very different microarchitectures internally.
To start with is their mainstream processor in desktops, notebooks, servers, and supercomputers. This accounts for the bulk of their business, and what we think of as an "Intel processor". The latest version of this microarchitecture is "Broadwell". Previous versions have been Haswell, Ivy Bridge, Sandy Bridge. It's sold as the Xeon, Core i7/i5/i3, Pentium, Celeron, etc.
Then there is the low power processor to compete against ARM in cellphone devices known as the "Atom". There are have been two radically different versions of this processor. The older version of the microarchitecture from 2008 was known as "Bonnel", and it kinda sucked (dual-issue, but in-order). The newer version of the microarchitecture, "Silvermont", is out-of-order, and is much better. Atom processors are just as power efficient as ARM processors. Indeed, many phones use them without people really being aware of the difference. I point this out because there is a widespread misconception that ARM processors are more power efficient than Intel processors. Note that all these processors are 64-bit internally, though some are sold as 32-bit processors with the 64-bit feature disabled.
Then there is the ultra low power processor for markets where even cellphone processors are too large. Intel sells the "Quark" processor for this. It's actually just a 486 processor from the early 1990s running at 400 MHz. It's sometimes called a "Pentium-class" processor, but it's really just been updated with some Pentium instructions like CMOV so that it can run the latest Linux kernel. It's actually pretty worthless -- at this stage in technology, RISC really was better, and ARM equivalents will perform faster using less power. Also, Silvermont processors clocked down to the same 400 MHz use much the same low power -- although they are much bigger chips. These processors are of course only 32-bit, whereas all the other processors are 64-bit.
Finally, there is graphics processor markets which Intel addresses with it's Xeon Phi product (not to be confused with normal Xeons). This competes against GPUs from nVidia and AMD/ATI. GPUs are designed to be massively parallel computers, designed originally for games, but which also work well for many supercomputer applications. Since they have been encroaching on Intel's supercomputer business, they've responded with a GPU-like chip. This chip puts 72 Silvermont Atom cores on a chip, where the cores have been tweaked to support 512-bit SIMD (i.e. eight 64-bit floating point calculations per instruction). This is the same 512-bit AVX that will be appearing in the next desktop/laptop/server processors. This means such floating point intensive software can be written on a desktop, then run on a much faster super computer. The current Xeon Phi is used in the Tianhe-2 supercomputer -- which has been the fastest supercomputer in the world for almost 2 years.
Intel has defeated all other processors over the last couple decades by making their single processor line address all markets. Competitors, namely ARM and nVidia/ATI have therefore optimized for targets Intel can't go. These additional processor lines are therefore in response to these threats.
The Atom line is going badly -- Intel essentially gives them away for free. They are technically an excellent product, beating most ARM processors in power efficiency and speed, but that doesn't matter, because in the mobile space, ARM compatibility is already more important than x86. Also, Intel doesn't have the supporting hardware infrastructure of other chips that ARM has. Intel thus gives mobile phone developers a lot of "development" money to build products -- which in the end means they are essentially giving away Atom processors.
On the flip side, Intel's mainstream server processors are still more power efficient than ARM (or Atom) processors. Those processors work better in cellphones by simply being slower, but once you speed up processor for massive computation, Intel's mainstream processors are still more power efficient. That's why you hear a lot of bluster about people building ARM servers, but when those systems are eventually shipped (such as HP's Moonshot), they come with Intel.
You forgot the moribund IA64 (Titanium), 64-bit VLIW used pretty much only by HP UNIX servers.
There is also the i960 RISC architecture, which was essentially EOL-ed by 2000, but still lives on in some RAID controllers and military applications because it is optimized for Ada.
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