The original x86 CPU was the Intel 8086. This was followed by the 80186 and the 80286. All three were actually 16-bit. They were followed by the Intel 486, the Pentium, the Pentium 2, etc.
These days, x86 usually refers to the 32 bit version of the hardware architecture, although it occasionally is used in reference to the x86 processors, regardless of their "bit size". The 64 bit version is most often referred to by x86-64 or AMD64, the latter due to AMD beating Intel to market with 64-bit x86 based hardware.
8086: 16-bit chip, and the beginning of the line.
8088: An 8086 with an 8-bit bus (16-bit on the inside, 8-bit on the outside), lowering the cost of making motherboards. This was the chip in the original IBM PC and PC-XT.
80286: Still 16-bit, but capable of multitasking. The problem was that it couldn't multitask AND be 8086-compatible at the same time. The heart of the IBM PC-AT.
80386: The first 32-bit chip in the series, and the first that could multitask without sacrificing backward compatibility. This was a radical chip, and pretty much everything afterwards was basically a faster 386. But it took nearly a decade--by which time it was no longer around--for a popular OS (Windows 95) to really use its capabilities.
80486: Basically a 386 with an integrated floating point processor.
Pentium: Intel discovered the hard way that they couldn't trademark a number, so they called the would-be 80586 the Pentium. I think the biggest advantage was an internal cache, but I'm not sure about that.
These days, x86 usually refers to the 32 bit version of the hardware architecture, although it occasionally is used in reference to the x86 processors, regardless of their "bit size". The 64 bit version is most often referred to by x86-64 or AMD64, the latter due to AMD beating Intel to market with 64-bit x86 based hardware.
8086: 16-bit chip, and the beginning of the line.
8088: An 8086 with an 8-bit bus (16-bit on the inside, 8-bit on the outside), lowering the cost of making motherboards. This was the chip in the original IBM PC and PC-XT.
80286: Still 16-bit, but capable of multitasking. The problem was that it couldn't multitask AND be 8086-compatible at the same time. The heart of the IBM PC-AT.
80386: The first 32-bit chip in the series, and the first that could multitask without sacrificing backward compatibility. This was a radical chip, and pretty much everything afterwards was basically a faster 386. But it took nearly a decade--by which time it was no longer around--for a popular OS (Windows 95) to really use its capabilities.
80486: Basically a 386 with an integrated floating point processor.
Pentium: Intel discovered the hard way that they couldn't trademark a number, so they called the would-be 80586 the Pentium. I think the biggest advantage was an internal cache, but I'm not sure about that.