Spoiled for choice

There are now so many options available that it is becoming more confusing than ever to discover and understand the implications of what is on offer new and on the second-hand market. However, if you keep reading the articles made available on the web, such as this one, you should soon be able to distinguish the wood from the trees.
AMD's 64-bit processors are the Athlon 64, Athlon 64 FX, and its Athlon 64 X2 dual-core ranges. X2 stands for dual core, which means that two processor cores are housed in a single unit.
Dual-core processors run as if they're a single processor, but two processors appear in the Windows Device Manager - and under the Performance tab of the Windows Task Manager that you bring up by pressing the Ctrl+Alt+Del key combination.
Read Managing Processes and Tasks in Windows Vista to find out what the differences are between the Task Manager in Windows XP and Windows Vista.
However, note that for both AMD and Intel dual-core processors, if the motherboard was initially manufactured to run a single-core processor, a BIOS update that allows the system to be configured to run a dual-core processor is probably required. If such an update is not available for such a motherboard, it won't be able to use a dual-core processor. This will not be the case if the motherboard was manufactured to be able to run dual-core processors out of the box.
To run AMD Athlon 64 X2 dual-core processors, motherboards that support both single-core and dual-core processors only require a BIOS update. However, Intel's dual-core processors only work with certain motherboard chipsets, so just having a Socket LGA775 motherboard doesn't mean that it can run Intel's dual-core processors. Intel's Pentium D 800 and 900 series of dual-core processors require a motherboard that uses Intel's 965 chipset or higher or a motherboard with an nVidia nForce 4 chipset. Intel's latest Core 2 Duo processors, including the Core 2 Extreme X6800, require a motherboard with at least a 975 chipset, or a motherboard with an nVidia nForce 5 chipset.
If in doubt, you can easily check the make and model of a motherboard at its manufacturer's site to find out which processors it supports.
Note that if you are upgrading a PC's motherboard and processor, you must also find out if you have to upgrade the RAM memory, because the current types - DDR and DDR2 RAM - are incompatible with each other.
A few of the early Socket LGA775 motherboards that run Intel processors support DDR memory, but most of them require DDR2 memory.
The Socket 939 motherboards that can run some of AMD's Athlon 64 processors require DDR memory, but the Socket AM2 motherboards that run the latest Athlon 64 processors require DDR2 memory.
With dual cores, each processor contains two separate cores capable of running independently. This should not be confused with Intel's HyperThreading technology that allows a single processor to emulate two processors. Nor should it be confused with multiple processors that are discussed further down this page.
Intel has Pentium 4 single-core, the Pentium D (the first range of dual-core processors), and the latest Core 2 Duo dual-core products. Visit http://www.intel.com/ to find out what the current ranges of desktop PC and notebook PC processors being made available by Intel are.
AMD's dual cores consist of a single piece of silicon, while Intel puts two single-core processors into its Socket 775 processor packages - the Pentium D 900 and the Core 2 Duo ranges.
Intel has predicted that 70% of its processors will have two processing cores by the end of 2006.
In AMD's design, the processor cores are interconnected within the processing unit itself. In Intel's design, the motherboard's system bus is used to connect the two cores. Moreover, the AMD design integrates the memory controller within the processor, while Intel follows the classic approach of having the memory controller built into the motherboard - even with its latest Core 2 Duo dual-core processors.
The advantages of AMD's design are shorter memory latencies and thus higher memory efficiency, which is one reason why Athlon 64 processors outperform the Pentium processors in the majority of benchmark tests. Moreover, AMD's integrated approach and a more elaborate manufacturing process produces superior energy efficiency compared to Intel's non-integrated approach.
Note that to say that the two versions of Windows XP Home Edition prior to SP2 (the original XP Home and XP Home SP1) don't support Intel's HyperThreading technology because they don't support multiple processors is false. Although that was the information that Microsoft supplied, it is incorrect. Those two versions of Windows XP Home Edition support HyperThreading and dual-core processors.
However, you should note that only Windows XP Professional Edition supports multiple processors (a motherboard running two or more independent processor units). That said, systems running multiple processors are very seldom used as home PCs.