What is a CPU/Processor?

The CPU (Central Processing Unit) is essentially the brain of the computer. It interprets and executes instructions and data contained in software programs. The more generic term "processor" is often used to refer to a CPU as well, and the more specific term "microprocessor", meaning CPUs that are manufactured on integrated circuits, is also widely used nowadays. These three words mean exactly the same thing in this article, and elsewhere in most cases.

What are the basics I need to know when selecting my CPU?

There are many different ways of classifying processors, and the most common ones are:

By CPU brand name (Intel, AMD) and series - e.g. Core 2, Athlon 64 X2, etc.
By processor core: Prescott, Conroe and Windsor, etc.
CPU socket geometry, e.g. Socket 939/AM2, LGA 775, etc.

Major Manufacturers and Product Series

Intel and AMD are the two most prolific CPU manufacturers in the current PC market; they provide almost all the processors used in PCs.



There are several different Intel desktop processor product lines on offer today: the very well-known Pentium 4 and Pentium D (dual-core) is prepared for the mainstream segment, the Celeron D is for budget and entry-level users, the Core 2 Extreme and Pentium Extreme Edition is for high-end users/enthusiasts just as the name suggests. The latest Core 2 Duo processor is a dual-core processor that intends to replace the current Pentium 4/D in the future.

For mobile computing or laptops/notebooks, Intel provides Core Duo/Core Solo, Pentium M and Celeron M processors and the latest Core 2 Duo processors. With proper motherboard, you can build a desktop computer using these processors too. Xeon series processors aim at workstation/server market and are usually more expensive.



AMD offers four desktop processor product series. The best-known Athlon 64 is provided for the mainstream segment, the Sempron (include Sempron 64) for entry-level users, the Athlon 64 FX for high-end users/gamers, and the cutting edge Athlon 64 X2 is a dual-core processor that intends to replace the current Athlon 64 soon.

Mobile Athlon 64/Sempron and Turion 64 (X2) processors are AMD's offerings for mobile computing, and Opteron is AMD's workstation/server product.

The following table gives a quick reference on the processor series.



What is the Processor Core?

We often use the term "core" (this is not the same as Intel's "Core" brand of processors or "Core microarchitecture") to represent the microarchitecture (cache size, number of pipeline stages etc.) of the processor. For example, the Pentium 4 has been produced using such cores as the Willamette, Northwood and Prescott etc. Their internal microarchitectures are different, and their performance levels are different at equal clock speeds.

Socket Type and Platform

The CPU socket is the interface between the processor and the motherboard. When building a computer system, you must make sure the CPU socket matches the motherboard's CPU socket (i.e. Socket AM2 processors for Socket AM2 motherboards, LGA775 processors for LGA 775 motherboards), and that the motherboard supports the particular CPU model. The example below is of a LGA775 (or Socket T) motherboard socket.

Demystifying the Specifications

The specification of a processor may seem boring for most people, and you do not have to know all these technical stuffs to choose the right processor for you. But if you are willing to know a bit more things about processor, this section should be able to help you.

Clock Speed/Operating Frequency
A processor can execute instructions more quickly using a faster clock speed, resulting in increased performance of the processor and system. Clock speed is still an important feature contributing to performance, especially when comparing processors based on the same core, for example, a 3GHz Prescott core Pentium 4 is faster than a 2.8GHz processor using the same core.

FSB
The front side bus carries all data that travels between the CPU and other devices of the system such as system memory and graphics. A faster front side bus can increase performance and responsiveness by transferring data faster. Current Intel desktop processors feature FSB speeds of 533MHz, 800MHz and 1066MHz.

L2 Cache
A larger capacity (e.g. 2MB vs. 1MB) allows more data to be accessible from the fast L2 Cache storage area, and benefits most applications by increasing performance and responsiveness.

Process Type/Manufacturing Process
The manufacturing process is the typical width of basic wiring that connects parts of the semiconductor to the assembly circuit. Contemporary processors utilize the 130nm (0.13 µm), 90nm and 65nm manufacturing processes. The smaller this value is, the higher the number of transistors that can be integrated into the same-sized piece of silicon, and the higher the clock speed the processor can reach. Advanced (smaller) manufacturing processes reduce processor power consumption and production cost as well.

Multi-Core
With the Intel Pentium D and AMD Athlon 64 X2 dual core processors successfully hitting the desktop market in 2005, the core count became a new way of establishing processor performance. Multi-core design is the acknowledged trend for the future. Where multi-core or dual-core processors have the advantage are in multi-threading applications where multiple programs are running simultaneously, and/or applications specifically optimized for multi-threading.

As Intel and AMD are both pursuing a multi-core future, we can expect there to be an increasing number of applications/programs optimized for multi-threading. Choosing a dual-core processor now can safeguard your investment for a considerable amount of time.

In practice, dual-core processors excel when running two or more computing-intensive program simultaneously. For example, you can perform video encoding in the background while playing 3D games. There are also applications that can take advantage of dual-core processors now, with video processing/encoding/decoding being some of the most attractive. Dual-core processors can boost performance by up to 50% or even more in these applications when compared with single-core processors of the same core design and same clock speed.

Hyper-Threading and Hyper-Transport
Hyper-Threading enables multi-threaded software applications to execute two software threads in parallel on a single processor execution core, thereby improving system responsiveness. Hyper-Threading is an Intel technology and is helpful when running multi-threaded applications or multiple tasks simultaneously (e.g. running virus scanning software while using your everyday software).

HyperTransport Technology is a high-speed, low latency, point-to-point link designed to increase the communication speed between integrated circuits in computers. AMD K8 processors utilize this technology for communications between the processor and the chipset. Socket 754 K8 processors support 800MHz HyperTransport, while 1GHz HT is supported by the Socket AM2 and Socket 939 K8 processors. That is 1600MT/s (million transfers per second) and 2000MT/s or 6.4GB/s and 8GB/s respectively.

64-bit Support
AMD64 from AMD and EM64T from Intel bring 64-bit support to desktop PC processors. They are both designed to enable simultaneous 32- and 64-bit computing, and improve performance by allowing the system to address more than 4 GB of memory.
Note: EM64T and AMD64 require a computer system with a processor, chipset, BIOS, operating system, device drivers and applications enabled for them (or x86-64). Otherwise, the processor will still work in 32-bit mode.

Power Consumption
Performance is definitely not the only requirement to consider as power consumption and heat dissipation are both currently very serious problems and deserve extra attention. A lower power bill is usually pretty nice to have as well. New technologies such as EIST (Enhanced Intel SpeedStep Technology) from Intel and Cool'n'Quiet from AMD have been developed to reduce processor power consumption.

Retail vs. OEM
There are two types of the packaging often seen in the retail market: boxed (retail) and tray (OEM or Original Equipment Manufacturer). The boxed version is for the retail market with a processor and a CPU cooler included. The OEM package, which is often cheaper and contains only a processor, was originally provided only to the PC manufacturers. Boxed/retail processors usually have better/longer warranties.

CPU Cooler for the BTX Form Factor
Some Intel boxed processors come with a BTX CPU cooler now, instead of a "traditional" ATX cooler. This BTX cooler must be used on a BTX motherboard and installed in a BTX case. The BTX cooler is not compatible with ATX cases. The processor itself is the same, however, and you can install it in both ATX and BTX systems. If you don't have a BTX-compatible motherboard and case, do not buy boxed processors with BTX coolers unless you have or are willing to buy another suitable CPU cooler.

Choosing the Right Processor

As the brain of a computer, the processor (or CPU) plays a defining role in the total PC system. The performance of a PC system is roughly determined by the processor, so choosing the right processor is key when building your own computer. The other components, such as RAM and hard disk drive, also play important roles, while the video card is crucial when it comes to 3D graphics performance.

Zero-in on Your Applications

It is very important to figure out the applications you will run most often and your real performance requirements when choosing your processor. Processors of different cores (or microarchitectures) perform differently according to the application.

Price/Budget Concern

Price is always an important factor to consider regardless of what you are buying. Finding the price/performance sweet spot is usually the best way to choose a processor for most users.

As a matter of course, processors with higher clock speeds typically cost more (vs. products of the same series/core) but provide higher levels of performance. After choosing the processor series based on your own applications/requirements, you should consider your budget when deciding what clock speed to get.

For Mainstream Users

A 3.2GHz Pentium 4 or an Athlon 64 3200+ may provide sufficient performance for many users (for web browsing, word processing, multimedia application, gaming etc.), but if you perform video processing/encoding very often or want to play the latest 3D games under very demanding graphics settings, you may want to look at processors with higher clock frequencies.

For Power Gamers/Hi-End Users
If you are a power gamer or require extremely high computing power, the Athlon 64 FX processors from AMD and the Core 2 Extreme from Intel are made especially for you. They are the most powerful desktop processors available at the moment. Intel also provides the Pentium Extreme Edition processor that is capable of running four threads simultaneously, which is great for multi-tasking and multi-threading situations.

For Mainstream/Performance Users
The Core 2 Duo processors from Intel and the Athlon 64 X2 processors from AMD are the only choices if you want decent performance at a reasonable price. Intel's Core 2 Duo processors are able to deliver top-of-the-line computing power and low power consumption, while Athlon 64 X2 processors offer attractive price-to-performance ratios.

For Budget and Entry-Level Users
If your computing requirements are not very high, or your budget is somewhat tight, a budget processor may be all that you need – here we can call it an entry-level processor. Both AMD and Intel provide entry-level processors in the form of the Sempron and Celeron D series products respectively. Entry-level processors are always performance and/or feature-reduced versions of mainstream processors: the Celeron D is a humbler version of the Pentium 4, just as the Sempron (Socket 754/AM2) is a junior Athlon 64. These processors perform more than well enough for users who do not run CPU intensive applications such as gaming or multimedia encoding/editing.

Provided by NewEgg