How To Assemble A Desktop PC/Choosing the parts/CPU
The Central Processing Unit (CPU), also called a processor, is the heart of your computer. It performs nearly all the actual computation that takes place as the computer is used. The choice of a CPU will affect the ultimate speed of the computer more than any other single component (gaming systems excepted; there the GPU is usually the bottleneck). CPUs can be divided in various sub-sections such as the ALU (arithmetic and Logic Unit), the control unit, several general and specific purpose registers and a math co-processor as well.
- 1 Vocabulary
- 2 Multiple cores
- 3 Descriptions
- 4 Intel
- 5 Naming schemes
- 6 TDP(Thermal Design Power)
- 7 CPU cooling
- 8 64-bit
- 9 Privacy concerns
Before we can explain the differences between CPUs, you must first be familiar with certain CPU terms.
Clock speed, measured in gigahertz (GHz) or megahertz (MHz) (1 GHz = 1000 MHz), is the number of calculation cycles that your CPU can perform per second. Therefore, a higher clock speed generally indicates a faster processor. But not all CPUs perform an equal quantity of work per cycle, meaning two CPUs at the same clock speed can potentially perform at very different levels: Clock speeds should not be compared for CPUs from two different architectures (AMD Phenom versus Intel i7, etc.) - in such cases, use reviews and benchmarks to judge relative performance.
IPC, or instructions per cycle, is the amount of work a CPU can do in a cycle. With modern processors this number is an average.
Front side bus speed (FSB)
Front side bus speed is the rate at which the CPU communicates with the northbridge chipset component on your motherboard,and, through the northbridge with main memory, measured in MHz. A larger FSB value shows that your CPU is able to communicate with memory and other components on the motherboard at a higher speed. In an AMD processor the front side bus depends on the version of HyperTransport it has: HT 1.x 800MHz, 2.0 1400MHz, 3.0 2600MHz, and 3.1 3200MHz. This feature has been replaced(or depreciated at least) by features like QPI(QuickPath Interconnect) starting with the Nehalem architecture for Intel(1st generation Core i processors).
CPU’s plug into a socket on the motherboard. It is very important that your CPU is a COMPLETE MATCH to your motherboard CPU socket. Plugging a CPU into the wrong socket will never work and will usually break either the CPU, the socket, or both.
Modern processors are either 32-bit or 64-bit (this is a simplification; see http://en.wikipedia.org/wiki/64-bit for details). For our purposes a processor can be called 64-bit if it will support running a 64-bit operating system. The newer chips from Intel and AMD all support this for most 64-bit OS’s. If you have any doubts, check the support materials for the 64-bit OS you are interested in running. Intel supports x64 with Core 2 and higher.
Hyper-threading is an Intel technology which allows a single core processor to simulate having two cores, giving a performance boost when running several programs at once. It requires motherboards and chipsets supporting Hyper-Threading technology. The advantages of the Hyper-Threading technology offer a performance boost of nearly 30% with its virtual cores , unlike the times of the Pentium 4 when it sometimes slowed software. Hyper-threading has since been introduced in all processor lines with the exception of the Core 2 line(Duo , Quad , Extreme , Solo). To give an example , an i5 4690K(which does not have HT) with an overclocked 4.6 Ghz performs nearly the same as an stock i7-4770K(which has HT) running at about 3.5 Ghz.
Cache is memory implemented directly on the CPU. Data which is being used in computations is stored in the cache as much as possible and can be retrieved from there much faster than the same data can be pulled through the northbridge from main memory. Generally, the larger the cache, the faster the system will run. Cache comes in (usually) three varieties, L1, L2, and L3. L1 being the smallest and fastest, and L3 being the largest and slowest. Usually only the L3 cache size will be shown, as L4 is rarely used in processor design, and L1 and L2 will often stay the same size throughout an entire processor product line. Note that L4 is only in special Intel Haswell high-end CPU's , which contain Iris Pro graphics. They contain an embedded 128MB DRAM inside , which is represented as L4.
The core is the heart of the CPU. Often several cores will be marketed under the same name, so look at what core you are buying. It’s a mistake to choose a processor based solely on it’s rated speed in hertz . This number, while easy to understand, does not tell the whole story. The number of cores and the way they communicate will have a big effect, as will the fundamental architecture of the core or cores themselves.
Slower processors are generally preferred for overclocking, as they can often achieve higher overclocking percentages. Retail CPU's come in a package containing a HSF (Heat Sink Fan), instructions, and a warranty, often 3 years. OEM CPUs may not include these.
The current CPU speeds and advantages change frequently, so for up-to-date comparisons, you may want to check a website that specializes in Hardware reviews, such as Tom's Hardware Guide or Anandtech. A current (as of 14 February 2006) beginner's explanation can be found at Behardware.
- Dual-core processors are commonplace , built by both major processor manufacturers (Intel Core 2 Duo / Core 2 Quad and AMD Athlon 64 X2).
- Multitasking: Each processor has two or more , depends on the number of processing centers (cores) for a theoretical maximum of twice the operating power and for better multitasking. Major advantages of multi processors are evident when doing heavy multitasking, such as encoding video and playing video games at the same time.
- Application Support: Newer applications are being written to take advantage of this technology by using a technique known as Multi-threading.
- Power Saving: Multi core processors have the ability to turn off one or more of their cores when application demand is low to save power.
Back in 2005 , multi-core were fairly new and also expensive , but now all computers have at least 2 cores. This also reduces the need of multi-processor(more than 1 CPU) systems , which are expensive and have drawbacks.
- Support: Older programs (with certain notable exceptions) do not support multi-threading and may run very slightly slower on dual core CPUs. Gamers should also take note of this as many games (typically those released before 2006, when the dual-core Intel and AMD processors were released) do not support processing with multiple cores that well, although most current games will take advantage of using multiple cores.
- Cost: Multi cores(especially greater than 4) are not cheap. For instance , high-end Xeons which feature 18 cores have their cost at over $4500!
The future of Multi-Core Processing
CPU's with 4 , 6 and even 8 have already released. Many laptops now feature quad-core , with desktops possibly featuring 6 or 8. Servers can have even more , all the way up to 18(and maybe even more!). By now , quad-cores have already caught up with dual-cores on clock speed and are even beating them(the fastest dual-core i3 runs at 3.8 GHz , now the i7-4790K runs at 4 GHz with turbo to 4.4 GHz). However , that is not the case for octa(8) cores yet.
Often in advertisements (especially for pre-built systems) a processor will be described briefly, like this:
- AMD FX-6300 at 3.5GHz
But there’s more to it than that, a more detailed specification would read as follows:
- AMD FX-6300 six core processor at 3.5GHz/4.1GHz, AM3+ socket, 8MB L3 Cache, 6MB L2 Cache
Which parses out to:
- Model: AMD FX-6300
- Base Clock Speed: 3.5GHz (3500 MHz)
- Turbo Clock Speed: 4.1 GHZ (4100 MHz)
- Socket: AM3+
- L3 Cache: 8MB, L2 Cache: 3x2MB
So we can see that while 3.5 GHz is a fast clock speed, this processor might not be as fast as, a higher end AMD FX-8320, which runs at the same 3.5GHz base clock speed, but has 2MB more L2 cache and an additional two processing cores.
For an Intel example ,
- Intel Pentium 4 3.2GHz LGA775 FSB800 HT L2-2MB
- Model: Intel Pentium 4
- Clock Speed: 3.2GHz (=3200MHz)
- Interface: Land Grid Array 775
- L2-Cache: 2MB (=2048 kB)
- Front speed Bus(FSB): 800 MHz
- Other Spec: HT technology
Intel classifies its CPUs using a series of numbers. 3xx, 4xx, 5xx, 6xx and 7xx of which 7xx denominates the highest end products. Generally, the higher the number, the faster the CPU and the more expensive. Usually, models and ratings correspond. For instance: an Intel Core 2-Quad processor is at 2.4 while an AMD Phenom Quad-Core is at 2.2. An Intel Core 2-Duo's speed is not very different from an AMD Phenom Quad-Core's speed. Here is a list of most modern Intel Desktop CPUs:
- Intel Celeron (Dual core)
The Celeron series is a range of CPUs for budget computers and used to feature just one core. The last single core Celeron was released as part of the Sandy Bridge line-up, and since then all Celeron G-series processors have been dual-core.
- Intel Pentium (Dual core)
The Pentium series was part of Intel's most popular CPUs. Earlier Intels all featured just one core, although the newer Pentiums feature dual-core support, such as the Pentium D, the Pentium Dual-Core, and the Pentium G-series processors.
- Intel Core i3 (Dual core)
These are dual core processors that have hyperthreading enabled, allowing them to make use of multi-threaded software more efficiently. This CPU series is made for LGA 1156, 1155, and 1150, depending on generation. This processor lineup is adequate for most applications, including the majority of games.
- Intel Core i5 (Quad core)
These are quad core(with two low-wattage exceptions) processors without hyperthreading(dual-core variants do have it). Like the rest of the 'i' lineup, they are made for LGA 1156,1155, and 1150 depending on generation. This series can take almost any game without bottlenecking the graphics card. Turbo boost is included , which allows the processor to dynamically overclock to higher click speeds when power and thermal limits allow for.
- Intel Core i7 (Quad/Hexa/Octa core)
Intel's newest line of consumer microprocessors, these CPUs all have 4 - 8 cores , feature Hyper Threading and feature higher amounts of cache and Intel's new "Turbo Boost" technology, which allows all cores to automatically clock themselves to appropriate frequencies in intervals of 133(Nehalem only)/100(Sandy Bridge and higher) MHz without stressing the processor and risking overheating. This feature is unavailable on LGA775-based Core 2 , but most of them utilize a partial overclock by raising the multiplier by 0.5 when one core for every 2 cores is not in used. This means 2 cores can be turbo overclocked on a Core 2 Quad. It also is only compatible with DDR3(Haswell Extreme(E) uses DDR4) memory and does not use a FSB (Front Side Bus), but rather uses an Intel QuickPath interface. Turbo Boost is also available on i5 , but not i3.
- Intel Xeon (2 - 18 cores)
The Xeon brand was a brand of Intel x86/64 processors for workstations, servers, and embedded systems. The Xeon brand features single, dual, quad, , hexa(actually up to 18). core processors (although don't get excited - remember that these are for servers and similar systems, not your "Ultra-awesome high-tech bleeding-edge owns-everybody-else's computer" with a 790i Ultra SLi motherboard and 4 graphics cards)
- Intel Core 2 Duo (Dual core)
An extremely popular brand of Intel chips, the Core 2 Duo processors all support dual-core technology while fitting in to Intel's most common socket type, LGA 775 (Land Grid Array 775). Many older desktop computers from 2007-2010 will tend to use this CPU or another processor in the Core 2 series.
- Intel Core 2 Quad (Quad core)
The Core 2 Quad range of processors feature 4 processing cores and have been made for both gaming (although gamers should be aware of the lack of multi-core support for games released before 2006) and professional 3D graphics design, video editing, etc. Keep in mind that the hardware level the Core 2 Quad processors implement may cause bottlenecking, but usually most Core 2 Quad users would not have to worry about that.
- Intel Core 2 Extreme (Dual and Quad core)
This range of CPUs tends to be directed at enthusiasts and are basically improved versions of Core 2 Duo and Core 2 Quad processors. Be aware that these processors are quite expensive, even today, and typically aren't worth the buy (but if you really want it, nobody's going to stop you)
Additional Intel features
These features may not be there in every model.
- XD Technology: A CPU's model number followed by suffix J signifies XD (eXecute Disable) technology, which is an added security feature on Intel CPUs. Note that AMD processors have a similar technology dubbed EVP, or "Enhanced Virus Protection. Note that it is now included with every processor as it is required since Windows 8.
- VT-X In 2006 , Intel and AMD introduced a feature known as hardware virtualization which boosts speeds when using more than 1 OS at the same time. This feature is available on some Intel Core 2 and most processors after that.
Naming schemes determine how a CPU is named based on its performance , clockspeed and price.
The consumer logic for processor speed may be misleading because many consumers think that clock speed, which is measured in gigahertz (GHz) or megahertz (MHz) is equal to system speed. While a higher clock speed will allow the CPU to do cycles more frequently and it does have a fundamental effect on speed, it is not the sole factor as the number of calculations (and data handled) per cycle is different for each different manufacturer and model. In addition, other factors, such as FSB speed will affect the CPU's ability to process data efficiently. If the FSB and RAM aren't able to get data to the CPU as quickly as the CPU can process it, then the CPU will spend some of the cycles doing nothing. A cycle during which the CPU does nothing is called a wasted cycle.
"Intel Pentium 4 3.0Ghz L2-1MB with HT" will easily convert to just "Intel Pentium 4 530J"
For the Intel Pentium 4/D/Extreme Edition , the following naming convection is used.
- 3xx Series: Intel Celeron (L2-128KB)
- 4xx Series: Intel Celeron D (L2-512KB)
- 5xx Series: Intel Pentium 4 / Celeron D (L2-1MB)
- 6xx Series: Intel Pentium 4 / Pentium 4 XE (L2-2MB)
- 7xx Series: Intel Pentium 4 XE
- 8xx/9xx Series: Intel Pentium D
The number followed by suffix J signifies XD technology.
E.g. Intel Pentium 4 3.0GHz L2-1MB with HT --> Intel Pentium 4 530J
Core 2 Duo
It's naming scheme is relatively normal, except for the models ending with 50, they have 1333mhz FSB.
- E6300/E6320: 1.86Ghz, 2MB L2 Cache (E6320 has 4MB), 1066MHz FSB
- E6400/E6420: 2.13Ghz, same as above
- E6540: 2.33Ghz, 4MB L2 Cache, 1333MHZ FSB
- E6550: 2.33Ghz, same as above
- E6600: 2.4Ghz, 4MB L2 Cache, 1066MHZ FSB
- E6700: 2.66Ghz, same as above
- E6750: 2.66Ghz, 4MB L2 Cache, 1333MHZ FSB
- E6850: 3.0Ghz, same as above
- X6800: 2.93Ghz, same as above except multiplier unlocked
Nehalem and higher(Core i architecture)
The Nehalem/Lynnfield/Sandy Bridge/Ivy Bridge/Haswell series line-up uses a different naming scheme as follows.
- Celeron/Pentium indicates a basic dual core. Pentiums usually have more cache and higher clockspeed than Celerons.
- i3 denotes dual core with hyperthreading. No Turbo functionality.
- i5 usually denotes a quad core without hyperthreading, and all feature turbo functionality which allows the processor to raise its clockspeed under load. However, certain(2) low wattage(35W) i5 are dual core hyperthreaded.
- i7 denotes quad/hexa/octa cores with hyperthreading, and all feature turbo functionality.
To find the generation and the socket for the processor, it is necessary to look at the numbering of the processors.
- Any cpu that has the i designation and 3 digits is meant for LGA 1156(Nehalem)
- Any cpu that has the ix-2xxx(Sandy Bridge)/ix-3xxx(Ivy Bridge) type naming is for LGA 1155
- Any cpu that has the ix-4xxx(Haswell) or ix-5xxx(Broadwell) naming is for LGA 1150
- Any CPU that has the ix-6xxx(Skylake) naming is for LGA 1151
The exception to this is the E(Extreme) series of the generation.
- The i7-9xx series(Nehalem) use LGA 1366.
- The i7-3820/39x0 series(Sandy Bridge) and the i7-4820K/49x0 series(Ivy Bridge) use LGA 2011.
- The i7-5820K/59x0 series(Haswell) use LGA 2011-v3 , which is incomparable with LGA 2011.
For the budget Celeron/Pentium ,
- Celeron G1101/Pentium G6950 is meant for LGA 1156
- Celeron G4xx and G5xx/Pentium G6xx and G8xx series are for LGA 1155
- Celeron G16xx/Pentium G2xxx are for LGA1155
- Celeron G18xx/Pentium G3xxx are for LGA 1150
Each processor has a letter after the model number which tells the type of CPU. To find out , use this:-
- T:- These types of processors use very less power than other variants(usually between 35-45 W). Processors below i5(and i5-4570T , i7-4765T and i7-4785T) use 35 W , while others use 45W. Performance is usually somewhat reducedcompared to other variants , especially for the i5/i7 35W variants.
- S:- These types of processors , while using more power that the T series , use less than their usual(no letter) variants. This is found only on i5 and i7 processors and use 65 W.
- No letter:- These types of processors use the full power. They range from 53 W(up to i5) till 84 W(i5 , i7). Nehalem CPU's can use up to over 130 W.
- K/X:- These types of processors , only in i5 , i7 , i7 Extreme and the Pentium G3258 processors , can be overclocked beyond their normal clock speeds. They use between 53 W(Pentium) to over 140W(Extreme).
- R:- These processors(i5 - 4570R/4670R , i7-4770R , i5-5565R/5665R , i5-5775R) are not the ones you'll be building , as they are meant to be used in all-in-one PC types and they do not use the normal LGA1150 , they use BGA1164 socket. This variant has better graphics than the normal CPU's(Iris Pro). They use 65W of power. These processors cannot overclock(which the C series can).
- E:- Embedded processors. Not the ones you'll typically encounter.
- P:- Does not contain Intel's integrated graphics. Applies only to Sandy Bridge and Ivy Bridge.
- C:- These are i5 and i7 processors(i5-5665C , i7-5775C) which contain Iris Pro , Intel's top of the line integrated graphics. These processors can overclock and have a S series TDP(65 W). The main difference between it and the R series processors is that the C series uses the standard LGA 1150 socket , which the R series do not.
and for mobile processors ,
- Y:- Uses very little power , about 11.5(Haswell) to 13(Ivy Bridge)W.
- U:- Uses less power , from 15 to 28 W(though 15W is more common). This SKU is used in computers such as the MacBook Air and Surface Pro 3.
- M:- Uses about 37W , they are found in mainstream notebooks and some all-in-one PC's. i7 quad-core variants can use up to 47W depending on model. This type of CPU is easier to remove(Socket G1/PGA) , though not as easy as the desktop variants. Also you may have to find your desired replacement CPU on the Internet , as you would not find mobile Intel CPU's in most shops.
- E:- Embedded processors. Not the ones you'll typically encounter.
- Q:- Quad-core. Usually paired with H or Q to indicate a mobile quad-core processor. Example:- i7-4700MQ. Applies only to i7.
- H:- Used in all-in-one PC's , uses about 47W of power. This type of CPU cannot be easily removed(mostly soldered to the motherboard) because of the type of socket it uses(BGA).
- X:- Extreme series , they can be overclocked. Uses about 57W of power. These processors are very expensive and are found only in i7's.
- C:- Special embedded processors.
- Core M - Considered as the successor of the Y series of Haswell , these processors are used in ultra-light tablets and notebooks. These processors have a TDP of 3.5-6 W that can be configured by the manufacturer if required. Some devices come without a fan at this level.(eg - MacBook)
Note:- There are some exceptions to this. This applies only to Nehalem(1st generation i series and higher)
- The i7-3820 processor is overclockable , but has a multiplier limitation of 43x which can be partially overcome by increasing the BCLK speeds. This processor is an Extreme i7 processor and uses 130W.
- Nehalem ultra low low-wattage mobile(18 W) CPU's are marked as 'UM' and not just as 'U' as in Sandy Bridge and later.
- Nehalem low wattage models(26 W) mobile CPU's are marked as 'LM'. Sandy Bridge and Ivy Bridge do not have this , and Haswell(28 W) are marked as 'U' only.
AMD CPUs have a different classification. The AMD Athlon CPU rating are not of the actual clock speed but rather the equivalence bench mark performance corresponding to a comparison to the AMD Athlon Thunderbird 1.0Ghz. The conversion Table is as follows:
- AMD Athlon 1500+ = Actually runs at 1.33 GHz
- AMD Athlon 1600+ = Actually runs at 1.40 GHz
- AMD Athlon 1700+ = Actually runs at 1.47 GHz
- AMD Athlon 1800+ = Actually runs at 1.53 GHz
- AMD Athlon 1900+ = Actually runs at 1.60 GHz
- AMD Athlon 2000+ = Actually runs at 1.67 GHz
- AMD Athlon 2100+ = Actually runs at 1.73 GHz
- AMD Athlon 2200+ = Actually runs at 1.80 GHz
- AMD Athlon 2400+ = Actually runs at 1.93 GHz
- AMD Athlon 2500+ = Actually runs at 1.833 GHz
- AMD Athlon 2600+ = Actually runs at 2.133 GHz
- AMD Athlon 2700+ = Actually runs at 2.17 GHz
- AMD Athlon 2800+ = Actually runs at 2.083 GHz
- AMD Athlon 3000+ = Actually runs at 2.167 GHz
- AMD Athlon 3200+ = Actually runs at 2.20 GHz
- AMD Octeron = Low-Power Quad-Core
- AMD Phenom x3 = Tri-Core
- AMD Phenom x4 = Quad-Core
- AMD Phenom II x4 = Quad-Core
TDP(Thermal Design Power)
The TDP of a processor gives an idea of how much power would it consume in a standard heavy use scenario.
But note that it does not give the absolute maximum power it would consume. For instance , if you try to stress your CPU by running Prime95(a popular CPU stressing tool) or something of that sort , it is likely to exceed the TDP rating(atleast for a short period of time , this depends on the cooling efficiency.)
In some cases , it can nearly be the double. For instance , a MacBook Air with 15W TDP can hit up to 29W when running graphics-heavy workloads.
The TDP in a laptop is lower than a desktop , because laptops have space and battery requirements.
|CPU Model||Generation||SDP/<TDP(if it exists)||TDP||>TDP(if it exists)||No of cores|
|Y Series||4||4.5 - 6||11.5||2|
|U Series||4 - 5||11.5||15||25||2|
|U Series||4 - 5||23||28||2|
|LE Series||2 - 3||25||2|
|M Series||1 - 3||35||2|
|E Series||1 - 3||35||2|
|QM Series²||1 - 3||45||4|
|QE Series||2 - 3||45||4|
|H Series||4 - 5||47||2|
|EQ Series||4 - 5||47||4|
|HQ Series||4 - 5||47||55||4|
|MX Series||1 - 4||55||65||4|
|T Series||All||2 - 4||35||2 - 4|
|T Series||i5 and i7||3 - 4||45||4|
|<no name>||Up to and including Pentium||4||53||2|
|<no name>||Up to and including i3||3||55||2|
|S Series||i5 and i7||2 - 4||65||4|
|<no name>||Up to and including i3||2||65||2|
|R Series||i5 and i7||4 - 5||65||4|
|C Series||i5 and i7||5||65||4|
|<no name>||i5 and i7||3||77||4|
|K Series||i5 and i7||3||77||4|
|S Series||i5 and i7||1||82||4|
|<no name>||i5 and i7||4||84||4|
|K Series||i5 and i7||4||84||4|
|K Series||i5 and i7||4||88||4|
|K Series||i5 and i7||6||91||4|
|<no name>||i5 and i7||1 - 2||95||4|
|K Series||i5 and i7||2||95||4|
|K Series||i7||2 - 3||130||4 - 6|
|X Series||i7||2 - 3||130||6|
- The number listed in 'Generations' represent the following:- 1 - Nehalem/Westmere , 2 - Sandy Bridge , 3 - Ivy Bridge , 4 - Haswell and 5 - Broadwell.
- 'MX' and 'QX' are the same thing.
- These lists does not include pre-Nehalem(Core 2 Duo/Quad) generation or the Pentium 4(NetBurst) architecture(for see , please refer to the Naming section)
- These lists sure are long , and remember that the same series can come in different generations and even different TDP!
- <no name> means that there is no specific letter attached to the end of the model name. For example , i5-4690.
- There are some processors with different TDP which are not included because of their uniqueness. Here are some of them:-
|i3 2115/3115 C||35||2/3|
CPU cooling is very important and should not be overlooked. A less than average CPU temperature prolongs CPU life (up to more than 10 years). On the other hand, high CPU temperatures can cause unreliable operation, such as computer freezes, or slow operation. Extremely high temperatures can cause immediate CPU destruction by melting the materials in the chip and changing the physical shape of the sensitive transistors on the CPU. Because of this, never switch on the computer if your CPU has no cooling at all. It is an extremely stupid thing to do. Turn your computer on "just to test whether my CPU works" and you may find that the CPU fries in less than 5 seconds and you will be off to buy a new one. If your computer turns off during use , it could be because of inefficient cooling. Modern CPU's automatically throttle when the temperature reaches its TJunction(usually 100C) and halts if it keeps on climbing.
Most CPU installations use forced-air cooling, but convection cooling and water cooling and even oil submersion cooling are options. For traditional forced-air cooling, the heat sink and fan (HSF) included with most retail CPUs is usually sufficient to cool the CPU at stock speed. Overclockers might want to use a more powerful after-market fan, or even try water cooling to combat the increased heat engendered by overclocking.
Many retail HSF units have a thermal pad installed. These transfer heat from the CPU to the fan, helping to diffuse the heat created by the CPU. This pad is usable only once. If you wish to remove the fan from another CPU so that you can use it on your new one, or need to take it off for some reason, you will need to remove the pad and apply a thermal paste or another thermal pad. Note that some of the cheaper pads can melt in unexpected heat and may cause problems and potentially even damage if you are overclocking. In either case, thermal paste is usually more effective, just harder to apply. If you plan to do any high performance computing, or remove and replace the HSF often, thermal paste is suggested. If you are planning on a long term installation a thermal pad is often best. Using one or the other is essential to ensure consistent heat conduction between the CPU and heatsink.
Electrically insulating thermal pastes made up of silicon are the cheapest and safest, but silver-based thermal pastes sometimes perform better and carbon-based ones perform better still. When applied improperly both can be conductive, causing electrical shorts upon contact with the motherboard. A thin properly-applied layer will usually prevent this problem, although some pastes can become runny when they get hot. Users should also beware that many "silver" thermal pastes do not actually contain any silver metal.
For quiet operation, start with a low-heat (low wattage) CPU. You can also underclock your CPU, giving up some unneeded performance for some peace and quiet. Another option is to choose a large copper heat sink with an open fin pattern. However, true fanless operation is difficult to achieve in most case designs. You can position a case fan to blow across the heat sink, or mount a fan on the heat sink. With either choice, a large and slow fan will give better airflow and less noise than a small and fast fan.
Some low-noise CPU cooling fans require special mounting hardware on the motherboard. Be sure that the cooling systems you choose are compatible with your motherboard.
A 64-bit system is efficient in handling large amounts of RAM better than 32-bit. In a 32-bit system, efficiency drops beyond about 512 to 864MB of RAM, and becomes significantly less efficient beyond 4GB of RAM. Most processors for gaming are about 3.2 - 4 Ghz.
A 64-bit processor is not necessary yet as most applications run on the 32-bit system (which the 64-bit systems are backwards-compatible with). However, there is no doubt that the 32-bit system would gradually be replaced by the 64-bit system when the prices fall over a few years time. Also , almost all processors currently support 64-bit and 32-bit. It is unlikely that the 64-bit system would completely replace the 32-bit system within 5 years but Linux users might find a great improvement in speed when a 64-bit processor is used. Note that there are processors that can run 32-bit code and 64-bit code; they are very popular and may prove a very wise investment for the future of computing, which will invariably be 64-bit(and that is the only choice now!). It should be noted that AMD has invested in this market faithfully, and therefore all of their processors, even their low-end Sempron line, runs both types of code. Intel has also jumped on the bandwagon , and now all of their recent products are 64-bit and 32-bit capable.
However , if you're running a server , then you're mostly limited to 64-bit as Windows Server dropped 32-bit with Server 2008 R2. Also some recent programs work with 64-bit only.
As an interesting side note, CPUs have raised privacy concerns in the past few years. Intel's Pentium III processor came equipped with a serial number embedded in each processor. When the serial number feature was enabled, websites could read it, thus uniquely identifying the computer over any period of time, sort of like a hardware cookie. Due to privacy concerns, the processors were shipped with this feature disabled.