# Intel CPU Vs AMD CPU Explained



## panzer (Feb 17, 2006)

Some things I want to note before I start, 
 This is not to start a flame war or a Fanboy thread, so don't turn it into that please. 


The purpose of this is to enlighten newbies and/or enthusiasts as to get the best CPU for the money, and to put a stop to all the "What CPU should I get?" threads.  I want this to be very informational w/o getting into "AMD sux!" or "Intel Sux!" posts. I will try to be as Un-Biased as possible and I will try not to get extremely technical as newbies to computers will be the ones I am aiming to, so do not criticize me because I do not say how the electron moves in the CPU. 

*Intel Pentium 4 Processors:* 

The main thing to point out is that the Pentium 4 uses the traditional "Front Side Bus". This is the "data pipeline" in which information moves from the CPU to the Motherboard. This is actually composed of 3 bus's in itself, a "Data", "Command", and "Address". Maybe you heard of the 800MHz Front Side Bus before, the truth is is that only the "Data" bus runs at 800MHz, the "Command" & "Address" run at 200MHz (I will explain system clock speeds and Front Side Bus speeds at the end). 

On a Pentium 4, the Memory (RAM) is accessed via the Northbridge, which means that the CPU must first access the Northbridge which in turn accesses the Memory. After retrieving the data from the Memory, it than goes back through the Northbridge on the Front Side Bus back into the CPU for processing. This is actually a con on the Pentium 4, because the Front Side Bus is a Half Duplex, Bidirectional Bus. That means that it cannot send and receive information to and from the CPU to Northbridge at the same time, and it uses the same bus for communication. This creates latencies when accessing Memory and other things such as information from Southbridge. 

With the Prescott core on newer Pentium 4's, another concern arises: Heat. The Prescott core runs very hot compared to Northwood or Athlon 64 cores, which means that if you plan to purchase an Intel Pentium 4 system with Prescott core, make sure to purchase an Aftermarket Cooler with it. The Prescott though, can be overclocked very high, so if you're an Overclocking Enthusiast or want to get into overclocking, the Prescott Pentium 4 will not let you down, just make sure to get a very good Aftermarket Heatsink & Fan to cool it. 

The Prescott Pentium 4 also has a smaller Level 1 Cache than the Athlon 64, avg. of 48KB Level 1 vs. 128KB Level 1 in the Athlon 64, which I believe is another reason for why the Pentium 4 is not as good in Games as the Athlon 64. The Pentium 4 Prescott has larger Level 2 Cache, 2MB vs. 512KB or 1MB in the Athlon 64. Which is in place to leverage the bottlenecked Front Side Bus, but I personally believe that larger Level 2 Cache does not mean greater performance, and in some cases, I believe it to decrease performance. 

One renowned thing about the Pentium 4, is HyperThreading. HyperThreading fakes the Operating System into thinking that there is 2 processors inside the chip, kinda like Dual-Core but there really isn't a 2nd processor. This works by (Not getting too technical) allowing the CPU to operate on 2 threads vs. 1 on a Non-HyperThreaded CPU. One thing to note though, if I recall correctly, is that HyperThreading is Asynchronous, meaning the CPU cannot process both threads at the same time. This does help in Multi-Tasking as it allows the CPU to start processing another thread w/o wasting CPU clock cycles sittng idle waiting for a program to end. 

The first Pentium 4's ran on Socket 478, which is Dual Channel, DDR1 Memory. The newer generation of Pentium 4's is on Socket 775 (Socket T) and uses Dual Channel DDR2 Memory. If you buy a Socket 775, make sure you purchase the right Memory, all the 6xx Series processors are Socket 775, as well as the EM64T 5xx Series CPU's. 

Another thing to note is whether or not to get 64-bit processor. I strongly recommend getting a 64-bit CPU, so if you want that, you must get one of the 6xx Series Pentium 4's (Or one of the newer 5xx Series, but I recommend a 6xx Series). Seeing as how I recommend a 6xx Series CPU, here are some prices (Prices quoted from Newegg.com): 

Pentium 4 630 (3.0GHz): $178.00 
*Pentium 4 640 (3.2GHz): $219.50 <--Recommended 6xx Series Processor* 
Pentium 4 650 (3.4GHz): $277.00 
Pentium 4 660 (3.6GHz): $409.00 
Pentium 4 670 (3.8GHz): $633.00 

*Intel Pentium D 8xx & 9xx Processors: *

The Intel Pentium D 8xx & 9xx CPU's are Dual-Core, meaning there is 2 processors on 1 chip. The 2 processors in the 8xx and 9xx series communicate to each other over the standard Front Side Bus, thus again creating another bottleneck and latency issue as stated in the Pentium 4. The 8xx and 9xx Pentium D's also run on 800MHz Front Side Bus as stated, with the exception of the new Intel Pentium D 9xx Extreme Editions which have a 1066MHz Front Side Bus. 

On the Intel Pentium D 8xx Series, the standard models (820 to 840) do not have HyperThreading, only the Extreme Edition has HyperThreading turned on, which makes it seem like you have 4 Processors (HyperThreading 2 x 2 CPU's). The Same goes for the Intel Pentium D 9xx Series, the 920 to 950 have 800MHz Front Side Bus w/o HyperThreading, the 955 Extreme has 1066MHz Front Side Bus and HyperThreading turned on. Another thing to note is the 8xx Series is 90nm process, whereas the 9xx Series is 65nm. 65nm will aid in overclocking and heat issues, thus making the 9xx Series superior to the 8xx Series. I would not recommend a 8xx Series, better to get the 9xx Series. 

The 9xx Series also has 4MB Level 2 Cache (2MB Per Core) vs. the 8xx Series which has 2MB Level 2 Cache (1MB Per Core). The Pentium D's, both 8xx and 9xx, run on Socket 775. So remember what I said bout Socket 775 and memory in the Pentium 4 posting. Being as how I recommend only the 9xx Series for Dual-Core, here are some prices for them (Prices quoted from Newegg.com): 

Pentium D 920 (2.8GHz): $262.00 
*Pentium D 930 (3.0GHz): $336.00 <--Recommended 9xx Series Processor* 
Pentium D 940 (3.2GHz): $445.00 
Pentium D 950 (3.4GHz): $715.00 
Pentium D 955 (3.46GHz Extreme Edition): $1,158.00 


*AMD Athlon 64 Processors: *

The AMD Athlon 64 processors comes in 2 packages, Socket 754 and Socket 939. The main difference is Socket 939 utilizes Dual Channel memory, where the Socket 754 uses Single Channel memory. The fastest Socket 754 Athlon 64 CPU you can get, is the AMD Athlon 64 3700+ 2.4GHz Clawhammer. The Fastest Athlon 64 Socket 939 is the Athlon 64 4000+ San Diego 2.4GHz. 

The Athlon 64 is different from the Pentium 4 in a few ways, mainly is the Onboard Memory Controller and the use of HyperTransport instead of the traditional Front Side Bus. The Onboard Memory Controller means that the CPU can access the memory directly w/o having to go through the Northbridge to retrieve information from memory. This reduces latencies and bottlenecks and provides more efficient throughput than the Pentium 4 processor. 

The use of HyperTransport is a big step for AMD, this takes the 3 bus's in the Front Side Bus (Data, Address, & Command) and groups them into 32-bit packets. Think of it like a highway, instead of having 3 people run down the road as fast as they can, they all 3 hop into a car and drive down 1 busline (16-bit wide). Also one thing to note is the speed difference, Hypertransport allows speeds in current Athlon 64's of either 800MHz or 1000MHz (1GHz) Speeds. Also, HyperTransport is Full Duplex, UniDirectional architecture, and each link consists of 2 16-bit lanes for the packets to travel on. This also means that information can be sent and received from the CPU to Northbridge at the same time, each at 800MHz or 1000MHz (1GHz). 

It is important to know that Athlon 64 CPU's do not have a Front Side Bus, rather they use HyperTransport which very much acts like the Front Side Bus but it is a replacement to reduce latencies and bottlenecks. Having the Onboard Memory Controller also means a con, which is that when something wants to access RAM, such as loading information from the Hard Drive into RAM or Vice Versa, it means that it must interrupt the CPU to do so. Also, Athlon 64's have either 512KB of Level 2 Cache or 1MB of Level 2 Cache, as stated in the Pentium 4 part. All have 128KB of Level 1 Cache. 

The Socket 754 Athlon 64 CPU's are mostly made on 130nm, vs. 90nm for newer Socket 939 processors. There is 1 90nm Socket 754, it is the Athlon 64 3000+ Venice, and there are alot of 130nm Socket 939 processors. I recommend getting a Socket 939 90nm Athlon 64 CPU for best performance and overclocking potential. If you plan to overclock, one thing to note is that you must adjust the HyperTransport speed. HyperTransport becomes unstable after 1000MHz operation, so make sure to set it's multiplier to something lower if you overclock so as not to disrupt the stability of the system. 

I only recommend getting an Athlon 64 Socket 939 Processor, mainly because Socket 939 provides Dual Channel Memory Access, Faster Processors, and newer SLI & CrossFire Motherboards. Because of this, I have listed some Socket 939 Athlon 64 processors (All are 90nm) (Prices are quoted from Newegg.com): 

(CPU Speed/Core/L2 Cache) 
Athlon 64 3000+ (1.8GHz/Venice/512KB): $160.00 
*Athlon 64 3200+ (2.0GHz/Venice/512KB): $169.00 <--Recommended 939 A64 CPU *
Athlon 64 3500+ (2.2GHz/Venice/512KB): $201.00 
Athlon 64 3700+ (2.2GHz/SanDiego/1MB): $233.00 
Athlon 64 3800+ (2.4GHz/Venice/512KB): $282.00 
Athlon 64 4000+ (2.4GHz/SanDiego/1MB): $334.00 

*AMD Athlon 64 X2 Processors: *

The Athlon 64 X2 Processor is the Dual-Core Athlon 64, meaning it has 2 processors on 1 chip. The difference between this Dual-Core and the Pentium D Dual-Core, is mainly the way he 2 CPU's communicate. On the Athlon 64 X2 Processor, the 2 CPU's communicate via a "Crossbar", which is an area in the CPU that the 2 CPU's can communicate at CPU frequency, rather than using the Front Side Bus or HyperTransport to communicate, this provides better "Coherency", which is communication between multiple CPU's. 

All Athlon 64 X2 processors are on Socket 939, with newer ones being released for Socket AM2 when it is released. I don't shun away from any X2 CPU, so I state them all (Prices quoted from Newegg.com)(All Athlon 64 X2's with 1MB L2 Cache per core run on Toledo Core, X2's with 512KB per core run on Manchester Core): 

(Speed/L2Cache Per Core) 
Athlon 64 X2 3800+ (2.0GHz/512KB): $295.00 
Athlon 64 X2 4200+ (2.2GHz/512KB): $362.00 
*Athlon 64 X2 4400+ (2.2GHz/1MB): $460.00 <--Recommended 939 A64 X2 Processor* 
Athlon 64 X2 4600+ (2.4GHz/512KB): $552.00 
Athlon 64 X2 4800+ (2.4GHz/1MB): $630.00 

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Now for some technical stuff and explanations of clock frequencies and multpliers. This needs some tuning up, so anybody willing, please help to add some (don't start talking about TDP's or extremely technical things as this is geared towards newbies). 

On every Athlon 64, X2, Penium 4, and Pentium D processor (excluding Pentium Extreme Editions) there is a 200MHz Core Clock frequency, I like to refer to this as the "Crystal Clock". This is the speed at which the Processor truly runs at. There is something called "Clock Stepping" or "Multiplier" as it is commonly known, where this allows the Internal Clock Frequency of the CPU to run at a much higher rate than he External Clock (Front Side Bus/HyperTransport). 

Running a 200MHz Crystal Clock and a 10x Muliplier, means your CPU is running at 2000MHz (2GHz) Internal Speed, but this has no bearing on the speed of the Front Side Bus/HyperTransport. HyperTransport operates on Multiplier of it's own, up to 5x for 200MHz x5 = 1000MHz (1GHz) Operation, and HyperTransport is Full Duplex so it is 2000Mhz (2GHz) effective speed. Front Side Bus runs 200MHz Quad Pumped (All 4 sides of the Square Wave) which equals 800MHz effective speed since the Front Side Bus is Half Duplex. 

With standard DDR1 Memory, it has 184 pins, and has very low latencies (2-2-2-5 and below) and provides up to 300MHz x2 Double Data Rate performance (with higher timings). On DDR2, it uses 240 pins, has higher latencies (3-3-3-8 and above) but runs on 333MHz x2 Double Data Rate and above, providing higher bandwidth than DDR1 at a price of higher latencies. DDR1 and DDR2 allow Dual Channel operation, meaning it has 2 lanes for information to pull from. 

The Athlon 64 Socket 754 has a 64-bit Memory Controller, meaning it can only run Single Channel Operation, Socket 939 Athlon 64's as well as Socket 478 and Socket 775 use 128-bit Memory Controllers that allow Dual Channel Operation. Double Data Rate means it sends the pulse twice per clock cycle, or "Double Pumped", don't confuse this with Single & Dual Channel. 

( I did not write this down totally but found this info on the web)


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## vijay_7287 (Feb 17, 2006)

excellent post


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## kumarmohit (Feb 18, 2006)

quote source plz


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## readermaniax (Feb 18, 2006)

Hey if we get the source then We will able able to get to know it better....PLz source


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## RCuber (Feb 18, 2006)

Excelent post panzer , but you should have also posted the proginal source


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