Atx Cpu Power

How to Build Your Own Pc - the Smart Way (part 1)

Even experienced vendors and system builders get it wrong with all the tools and support they have.  Although in some ways its never been easier to build your own, there have also never been so many choices and therefore pitfalls.  A modern computer is a complex system of interdependent components.  The performance of all components in the system is often limited by the capability of the least common denominator.  In other words, you can't have a top performance graphics PC by installing the latest graphics card (GPU) without also having a CPU powerful enough to keep the GPU pipelines busy with work, and fast memory within which to work.

With this in mind your approach to the architecture, design and build of computers of any size needs to be the same.  Carefully select individual components that you know will all compliment each other and work well together.  Then thoroughly test and benchmark your designs to ensure they work as well as you expected them to.  The last thing you want is an unexpected crash at a vulnerable time.  I’ve taken key snippets out of our own internal build & design process and best practice documentation to help you do your own.

There’s just too much to this subject to do it justice in one article so I’ve split it into two parts which also makes it a little more digestible.  In this article we will look at the heart of a PC build with:

• The CPU (processor)
• The Memory (RAM)
• The Motherboard (or main board)
• The Power supply (PSU)

In part 2 will continue by looking at the remainder of the PC:

• The Storage subsystem (hard disk or HDD)
• The Graphics Processor (GPU)
• The Case
• The Cooling (HSF or heatsink & fan)

Why build your own?

The benefits to you of doing it yourself are:

Pros

• You know best what you want and therefore you can build it exactly the way you want it
• You can choose exactly the components you want and shop around for the best prices
• If you built it you will know how to fix it yourself and might save time in the event something goes wrong
• It can be fun!

Cons

• If you get any component choices wrong then you might just have to settle for what you ended up with, or, sell it on at a loss
• You will get limited support from component retailers in the event of compatibility or stability problems between components
• Quality of advice on the best component selection from the retailers is highly variable, and sometimes downright dubious and self serving
• You are the designer, builder, installer, tester and support engineer, be ready for the possibility of some long nights and a rough ride with little support
• You will spend potentially a lot of time learning a lot of things you might never have wanted to know
• Ill just say; drivers, drivers, drivers….

You might have expected me to put price or cost on the list of Pros.  I haven’t because generally it just isn’t true any more.  There are plenty of machines out there built ready for you to buy that barely cost any more than it would cost if you bought the component parts yourself.  If you take labour cost hours into account then it’s a no brainer, just buy it ready built.

Design...Select...Standardise...Optimise and Build...

Assuming I haven’t put you off lets get on with looking at all the component parts and the things you need to be thinking about.  For some of the components a bit of history is worthwhile as believe it or not we are living today with the legacy of design and architecture decisions made twenty or more years ago.

The CPU (processor)

The CPU is probably the single most important element of the computer.  Everything the computer does is touched by the CPU (Central Processing Unit).  Modern processors are made up of millions of transistors networked together to perform instructions set by the operating system and software that runs on your computer.  Each instruction it can execute takes a certain number of clock cycles to run through, so for example a 1GHz processor can run a thousand million cycles worth of instructions a second.  That sounds a lot, but when you consider that the average application or game now contains millions upon millions of instructions you can see that the processors have their work cut out to keep up with demands.  A concept known as Moore's Law has accurately described an exponential increase in computing performance and power since the early 1970's.  You can be pretty sure that a computer on the market in three years time will be more or less twice as powerful as the equivalent today.

Traditionally therefore the way for processor manufacturers to increase performance was simply to increase the speed of the clock for the processor.  That way it could execute more instructions in less time.  Hence how the old Intel processors between the 1980s and just a few years ago went up from 5MHz clock speed and 20,000 transistors to the best single core Pentium at 3.8GHz and 55 million transistors in 2006.  At this point Intel hit the buffers with the technology with a problem known as silicon junction leakage.  Where beyond these clock speeds the semi-conductor technology we currently use simply ceases to function correctly.  Primarily due to the large amount of energy leakage around the transistor junction and the heat generated in operation.  Hence also why over time CPU heatsinks have got bigger and bigger, and fans more and more powerful, and noisy.

Intel tackled the issue tangentially with the idea of running multiple processors on a single silicon die with the Core 2 Duo and Core 2 Quad technology (see picture right).  As the picture above shows this deals with the workload presented by games and applications by processing it in parallel rather than having to do instructions one at a time (known as multi-threading).  The multi-core processors until recently were still produced on the 65nm manufacturing process that the last Pentium was fabricated on.  Then in Q1 2008 Intel started producing 45nm processors based on new Hafnium Hi-K semi-conductor technology using the same Core 2 designs, codenamed Yorkfield, which runs cooler and more efficiently than the old silicon technology.  Now from, Q4 2008 we have a new processor architecture with Nehalem.  It has an integrated memory controller and the FSB has gone to be replaced by a much master QPI (Quick path interconnect) and a new socket (LGA1366).  By 2010 we should see a new die shrink to 32nm with the Westmere codenamed processors, after that the roadmap gets a bit more vague.  See the Intel site for more information.

You need to look closely at both Intel and AMD on processor technology to careful assess how they can best deliver the highest performance computing from the technology roadmap.  The new Core i7 and Yorkfield processors together with high performance cooling have raised the bar again in Intel’s favour in (this article being dated Q1 2009) by exceeding 3GHz clock speeds in a quad core machine (33%+ over performance!), and around 4GHz when overclocked.  The Core i7 is a big hot CPU with more going on in it than ever before with its built in memory controller so you wont be able to take full advantage of its performance ceiling without efficient and effective cooling technology and delivery of clean stable power to the processor.  Mainstream PC's otherwise typically have a maximum factory clock speed of 3.2GHz.

The Memory

Memory can be a crucial bottleneck to potential performance and is rarely paid much attention at all by main stream system builders.  Memory comes in a variety of forms and bandwidths from PC2-3200 to PC3-16000 and up.  Where PC2 or PC3 indicates DDR2 or DDR3 memory respectively, and 3200 or 16000 refers to the bandwidth in MB/s.  Of course it goes without saying that you should use the highest bandwidth memory you can afford whether in double bus speed DDR2 or quad bus speed DDR3 forms.  If you are planning to use your self built PC for video, photography, CAD, 3D graphics or gaming the memory speed does make a difference.  However there are a number of other qualities that hugely impact on memory performance and we also take these into careful consideration:

• Core clock speed - the speed the memory bus runs at (adjusted for DDR2/3)
• Data rate (DDR, DDR2, DDR3) core memory bus speed multiplier
• Latency (access cycle delays) - memory can be made to run at higher clock speeds but also with higher latency delays, making it on occasions actually slower than high quality memory running at lower frequencies with lower latencies.  For example PC2-6400 memory at 800MHz and latencies of 4-4-3-5 will generally perform better than PC2-8500 at 1066MHz and latencies of 5-5-5-15

A lot of manufacturers currently ship PC's with memory of PC2-5300 (667MHz) specification with average latencies in standard packages.  That’s usually because they have a heap of it in a warehouse to shift.  The minimum specification memory you should use is PC2-8500 (1066MHz).  With low latencies in an enhanced package for better cooling it can even outperform even some of the faster DDR3 memory.  The highest specification memory available often runs ahead of being specified in terms of JDEC standards.  If you want to be future proof you should consider some mid range DDR3 memory (say 1600MHz C8).

Clearly you need to make sure you’ve got enough as well.  For dual channel boards the minimum to consider ought to be 2GB - 4GB and for triple channel boards (DDR3 only) .  Bearing in mind if you are stuck with a 32-bit OS (Windows) you have a practical limit of around 3GB anyway, for 64-bit fill your boots.

The Motherboard (main board)

Critical to good performance between the components of a PC is the motherboard on which it is all installed and interconnected.  The motherboard chipset (usually either nVidia or Intel based, known as Northbridge and Southbridge) hosts all the vital interfaces such as the PCI bus (PCIe 2.0, for the graphics and sound cards), the network (USB2, Firewire IEEE1394, WiFi and Ethernet), the storage (IDE, SATA-II, RAID), BIOS configuration, bus clock management, memory controller, hardware management and monitoring, power supply regulation to the CPU and memory.  The motherboard chipset dictates which CPU's it supports, the maximum FSB (front side bus) speed supported, the range of CPU's supported (by socket such as Intel LGA775, or AMD).  Intel’s Nehalem and X58 Chipset has changed all this now that the memory controller has moved off the motherboard and inside the CPU.   This unlocks a phenomenal amount of additional memory bandwidth.

A sophisticated BIOS is important to allow fine enough control and monitoring of system components for the high degree of performance tuning required.  Due to the compatibility and support dependencies most manufacturers tend to choose fairly mature motherboards and chipsets, perhaps a year or two old.  You could choose the low risk approach and do the same thing, or, go high risk and try the bleeding edge technology.  Whatever you decide make sure it’s a board that has a reputation for being overclock friendly if that’s what you want to do (you will need flexible Base Clock speeds for Core i7).  Make sure it supports the latest CPU's, high bandwidth storage and PCI bus, highly flexible BIOS and preferably DDR3 high speed memory.  However a good DDR2 board is now excellent value for money and can match some DDR3.

Pay careful attention to the PCI express lanes.  Every Intel chipset has a set number of total lanes that can be allocated across all the PCIe slots the board designers have chosen to give you.  The more lanes a given slot has the faster it can run as they move data to and form the card in parallel.  I’ve listed below some of the current main chipsets and how many lanes they provide:

• P45 - 16 lanes (2 of PCIe x8)
• P55 – 16 lanes (2 of PCIe x8)
• X48 – 32 lanes (2 of PCIe x16)
• X38 – 32 lanes (2 of PCIe x16)
• X58 – 32 lanes (2 of PCIe x16, or 4 of PCIe x8)
• nVidia 680 – 46 lanes (2 of PCIe x16, 1 of PCIe x8, 6 of PCIe x1)
• nVidia 750 – 32 lanes (2 of PCIe x 16)
• nVidia 780 -  48 lanes (2 of PCIe x16, 1 of PCIe x16 (1.0))
• nVidia 790 – 48 lanes (2 of PCIe x16, 1 of PCIe x16 (1.0))

If you’re hoping for a smoking big SLI setup you will need as many x16 lane PCIe slots as you can get.  At the least aim for a board with 2 PCIe x16 slots then you have an upgrade path if you need it.

The Power supply (PSU)

One of the side effects of delivering more and more power form your PC is that it requires more and more electrical current to function.  The power supply is not only critical for the delivery of power, but also the smooth, stable and reliable delivery of power at the instant it is required, transient power.  The ATX standard 2.3 dictates what the power supply should be able tot deliver.  Its surprising how many big manufacturers commonly used power supplies would fail this basic test.  Many mainstream power supplies are also woefully inadequate at 300-400W.  When you consider the CPU can draw over 100W, each high power graphics card up to 200W, the multitude of fans and disk drives, PCI adapters, attached USB devices and perhaps a water cooling system.  It's to see how you can soon hit the magic 1kW (1000W) power requirement.  It's surprising just how much power a modern PC with powerful graphics, CPU and storage actually requires. 

To give yourself a bit of upgradability headroom you want to be buying 600-800W or more and exceed the ATX standard requirements.  Most modern switch mode power supplies are multi-rail as it’s an easier and cheaper design to use.  However a single rail at over 100A of current gives your build more flexibility, otherwise you have to be careful which rails you use for what as they all have individual current limits.  Not to compromise on noise you should prefer to use power supplies with large 120-140mm fans to increase air flow, and reduce air speed in turn reducing cooling noise.

About the Author

Chief Technologist at Cryo Performance Computers. Leading the development of innovative PC design. Cryo PC supply high performance specialist PC's including professional custom built pc's and extreme gaming pc's.

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