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PC Building, P6 - Graphics and Power

Posted May 30, 2014 12:00 AM by cheme_wordsmithy

As you can see from the number of parts to this series, there's a lot involved in selecting the right parts for a computer build! But, I'm finally nearing the end with my last two big ticket items: the graphics card and the power supply.

The graphics card is an expansion card (typically connected to a PCI-Express slot on the motherboard) that is dedicated to rendering the picture displayed on the computer monitor or display. Because most motherboards today have built in graphics processing (on-board video as it's called), graphics cards are not essential for everyday computing needs. But graphics files contain a lot of data, especially those generated from video gaming, video editing, and computer modeling. Thus, if you want to run these types of applications, you'll need the dedicated video processing of a graphics card.

Most graphics cards built today are mini-computers -- they contain their own memory, processor (called the graphics processing unit or GPU) and sometimes even built-in cooling for the GPU. The specification list for graphics cards is therefore quite long, but the most important considerations are core speed and memory.

Core speed is simply the speed that GPU runs, measured (like the CPU) in MHz or GHz. Higher speed means faster processing of graphics files, meaning better and more complex visuals can be generated on your display.

Memory on a graphics card is similar to computer RAM (see P5 for info), and acts as the temporary storage point for data processed by the GPU. More memory typically indicates a higher performing card. Keep in mind that software has a limit to the amount of memory it can utilize, so having more memory than needed may not yield an increase in performance.

There are other specifications that affect compatibility (type of ports, slot type, etc.) and performance (number of cores, GPU architecture, etc.), but I will leave those details to the many reviews and benchmark studies that can be found online. The end result for me (shown right) was an ASUS Geforce GTX 760 with 2GB memory and a core clock of 1006MHz.

The power supply unit (PSU) was my last component to select. It does exactly what its name implies -- it supplies power to the computer. More specifically, it takes electrical power from an AC power source and converts it to DC power to meet the energy demands of the computer.

The two factors that are crucial to understanding power supplies are max wattage (total power) and efficiency.

Total power is the maximum wattage (measured in Watts (W)) the power supply can provide to your computer. A PSU must be able to supply the power demand from the hardware -- otherwise, the system will not run, or if it does, it could damage the PSU and other computer parts. This is why I chose to select the PSU last -- using a power supply calculator, I was able to get a good estimate on the "size" PSU I would need for my system.

It is important to note that the size of a PSU does not directly affect how much electricity it uses. A PSU only supplies to the computer the power it needs to run -- it is the PSU's efficiency that determines how much power is "spent" (wasted as heat) going from the power source (e.g., the wall socket) to the computer. Efficiency is simply how well the power supply converts AC power to DC power. Hypothetically, a 50% efficient (bad!) power supply would need to draw 400W AC from the wall to power a system requiring 200W DC (200W/0.50 = 400W). A 75% efficient unit will only draw ~267W to power that same system (200W/0.75 = ~267W). Higher efficiency means less wasted energy and lower electricity bills.

Unfortunately, you can't just look up a PSU's efficiency -- it's not set in stone like other specifications. The best way to determine efficiency is to look for efficiency certifications specified by PSU manufacturers (my PSU has an 80+ bronze certification, which means it has a guaranteed >80% efficiency). Uncertified PSU efficiencies are not guaranteed, and will typically be below 80%.

So if efficiency is all that matters, does PSU size play a factor? Yes, it does. Technically you could run a system requiring 200W with a 200W, 400W, 600W or 800W PSU

(essentially any PSU above 200W). However, performance tests have revealed that PSUs will perform optimally between 20% and 80% of their max output. The 200W PSU (operating at 100% load) would thus be less efficient and require more power. Running at much higher or lower loading can also shorten the lifespan of the PSU or possibly damage computer parts. Ideally then, the normal power requirements of your computer should be 40-60% of your PSU's max power output. For my system (with a power requirement of about 375W), I decided on a 600W power supply, giving me a loading percentage averaging 62.5%.

So now I have all the guts of my computer selected. The last step is to pick out my case and begin construction of the computer, which I will detail in my next post…


Monitor Image -

Pudget Systems - Graphics Card Specs Explained


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Re: PC Building, P6 - Graphics and Power

05/31/2014 5:50 AM

I read through your excellent post, but I missed (to my mind) two important considerations which I bet you know of but did not mention.

For example, if you need out and out video rendering and the like, and/or are you going to run high performance games, if so you need a high end graphics card = expensive. I like AMD Video products....

But you could also get away with a much cheaper one if you are basically only want to run MS Office for example....

Its great having a power supply from a good manufacturer that can supply all the needs of the computer with say only 50% of its output. That way its working in the "middle" of its possible range, where a good, well made supply will be most efficient/cool and still have some power over for future expansion. One that carefully reduces fan speed to suit load and has a very quiet fan anyway.....

That would be my personal choice as a builder of my own PCs and for a few others since around 1984. By the way, I am not a gamer, but I always put a high performance video card in nowadays that can re-render videos in a short space of time. Faster than the main processor can!!! Though I am today a believer in Quad Core 2.6 Ghz processors as the one I have from Intel in my laptop, runs almost cold when doing average work......

(Video cards today can do video digitising and the like that faster than most main processors nowadays and modern video processing software should take advantage of such a card like this if properly written!)

I really like your blogs, keep up the interesting work please!

"What others say about you reveals more about them, than it does you." Anon.
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