Tuesday, January 18, 2011


(Assembled is a series in which The Indian Geek is looking at how to choose the components for assembling your own home Desktop PC. This week's article is about selecting the RAM, chassis case and the Power Supply Unit, or SMPS)

HyperX RAM

If you have been following our Assembled series, by now you have been armed with the knowledge to choose a CPU, decide on a graphics card, purchase a hard drive, and decide the motherboard that you’ll be buying for your very own mid-range, value for money Assembled PC. Put that all together, and you get an undressed computer, with no working memory (RAM) or means to distribute input power.

This article looks at the factors that play an important part in selecting the RAM modules, the case (chassis or tower) unit, and the Power Supply Unit (SMPS).

Memory

The Random Access Memory (RAM) is an important component that directly affects your computer’s performance. It’s your CPU’s workspace or playing field. Any application you run, file you open, game you play, is read from your storage device (HDD, DVD, flash drive) and copied to your RAM. The RAM is from where the CPU does all its work. So it only makes sense that the bigger and faster this workspace is, the better your computer will perform.

Capacity

The more RAM you have, the more space your computer has to keep applications and files open. With today’s multi-threading CPUs and multiple monitors, we tend to keep more and more windows and applications open all at once. The more RAM your computer has, the more applications will run smoothly. While Windows 7 says that you need to have a minimum of 1GB of RAM to run it, Windows itself will take up 80% of that, with only about 20% left for your applications. Hence we recommend having at least 2GB for an office PC that you’re going to use to check your email and type documents. For the average user who likes to keep about half a dozen windows open, edit holiday photos and play games, we recommend 4GB of RAM. You will rarely see any lag or issues due to lack of RAM with this setup. Even today’s latest games will be quite happy with 4GB. If you are the kind that has an aversion to the ‘x’ button and likes to keep a gazillion windows open, while playing Grand Theft Auto IV and playing a 1080p video, you might want to upgrade to 8GB. Some users with special requirements such as photographers and video editors may also need a lot of RAM to work on their large creations.

Clock Speed

This the easiest way to measure your RAM’s speed. The older DDR2 ranged from 400MHz up to 1066MHz. DDR3 has a slight overlap ranging from 800MHz to 2133MHz. Most motherboard available today use DDR3 RAM at 1066, 1300 or 1600MHz, though some high-end motherboards provide options to overclock your RAM to run at much higher speeds. This is why RAM modules come in a variety of speeds, some with rated speeds up to 2500MHz. The average user however should be fine with buying and running RAM at the standard frequency your motherboard specifies. Please keep in mind, that faster RAM will run fine at slower speeds, meaning that a 2500MHz DDR3 module will operate fine at 1066MHz on a slower motherboard. However, DDR2 and DDR3 are not interchangeable in any way whatsoever. (We have seen issues crop up due to RAM modules that are mismatched - either with each other, or with the motherboard. Hence, if your motherboard specifications say that it can support a maximum of 1066 Mhz DDR3 RAM, we strongly suggest that you stick to buying 1066 Mhz DDR3 RAM)

Channels

The memory controller on the CPU has channels through which it communicates with the RAM. The more channels your computer has, the more information can be transferred at any time. There are usually two such channels or three in the case Intel’s Core 2010 family of processor series. These channels run to physical RAM slots on your computer. So if you want your RAM to run in dual channels, you will need to install two RAM modules of equal capacity into specific RAM slots no your motherboard. The RAM slots are always colour coded to show you which slots to use in sets. Two 2GB modules running in dual channel mode will perform better than one 4GB module. This benefit is increased with three modules running in triple channel mode. The downside it that you will end up using a lot of RAM slots, giving you little or no space for future upgrade. Also, the performance gain of dual channels may be as low as only 15%

Dual channel memory slots

CAS Latency (Column Address Strobe Latency or simply CL)

Once you’ve decided on the capacity and frequency of your RAM modules, you’ll head out to the store, only to find that each manufacturer has several models with the same capacity and frequency, but with hugely varying pricing. Some will have big heatsinks with even fans, while some will be bare. So if they run at the same frequency, why do some cost twice as much as other? The secret is in the CAS Latency. In layman’s terms, it is the time taken from when the memory controller requests a particular data (memory column) from the RAM and when the RAM sends the data back. The shorter this time, the faster your RAM will perform. Budget or value RAM modules will have a slightly longer delay, while high performance ones will be quicker. It is measured in number of clock cycles. A low-end DDR3 1066MHz RAM may have a CL of 9, while a high-end module may have a CL of 6 or less. Please keep in mind though that the higher the frequency of the RAM, the bigger the CL value will be. DDR-333 may have a CL of 2, DDR2-667 may have 4 and today's DDR3-1333 may have 8. While this sounds like things are getting slower, infact the CL has remained the 10-15 nanosecond range for the last decade or so. CL is not an absolute unit, but rather the number of cycles. 2 clock cycles at 333MHz, 6 at 667MHz and 8 at 1333MHz all work out to about 12 nanoseconds. At the end of the day though, unless you are building a high-end gaming rig, we’d recommend sticking with budget modules with higher CL since most budget PCs will not be able to take advantage of the extra speed. Even if they do, the performance advantage will be minimal, though the price premium may be high.

Please do check out Hotwardware’s comparison of RAM modules in different frequency, channel and CL configurations. Even if you are not in the mood for reading, their charts should give you a good idea about how each RAM module performs. Keep in mind though, that they use a high-end Core i7 processor and motherboard that can take full advantage of high performance RAM.

Case/Chassis

The case or chassis is the big box that’s going to house all the internal components of your computer. Here’s what you need to understand and decide on, while shopping for one.

Size

The size of a case is designated by the largest possible motherboard it can house. While there are many case sizes and variations the two most common sizes are the standard ATX and microATX (µATX). If you have a microATX motherboard and want a compact PC, a microATX case is a good choice. However, with smaller dimensions comes limited space for expansion. Furthermore, some of today’s high end graphics cards are just too big to fit in microATX cases. So unless you plan to stick to a basic no-frills configuration, we’d recommend going for an ATX case. These can house an ATX or a microATX motherboards. They will also give you more space to add additional hardware such as extra drives, graphics and add-in cards..

Interior Layout

While an ATX case will give you more space, that space may not always be usable. Keep an eye out for the number of 5.25” drive bays for optical drives as well as the number of 3.5” slots for hard drives. Also check their locations. Some slots may be hard to access once all the components have been installed. Some cases may have motherboard trays that will let you remove the motherboard with little effort. Some cases come with cable management systems that include holes and slots which you can use to hide all the cables running inside your case, making your case not only look neater, but also increasing airflow and ease of access.

PC chassis - Interior layout

Exterior Layout

Most cases nowadays are towers that stand upright. They replaced the older flat cases since they take up much less space. But now-a-days flat cases are making a comeback in HTPCs (Home Theatre PCs). A case on its side will fit in well under your TV with your receiver and other equipment. So find a case that will fit best in the spot you intend to set it up in. Also, check where the case’s power button, LEDs, front audio/USB ports are. Some cases may have them close to the top, making them easily accessible if your computer is going to be closer to the ground. This will be a hassle though if it’s on a high desk.

clip_image007PC chassis - Exterior layout

Ventilation

Ventilation is very crucial now-a-days with almost every single component in your computer producing significant amount of heat. CPUs, motherboard’s controllers, memory, video cards, PSUs was well as hard drives, all have some form of active or passive cooling device on them. Your case should be able to provide them with plenty of fresh cool air to expel heat. Check if the case has any fans installed and also for any provision to add additional fans later. Then try to imagine how/where you want want fresh air to enter, how it will flow over your components and where/how it will exit your case. Once you’ve done this, check if the fans are located in the right spot, if there are sufficient vents for the air and if the air will reach all the components. While adding three dozen fans will keep your computer nice and cool, please keep in mind that more fans = more noise and more electricity consumption. You don’t want your PC sounding like a WWII plane! Also, more airflow = more dust. Check for dust filters at all intake fans. Even if they are not provided, we’d recommend making you own. The easiest way would be from a piece of cloth; a fabric that’s dense enough to catch dust, but not so much to prevent airflow. Socks material is a good example (preferably from a new one that does not smell of stinky feet!).

Ventilation requirements for a PC chassis case

Aesthetics

This is completely upto you. Cases come in different shapes and designs, and everyone’s taste is different. Find one that you won’t mind looking at everyday. If you have a lot of fancy equipment in your computer, you might want a case with a glass window on the side. Along with a few LEDs and/or UV lights, you’ll have your own geeky showcase for the world to marvel at!

LED lighting inside the chassis case

Power Supply Unit (PSU)

Also know as an SMPS (Switching Mode Power Supply), this is the device that converts your 240v AC supply, into low-voltage DC supply that your computer uses.

Brand Name

Everyone loves a good brand name. While we stick with known brand names for most of our components, the PSU’s is usually overlooked. The PSU is probably the only component of your computer that can ruin other components. It supplies power to all your components. If it’s sending more voltage than it should, more often than not, the only way you’ll find out is when your computer starts sending you smoke signals (literally!). A bad PSU can ruin almost any component of your computer, the motherboard being the most likely victim. It should be able to provide a clean and accurate supply of power regardless of spikes and fluctuations that our electricity board is so proficient at supplying! The best bet to get a quality PSU is to stick with a good brand name PSU (Corsair, Antec, OCZ, etc.) and it is usually worth the extra cost. While an occasional unknown brand PSU might be a gem, it is a risk we would not suggest you take since the stakes are high.

Power & Efficiency

First determine how much power you need. This can be about 300W for a basic office PC, 600W for a mid-range PC or more than 1200W for a high-end gaming PC. The eXtreme Power Supply Calculator (http://extreme.outervision.com/psucalculatorlite.jsp) is a superb tool to give you an idea about how much power your computer needs. Please ensure that you are looking at the maximum continuous power rating and not the maximum peak output, since the real value you are looking for and need is the former. Keep in mind that its always recommended to get a power rating higher than what you need. This gives you headroom for future upgrades and usually also increases your PSU’s efficiency. Efficiency is measured in percentage. So a power supply with a 70% efficiency rating is going to convert only 70% of the input power into output electricity and the other 30% is wasted as heat. Units that have an 80 PLUS certification have an efficiency of 80% or more. The higher the number, the lower your electricity bill will be and the longer our planet will stay green.

Number of 12V Rails

Though a PSU may say it’s got 500W of power, it does not mean all 500W are going to come down one single cable. Rather, its divided over several channels or ‘rails’. The number of rails going to your motherboard is usually the same in all power supply. All your additional drives and devices use 12V rails and therefore there is usually more than one rail. Distributing the power ensures that too much power is never sent through a single rail, thereby making it safer and the cables less bulky. Hard drives and optical drives individually consume little power, so even if you have many, they can be distributed among the rails. But modern graphics cards are a lot thirstier. Please make sure your PSU has a rail with enough juice to power it, since combining two less-powerful rails is not recommended.

Connectors & Cables

Please ensure the PSU has sufficient pins for all your devices. All PSUs should have the standard 24 or 20+4 pin ATX main power cable and a 4 pin ATX +12 volt power cable that connect to your motherboard. Please note that due to higher CPU power demands, many of today’s motherboards use an 8 pin EPS ATX +12 volt power cable instead of the older 4 pin. Not all PSUs have this connector, so if your motherboard requires one, please ensure your PSU has it. Check that there are sufficient SATA and IDE connectors for all your devices as well as PCIe connectors. Also check if the cables are long enough to reach that drive that’s at the far end of the case. Cable length can become an issue especially if your case houses the PSU at the bottom. Cables that have been sleeved are also desirable since they keep things neat and tidy.

PSU power cables

4 pin and 8 pin ATX +12 volt power connectors

The following website has a detailed account of the various types of power connectors available. Please do read, if you have the time : http://www.playtool.com/pages/psuconnectors/connectors.html

This was a lengthy piece on three more components that would need to be selected when looking to assemble your own, mid-range value for money Desktop PC. With this, we have nearly come to the end of the Assembled series; we only have monitors, optical drives, speakers, add-on cards and other peripherals to look at. So keep a lookout – The Indian Geek brings you the Assembled series on Wednesdays.

Other articles in our Assembled series:

Choosing the right CPU

How to choose your graphics card

Hard drives made easy

All about motherboard basics

1 comments:

AVRChandran said...

Hi, I am Ramachandran. your tutorial on assembled PC was great and informative. Could you please give me an idea about the best possible cases available in India and also about where to procure an aesthetic case. Please do also tell me about the number of fans that is ideal for an ATX case.
Thanking ypu in anticipation

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