A definitive guide on how to choose your new PC

As an information technology specialist myself I find it constantly frustrating how I’m mislead or not informed by vendors and retailers about buying decisions I might make.  There are lots of PC buying guides available out there but they are either too specific about technology choices so they date very fast or do not help you meet your specific requirements.  They are often too high level and only explain the very simplest of specification details and the minute a sales rep or consultant gives you other options or explanations you are lost.  This guide is aimed at the novice to moderately experienced PC user.  If you are a guru or expert you should know most of this already.

As an example of how easy it is to be mislead a very well-known big leading PC brand was recently advertising its 'xyz-wizbang' PC with an amazing 12GB of memory, Extreme Intel Quad core processor and Quad graphics cards.  Sounds impressive huh!?  When I saw the low price I became suspicious.  When you click on the link for more details, then click on the options, then click on the technical specification, then read it very carefully and you find it only has 3GB of memory but is expandable to 12GB, has a standard Intel processor but has an option for the Extreme, and supports Quad graphics cards but comes with just one.  You can imagine without digging into the detail the price would have been quite seductive.

A favourite proverb of mine goes something like 'Give a hungry man a fish and feed him for a day, give him the tools to fish and feed him for life'.  Well that about perfectly summarises the intention of this guide.  Given just a little more information you can adequately specify your own requirements, cross-examine vendors and retailers about their advertised machine specifications and reward yourself with a good quality PC that will last and do all that you want it to.  The added bonus to learning how to buy this way is that it wont date, the same concepts as I explain here have applied broadly since the mid 1980’s.  A lot of the understanding lies in demystifying the jargon and I will do a lot of that using simple terms.  Clearly more understanding is needed as I still get asked from time to time 'What is the difference between 4GB RAM and 300GB of hard disk, and which do I need?'.  Hmmmm, if you are in this category you need to read this now....

The components of the PC

Before we can make decisions we need to know what everything in the PC does and how it does it.

·                     The CPU or Processor - The processor is the engine of your PC it executes instructions millions of times a second to get the work you want done finished.  Modern processors will have multiple cores and are known as Dual core (2 cores) or Quad core (4 cores, soon ‘Octa’ 8 core processors will be available) which makes them a bit like my wife i.e. capable of doing more than one thing at a time, or multi-task.

So lets say I ask my computer to give me a million lottery numbers and it takes eight seconds to complete (it would actually finish in the blink of an eye).  With a Dual core this would only take four seconds as I could get one core to give me half a million numbers and the other to do the same, at the same time.  So on a Quad core using the same logic it would only take two seconds.  Breaking up tasks like this is called multi-threading.  So that's the theory if you can break up a big task into multiple smaller tasks that can all be executed simultaneously then the more cores the better.  However there's a catch.  Not all tasks can be broken up this way and not all software vendors write their programs this way so you need to make sure what you do is able to take advantage of it then you will know whether you should go for a Duo, a Quad or even an Octa core processor.

The other factor that affects performance is the clock speed of the CPU expressed in GHz (cycles per second).  Most processors these days are somewhere between 1.8GHz and 3.3GHz.  All cores in a multi core CPU will be running at the same clock speed.  So if you see a manufacturer describe a PC as 12GHz, then what they are probably doing is multiplying the clock speed by the number of cores (4 cores by 3GHz).  Perhaps to make their PC's look phenomenally faster than anyone else’s, who knows.  Clock speed is simpler than number of cores, a faster clock speed simply means faster execution times, period.  Therefore if you can’t get the benefit of more cores you should be able to get the benefit of higher GHz.

·                     The Memory (or RAM) - While the computer is on the memory is where the CPU stores its work in progress.  Computer memory is the fastest place the PC can store information so when its doing your work that is where it prefers to do it.  However if it runs out of available memory it will start storing things on your hard disk instead (known as Paging to Virtual memory) and this is when things slow down dramatically.  So make sure you don't skimp on memory get more than enough of it, as much as you can afford.  Secondary to that is how fast it is in itself.  As a guide Windows Vista really eats the first 1GB so your minimum memory ought to be 2GB (DDR2) or 3GB (DDR3) for general light use, and 4GB (for DDR2) to 6GB (for DDR3) or more for demanding games or applications.

Memory speed is measured in a combination of MHz, Type and Latency.  Its also important to remember that bandwidth is different to speed.  Imagine the memory bus is like a road.  A single lane road with cars travelling fast at say 70mph, each car will get to its destination quickly but there will only be so many cars you can fit on the road.  On the other hand a four-lane highway even if it’s slower at 55mph will get more cars to their destination in the same time period although all the cars individually will take longer to get there, this is akin to bandwidth.  None-the-less the two are interlinked as clearly a narrow road can match the bandwidth of a multi-lane highway if the cars are able to move fast enough.

Different demanding tasks you might do on a computer demand bandwidth or speed, or a balance of both to work optimally.  The memory bus technology type used also influences bandwidth i.e. DDR, DDR2, DDR3 etc.  The DDR means Dual Data Rate and the number after it indicates how many parallel channels it uses to communicate.  Clearly the more channels it uses the more bandwidth it will have.  Therefore DDR2 has twice the bandwidth of DDR and DDR3 in turn 150% more bandwidth.  As a rough rule of thumb memory speed in MHz should double for each level of DDR as each has a latency penalty roughly double that of its predecessor.  So to get DDR2 memory as fast as DDR 400MHz, the DDR2 needs to be 800MHz, and because its dual channel you will get greatly increased bandwidth.  Think about this carefully because DDR3 1333MHz is not automatically better than DDR2 1100MHz for the reasons explained, its is often assumed the latest technology is better and it isn’t always the case.

At the time of writing you ought to expect to be getting a new PC with DDR3 1333MHz to 1600MHz memory.  Or if it has DDR2 then 800MHz or more.  As far as latency is concerned it gets complicated to explain but if you are doing demanding work make sure its low latency memory.  For gaming and general work speed is more important than bandwidth for video encoding or other tasks that move a lot of data volume around bandwidth is the priority.

·                     The Hard disk (HDD or Storage) – The hard disk unlike memory is a slower but permanent store.  When your computer is switched off all your files remain there ready for when you switch it back on again.  For the vast majority of people the only thing of relevance is whether the store is big enough.  Mechanical hard disks are so cheap now you can get an awful lot more capacity than your ever likely to need for not a lot of money.  Typically a new PC should have at least 300GB of storage capacity.

If you do a lot of photography, database or video work then the speed of the disk is important to you.  Four things affect hard disk speed 1) Its rotational speed (usually 7200 rpm, but up to 15000rpm), 2) How much data it stores per square of its surface (the platter), i.e. areal density, 3) the interface speed to the PC, it should now be SATA-II which can transfer data at up to 300MB/s, and 4) the speed at which the drive head can move across the surface (average seek time usually around 8ms).  The latter is usually the least important.

A new technology that is quickly maturing is the Solid State Disk or SSD.  It has no moving parts and uses a special type of permanent memory (flash memory like USB sticks have) to store the computers data just like a hard drive.  It’s a complex topic in itself and a specialised area.  For the vast majority of people they are too expensive at present to offer much value and cheap SSD’s will only outperform a good hard drive in limited scenarios.

·                     The Graphics Card (or GPU, Graphics Processing Unit) – If you don’t play games, edit video, do 3D graphical modelling, CAD or design work you can skip this section as any modern graphics card should do.  That includes photographers as photographic work is still chiefly constrained by the CPU and not the graphics card.  The motivation for investing a lot of technology in graphics cards has been the demands of 3D graphics processing, in real-time.  This is so demanding there is now arguable more processing power in the GPU of high end cards than in the main processor of the PC.

There are essentially two contenders in the field ATI and nVidia.  Both are excellent and offer very similar performance in terms of price-value.  They keep swapping the crown between each other as to who is the ultimate fastest at any one time.  Generally unless you need the best of the best the second or third card down from the top of the range should do all you need and will be considerably cheaper.  Graphics cards have their own dedicated processor at their heart known as the GPU.  The speed of this GPU is measured just like you main processor i.e. in terms of cores (streams) and MHz.   More cores and higher MHz generally make it faster.  There are architectural differences between the design of the ATI and nVidia GPU’s so you cannot reliably compare them core for core, MHz to MHz.  You need to look within the same vendor to do that kind of comparison.

Almost all cards now support dual DVI (digital) monitor outputs so you can have two monitors attached simultaneously.  The other important thing that varies is the screen resolution they support you should expect a minimum of 1600x1200, the higher you go the more memory you will need on the card (as its acts as a frame buffer) and the more powerful the card will need to be to quickly render the larger screen size.

Multiple graphics cards can now be installed using ATI Crossfire or nVidia SLI inter-GPU communications standards and interfaces.  It’s also possible to have two GPU’s on a single card in which case SLI or Crossfire will be running to link the two GPU’s on the one card.  Beware of this method of increasing your graphics performance as some applications and games are not designed to use it effectively and it doesn’t scale up linearly each card (or GPU) is likely to give you an additional 40-60% performance gain over the single card (or GPU).

·                     Windows 32 or 64-bit (or the Operating System) – this is all about memory.  Computers use the binary system of 1’s and 0’s to express numbers and the number of ones and zeros they use determines how big a number the computer can use.  Each memory location in the computer is referenced by a sequential number just like a street address for the postal service.  Having 32-bits enabled the computer to address up to 4GB of memory, you can add more but the computer just wont see it and that’s no longer enough.  So now the standard address is 64-bit and that means we can reference 2^64 memory locations, or, 17.2 billion gigabytes (or 16 exabytes)!  So it should be a while before we need to change that again.  Though most of the latest motherboards are accepting up to six sticks of RAM which has densities of up to 4GB per stick, so 24GB is the practical limit.

·                     Optical Drives (DVD, CD and Blu-ray) - Optical drives come in three flavours DVD Rewriter (DVD-RW), DVD/Blu-ray Reader (BD-R / DVD-R) and Blu-ray Rewriter (BD-RW).  They really speak for themselves Blu-ray is superior to DVD in two ways 1) it uses Blue laser light which records at a much higher density than a red DVD laser so they have a greater capacity at 50GB over a DVD at typically 8.5GB, 2) you can play Blu-ray movies on a Blu-ray Reader or Rewriter.  If you don’t care about either of those features you don’t need Blu-ray and can save yourself some money.  Generally only film aficionados or video editors make use of Blu-ray.

·                     Interfaces (connections to your PC for peripherals and accessories) - All modern PC's should have interfaces supporting the following standards; Firewire (IEEE1394), USB2, eSATA and HD Multichannel Audio.  So expect this as a minimum.

·                     The Case - for your average PC it really doesn’t matter what you choose.  However, if you think you are likely to want to upgrade regularly then choose a standard size and construction and not a branded case.  Main brand cases are often deliberately designed to be throw away as they have no upgrade room, non-standard sizes or are very difficult to work on and remove outdated components.  Also make sure it has good cooling, front, rear and top fans ideally, and is quiet.  If you can afford it choose a aluminium tool-less case rather than pressed steel.  They generally look better and are far more easily upgradable.  Also make sure that some of the PC interfaces have sockets on the chassis i.e. USB2, Audio, Firewire (IEEE1394) and eSATA.

There are a lot of more advanced factors that affect performance that I will cover very briefly as a detailed explanation is beyond this article.  Please refer to my other articles for more information where I go into all of these in some depth (some justify having a whole article dedicated to them).

Conclusion

Now you are armed with all the tools to take any vendors and retailers to task over their inadequate or incorrect specifications and dubious sales tactics.  Get value for money and be firm about what your requirements are and what you expect for your money.  Make sure its up to date and neither over specified or under specified for your personal needs.  Above all, have fun and enjoy it…