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Whether it is a laptop or a desktop, any computer is made up of several pieces of hardware that communicate with each other. Sending data back and forth to ensure that the user gets the desired results.

I have seen some theoretical stuff on computers & hardware, but I wonder how it all comes together.

  • CPU
  • RAM
  • Graphics Card
  • L1 CACHE
  • L2 CACHE
  • L3 CACHE
  • FSB
  • ...

And all other things. Which is the biggest bottle neck? Why would a person not want/need a big value in one of those categories in certain situations?

P.S.: when reading the specs of the i5 750 processor, I came across this description:

In place of the FSB, one or more high speed, point-to-point buses called Quick Path Interconnect (QPI) are used, formerly known as Common Serial Interconnect Bus or CSI. QPI features higher bandwidth than the traditional FSB and is better suited to system scaling.

What is this, and how does it compare to FSB?

EDIT: I am not planning to buy a computer at all. The goal of this question is to understand the internal relation of various hardware pieces, their specific functions and how they work together.

For instance, I have heard to a somewhat higher-than-usual amount of L2/L3 Cache can help speed up your computer. What's up with saying that? Also I forgot to mention Hard-disk RPM.

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First one isn't really related. With this question I wish to understand the internal relation of computer hardware for future reference. –  KdgDev Nov 19 '09 at 19:40
Alot of people forget about your hard drive. Get an Solid State Disc and see how much faster your programs load, and how fast you can move things around. –  AskaGamer Nov 19 '09 at 19:49
Side note: The item with probably the biggest increase in "bottleneckness" in recent years is memory latency. While almost all other parts of a computer have improved significantly over the years, memory latency has seen very little change. 10-15 years ago memory latency was not an issue at all (CPUs were too slow to run into this problem). These days we need CPU caches in multiple tiers to mitigate this problem. –  user12889 May 20 '10 at 23:08

5 Answers 5

up vote 3 down vote accepted

As always, it depends.

It helps to know what, exactly, you need the machine to do. Ask a couple of friends who use theirs the same way to let you look at their performance, and try to determine exactly what is the bottleneck for their machine. Then take you best guess.

I've generally found that it is worth given up a little bit of processor frequency in favor of more RAM or a faster hard-drive[*]. But that was for running medium-to-largish physics simulation and analysis codes. (These codes hold a lot in memory and do a lot of looking things up in on-disk databases, logging, and flushing of buffers to insure against large data losses in the event of a crash; thus the biggest demand is for RAM and fast disks...)

If you are trying to build a very general purpose machine, I would recommend trying to get all your components just below the price point where you hit diminishing returns for that widget. That should work out pretty well.

[*] "Fast" for hard drives means both high throughput and a large cache.

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In my personal experience the slowest component of any modern PC is the hard drive.

Proof: pay attention to what operations make you wait the most in front of the PC, and note if HDD diode is flashing or not during those wait times.

So if you intend to max-out all the components of your new PC as far as performance per dollar is concerned, your HDD will be the slowest component.

RAID could help, but that really adds noise and vibration - unless you make a RAID of SSDs.

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It is certainly the case that the hard drive crawls, but for some uses hard drive access are a rare event, and for others they happen a lot. You have to know what you're going to be doing. –  dmckee Nov 19 '09 at 18:35
I agree, that some specific uses/tasks will need very little HDD performance. But most day-to-day tasks are hampered by HDDs: OS loading/startup, archiving/extracting (unless using 7Z Ultra or similar), starting up any common applications (office/internet/media/games), compiling, copying/moving files between partitions or to/from external devices, navigating directories full of photos/videos in 'thumbnails' mode, ... I believe I could continue for a while. Even if you never have CPU use under 90%, you will still be very often limited by the HDD. –  chronos Nov 19 '09 at 22:58
Hard drive and RAM are not independent. If you have not enough RAM the OS will use the hardrive to extend memory (very slow). If you have more than enough RAM the OS will use spare RAM as cache for the harddrive. So, unless you write a lot of data to the drive, more RAM can mitigate the slowness of harddrives. –  user12889 May 20 '10 at 23:03

Even though this topic is going on two years old, I agree that (even two years later) the hard drive is generally the biggest bottleneck. My home computer is running a Core i3 with an SSD and my work computer is running a quad core i7 with a HDD. My home computer boots up and logs in in literally 10 seconds or less, and my work computer sometimes takes several minutes. Granted my work computer is a managed machine so it requires some scripts to run, but even day to day functionality is significantly slower on the i7 machine. In my opinion, at least in the business world, HDD's are by far the single biggest cause of computer slowness and, ultimately, user frustration, particularly on laptops (5400 RPM hard drives should be made illegal.)

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Jeff wrote a blog on the very subject. It's constantly in flux, depending on what you use it for.

I could have a 3rpm hdd, but if I used only webapps in lynx, I probably wouldn't mind too much.

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Ouch, webapps in lynx? Did you mean to say 'websites'? Also, I wonder if lynx does any disk-based caching - 3rpm HDD wouldn't be at all funny then. –  chronos Nov 19 '09 at 23:01
Some builds of lynx can do a little javascript, and many webapps basically work without it. I think you can easily turn any caching off, too! :D (Of course, to use webapps in lynx you'd HAVE to be mentally unstable or burdened with a HDD that barely spins. –  Phoshi Nov 20 '09 at 8:17

Q: Which is the biggest bottleneck?

A: The hard disk. Most of the PC users still use the good old rotating hard disks. Those are the real bottlenecks when it comes to data transfer.

The CPU, the RAM, the Cache and the GPU are pretty much "fast" except the HDD.

Try getting your hands on an SSD and you'll see the difference: http://www.youtube.com/watch?v=T_Jz7IMwBt4&feature=related

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