The bottlenecks of any computer, what to look for?
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.
Bottlenecks, Performance loss and Crashes - explained.
A lot of computer parts can bottleneck another parts.
Here I will bring a list of what can cause bottlenecks, loss of performance, crashes, explain why, and how to fix it. The list is too long, and I will split them into two parts, software and hardware.
Note 1: As it's too long, I think you won't read all the text, jump to the part that interests you much ;)
Note 2: Feel free to edit, or tell me if I miss something or tell something wrong. Feedback is good.
Let's start from the software side.
Software:
- Software/Game: In case of performance loss/bottlenecks first of all take a look at software/game specifications. Maybe that piece of software simply is not designed to run in your OS or hardware.
- Drivers: Incompatible drivers may cause a lot of headache. Make sure you have latest drivers installed. New drivers can also cause troubles (most common example is videocard), in that case rolling back to more stable version is a solution.
Some old hardware can have old drivers which are compatible with new OSes (e.g. using driver for Windows XP on Windows 7). They can be marked as compatible, but also can cause errors. If the manufacturer hasn't made new driver for new OS then changing hardware is the only option. - OS: A 64-bit OS with 64-bit CPU handles 4GB+ RAM more efficiently. A 32-bit OS may handle 4GB+ RAM and 64-bit OS may handle 4GB- RAM with a performance loss. But that's usually a little loss, and depends highly on CPU and OS.
Hardware:
Hard drives:
Note: speed of hard drive is usually visible when starting programs (because programs move to RAM), and when booting to OS. Shortly, if you have fast drives, your programs and games will load rapidly. (Not talking about servers or high-load computers)
When running low on RAM, drive speed can cause performance loss.
OS moves memory pages from RAM to HDD (and vice versa) so if HDD speed is slow then performance will suffer a lot. If you're always running low on memory, set bigger page-file size, and if that doesn't help, the only way is to buy bigger RAM or faster HDD (or both).- Faulty/bad hard drives often cause very random crashes and bottlenecks. These errors can be various and it's not easy to see that the reason is hard drive. If you don't shut down computer properly or if you have unstable electricity then hard drive suffers a lot. Check disk for errors (e.g. run CheckDisk), that usually solves the problem.
- Fragmentation may cause performance loss. Defragment it frequently. Some OSes (e.g. Windows 7+) defragment hard drives automatically, so usually you don't have to care about it.
Memory (RAM):
Note: RAM speed and size are essential for building fast computer because most of computer parts talk with RAM frequently. So, slow and little RAM usually reduces overall performance. For example, if you have Core i7, fast hard drive but have 1GB RAM on DDR3-1333MHz, you will not feel the full power of your "fast" computer. Look at frequency, size and CAS Latency (CL) when buying RAMs.
Two different RAMs sometimes may crash or work with errors when put together. When buying 2 or more RAM chips, consider buying a RAM kit.
Paging file (or swap) size may cause performance loss. OS moves inactive memory pages from RAM to paging file (on HDD) and vice versa to allocate more memory for active processes. When RAM is not big and page file size is little, then you may run out of memory. On the other hand if RAM size is big then big paging file can slow down computer. So if page file size is selected correctly, it will improve performance, otherwise it can slow down computer.
Fast RAM on slower frequency slot is another mistake. In that case RAM will run on slow frequency (e.g. DDR3-2133 may run on 1600MHz), and you will not notice fast performance until you overclock it. Make sure that motherboard supports your RAM speed before buying it.
CPU:
CPU overheating can cause crash, performance loss, computer freeze, BSOD and so on. Overheating is the most common issue when talking about CPU. So buy quality fans /make sure your fans are running properly and remember to change thermal paste when necessary. Use tools like this to monitor your CPU temperature and fan speeds, and change thermal paste when CPU temperature is close to maximum allowed temperature.
Note: (for newbies only!) obviously, CPU frequency, core and thread count are the most important things for computer performance. Nothing will help your fast drives, memory, videocard, if your CPU is still Pentium 3.
Graphics card (videocard, GPU):
- GPU overheating can lead to unexpected results (even to crash and burn). Make sure to have good cooling on your graphics card or you will lose them at all.
- When buying PSU (power supply unit), make sure you have a lot of headroom for your graphics card. Some videocards may tell that they use X watts, but in full load they may run up to e.g. 70+x watts, and then you may experience sudden crash/freeze/black screen/blue screen or just lag in game (if you're lucky). Read reviews about your videocard to find out the maximum wattage and check if your PSU can take it.
- Fast videocards on slow slots will cause bottlenecks. Make sure your motherboard has exactly the same slot which is required by videocard.
For example, if your graphics card requires PCI-E2 x16 slot, then it may run on PCI-E2 speeds, so putting it on PCI-E1 x8 (yes, it's possible) slot will cause about 4x performance loss.
PCI-Express slots are forward and backward compatible, so PCI-E3 card can be put on PCI-E1.x slot, but you will lose a lot of performance (also some new videocards may not work on PCI-E1.x). Putting PCI-E3 card on PCIE-2 slot will cause a little performance loss, because today's cards are not really running on high PCI-E3 speeds. But it can change tomorrow.
Read this good article to understand all this mess about PCI-Express.
PSU (Power Supply Unit) - The ignored father of random crashes:
- Note: It seems that PSU is less important and not harmful part of any computer, but in fact it can cause a lot of random crashes/black screens/freeze/and even burn hardware when it's not chosen properly!
Some CPUs, videocards (and other parts) may use more watts when in high load or in high temperature, and if PSU can't supply enough energy for computer, it may behave in 3 ways:
1) Power off - in this case, you know, your work will not be saved. Also some computer parts may struggle a little bit. But it's the best thing that can happen.
2) PSU doesn't care, and supplies low wattage - here you may see sudden crash/slow performance/freeze/lag/black or blue screen. Sometimes it can decrease hardware lifetime.
3) PSU doesn't care at all - some low quality PSUs can really burn your hardware! They can simply ignore it and supply more current to your wires, then wires can get hot or melt or even burn! Anyway, it may immediately kill the hardware if it gets out of control.So, when buying a PSU make sure it can supply enough power to your computer when computer is in full load, and leave about 50-100 watts for headroom.
On top of that, pay attention to PSU efficiency and constant/continuous wattage.
PSU efficiency shows how much energy PSU supplies to computer. For example, if it's 80% then it only 80% of energy will be supplied to computer, and other 20% will be wasted (on heating or fans).
Continuous wattage shows how much energy PSU can supply to computer, no matter how much PC is loaded. For example, if continuous wattage is 500W then you can be sure that it will stay stable even if computer is on high load. But cheap manufacturers often write maximum wattage on specification, and not the real stable wattage. So be sure to add another 50-100W headroom if you buy a cheap PSU. For more info about PSU, check this article.