I'm trying to determine what is the limiting factor in my PC build (it's already slightly dated, and I'm considering an upgrade of one of the parts). Since I use my PC for recording high quality screen captures (that's when I feel that the PC is acting rather slow), I decided to monitor the performance of the CPU and the disk during recording in order to determine which one is more likely a limiting factor.
Here are my results:
CPU cores 0 and 1
CPU cores 2 and 3
Disk write in SI MB/s
First half of the graph shows the performance while recording a 3D game in full HD using Fraps, and the latter half shows CrystalMark disk benchmark being run.
The drops in disk write speed correspond to lag spikes I get in the game, as well as to when Fraps reaches the 4 GiB file limit and decides to split the video.
Now, how do I interpret the data? CPU usage doesn't seem to be at its height (especially for core 1), although it's still rather high, given that on multi-core setups, the cores still have to wait for the others, so the core usage is not always at its peak.
The disk data is even more puzzling. CrystalDiskMark has 4*2 stages, 4 of which are reflected here (as only the write data is displayed here): sequential write with 1024KiB blocks, random write with 512KiB blocks, random write with 4KiB blocks and random write with 4 KiB blocks and 32 Queue Depth. In my graphs, the first block after I stopped recording was when the program was preparing the data (4000 MB), so it wasn't tested yet. The test phases are from 12:28:00 to 12:29:30, 12:29:30 to 12:30:30, 12:30:30 to 12:31:00 and 12:31:00 to 12:31:30, if I recall correctly.
Why are the speeds so different? Why is a sequential write so much faster than a random write? And how does it compare to the real-life data - is my disk during the recording at its maximum capability for the type of data being written to disk, or is it not even close to the limit?
Lastly, why do I get lag spikes when Fraps changes the file? From the CPU graphs, you can see that CPU usage skyrockets at that point, then falls down rapidly, and then resumes, while disk write halts for a while, and then resumes. What causes the lag, then - the disk, or the CPU?
And, most importantly, which one is stressed more overall - the disk or the CPU?