Well, your SATA controller apparently maxes out right around 120MB/sec, so don't bother getting anything faster. Why? All hard drives have that blue arc downward. Platters are circular - when a platter spins at a fixed speed the read/write head can cover more surface area on the edge, and thus reads or writes more information.
When a drive goes straight like that, it means your SATA controller is bottlenecking it. The drive is capable of higher speeds, but other parts of your computer are not.
Also, notice the yellow dots only go half-way into this benchmark?
That's because HDTune v255 uses 32bit signed ints for its tests. That's approximately 2 billion; 2 billion 512b sectors equal 1TB. HDTune v255 is only testing the first half of the drive, so this Seagate drive's access times are actually far higher than it claims. (Probably a little under 19ms)
HDTune Pro actually reveals a lot more information than HDTune v255. It has a RandomAccess test that can reveal how a drive performs when reading or writing files/blocks of certain sizes. Here's an example:
These are all random reads. They involve seeking to a location on the drive (such as a file) and then reading a certain amount of data. The graph shows that when reading in 4KB chunks, my drive only manages 0.239MB/sec... ouch. But when reading slightly larger files, it's much better performing. Most games have fairly large models and textures (at least 1MB large), so that number is probably most relevant to game loadtimes.
The reason the 64KB and 4KB read scores are so low is because every read or write requires a seek before the data can be accessed. Those seeks take on average 10-25ms. 7200RPM drives are usually in the 10-18ms range, and 5400RPM drives are usually in the 15-25ms range. If a seek takes 25 ms, and there are 1000ms in a second, you can only do 40 of those per second.
Now take a look at this graph:
The sequential speeds there actually tell me a surprising amount. on the edge my drive is very near 135-150MB/sec. If you divide by 1000, you're left with 135 to 150KB/ms
. This is important for understanding a drive's performance.
Lets say my drive needs to seek to a file to read it? That will take somewhere around 14-20ms on average. Reading a 4KB file would take exactly that long. Now, if the file is 250KB, because we know the KB/ms speed, we can estimate it will take 2ms extra to read all that data. If it's reading 1MB, it will take 8ms extra. (22-28ms) If it's 2MB, 16ms extra (30-36ms) In the time my drive can read two 4KB files, it can read 2MB of data sequentially. That is why hard drives love larger reads/writes, and especially love video work or screen recording.
One final thing - when only part of a drive is in use, the head can stick around closer to where it is needed. This results in lower seek times to actual data than the benchmarks claim. To help with visualizing this, you can tell HDTune Pro to "short-stroke" a drive. (only use the first part of it, up to whatever capacity)
Here's an example:
I have 500GB of games on my Steam drive, so this benchmark is actually more relevant to how my drive will perform than the farther above RandomAccess test.
Well, that's most of what you/I can glean from these graphs. If you have any other questions, I'll try to answer them as best I can.