I have been using Samsung 840 PRO SSD for the last few months. It is an amazing SSD with blazing speed and responsiveness. It takes 2-3 seconds to boot my Kubuntu or Windows system.

The disk works fine on Kubuntu. But on Windows it gives a little lack in performance. I didn't notice it cause I barely use Windows.

I used several benchmarking tools like AS SSD Benchmark, Samsung Magician, CrystalDiskMark etc. All of them reported that my SSD is working at half of its expected performance. I couldn't understand why. Later I looked into the issue and found some amazing solutions. I am sharing my experience.

1. Port: Make sure that your SSD is connected to "Intel SATA III 6Gb/s" port, not regular SATA ports of your motherboard. If possible buy other SATA controller like Marvell's.
2. SATA Mode: Set SATA mode to AHCI. This makes the device hot swappable.
3. 4K Alignment: This is very important. Partition your SSD with correct 4K alignment. Look here for more information on 4K alignment and how it affects your performance.
4. Partitioning Tool: Avoid built in partitioning tools on Windows. I prefer GParted.
5. Drivers: Don't ever forget to install correct and updated drivers for your board and controllers. Install Chipset driver, Rapid Storage driver, Management Engine driver and all.

After doing all these things properly I retested my SSD and got expected result. Sequential read and write rate reached upto 500MB/s. (Sorry for the choppy image)

Samsung Magician also shows the similar result. IOPS is almost close to its expected result.