The 250 GB model has the same body as the 120 GB. It's a thin (7 mm), lightweight (44 grams) 2.5" drive with a SATA III interface (6 Gbps)... all good things for a laptop. It has an MEX Controller with three ARM Cortex-R4 cores clocked at 400 MHz and uses a 19 nm process.
But one thing's different: the buffer system (TLC NAND simulated as SLC, with one bit instead of three) is twice the size in order to boost the speeds. The 250 GB has a 6 GB buffer, whereas the 120 GB has just 3 GB.
Samsung also gave it a built-in temperature sensor that allows the drive to sense when it's overheating and then limit the speeds until the drive cools down.
Data transfer speeds
File transfers (photos, videos...): sequential speeds
Samsung's right about the speeds. The 840 Evo 250 GB reads at 504 MB/s and writes at 492 MB/s, rivalling last year's Samsung 840 Pro, our current all-time reference.
However, as with the 120 GB, you can only reach these speeds with files that are smaller than the buffer. When you transfer files larger than 6 GB (such as a Full HD movie), the speeds drops to nearly 100 MB/s.
Samsung SSD Magician
Samsung Magician (results not from the 840 Evo 250 GB)
Also in the box is a CD for SSD Magician, or you can download it from Samsung's website. This is an intuitive programme that offers a variety of functions, such as system info, benchmarking, SSD/OS performance optimisation, firmware updates, secure deletion and over-provisioning.
In the CD you'll also find a cloning programme for transferring data from another drive to the SSD. It's quick and easy to do, perfect for when you want to replace your old drives!