A Closer Look at Samsung 840 EVO 250GB
Samsung’s solid-state drives may come in different versions as desktop or mobile upgrade kits but ours is an OEM version. Even in this case the Samsung 840 EVO is packed into a neat small box. Besides the SSD, the box contains some papers and a CD with software and electronic user manual.
The restrained design of the packaging is Samsung’s typical. The box is made of black cardboard, showing a picture of the SSD on its front. The contents of the box are listed on its back with a few marketing slogans.
The exterior design of the SSD has somewhat changed since Samsung’s earlier products. The shape and materials of the case are the same but the 2.5-inch metallic brick is painted differently. Instead of lusterless powder paint, we have a “wet-asphalt” coating. The manufacturer’s logo on the top of the drive is now black.
The SSD is 7 mm in height, so it can be easily installed into ultra-slim notebooks. The Samsung 840 EVO is also very light at just 43 grams.
There’s a sticker on the bottom of the SSD with its name, serial and part numbers, and other information which is hardly important for end-users. What is important, you can see a PSID, which may be required to reset the encryption password (losing all data at that).
The humble-looking case contains most extraordinary internals. The PCB installed inside the Samsung 840 EVO is amazingly small. We’ve never seen such tiny PCBs inside 2.5-inch SSDs before.
Even more amazingly, there are only four chips on the PCB. The most important of them is the S4LN045X01-B030 controller. The Samsung 840 EVO employs LPDDR2-1066 SDRAM for storing firmware and address translation table. It is represented by a single 256MB chip. The other SSDs in this series have different amounts of SDRAM: 1 MB of cache per 1 GB of storage capacity.
Now, the most interesting thing is how 256 gigabytes of TLC flash memory can fit into just a couple of chips. It turns out that each chip is 128 gigabytes in capacity, consisting of eight 128-gigabit TLC NAND flash memory dies. Samsung has achieved an unprecedented level of component density with the transition to 19nm technology as earlier we only had chips with up to four dies inside.
The 8-channel Samsung MEX controller only uses 2-way interleaving on each channel in this SSD. That’s not the fastest option possible because 4-way interleaving ensures higher speed. That’s the downside of Samsung’s transition to 128-gigabit NAND devices. As with the Crucial M500 series, the Samsung 840 EVO will deliver maximum performance in its 500GB and larger-capacity versions. The two junior versions, including the 250GB one we’ve got for our tests, are somewhat slower.
Interestingly, the new SSD from Samsung lacks any thermal interfaces. None of the chips has contact with the case but that’s not really necessary. They do not get very hot at work. Samsung also says that the SSD features overheat protection which is triggered when the controller gets hotter than 70°C.
The specifications of the Samsung 840 EVO 250GB are listed below:
- Controller: Samsung MEX
- Interface: SATA 3.1 (6 Gbit/s)
- Flash memory: synchronous 19nm Toggle Mode 2.0 TLC NAND
- Storage capacity: 250 GB (233 gibibytes)
- Cache memory: 256 MB LPDDR2-1066 SDRAM
- Sequential read speed: 540 MB/s
- Sequential write speed: 520 MB/s
- Random read speed (in 4KB data blocks): 97,000 IOPS
- Random write speed (in 4 KB data blocks): 66,000 IOPS
As expected, the Samsung 840 EVO 250GB is somewhat slower than the senior modifications, mostly in terms of random writing. The TurboWrite cache is capable of making up for that, so the performance difference will only be noticeable in applications that write a lot of data continuously.