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Closer Look at Samsung 840 Pro 256 GB

Being a major manufacturer of NAND flash, Samsung can easily introduce cutting-edge memory types into its serially produced SSDs. The new 840 series is a good example as both the basic and Pro versions boast 21nm flash with Toggle Mode 2.0 interface whose bandwidth has been increased up to 400 Mbit/s. That’s not the key feature of Samsung's new products, though. Their main advantage is the fourth-generation MDX controller. Samsung has been improving its controller noticeably with each new SSD series, so the chip employed in the 840 series aspires to be the fastest consumer-class SSD controller available right now.

It is based on three 300MHz ARM Cortex-R4 cores. Besides a faster version of the ARM architecture, the controller offers a 40% advantage in clock rate in comparison with its predecessor from the Samsung 830 series. The previous MCX controller could hardly be blamed for low performance and the new MDX has even better computing resources, which is important in terms of Samsung's declared priorities. When developing the new products, the company focused on making them faster at processing random-address data. This kind of load is typical of a lot of everyday tasks and today's SSDs are not as good at handling it as they are at sequential reading and writing.

To process a lot of unrelated I/O requests the SSD controller must translate LBA addresses used by the OS into the actual position of data in the flash memory. It is here that today’s SSDs may improve yet. The speed of processing random-address data blocks is much lower than the SATA 3 bandwidth, so Samsung focused on increasing it. This is indicated by the specified characteristics of the new SSDs we can compare with the specs of the older Samsung 830:

The manufacturer promises a 25% increase in random read speed whereas random writing may be up to 2.5 times as fast as before. That’s impressive, we must admit. Featuring faster memory and no artificial bottlenecks, the Samsung 840 Pro is expected to deliver the highest performance, so we are going to start with it.

Our sample of the Samsung 840 Pro was packed into a small and stylishly designed cardboard box painted mostly black. The storage capacity is indicated by a sticker on the front of the box. The product’s key features and specifications are listed on the back.


The SSD is fixed in a plastic wrap along with its accessories which do not include a 2.5->3.5-inch system case adapter. There are just a few documents, a couple of stickers and a CD with electronic manual and software.

The SSD itself looks gorgeous. Made out of aluminum alloy, it is black-anodized and has shiny fascias on its face side. A manufacturer logo and terracotta square are painted on the top of the case, so you can easily identify the 840 series. On the bottom of the case there is a dark-gray sticker with full product name, part number, barcodes and serial number.


The case is 7 mm thick and Samsung doesn’t offer any frames or faceplates to increase its thickness to the more conventional 9.5 mm.

The PCB is populated on one side only. All of the chips we can see on it are manufactured by Samsung itself.


There are three kinds of chips in this SSD. First, it is the above-described Samsung MDX controller. Second, there is a low-voltage LPDDR2-1066 SDRAM chip for 512 MB of cache memory. Both the 256GB and 512GB models are equipped with that much cache whereas the 128GB Samsung 840 Pro comes with 256 MB of cache. And third, we can see eight flash memory chips with Toggle Mode 2.0 interface. Each of them has a capacity of 32 GB and contains four 64-gigabit MLC NAND devices manufactured on Samsung’s 21nm facilities. Thus, the MDX controller can use 4-way interleaving on each of its eight channels in the 256GB SSD.

Here is a summary of the Samsung 840 Pro 256GB specifications:

  • Controller: Samsung MDX;
  • Interface: SATA 6 Gbps;
  • Flash-memory: synchronous 21 nm Toggle Mode 2.0 MLC NAND;
  • Size: 256 GB / 238 GiB;
  • Cache-memory: 512 MB LPDDR2-1066 SDRAM;
  • Sequential read speed: up to 540 MB/s;
  • Sequential write speed: up to 520 MB/s;
  • Random read speed (4 KB blocks): 100,000 IOPS
  • Random write speed (4 KB blocks): 90,000 IOPS.

The new controller's high performance helped implement AES-256 encryption in the Samsung 840 Pro. You can enable it and enter the encryption key through the mainboard’s BIOS.

Excellent software support is yet another advantage of Samsung's SSDs. The Samsung Magician utility is one of the best tools for working with SSDs. It is as good as Intel SSD Toolbox in its functionality.

Besides standard functions (viewing SMART information, updating firmware and performing Secure Erase), the Magician utility provides a number of extras including a synthetic performance benchmark.

It can optimize OS settings for SSDs and issue the TRIM command.

It can also create a reserve pool on the SSD (up to 10% of its total capacity) that is used for more efficient garbage collection and helps improve the device's service life in high-load environments.

It must be noted that even without any tricks with Magician the formatted capacity of a Samsung 840 Pro 256GB is 238 gibibytes, so the manufacturer has already allotted 7% of the drive's total capacity for the reserve pool. Considering that the Samsung 840 Pro is positioned as a professional solution, it is no wonder that it comes with a 5-year warranty.

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