Inside The Drives

There are three different PCB designs in the 850 EVO lineup. The 120GB and 250GB models (above) use a tiny PCB with room for two NAND packages (one on each side). Interestingly enough, both use octal-die packages, meaning that the 120GB 850 EVO only has a single 128GB (8*16GB) NAND package. Decoding the part number reveals that the packages are equipped with eight chip enablers (CEs), so a single NAND package is viable since all eight dies can be accessed simultaneously.

The use of octal-die packages is actually true for all capacities. It's an interesting choice nevertheless, but I suspect Samsung's packaging technology is advanced and mature enough that it's more cost efficient to use high die count packages and small PCBs instead of larger PCBs with more and less dense NAND packages.

Samsung SSD 850 EVO NAND Configurations
Capacity 120GB 250GB 500GB 1TB
# of NAND Packages 1 2 4 8
# of Die Per Package 8 8 8 8
Total # of Die 8 16 32 64
Die Capacity 128Gbit 128Gbit 128Gbit 128Gbit
Raw NAND Capacity 128GiB 256GiB 512GiB 1024GiB
Over-Provisioning 12.7% 9.1% 9.1% 9.1%


TurboWrite is a feature that Samsung brought to the 840 EVO to increase write performance. The idea of running a small portion of the NAND in SLC mode was nothing new, but it was the first time it truly made sense because the 840 EVO used slower TLC NAND and hence the SLC buffer could provide significant improvements to write performance and user experience. Unsurprisingly, TurboWrite is also present in the 850 EVO.

Samsung SSD 850 EVO TurboWrite SLC Buffer Size
Capacity 120GB 250GB 500GB 1TB
TurboWrite Buffer Size 3GB 3GB 6GB 12GB

The buffer sizes and core architecture have remained unchanged. All writes hit the SLC buffer first, from which they then get moved to the TLC array during idle time. The only exception is a case of long, sustained period of writes that exceeds the buffer size, in which case the data will be written straight to the TLC portion.

Write Performance With and Without TurboWrite
  With TurboWrite Without TurboWrite
  Sequential Write 4KB Random Write (QD32) Sequential Write 4KB Random Write (QD32)
120GB 520MB/s 88K IOPS 150MB/s 38K IOPS
250GB 520MB/s 88K IOPS 300MB/s 70K IOPS
500GB 520MB/s 90K IOPS 500MB/s 80K IOPS
1TB 520MB/s 90K IOPS 520MB/s 80K IOPS

Samsung's reviewer's guide states that the 850 EVO features "enhanced TurboWrite technology" with a focus on random write performance, but I don't have any additional details as to how the TurboWrite implementation in the 850 EVO differs from the 840 EVO. TurboWrite was always designed to cache all writes regardless of the nature of the write (random vs sequential), so I'm not sure if anything has actually changed. Obviously the algorithms have been optimized for the new NAND and controller architecture and it's possible that the whole batch of algorithms has improved in the process, but I'll provide an update when I hear back from Samsung.

I ran a quick sequential write test to see how TurboWrite behaves in the 850 EVO. At smaller capacities it clearly provides a tremendous performance boost, but at 500GB and 1TB there is enough NAND to provide the parallelism that is needed to max out the SATA 6Gbps interface. That is a big improvement over the 840 EVO as its write performance maxed out at ~400MB/s when writing to the TLC array, so the performance benefits of 3D NAND technology are already evident.

Introduction, The Drives & The Test Three Bits and Three Dimensions: What's the Deal?


View All Comments

  • djdownfawl - Thursday, June 04, 2015 - link

    @Kristian Vättö
    As of today's prices Samsung 850 EVO vs the PRO. Would you recommend buying the EVO or the PRO?
  • sylerner - Thursday, August 13, 2015 - link

    The over-provisioning figures in the article are larger than the actual over-provisioning values.

    The source of error is failure to account for the flash memory used for TurboWrite.

    The correct values are:
    120GB: 10.6%
    250GB, 500GB and 1TB: 8.0%
  • Lonerski - Sunday, January 31, 2016 - link

    Did you use Rapid Mode in those benches ? Reply
  • CricDasher - Thursday, March 03, 2016 - link

    Samsung SSD 850 Evo is a life-changer for anyone who uses it. With the sleek and beautiful build quality, Evo 850 does obviously come with a great price tag.

    There are of course different capacities of the given product, but I preferred to use the 120 GB version, largely due to the relatively low price and my actual need of owning an SSD.

    My major requirement was to install the Operating System and few other mostly used applications inside the SSD, so that the whole computer looks so fast. Samsung Evo 850 120 GB SSD has done the job fantastically for me so far and I highly recommend this product to everyone.

    Out of the sellers online, GearBest seems to offer the best package since GB is a trusted source of products. They are offering a flash sale at the moment and you may try it to get it for a relatively a low price.
  • Budburnicus - Friday, March 11, 2016 - link

    Samsung OWNS the SSD market! When I can buy an 850 EVO 500 GB model for just $110 and get for all intents and purposes, the BEST possible speed from a SATA 6 drive - there is REALLY NO POINT in buying ANY other brand!

    I mean the 850 EVO keeps up with, and sometimes even SURPASSES the 850 PRO - often in ways that will benefit the average power user/gamer more!

    I wonder how much of that is due to the 6 GB of SLC write cache - as the 850 PRO series has no SLC NAND whatsoever!

    Also, once the "Magical" storage capacity of 480 GB and above is reached, again, for JUST $110 - not only is that more than sufficient to hold my OS and all the games I play, but all SSDs tend to perform best at 480 GB and above, I would say for the 850 EVO series, this is DOUBLY TRUE! Due to the fact that the 500 GB model has a full 6 GB of SLC Turbo-write NAND (compared to 3 for the 250 and 120) - but it also has a full 512 MB of DDR3L on it!

    I dunno why Anandtech has it listed as DDR2L memory, but it is indeed DDR3L RAM on ALL Samsung 850 series drives!
  • Tornadotuan - Friday, July 08, 2016 - link

    Hi Hardware Community,
    I know this article is quite outdated right now, nevertheless the actual topic of the authors "Final Words" bug me right now. Especially now that enough time for longtime-endurance tests has passed.

    Anyway, I can´t choose between the Samsung EVO 850 1TB v2 (289€) and die SanDisk Extreme 960GB (281€).
    So pricewise the "Pro" is even cheaper right now compared to the Samsung. But there are some obvious differences:

    - TLC 3D V-NAND vs. MLC Planar
    - 5 years vs. 10 years warranty
    - 150 TBW vs. 80 TBW
    - higher Peak vs. consistency
    - Samsung Bugging vs. sudden death drives

    My usage:
    - Client for everything: gaming, programming, office, multimedia - averything
    - gonna split it in system and data-partition
    - gonne be in laptop that´s used as desktop
    - battery is wasted, so no concern about power consumption

    So, usually I use hardware until it´s broken so meaning about 8-10 years.
    Still I want steady performance without sudden decline in speed like with the EVO 840 :C
    I´d be really glad, if you could tell me your opinion on this :)
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    but couldn't find one. My mom has an aging Dell D830, which is very slow and I'm looking for a reasonably priced replacement, and I think this driver is great.
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