USED iMac 21.5 4K 2017 or 27" 5K 2015?

Discussion in 'iMac' started by gorgre, Jul 16, 2019.

  1. gorgre macrumors newbie

    Jul 16, 2019
    Hi, as the title suggest I am looking for an iMac and found two eligible options both priced almost the same (21,5 is 80 € cheaper). What are the main differences I should look for when deciding? 27" has a Fusion drive and bigger display (click for full specs, it's the second config), the 21,5" is newer and has USB-C (some advantage for me) (click for full specs, it's the base model). My main question are the processor and graphics. I have little experience in comparison thats why I decided to ask for more professional opinion. If I am correct, the 27" has i5-6500 and 21,5" i5-7400. Other than that i5-7400 is the newer, supposedly faster generation I have no clue how to compare them (or what the information on the web truly mean). For the graphics, the 27" has AMD Radeon R9 M390 and 21,5" Radeon Pro 555, I found this excerpt from Notebookcheck's ranking which states that the R9 is higher rated, but again I found comparisons which state otherwise.

    The iMac will be mainly used for normal work, on occasion there will be some photoshop/illustrator and film editing, but nothing too heavy. If you have any advice you can give me, it would be greatly appreciated. Thank you in advance!
  2. azentropy macrumors 68020


    Jul 19, 2002
    If the 21.5 just has the regular 1tb 5400rpm drive and you are not comfortable upgrading it yourself or making a USB-C external SSD drive your primary, then go with the 27". That drive totally ruins the system.
  3. whosthis macrumors member

    Aug 21, 2008
    For me, the Fusion drive would be a no-no (I hope the 4k has a SSD and not the HDD). Also, USB-C gives better speeds for external drives. Looks like the 4k is a better option, especially if you pair it up with a 2nd screen maybe later on.

    I guess they are from Apple's refurbished store?
  4. gorgre thread starter macrumors newbie

    Jul 16, 2019
    Yeah the HDD/FD difference was also one of my main concerns, but I avoided it just as azentropy said. Maybe upgrading SSD and RAM while I am at it or actually utilizing that Thunderbolt/USB-C port for primary drive (that's why I like the I/O difference). (so no, 4K currently only has HDD)

    They are not from Apple but are from a trusted source, I have the ability to check them and they are impeccable, the 21,5" is only 1yr old and the 27" 2 yrs, so they are bot very viable option.
  5. whosthis macrumors member

    Aug 21, 2008
    The prices should be extremely attractive then compared to Apple's refurbished to pick one or another. Basically the first thing you'd do with the 4k is hook up a good SSD externally and boot from it, adding costs, complexity and clutter.
  6. ruslan120 macrumors 6502


    Jul 12, 2009
    I would avoid those and go for an iMac with an SSD, but if you really want to do this deal, the 5K with a thunderbolt three SSD and a thunderbolt three to thunderbolt two adapter to boot from.
  7. frou macrumors 6502a


    Mar 14, 2009
    TB3 SSDs are rather expensive. Presumably that would blow away the budget the OP has in mind.

    Surely macOS running from a USB SSD is still way superior to an internal HDD/Fusion. Must admit I've never actually tried it though.
  8. frou macrumors 6502a


    Mar 14, 2009
    The M390 GPU uses a really old AMD architecture (Pitcairn) compared to the 555 (Polaris). The older machine will obviously be cut off from macOS support by Apple sooner too.
  9. Ledgem macrumors 68000


    Jan 18, 2008
    Hawaii, USA
    As long as the screen sizes don't make a difference to you, I'd go with the 2017 model. It doesn't have much to do with the internals of the computers, which don't seem overly different; it has to do with the expandability. With Thunderbolt 3 you can run a SSD that would be faster than the ones that Apple supplied with these computers; you can use an external graphics card that will give you more power than anything Apple put into these systems. You can also run a 5K display, if you wanted.

    With the 2015 model you're limited to Thunderbolt 2. While not bad in its own way, it hasn't received support in the way that things are really taking off for Thunderbolt 3. While you might think that there'd be a fire sale on Thunderbolt 2 peripherals, it's not the case: they're still very expensive, in some cases just as expensive as Thunderbolt 3 peripherals.

    I have the Late 2015 27" iMac. Great machine, but as I contemplate future upgrades, I'm really feeling the lack of Thunderbolt 3.
  10. mikehalloran macrumors 68000

    Oct 14, 2018
    The Sillie Con Valley
    If a late 2015, the 27” can be made nearly as fast as the 2017. Replace the slooooow AHCI SSD with a fast NVMe 3 x4 SSD and Sintech adapter. Throw away the HDD. This will increase the speed of all drive operations three-fold.

    The Samsung 970 EVO and WD 3D Blue are perfect for this. The less expensive Intel 660p works but isn’t as fast (2x instead of 3x).

    The late 2015 is the only iMac that benefits to this degree. It comes from Apple with a PCIe 3 x4 bus like the 2017-19 but the blade is AHCI like all 2013–14 and early 2015 21.5”.

    Any experienced tech can do this job well under a half hour.

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9 July 16, 2019