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My iMac 2015 has 1-terabyte fusion drive containing a small 24-gig SSD. Can I upgrade the internal SSD to a much larger SSD, making the internal hard drive for storage only as a separate partition?
It would help if you gave your exact model number.

I'm guessing it is a 21.5" Late 2015 iMac16,1 or iMac 16,2. On that model the SSD is a PCIe "blade" card.

If you can find a compatible replacement (which isn't easy; the product lookups are assuming you want to replace the hard disk drive), you can swap it. But the SSD card is on the back of the logic board. The replacement process is... daunting.
 


My iMac 2015 has 1-terabyte fusion drive containing a small 24-gig SSD. Can I upgrade the internal SSD to a much larger SSD, making the internal hard drive for storage only as a separate partition?
Ted, unless funds are tight, it's absolutely time to bail on the Fusion drive and go full-SSD. There are many online resources to assist in this procedure / upgrade. I recommend Samsung 860 EVO SSDs.

Basic steps:
• Place SSD in an external USB 3 enclosure.​
• Use Carbon Copy Cloner software to clone entire contents of internal Fusion to external SSD.​
• Open iMac up and replace hard drive with SSD. No need to spend money on an SSD bracket if you don't wish - double sided foam tape is perfectly fine. The hard drive can be attached externally to be used as a backup drive or data storage.​
• Boot iMac and experience the awesomeness of pure solid state technology.​
• Use the Disk Sensei app to activate Trim on the SSD.​
• Use Disk Utility to erase the small Apple internal SSD that was formerly part of the Fusion combo. That drive could be designated as a scratch disk if you're a designer.​

Done.
 


Thanks, Todd. Great information there. I'll let my friend know your plan. Your plan makes it seem a lot easier to do. I would help him to remove the display section, but since it's glued, he'll be going to a Mac repair shop in town.
Finally had the job done. The company that performed the service is iPower Resale Group, based out of Carpenteria, California. Since the friend lives close to them, he delivered the iMac to them with the replacement blade SSD and a regular SSD. A few days later he received a call that the iMac was ready for pickup. After picking up the iMac, he is very happy after testing it. (Yeah, the screen assembly seemed to be too fragile for me to try.)
 


So, for these two 2017 iMac 5K machines, both with 40 GB of RAM, we've got

ConfigurationAlternating:
4GB 16GB 4GB 16GB
Paired:
16GB 16GB 4GB 4GB
Memory Copy15.4 GB/s13.3 GB/s
Memory Latency72.3 ns70.6 ns
Memory Bandwidth26.5 GB/s20.1 GB/s

So, the big question is what specs does your iMac 5K have? As listed in the Geekbench results linked earlier, the one I tested has:
Intel Core i7-7700K @ 4.20 GHz​
1 processor, 4 cores, 8 threads​
Sorry, should have included: exactly the same CPU.

I did not, however, stop all other interactive processes, nor background ones, such as Time Machine and Backblaze. And I only ran Geekbench 4 once, rather than, say, averaging results from three runs.
 


I need some advice, please, with a new 2019 iMac and challenges with new RAM...
FWIW, I had the same problems with a new 2019 27" 5K iMac that came with default 2 x 4GB RAM, and I added 2 x 16GB from OWC. With both sets installed, I got random freezing and black startup screens.

After a lengthy attempt to troubleshoot different install variations, I determined the iMac would work properly with either the Apple RAM or OWC RAM but not both. I then received the following note from one of OWC's more knowledgeable techs:
In most of our user's cases, we are able to get them [Apple and OWC RAM] to work together just fine. However we do on occasion run into a case where they simply won't together properly. These are rare cases, we are happy to provide a refund for our RAM or a user might simply choose to work with the upgraded set.
I opted to stick with just the OWC 16GB modules, which meet my foreseeable needs, and am keeping the Apple ones around to swap back in case the iMac needs AppleCare servicing.

My point is that you may not have either bad slots or RAM, just bad luck with incompatible RAM modules.
 


FWIW, I had the same problems with a new 2019 27" 5K iMac that came with default 2 x 4GB RAM, and I added 2 x 16GB from OWC. With both sets installed, I got random freezing and black startup screens.
After a lengthy attempt to troubleshoot different install variations, I determined the iMac would work properly with either the Apple RAM or OWC RAM but not both. I then received the following note from one of OWC's more knowledgeable techs:

I opted to stick with just the OWC 16GB modules, which meet my foreseeable needs, and am keeping the Apple ones around to swap back in case the iMac needs AppleCare servicing. My point is that you may not have either bad slots or RAM, just bad luck with incompatible RAM modules.
I have a 2019 27" iMac, ordered with 2 x 4GB RAM, and I added 2 x 16GB from Crucial. I also had the crashing and black screen issues.

I recently replaced the Apple RAM with an additional 2 x 16GB modules and haven't had a crash since. Keeping fingers crossed that this solves the problem.

After installing aftermarket RAM for more than two decades on a dozen or more Macs, not counting client Macs, this is the first time I've seen this kind of issue.
 


Not only do we never leave OEM RAM in systems when upgrading memory, we also try to avoid mixing modules from the same manufacturer that aren't sourced together at the same time from the same manufacturing batch.
 


I have a 2019 27" iMac, ordered with 2 x 4GB RAM, and I added 2 x 16GB from Crucial. I also had the crashing and black screen issues.
I recently replaced the Apple RAM with an additional 2 x 16GB modules and haven't had a crash since. Keeping fingers crossed that this solves the problem.
After installing aftermarket RAM for more than two decades on a dozen or more Macs, not counting client Macs, this is the first time I've seen this kind of issue.
Actually, this issue doesn't surprise me. Never leaving money on the table also means never spending more than is absolutely necessary. It's cheap Apple RAM; what more can you say?
 


I have a 2019 27" iMac, ordered with 2 x 4GB RAM, and I added 2 x 16GB from Crucial. I also had the crashing and black screen issues.
I recently replaced the Apple RAM with an additional 2 x 16GB modules and haven't had a crash since. Keeping fingers crossed that this solves the problem.
After installing aftermarket RAM for more than two decades on a dozen or more Macs, not counting client Macs, this is the first time I've seen this kind of issue.
I had an iMac where it wouldn't boot after upgrading one of the two modules, but after swapping the positions (e.g. from from 2GB 4GB to 4GB 2GB), it worked perfectly. your milage may vary.
 


... surprised to trip over PDF repair guides for 2019 iMacs at Apple Support Manuals.
Which are, perhaps not too surprisingly, superficial in detail (e.g., they don't outline the memory channel pairing issues).

If you bring up System Information app (e.g. Option key + About This Mac) and go to the Memory section, that report labels DIMM 0 (or 1) and Channel ["Bank"] 0 (or 1) corresponding to the memory channel controller on the CPU.

It is best to put dual-rank DIMMS on the same channel. One of the differences between these 4GB and 8-16GB DIMMs is that the former are often single-rank, and the latter are dual-rank. (Rank pragmatically is a set of memory chips on the DIMMs.) You can mix single and dual rank, but if the implementions differ a bit, that is more likely to shake out a quirk.
 


That's really interesting to hear that Charles and Phillip both had the same black screen issues on a 2019 iMac, one with OWC and one with Crucial RAM.

[Good ideas] that maybe Apple's RAM is cheaper, or perhaps mixing single-rank with dual-rank DIMMs can cause problems. Thanks everyone for sharing!

In my case, the first set of OWC RAM produced black screens but not the second or third set. I received the iMac today after taking it to Apple. The tech, whom I believe, said he ran Apple's diagnostics for 48 hours through multiple power cycles and could never get anything to fail. That was with only Apple's RAM installed, but my Apple RAM would frequently abort testing with Rember/MemTest 4.22. The tech theorized that MemTest being a 32-bit version might be incompatible. He also tried MemTest 86 v8.2, and that froze, even on an in-store 2019 iMac.

His conclusion was that Apple changed something in 2019 iMacs that's incompatible with anything but Apple's diagnostics. That seems logical, so I guess I'll disregard MemTest, not try MemTest86's current version, and keep this OWC RAM. Perhaps I should be content with just OWC's 32 GB of RAM, and leave the 8 GB out -- just in case there's a subtle problem. Since this is not ECC RAM, it seems wise to be even more cautious.
 


Which are, perhaps not too surprisingly, superficial in detail (e.g., they don't outline the memory channel pairing issues).
If you bring up System Information app (e.g. Option key + About This Mac) and go to the Memory section, that report labels DIMM 0 (or 1) and Channel ["Bank"] 0 (or 1) corresponding to the memory channel controller on the CPU.

It is best to put dual-rank DIMMS on the same channel. One of the differences between these 4GB and 8-16GB DIMMs is that the former are often single-rank, and the latter are dual-rank. (Rank pragmatically is a set of memory chips on the DIMMs.) You can mix single and dual rank, but if the implementions differ a bit, that is more likely to shake out a quirk.
Thanks for posting this; I did not know about this System Info window. On my 2019 iMac, it shows Banks 0 & 1 are Channel A and Banks 2 & 3 are Channel B. The two Apple 4GB DIMMs are in Channel A and the two OWC 16GB are in Channel B, just like the fellow at OWC told me to do.
 


Ric Ford

MacInTouch
After a lot of false starts and detours, I'm currently running a standalone, bootable memory tester on the 2017 iMac 5K, using essentially this sequence of steps:
  1. Back up your main drive(s)
  2. Disconnect all external drives
  3. Go to https://www.memtest86.com/download.htm
  4. Download MemTest86 Free:
    https://www.memtest86.com/downloads/memtest86-usb.zip
  5. Unzip the package
  6. Read readme.txt
  7. Insert a USB flash drive (it can be tiny — 4 GB is more than enough).
  8. This part may not be necessary, but it's what I did:
    Use Disk Utility to format the USB flash drive with GUID partition and FAT32 file system (naming the volume MEMTEST). Right-click on the volume and Unmount it.
  9. In Terminal:
    diskutil list
  10. Note the disk ID of the flash drive and don't get this wrong. Let's say mine was /dev/disk2 (external, physical)
  11. Type (for "SuperUser DD Input File="):
    sudo dd if=
  12. Drag the icon for the file memtest86-usb.img onto the command line to get something like
    sudo dd if=/Users/myusername/Desktop/memtest86-usb/memtest86-usb.img
  13. Type a space, then type something like this, where you make certain you're typing the correct disk ID of your flash drive and not anything else!
    of=/dev/disk2
  14. You should now see something like this where your own account name and disk ID replace what I've typed in red:
    sudo dd if=/Users/myusername/Desktop/memtest86-usb/memtest86-usb.img of=/dev/disk2
  15. Press Return to execute the command, then enter your administrator password (to authorize "sudo" to perform the command).
  16. Wait for a number of minutes for 524 MB to be written to the flash drive, and then for completion, e.g.
    524288000 bytes transferred in 441.929435 secs...
  17. If that all goes well, shut down your Mac.
  18. Make sure you have a wired keyboard and mouse connected and have the Memtest flash drive in a USB port.
  19. Reboot your Mac and hold the Option key at boot to select a startup volume.
  20. Select an EFI Boot volume.
  21. You should see an old-fashioned menu-based interface, where you can run a memory benchmark and memory tests, with a variety of options to choose from. (The defaults should be fine.) On an iMac 5K display, the initial menu items will be very small (but the actual test run displays larger text).
Let me know if you see or have any issues with this procedure!

#memory #testing #RAM #memtest86 #dd
 


Ric Ford

MacInTouch
On this 2017 iMac 5K, 4GB and 16GB cards are installed in alternating slots (not in adjacent pairs). Running macOS Sierra, About This Mac > Memory shows...
After a lot of false starts and detours, I'm currently running a standalone, bootable memory tester on the 2017 iMac 5K, using essentially this sequence of steps...
The memory test was set to repeat the full suite of tests four times. I checked after the first set of tests had completed, which took about an hour, and let testing continue overnight. No errors were reported after the first set and part way through the second. In the morning, there was no report at all and the testing program had returned to the starting screen. Hopefully, this means there were no errors.

If you pay for a $44 "Pro" version of MemTest86, you get options to save results that aren't available in the Free version.

MemTest86 reported 22.83 GB/s for memory speed, lower than what Geekbench reported. (There is 40 GB of PC4-19200 DDR4 2400MHz installed, including Apple and OWC RAM.)

In any case, I feel more confident about my RAM in this 2017 iMac 5K now, despite questions about the order of memory cards. At least for me and this memory, the alternating arrangement of 16GB OWC memory cards and stock 4GB Apple cards seems to be working fine, so far.

Bank 0
DIMM 0
Bank 0
DIMM 1
Bank 1
DIMM 0
Bank 1
DIMM 1
4GB16GB4GB16GB

I haven't tried swapping things around and re-doing all the tests, but other possibilities include:

4GB4GB16GB16GB
16GB16GB4GB4GB
16GB16GB
16GB16GB
16GB16GB
 


Ric Ford

MacInTouch
If you pay for a $44 "Pro" version of MemTest86, you get options to save results that aren't available in the Free version.
I bought the Pro version, downloaded it, then wrote the Pro image onto the USB flash drive (per my earlier procedure) and re-ran the tests. This time, I was able to save the results (no errors found in one pass) — it stored its various files on the flash boot drive in:
/Volumes/MEMTESTPRO/EFI/BOOT
including configuration information (i.e. RAM slots and cards), a RAM benchmark test, a detailed log file, test configuration information and results, etc.
 


Any reason why Apple cannot provide a Safari 13 update for macOS Sierra? I'm getting the feeling that I'm going to be forced to upgrade at least to Mojave, which I've been reluctant to do on this non-SSD iMac.
Robert, you don't note which iMac you have, but putting a SATA SSD into an older iMac is one way to keep an older machine going. Alternatively, you could, like a few people here have done, set up an external SSD startup disk.

I've done a number of the internal installs, mostly to 2013 vintage 27" iMacs with good results. Systems boot faster and just feel more responsive overall. Cost for parts is ~$150 for SSD, adapter (2.5"-3.5") and adhesive tape for the remounting of the display. Having done a few, it takes me about 30 minutes, not including transferring OS/data back to the new drive.
 


Robert, you don't note which iMac you have, but putting a SATA SSD into an older iMac is one way to keep an older machine going. Alternatively, you could, like a few people here have done, set up an external SSD startup disk.

I've done a number of the internal installs, mostly to 2013 vintage 27" iMacs with good results. Systems boot faster and just feel more responsive overall. Cost for parts is ~$150 for SSD, adapter (2.5"-3.5") and adhesive tape for the remounting of the display. Having done a few, it takes me about 30 minutes, not including transferring OS/data back to the new drive.
I have a mid-2015 iMac with a fusion drive. I'd like to keep the internal hard drive for storage and replace the smallish flash drive with a much larger one, making it the boot drive. I gather I can boot from the new flash drive and mount the internal hard drive only as needed?
 


Several years ago I bought a Samsung T3 1TB drive and taped it to the upright support on my iMac and made it my boot drive. The performance is wonderful and have no reason to hassle with doing anything to the internal drive, which I just leave unmounted. I now have multiple T3 drives taped to the support. The T5 version is cheaper. [Amazon link]
 


Several years ago I bought a Samsung T3 1TB drive and taped it to the upright support on my iMac and made it my boot drive. The performance is wonderful and have no reason to hassle with doing anything to the internal drive, which I just leave unmounted. I now have multiple T3 drives taped to the support. The T5 version is cheaper. [Amazon link]
If you're willing and able to remove virtually everything from inside your iMac and reassemble it, you can boost your performance quite a bit more by replacing the small PCIe-attached SSD module with a much larger module that becomes your boot volume, with read/write times approaching 3 Gbits/sec (as opposed to about 500 Mbits/sec for an internal SATA SSD or the throughput rates you've already listed for a USB3 external bus module). The notion of working inside that, oh, so thin box is all by itself an obstacle, of course.
 


Ric Ford

MacInTouch
If you're willing and able to remove virtually everything from inside your iMac and reassemble it, you can boost your performance quite a bit more by replacing the small PCIe-attached SSD module with a much larger module that becomes your boot volume, with read/write times approaching 3 Gbits/sec (as opposed to about 500 Mbits/sec for an internal SATA SSD or the throughput rates you've already listed for a USB3 external bus module). The notion of working inside that, oh, so thin box is all by itself an obstacle, of course.
Alternatively, if you have an iMac with Thunderbolt 3 (2017 and later, I believe), you can get the same ultra-high performance via an external Thunderbolt 3 storage device (e.g. Samsung X5 [Amazon link]).

For Macs with Thunderbolt 2 (or Thunderbolt 1), you can get maximum external drive performance via a Thunderbolt 3 powered dock (e.g. CalDigit TS3 Plus) and a Thunderbolt 3-Thunderbolt 2 adapter.
 


Robert, you don't note which iMac you have, but putting a SATA SSD into an older iMac is one way to keep an older machine going. Alternatively, you could, like a few people here have done, set up an external SSD startup disk. I've done a number of the internal installs, mostly to 2013 vintage 27" iMacs with good results. Systems boot faster and just feel more responsive overall. Cost for parts is ~$150 for SSD, adapter (2.5"-3.5") and adhesive tape for the remounting of the display. Having done a few, it takes me about 30 minutes, not including transferring OS/data back to the new drive.
I believe I bought this machine in mid-2014 or so, 23" iMac. However, I wouldn't try to upgrade the drive myself. I removed the drive from an older iMac (the thick one), and that was a hell of a job in and of itself, and the machine wasn't even working, so I didn't have to be very careful. But that whole operation took me at least an hour or more, and the foil tape was torn around the edges of the case.
 


Alternatively, if you have an iMac with Thunderbolt 3 (2017 and later, I believe), you can get the same ultra-high performance via an external Thunderbolt 3 storage device (e.g. Samsung X5 [Amazon link]).
For Macs with Thunderbolt 2 (or Thunderbolt 1), you can get maximum external drive performance via a Thunderbolt 3 powered dock (e.g. CalDigit TS3 Plus) and a Thunderbolt 3-Thunderbolt 2 adapter.
Or, if you have a 2017 iMac 5K like mine, you can go the OWC route and purchase various-sized Thunderbolt 3 external enclosures with OWC's internal NVMe SSD inside, giving you blistering read/write speeds. (Those speeds, as per Blackmagic Disk Speed Test, are on par with the speeds of a 2019 MacBook Pro 15" internal SSD.)
 


Ric Ford

MacInTouch
Or, if you have a 2017 iMac 5K like mine, you can go the OWC route and purchase various-sized Thunderbolt 3 external enclosures with OWC's internal NVMe SSD inside, giving you blistering read/write speeds.
I actually did that... and, no, it didn't have blistering speed! :-)

Of course, it depends on the exact product. I bought an OWC Express 4M2 and installed a super-fast Samsung SSD, but it was really slow. Huh? As we subsequently discovered (and documented here), this device has only a single PCIe lane per SSD M.2 slot, radically reducing performance if you didn't install multiple SSDs in a software RAID0 that doesn't support FileVault. So... no go for me.

OWC does have other Thunderbolt 3 SSDs that are not dependent on software RAID0 for their performance, but you really have to be careful about what you're buying.
 


"3 Gbits/sec (as opposed to about 500 Mbits/sec for an internal SATA SSD
I guess you probably meant 3 GB/s (speed possible only with NVMe SSD) and about 500 MB/s (SATA III speed). We run (at a customer's) external Thunderbolt 2 / SATA III LaCie rugged enclosures and get 350-370 MB/s, and USB 3.0 can be even better, but we need all the USB ports. TRIM is supported with this configuration, maybe not with USB 3.0?
 


Ric Ford

MacInTouch
This looks like a pretty powerful Mac on sale at a pretty low price for a very limited time:


I don't like the 1TB Fusion drive, but you can hook up a Samsung T2 or super-fast Samsung X5 to solve that problem. RAM is expandable (inexpensively), and, of course, it has a great display. It also runs macOS Sierra and up.
 


During my career in the graphics department at a public television broadcast facility, I eventually supported 9 or 10 original Mac Pros. That responsibility was earned beginning back in 1989 when I—not being a particularly techie person—fearlessly cracked open the case of one of our first Macs—an SE/30. I installed more RAM, a faster CPU card, and a Radius video card to drive our "huge" new 19" Radius monitor. When I put it back together and everything worked, the die was cast. I was the department tech guy.

I achieved a certain level of competence during those days, but it's been 8 years since retirement and 9 since my last new personal iMac. Competence fades with lack of exercise. I'm about to order a new iMac and face a questions I always knew how to answer. Apple RAM or ?
I always in the past ordered minimum Apple configs and then filled the slots with RAM from the likes of Techworks, Crucial, OWC, etc. Is that still preferred practice? If so, which brand is favored?

And do I need to upgrade the video card to the Vega option for occasional short (4–5 min.) FCP editing?

Thanks for your thoughts.
 


Ric Ford

MacInTouch
I'm about to order a new iMac and face a questions I always knew how to answer. Apple RAM or ? I always in the past ordered minimum Apple configs and then filled the slots with RAM from the likes of Techworks, Crucial, OWC, etc. Is that still preferred practice? If so, which brand is favored?
I ordered RAM from OWC (macsales.com) for a 2017 iMac 5K this year, and then I tested it rather thoroughly. It worked fine. (See that earlier discussion for more about configurations, etc.)
 


....I'm about to order a new iMac and face a questions I always knew how to answer. Apple RAM or ? I always in the past ordered minimum Apple configs and then filled the slots with RAM from the likes of Techworks, Crucial, OWC, etc. Is that still preferred practice? If so, which brand is favored?
Since Apple seldom gives much choice in RAM and is expensive, I think aftermarket RAM is still the way to go. I also have the 2017 iMac, and bought Crucial from Amazon (using the MacInTouch link if I recall correctly), a bit cheaper than OWC. Possibly more chance of a problem and a bit more trouble to resolve a problem with Amazon over OWC, but it's working fine. I try to balance price with vendor trust. Most other vendors I looked at were much more expensive, though.
 



... I'm about to order a new iMac and face a questions I always knew how to answer. Apple RAM or ? I always in the past ordered minimum Apple configs and then filled the slots with RAM from the likes of Techworks, Crucial, OWC, etc. Is that still preferred practice? If so, which brand is favored?
And do I need to upgrade the video card to the Vega option for occasional short (4–5 min.) FCP editing?
Techworks? I see Buffalo Technologies took over that brand. But that name goes back some. One I recall that is still around is Mushkin.

With the 27" iMac that has a user-accessible RAM door, I would get the minimum 8GB RAM config and then upgrade with Crucial or OWC.

Although the lower-end iMac 27" on Apple's site still shows configurable to a 32GB limit, it can take up to 128 GB, per OWC.

As for Vega upgrade, an 8GB video card would make some production, VR and gaming rendering better. Some posts mention the Vega might run cooler than the 580X, if that is important. Or don't go with Vega and consider an eGPU?
 



…and bought Crucial from Amazon (using the MacInTouch link if I recall correctly), a bit cheaper than OWC. Possibly more chance of a problem and a bit more trouble to resolve a problem with Amazon over OWC, but it's working fine. I try to balance price with vendor trust. …
I found that OWC is also accessible through the MacInTouch link and that's what I ordered: 64 GB worth of RAM. I can't forget that the first real computer I bought was an Atari 800. On the box was a prominent sticker proclaiming: "Now with 48K memory."
 





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