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Released June 2012, Model A1278. Intel processor with Turbo Boost, Up to 512 MB DDR5 Video RAM

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Optical drive replaced by SSD: maximum capacity of the SSD?


I have a MacBookPro mid 2012 13" 2.9 GHz Intel Core i7, 8 GB RAM with a 128 GB SSD.

I was wondering if replacing the optical drive with a 1 TB SSD was conceivable ?

Is there a maximum capacity not to reach for it not to lag ?

Would you recommend a 500 GB?

Thank you in advance,

Best regards,


Answered! View the answer I have this problem too

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Hi! I have been using my Macbook Pro Mid 2012 i7 with 16Gb RAM and Dual SSD 512 (Main bay) and the original 750HDD (Optical Bay) for over a year.

My only issue is with the RAM sticks which may be a problem with the hardware for that specific model

You will need to be careful when taking the drives out, and installing the new ones since the ribbon cables may burn/scratch against the tooled aluminum

I hope this works

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@Ed - Be careful here! There are issues with this series (and yours) with the Optical SATA port. Here's a good reference: OWC Data Doubler. Note the Red text at the bottom of the page.


Thank you @danj !


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The storage size of the SSD can be even larger than 1 TB! As an example Samsung offers a 2 TB drive. The OS can handle it and still larger drives. The only thing holding you back is the cost of these larger SSD drives.

As to using the optical drives SATA port using a dual drive frame. Sadly, this system has an issue with the optical drives SATA port its half way between SATA II (3.0 Gb/s) and SATA III (6.0 Gb/s). Most SSD's today are fixed at SATA III and the few that auto sense the SATA ports data rate won't work reliably, you'll need a fixed SATA II drive here.

Your best bet is just to swap out your current primary drive (HD) which you currently have a 128 GB SSD with the larger drive.

Update (05/12/2016)

What happens here is the OS and the SSD (or HD) get into a fight as the CRC check sums don't match depending on the direction of the data move. So lets say the OS has something that needs to go to the drive it sends it over the SATA connection to the drive the drive replies I got it you send ABD, the OS says back to the drive NO! I sent you ABC not ABD, here it is again.

This battle of sending and receiving goes on for a while until the given block sent is correct. But instead of this taking one transaction it took quit a few and we're only talking about a single block of stuff 512 bytes! Now when we have 100's or 1000's of blocks this taxes both the CPU & the drive creating more heat than what it should! It also means the reliability of the data could be suspect as if you shut the system down before this battle ends the transaction is lost: Now where were we in this battle the CPU or drive asks when it starts up again.

The Crucial BX200 480GB SSD is a fixed SATA III (6.0 Gb/s) drive. While the Crucial Web site will state its compatible, this is only when you swap out your HD for the SSD, not when you use the optical drive SATA port which has a known issue.

You'll need to get a Fixed SATA II (3.0 Gb/s) drive for the optical drive SATA port. Sorry ;-{

I've seen this many a time and I know its not something people see or expect so its always a bit of work explaining whats going on.

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As the price of the 1 TB drives has dropped over the last year we are now using Samsung 850 EVO SSD's as our primary choice for HD replacements of our field systems Vs Seagate SSHD's. We've tested the 2 TB drives and find them quite good just the cost is holding us back for jumping to these.


%#*@ that was the best answer i think we can ever get for the question asked. Thanks Dan!


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Thank you everyone !

I successfully replaced my 128 GB original SSD with a 480 GB Crucial BX200, and it works perfectly well (data transfer etc.) !

The only thing that has changed since the space of my SSD started being full (2 months ago), and still now that I have replaced the SSD, is my Mac tends to overheat rapidly... It might not be correlated though !

What do you guys think I should do ? Should I clean the ventilation ?

Thank you in advance !


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Sounds like you're facing the SATA speed issue I pointed you to above.

See above update for more.


Oh, I thought you meant the SATA III wasn't recognize as for the optical drive replacement, not for the Hard Disk replacement ... My bad ...


Hold that thought! What drive is where? My focus has been the optical drive SATA port.


Thank you for the help and the reactivity Dan !

Great news, that's what I thought in the first place ! I removed my old SSD by the new crucial one, but I left the optical drive at its place :)

- Is it compatible then ?

- Do you have any idea where the overheating comes from ?

- Should I try to optimize my battery ? (running on mains all the time, I heard that trying not to go under 80% and loading to 100% avoids using 'battery lives')

Thanks !



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