Mac Pro (2019) has 12 DIMM (memory) slots that support up to 1.5TB of 2933MHz memory when all 12 slots are full using DDR4 ECC DIMMs.

1. Dimm Slots On Motherboard
2. So Dimm Slot
3. Dimm Slot Order
4. Which Dimm Slots To Use

8-core, 12-core, and 16-core Mac Pro models support up to 768GB of memory.

Before you begin

White DIMM slots denote the first slot of a channel. For 1 DPC (DIMM per channel) populate white slots only. A minimum of one DIMM is required per processor. There are three (3) DIMM slots for each memory channel; twenty four (24) total slots for 2 processor server. Hello, I am new to this forum. Yesterday I purchased an Asus Maximus VII Ranger motherboard, and 2 RAM bars (Kingston 8GB each, 1600Mhz). I have a couple of questions. 1) The guide suggests to plug these 2 bars in slots DIMMA2 and DIMMB2. I did that but the computer would recognize only 8MB (I am using Win7 64-bits which I reinstalled completely following the change in motherboard). The DIMM.2 card is a riser designed to decongest the crowded motherboard that has no room for M.2 slots. The DIMM.2 accessory is a PCB with two 32 Gb/s M.2 slots, and a riser interface that's similar to a DDR3 DIMM (so inserting DDR3 DIMMs this slot won't work).

You can use either LR-DIMMs or R-DIMMs with your Mac Pro, but you can't mix these memory types. To check if you have R-DIMMs or LR-DIMMs installed and view your memory status, choose Apple menu  > About This Mac, then select the Memory tab.

Make sure that you use the same type of memory when installing additional DIMMs or replacing DIMMs. Learn more about Mac Pro (2019) memory specifications.

Apple recommends that you use Apple-approved DIMMs. You can purchase memory upgrade kits by visiting an Apple Store or Apple Authorized Reseller. If you need to order replacement memory, contact Apple.

Check supported configurations

Mac Pro supports up to 12 DIMMs installed in configurations of 4, 6, 8, or 12 DIMMs, as shown in the images below. These images can also be found on the inside of the DIMM covers. For maximum performance, install DIMMs in a 6 or 12 DIMM configuration. If your DIMMs aren't identical in capacity, learn how to install DIMMs of mixed capacities.

DIMM configurations of 5, 7, 9, 10, and 11 DIMMs are not supported. Other configurations of 1, 2, and 3 DIMMs are for diagnostic use only.

Each number represents a DIMM slot. For each DIMM configuration, insert DIMMs only into the dark grey slots and leave the light gray slots empty.

Installing DIMMs of mixed capacities

If your DIMMs are different capacities (like four 16GB DIMMs and four 32GB DIMMs), they must be installed according to these requirements:

Dimm Slots On Motherboard

• Install DIMMs in order of the channels.
• Install DIMMs in identical pairs for each channel.
• Install DIMMs in order of smallest to largest capacity.
• Use only R-DIMMs or only LR-DIMMs.
• Use a supported configuration.

How to install DIMMs of mixed capacities

1. Find out which slots to use for your DIMM configuration.
2. Starting with the lowest capacity pair of DIMMs, install your DIMMs in identical pairs from smallest to largest capacity in order of the memory channels:
   
   • Channel 1: Slots 5 and 8
   • Channel 2: Slots 3 and 10
   • Channel 3: Slots 1 and 12
   • Channel 4: Slots 6 and 7
   • Channel 5: Slots 4 and 9
   • Channel 6: Slots 2 and 11

Not all memory channels are used for every DIMM configuration. For example, an 8 DIMM configuration uses channels 1, 2, 4, and 5.

DIMM Channels

The 12 DIMM slots on the right form 6 total channel pairs as shown above.

So Dimm Slot

Remove or install memory

Learn how to remove the housing of your Mac Pro, remove DIMMs, and install DIMMs.

Remove the housing

1. Shut down your Mac Pro.
2. Wait approximately 5-10 minutes for the computer to cool down.
3. Unplug all cables except the power cord from your computer.
   
4. Touch the metal housing on the outside of the Mac Pro to discharge any static electricity, then unplug the power cord.
   Always discharge static before you touch parts or install components inside your Mac Pro. To avoid generating static, don’t move around the room until you finish installing the memory and slide the enclosure back onto the computer.
5. Flip the top latch up, then twist left to unlock the housing.
   
6. Lift the housing straight up and off of the computer. Carefully set it aside.
   Mac Pro won't turn on when its cover is removed.

Remove DIMMs

Your Mac Pro ships with DIMMs preinstalled in some or all of the DIMM slots. Before you can install memory, you might need to remove some of the DIMMs to match a supported configuration or to meet mixed capacity memory installation requirements.

1. Slide each lock to the left to unlock and open the DIMM covers.
   
   
2. Remove the DIMM covers.
   
3. Locate the DIMM(s) that you want to remove. Each slot is labeled with a number. Push down on the DIMM ejectors on each end of the DIMM, which slightly raises the DIMM out of the slot.
   
4. Use your thumb and index finger from each hand to gently grip the DIMM at each end, then carefully remove the DIMM by pulling the DIMM straight out of the DIMM slot. Don’t twist or force the DIMM out of the socket or damage might occur.
5. Place the removed DIMMs into an electrostatic discharge (ESD) protective bag.

Install DIMMs

1. Locate an empty DIMM slot.
   
2. If possible, use canned air to blow dust out of the DIMM slot. Keep the can vertical.
3. Gently hold the DIMM ends and insert it into the slot. Make sure the DIMM is aligned with the slot before applying any force to insert it. When you insert the DIMM, make sure to follow these guidelines:
   • Don’t force the DIMM. If the DIMM doesn’t insert, verify that the notch and connectors are aligned with the notch in the DIMM slot.
   • Don’t rock the DIMM into the seated position.
   • Don’t bend or twist the DIMM when you insert it.
     
4. Insert the DIMM gently until the bottom edge of the DIMM is touching the gold contacts, then apply more force to fully seat the DIMM. The DIMM ejectors click into place once the DIMM is fully seated.
5. Replace the DIMM covers. Push down on the left side of the covers until they click into place.
   

If you don't replace the DIMM covers, system performance may be affected.

Reinstall the housing

1. Lower the housing over the Mac Pro.
   
2. After the housing is fully seated, twist the top latch right and flip it down to lock it.
   
   Top: Locked position (dots match)
   Bottom: Unlocked position (dots do not match)
3. Connect the power cord, display, and any other peripherals.

Verify your memory

To check the status of your memory, choose Apple menu  > About This Mac, then select the Memory tab.

Dimm Slot Order

If your DIMMs should be configured in different slots to maximize performance, macOS notifies you with recommendations for which slots to use for your currently installed DIMMs.

Other configurations

These DIMM configurations should be used only for troubleshooting issues with your memory:

Learn more

• If you received a replacement part from Apple, follow the steps to send your original part back to Apple.
• Look up Mac Pro (2019) memory specifications.
• Learn about some of the PCIe cards you can install in your Mac Pro.
• Install and replace parts in your Mac Pro.

Your computer’s motherboard sports slots into which memory is plugged. What’s important is how those slots are filled with memory; you can’t just plug memory into the motherboard willy-nilly.

Understand memory slot configuration

There are several ways that a motherboard with four memory banks can host common amounts of memory: 1GB or 2GB. Because DIMMs come in different memory sizes, memory can be set up in a variety of ways inside any PC. (Note: Not all motherboards have 4 slots. Some have more, some less.)

You may have many reasons for choosing different arrangements of memory in a PC. For instance, a single 2GB DIMM an cost ten times as much as a 256MB DIMM. Conversely, a reason for using, say, two 1GB DIMMs rather than four 512MB DIMMs to get 2GB of memory is expandability. Upgrading memory is easier later, when memory slots are available.

• Some PCs have a pairing requirement. The memory slots are organized in pairs, and every pair must have the same DIMM size. For example, you can have 3GB of memory in a PC with four memory banks. That’s two 1GB DIMMs in two slots and two 512MB DIMMs in the other two slots.

• Yes, you may end up throwing away memory to upgrade. If your PC is configured with 1GB of memory using 4 256 MB DIMMs and you want 2GB of memory total, you have to throw away all the 256MB DIMMs and replace them with a combination of DIMMs.

Which Dimm Slots To Use

Get the right DIMM

Not all DIMMs are alike. You must know the memory type, memory chip’s speed, and number of connectors, or pins.

There are several common types. Your computer uses only one memory type, and you must pick a DIMM that matches the type.

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The easiest way to know what kind of memory you need is to use a computer program to determine how much memory is installed in your computer and how best to update. Computer programs can figure out this stuff without the need to open the computer case.

One program that works well for this purpose can be found at www.crucial.com, which also, coincidentally, sells computer memory. Visit the web-site. Use the Crucial system scanner tool; follow the directions on the web page. Eventually, it tells you exactly how to upgrade your PC’s memory.