Random-access memory, or RAM, is an essential component in all devices, from PCs to smartphones to game consoles. Without RAM, doing just about anything on any system would be much, much slower. There is a sequence given in the ram slots as 1,2,3,4 if your mobo has 4 ram slots. Read your mobos instruction manual in ram section you will be able to see which slot is 1,2,3&4 respectively. If you closely see your mobos ram holders on top or at the bottom of the mobo there should be numbering there as well. Hope this helps. The same memory size and type needs to be installed into the matched DIMM slots for channels A, B and C. Usually the memory slots are color coded to make it easier to understand. Buy memory upgrades HP recommends purchasing memory directly from HP, an authorized HP dealer, or from a reputable computer parts supplier such as Crucial. Memory slots on system boards that support ddr3 are keyed to onlY accept ddr3 modules. Ddr2 will not fit into a ddr3 slot and ddr3 will not fit into a ddr2 slot. Memory configuration DDR memory can run in dual-channel mode, which allows the system to have twice the memory bandwidth using the same memory technology.

If you’ve ever taken a look at a product page for sticks of RAM, or at the specifications for a CPU or motherboard, you’ve probably seen “memory channels” mentioned.

For many beginners, this sparks questions like, “What’s the deal? Does dual-channel mean I can only use two sticks? What do multiple channels do that one channel doesn’t? Can I use quad-channel RAM on a dual-channel motherboard?”

The answers to those questions and more can be found below, so read on!

RAM Channels: The What

Simply put, memory channels are the links between your RAM and your CPU through which data moves between the two. The RAM is the computer’s short-term memory, and the CPU is the main processor that does stuff with the information in the memory; the RAM channels are how that information moves back and forth.

To be clear, these memory channels are actual wires that exist on/in the motherboard. Though RAM kits may call their arrangements “channels,” the actual number of channels and the number of RAM sticks are independent of each other; any mention of channel count on a RAM kit’s product/specification page is just an informal, technically-incorrect way of referring to how many sticks of RAM there are in the kit. In addition, the number of RAM slots on a motherboard is independent of the number of memory channels. A channel needs only one stick to be used, and any more than that doesn’t necessarily stop things from working.

Most modern motherboards have two to four memory channels. On the AMD side, every AM4 socket motherboard has two memory channels, and every TR4 socket motherboard has four channels. On Intel’s side, every LGA 1151 motherboard has two memory channels, and every LGA 2066 motherboard has four memory channels. This means that, on our main chart, every configuration up to and including the “Enthusiast” tier has two memory channels. The “Extremist” and “Monstrous” tiers are the only rows which have four memory channels.

In addition, CPUs also support a certain maximum amount of memory channels. You don’t really need to worry about this, as every CPU will handle the amount of memory channels available on their supporting motherboards. There are only two notable exceptions: Intel’s i5-7640X and i7-7740X, which are both LGA 2066 CPUs, and very odd purchases anyway.

RAM Channels: The How

To explain what multiple channels do, let’s try an analogy.

Imagine a manufacturer of products:

Let’s say this manufacturer (your CPU), with potentially many factories (cores) in need of materials, makes orders for materials from only one supplier (memory channel). Even if the supplier has a whole lot of materials (capacity / stored data), and may run multiple warehouses (RAM sticks) of their own, it has a limited capacity for making shipments, and so can’t handle multiple shipments to the manufacturer at once. There may be multiple shipments ready to go, but they can’t actually start shipping until the current shipment is done.

A single-channel supplier warehouse attempting to serve a quad-factory manufacturer with one truck

The problem is, this manufacturer can often use materials faster than their supplier can ship them, and the delay from waiting on the supplier’s logistics system for consecutive orders can slow things down. Especially when this manufacturer’s factories are being heavily loaded with orders of their own from vendors and customers (your other components) while relying on materials orders, the supplier can pose a problem.

So, the manufacturer contracts with a second supplier in addition to the first. Now, the manufacturer does something efficient: They alternate orders between the two suppliers. This way, the manufacturer can have two simultaneous shipments coming their way, and they suddenly find that waiting on consecutive orders to be shipped is now significantly less of an issue, since their effective capacity for getting shipments has been doubled. This same idea can extend even further across more suppliers.

Really, how much the number of suppliers the manufacturer uses actually matters all depends on: how quickly materials are being used, how many factories they have (since each might come in need of materials at any given moment), how busy the manufacturer or specific factories are, and how quickly the suppliers themselves can send shipments to the manufacturer. Most of the time, this isn’t a big deal, but when things line up well or poorly, the number of suppliers (i.e. memory channels) can make a notable difference.

DDR5: Breaking the Status Quo?

If you’ve been keeping up-to-date on DDR5 memory, you may have seen mention of DDR5 RAM sticks (yes, each stick itself) having two memory channels. And what they’re saying is true, from a certain point-of-view. From my understanding, these “channels” aren’t like the memory channels described above, but still apply a similar (though not quite the same) concept on the stick-by-stick level.

Micron, one of the only three manufacturers of memory chips, describes this development as “essentially turning an 8-channel system as we know it today into a 16-channel system.” So what is going on here?

From what I can tell, it seems that each stick can work with two separate bunches of data, though it can’t be moving data from both bunches across the actual (physical, on-the-motherboard) channels at the same time. For example, a stick could be receiving data on one half, and be preparing to send data on the other half in the meantime. This is still a significant improvement in design over previous iterations of RAM like DDR4, though not quite as dramatic as it sounds at first. Reality is often disappointing; we’ll just have to wait and see if this turns out to actually be the case.

Conclusion

Let’s make one thing clear: to use multiple channels, you need multiple RAM sticks. Those RAM sticks should be installed so that you have at least one stick in each channel. The best thing you can do here is place your RAM sticks according to what your motherboard manual says. Though the slots are usually color-coded, this isn’t always the case, so check that motherboard manual.

For many country versions of our main chart, the linked 8GB options (and every 4GB option) are single sticks; so, without another stick of RAM, only one memory channel will be used. This is not the case everywhere, though, and all 8GB kits in the US version of the chart have two sticks for dual-channel. The 16GB options are dominated by two-stick 16GB kits, though some countries still have one-stick options linked. However, it’s up to you to choose how many sticks will work best for your system and your program tasks—there’s no need to get the exact kits we link.

Choose your iMac model

If you're not sure which iMac you have, you can identify your iMac and then select it from the list below.

27-inch

24-inch

21.5-inch

• iMac (Retina 4K, 21.5-inch, 2019)*
• iMac (Retina 4K, 21.5-inch, 2017)*
• iMac (21.5-inch, 2017)*
• iMac (21.5 inch, Mid 2014)*
• iMac (21.5-inch, Late 2013)*
• iMac (21.5-inch, Late 2012)*

20-inch

17-inch

* Memory is not removable by users on iMac (21.5-inch, Late 2012), iMac (21.5-inch, Late 2013), iMac (21.5-inch, Mid 2014), iMac (21.5-inch, 2017), iMac (Retina 4K, 21.5-inch, 2017), and iMac (Retina 4K, 21.5-inch, 2019). If the memory in one of these computers needs repair service, contact an Apple Retail Store or Apple Authorized Service Provider. If you’d like to upgrade the memory in one of these models, an Apple Authorized Service Provider can help. Before you schedule an appointment, confirm that the specific Apple Authorized Service Provider offers memory upgrade services.

Memory in iMac (21.5-inch, Late 2015), and iMac (Retina 4K, 21.5-inch, Late 2015) is not upgradeable.

iMac (Retina 5K, 27-inch, 2020)

Get memory specifications for iMac (Retina 5K, 27-inch, 2020), then learn how to install memory in this model.

Memory specifications

This iMac model features Synchronous Dynamic Random-Access Memory (SDRAM) slots on the rear of the computer near the vents with these memory specifications:

For optimal memory performance, DIMMs should be the same capacity, speed, and vendor. Use Small Outline Dual Inline Memory Modules (SO-DIMM) that meet all of these criteria:

• PC4-21333
• Unbuffered
• Nonparity
• 260-pin
• 2666MHz DDR4 SDRAM

If you have mixed capacity DIMMs, see the install memory section for installation recommendations.

iMac (Retina 5K, 27-inch, 2019)

Get memory specifications for iMac (Retina 5K, 27-inch, 2019), then learn how to install memory in this model.

Memory specifications

This iMac model features Synchronous Dynamic Random-Access Memory (SDRAM) slots on the rear of the computer near the vents with these memory specifications:

Use Small Outline Dual Inline Memory Modules (SO-DIMM) that meet all of these criteria:

• PC4-21333
• Unbuffered
• Nonparity
• 260-pin
• 2666MHz DDR4 SDRAM

iMac (Retina 5K, 27-inch, 2017)

Get memory specifications for iMac (Retina 5K, 27-inch, 2017), then learn how to install memory in this model.

Memory specifications

This iMac model features Synchronous Dynamic Random-Access Memory (SDRAM) slots on the rear of the computer near the vents with these memory specifications:

Use Small Outline Dual Inline Memory Modules (SO-DIMM) that meet all of these criteria:

• PC4-2400 (19200)
• Unbuffered
• Nonparity
• 260-pin
• 2400MHz DDR4 SDRAM

iMac (Retina 5K, 27-inch, Late 2015)

Get memory specifications for iMac (Retina 5K, 27-inch, Late 2015), then learn how to install memory in this model.

Memory specifications

This iMac model features Synchronous Dynamic Random-Access Memory (SDRAM) slots on the rear of the computer near the vents with these memory specifications:

Use Small Outline Dual Inline Memory Modules (SO-DIMM) that meet all of these criteria:

• PC3-14900
• Unbuffered
• Nonparity
• 204-pin
• 1867MHz DDR3 SDRAM

For these 27-inch models

Get memory specifications for the following iMac models, then learn how to install memory in them:

• iMac (Retina 5K, 27-inch, Mid 2015)
• iMac (Retina 5K, 27-inch, Late 2014)
• iMac (27-inch, Late 2013)
• iMac (27-inch, Late 2012)

Memory specifications

These iMac models feature Synchronous Dynamic Random-Access Memory (SDRAM) slots on the rear of the computer near the vents with these memory specifications:

Use Small Outline Dual Inline Memory Modules (SO-DIMM) that meet all of these criteria:

• PC3-12800
• Unbuffered
• Nonparity
• 204-pin
• 1600MHz DDR3 SDRAM

Installing memory

The internal components of your iMac can be warm. If you've been using your iMac, wait ten minutes after shutting it down to let the internal components cool.

After you shut down your iMac and give it time to cool, follow these steps:

1. Disconnect the power cord and all other cables from your computer.
2. Place a soft, clean towel or cloth on the desk or other flat surface to prevent scratching the display.
3. Hold the sides of the computer and slowly lay the computer face-down on the towel or cloth.
4. Open the memory compartment door by pressing the small grey button located just above the AC power port:
5. The memory compartment door will open as the button is pushed in. Remove the compartment door and set it aside:
6. A diagram on the underside of the compartment door shows the memory cage levers and the orientation of the DIMM. Locate the two levers on the right and left sides of the memory cage. Push the two levers outward to release the memory cage:
7. After the memory cage is released, pull the memory cage levers toward you, allowing access to each DIMM slot.
8. Remove a DIMM by pulling the module straight up and out. Note the location of the notch on the bottom of the DIMM. When reinstalling DIMMs, the notch must be oriented correctly or the DIMM won't fully insert:
9. Replace or install a DIMM by setting it down into the slot and pressing firmly until you feel the DIMM click into the slot. When you insert a DIMM, make sure to align the notch on the DIMM to the DIMM slot. Find your model below for specific installation instructions and notch locations:
   • iMac (Retina 5K, 27-inch, 2020) DIMMs have a notch on the bottom, slightly left of the middle. If your DIMMs are mixed in capacity, minimize the capacity difference between Channel A (slots 1 and 2) and Channel B (slots 3 and 4) when possible.
     
   • iMac (Retina 5K, 27-inch, 2019) DIMMs have a notch on the bottom, slightly left of the middle:
   • iMac (27-inch, Late 2012) and iMac (Retina 5K, 27-inch, 2017) DIMMs have a notch on the bottom left:
     
   • iMac (27-inch, Late 2013) and iMac (Retina 5K, 27-inch, Late 2014, Mid 2015, and Late 2015) DIMMs have a notch on the bottom right:
     
10. After you install all of your DIMMs, push both memory cage levers back into the housing until they lock into place:
    
11. Replace the memory compartment door. You don't need to press the compartment door release button when replacing the compartment door.
12. Place the computer in its upright position. Reconnect the power cord and all other cables to the computer, then start up the computer.
    

Your iMac performs a memory initialization procedure when you first turn it on after upgrading memory or rearranging DIMMs. This process can take 30 seconds or more, and the display of your iMac remains dark until it's finished. Make sure to let the memory initialization complete.

For these 27-inch and 21.5-inch models

Get memory specifications for the following iMac models, then learn how to install memory in them:

• iMac (27-inch, Mid 2011)
• iMac (21.5-inch, Mid 2011)
• iMac (27-inch, Mid 2010)
• iMac (21.5-inch, Mid 2010)
• iMac (27-inch, Late 2009)
• iMac (21.5-inch, Late 2009)

Memory specifications

Use Small Outline Dual Inline Memory Modules (SO-DIMM) that meet all of these criteria:

i5 and i7 Quad Core iMac computers come with both top memory slots populated. These computers will not start up if only a single DIMM is installed in any bottom slot; these computers should operate normally with a single DIMM installed in any top slot.

Core Duo iMac computers should operate normally with a single DIMM installed in any slot, top or bottom. ('Top' and 'bottom' slots refer to the orientation of the slots in the pictures below. 'Top' refers to the slots closest to the display; 'bottom' refers to the slots closest to the stand.)

Installing memory

The internal components of your iMac can be warm. If you've been using your iMac, wait ten minutes after shutting it down to let the internal components cool.

After you shut down your iMac and give it time to cool, follow these steps:

1. Disconnect the power cord and all other cables from your computer.
2. Place a soft, clean towel or cloth on the desk or other flat surface to prevent scratching the display.
3. Hold the sides of the computer and slowly lay the computer face-down on the towel or cloth.
4. Using a Philips screwdriver, remove the RAM access door in the bottom of your computer:
   
5. Remove the access door and set it aside.
6. Untuck the tab in the memory compartment. If you're replacing a memory module, gently pull the tab to eject any installed memory module:
   
7. Insert your new or replacement SO-DIMM into the empty slot, noting the orientation of the keyway of the SO-DIMM as shown below.
8. After you insert it, press the DIMM up into the slot. There should be a slight click when you seat the memory correctly:
   
9. Tuck the tabs above the memory DIMMs, and reinstall the memory access door:
   
10. Place the computer in its upright position. Reconnect the power cord and all other cables to the computer, then start up the computer.

For these 24-inch and 20-inch models

Get memory specifications for the following iMac models, then learn how to install memory in them:

• iMac (24-inch, Early 2009)
• iMac (20-inch, Early 2009)
• iMac (24-inch, Early 2008)
• iMac (20-inch, Early 2008)
• iMac (24-inch Mid 2007)
• iMac (20-inch, Mid 2007)

Memory specifications

These iMac computers have two side-by-side Synchronous Dynamic Random-Access Memory (SDRAM) slots in the bottom of the computer.

The maximum amount of random-access memory (RAM) you can install in each computer is:

You can use a 1GB or 2GB RAM module in each slot for iMac (Mid 2007) and iMac (Early 2008). Use 1GB, 2GB, or 4GB modules in each slot for the iMac (Early 2009).

Use Small Outline Dual Inline Memory Modules (SO-DIMM) that meet all of these criteria:

DIMMs with any of the following features aren't supported:

• Registers or buffers
• PLLs
• Error-correcting code (ECC)
• Parity
• Extended data out (EDO) RAM

Installing memory

The internal components of your iMac can be warm. If you've been using your iMac, wait ten minutes after shutting it down to let the internal components cool.

After your iMac cools down, follow these steps:

1. Disconnect the power cord and all other cables from your computer.
2. Place a soft, clean towel or cloth on the desk or other flat surface to prevent scratching the display.
3. Hold the sides of the computer and slowly lay the computer face-down on the towel or cloth.
4. Using a Philips screwdriver, remove the RAM access door in the bottom of the computer:
   
5. Remove the access door and set it aside.
6. Untuck the tab in the memory compartment. If you're replacing a memory module, untuck the tab and pull it to eject any installed memory module:
   
7. Insert your new or replacement RAM SO-DIMM into the empty slot, noting the orientation of the keyway of the SO-DIMM as shown above.
8. After you insert it, press the DIMM up into the slot. There should be a slight click when you seat the memory correctly.
9. Tuck the tabs above the memory DIMMs, and reinstall the memory access door:
   
10. Place the computer in its upright position. Reconnect the power cord and all other cables to the computer, then start up the computer.

For these 20-inch and 17-inch models

Get memory specifications for the following iMac models, then learn how to install memory in them:

• iMac (20-inch Late 2006)
• iMac (17-inch, Late 2006 CD)
• iMac (17-inch, Late 2006)
• iMac (17-inch, Mid 2006)
• iMac (20-inch, Early 2006)
• iMac (17-inch, Early 2006)

Memory specifications

For best performance, fill both memory slots, installing an equal memory module in each slot.
*iMac (Late 2006) uses a maximum of 3 GB of RAM.

Installing memory in the bottom slot

The internal components of your iMac can be warm. If you've been using your iMac, wait ten minutes after shutting it down to let the internal components cool.

What Slot Does Ram Go Into Ketosis

After you shut down your iMac and give it time to cool, follow these steps:

What Slot Does Ram Go Into The Sun

1. Disconnect the power cord and all other cables from your computer.
2. Place a soft, clean towel or cloth on the desk or other flat surface to prevent scratching the display.
3. Hold the sides of the computer and slowly lay the computer face-down on the towel or cloth.
4. Using a Phillips screwdriver, remove the RAM access door on the bottom of the iMac and set it aside:
   
5. Move the DIMM ejector clips to their fully open position:
   
6. Insert your RAM SO-DIMM into the bottom slot, keeping in mind the orientation of the keyed SO-DIMM:
   
7. After you insert it, press the DIMM up into the slot with your thumbs. Don't use the DIMM ejector clips to push in the DIMM, as this might damage the SDRAM DIMM. There should be a slight click when you seat the memory fully.
8. Close the ejector clips:
   
9. Reinstall the memory access door:
   
10. Place the computer in its upright position. Reconnect the power cord and all other cables to the computer, then start up the computer.

Replacing memory in the top slot

After you shut down your iMac and give it time to cool, follow these steps:

1. Disconnect the power cord and all other cables from your computer.
2. Place a soft, clean towel or cloth on the desk or other flat surface to prevent scratching the display.
3. Hold the sides of the computer and slowly lay the computer face-down on the towel or cloth.
4. Using a Phillips screwdriver, remove the RAM access door on the bottom of the iMac and set it aside:
   
5. Pull the two levers on each side of the memory compartment to eject the memory module that's already installed:
   
6. Remove the memory module from your iMac as shown below:
   
7. Insert your RAM SO-DIMM into the top slot, noting the orientation of the keyed SO-DIMM:
   
8. After you insert it, press the DIMM up into the slot with your thumbs. Don't use the DIMM ejector clips to push in the DIMM, as this might damage the SDRAM DIMM. There should be a slight click when you seat the memory fully.
9. Close the ejector clips:
   
10. Reinstall the memory access door:
    
11. Place the computer in its upright position. Reconnect the power cord and all other cables to the computer, then start up the computer.

If your iMac makes a tone after you install memory

What Slot Does Ram Go Into

iMac models introduced before 2017 might make a warning sound when you start up after installing or replacing memory:

• One tone, repeating every five seconds signals that no RAM is installed.
• Three successive tones, then a five-second pause (repeating) signals that RAM doesn't pass a data integrity check.

If you hear these tones, confirm that the memory you installed is compatible with your iMac and that it's installed correctly by reseating the memory. If your Mac continues to make the tone, contact Apple Support.

What Slot Does Ram Go In

Confirm that your iMac recognizes its new memory

After you install memory, you should confirm that your iMac recognizes the new RAM by choosing Apple () menu > About This Mac.

The window that appears lists the total memory, including the amount of memory that originally came with the computer plus the newly added memory. If all the memory in the iMac has been replaced, it lists the new total of all installed RAM.

What Slot Does Ram Go Into Computer

For detailed information about the memory installed in your iMac, click System Report. Then choose Memory under the Hardware section in the left side of System Information.

If your computer doesn't recognize the memory or doesn't start up correctly, confirm that the RAM you installed is compatible with your iMac and that it's installed correctly by reseating the memory. If you continue to have issues with the memory in your iMac, contact Apple Support.