2019 iMac RAM confusion

[jonatious]

So like everyone already ordered RAM for their upcoming iMac, I also did buy the following one
https://www.amazon.com/gp/product/B06XRBS4Y5

Apple just updated their spec sheet for RAM swap for 2019 iMac.
https://support.apple.com/en-us/HT201191#27inch2019
which says the compatible version to be PC4-21333.

The main problem is there are no 21333 RAMs on Amazon/MacSales and the only version of 2666MHz is PC4-21300. So the question is whats the difference and is PC4-21300 compatible with the new iMac?

 

[jonatious]

Any insight from anyone?

I am new here, is there any Bump rule here?

 

[adamjackson]

That's from Apple's Site on 2019 Compatability:

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

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

----

To understand what the difference is from PC4-21333 and PC4-21300, this is a good place to start - https://www.hardwaresecrets.com/understanding-ram-timings/

via Wikipedia:

DDR4-xxxx and PC4-xxxx both denote per-bit data transfer rate, the former for DDR chips and the latter for modules (assembled DIMMs). It can be seen that the DDR4 module names are done differently than prior generations (e.g. DDR3), by using the per-bit data rate rather than the overall byte transfer rate (e.g. PC4-1866 vs. PC3-14900, both representing the same peak transfer rate). Module peak transfer rate is calculated by taking transfers per second and multiplying by eight. This is because DDR4 memory modules transfer data on a bus that is 64 data bits wide, and since a byte comprises 8 bits, this equates to 8 bytes of data per transfer.​

that figure is peak transfer. Lower integer wins so this means the iMac 27" can support up to 21333 transfer but if you put in a 21300, the iMac will just accept this lower figure. In reality, you won't notice the difference.

Someone please correct me if I'm wrong.

 

[curmudgeonette]

The main problem is there are no 21333 RAMs on Amazon/MacSales and the only version of 2666MHz is PC4-21300. So the question is whats the difference and is PC4-21300 compatible with the new iMac?

PC4-21333 and PC4-21300 are exactly the same thing. Some companies have simply chosen to round the value to three digits, while others took it out to five digits. (The "exact" number is 21333 and one third.)

A similar issue happened some years back with 1066 and 1866 MHz memory. The "exact" value there is xx66 and two thirds which some companies rounded up to xx67 while other truncated down to xx66.

 

[jonatious]

PC4-21333 and PC4-21300 are exactly the same thing. Some companies have simply chosen to round the value to three digits, while others took it out to five digits. (The "exact" number is 21333 and one third.)

A similar issue happened some years back with 1066 and 1866 MHz memory. The "exact" value there is xx66 and two thirds which some companies rounded up to xx67 while other truncated down to xx66.

Wow thats so much of a relief. Thanks bud

 

[CoastalOR]

I am new here, is there any Bump rule here?

Yes there is a rule against it, but it does not seem to be enforced.
https://macrumors.zendesk.com/hc/en-us/articles/201265337-Forum-Rules

 

[jonatious]

Yes there is a rule against it, but it does not seem to be enforced.
https://macrumors.zendesk.com/hc/en-us/articles/201265337-Forum-Rules

Thanks for the link. So if there was no reply to my thread and it goes down the list, I should just forget the question or recreate the thread? I believe duplicate threads are worse than bumps. So what should a legitimate user do in that case?

 

[CoastalOR]

Thanks for the link. So if there was no reply to my thread and it goes down the list, I should just forget the question or recreate the thread? I believe duplicate threads are worse than bumps. So what should a legitimate user do in that case?

I can't answer your forum rule questions since I did not make the forum rules. You asked about the rules so I provided the rules list for you.

One way to move your thread up is to provide some additional information. Let's be realistic, it wasn't even 24 hrs before bumping your post and it was still on the 1st page of the iMac forum. Sometimes patience is required because people that read your thread may not know the answer and it takes the right people to login that know your subject to provide a helpful response.

You could ask your bumping question about forum rule/policy on this sub forum if you like, maybe they have some insight:
https://forums.macrumors.com/forums/site-and-forum-feedback.66/

 

[jonatious]

I can't answer your forum rule questions since I did not make the forum rules. You asked about the rules so I provided the rules list for you.

One way to move your thread up is to provide some additional information. Let's be realistic, it wasn't even 24 hrs before bumping your post and it was still on the 1st page of the iMac forum. Sometimes patience is required because people that read your thread may not know the answer and it takes the right people to login that know your subject to provide a helpful response.

You could ask your bumping question about forum rule/policy on this sub forum if you like, maybe they have some insight:
https://forums.macrumors.com/forums/site-and-forum-feedback.66/

No offense was intended sir, I was just asking how it is generally done, since you are an old member

 

[Max Lucas]

Thanks for this question and the answers!! I was just about to ask this very same question.