about rank and organization

[frankmae]

Could somebody explain the difference between rank 1 and rank 2 memory and also how drastically x16 vs x8 organization differs?

 

[Flinx]

This should help with "Ranks"<A HREF="http://www.valueram.com/memoryranks/default.asp" target="_new">http://www.valueram.com/memoryranks/default.asp</A>

and love this

<A HREF="http://www.corsairmicro.com/memory_basics/153707/index.html" target="_new"> http://www.corsairmicro.com/memory_basics/153707/index.html</A>

Just not to play favorites.

The loving are the daring!<P ID="edit"><FONT SIZE=-1><EM>Edited by Flinx on 04/26/05 05:32 PM.</EM></FONT></P>

 

[frankmae]

ah, thank you.
so a rank 2, x8 organization piece of ram shouldn't adversely affect a comp's overall speed if it's slided in along with some rank 1, x16 pieces right?

 

[Rugger]

<A HREF="http://www.corsairmicro.com/memory_basics/153707/index.html" target="_new">Working clicky</A>

__________________________________________________
<font color=red>You're a boil on the arse of progress - don't make me squeeze you!</font color=red>

 

[BrentUnitedMem]

By definition RANK refers to the module side, whereas the BANK refers to the logical partition of chips on the PCB.

RANK0 = side 1
RANK1 = side 2

It is incorrect to use the RANK to describe the logical partation of chips.

x8 and x16 actually has nothing to do with the number of chips. x8 and x16 is a property of the module design. In many cases x8 and x16 are mutually exclusive with the motherboard chipset. Many older SDRAM motherboards can accept either x8 or x16, but not both.

For x8 there exists both 8 and 16 chips configurations:
512MB (32Mx8) 16 chip
512MB (64Mx8) 8 chip

For x16 configuration you can even have 4 chips:
256MB (32Mx16) 4 chip
Samsung PT# <A HREF="http://www.samsung.com/Products/Semiconductor/common/partnumbersearch.aspx?partnum=M378T3354BZ0&cd1=&x=11&y=7" target="_new">M378T3354BZ0-CD5</A>

And it is possible to have 2 banks per rank.

<font color=green>*****
"Memory with lifetime warranty? So, whose lifetime is that?"
<A HREF="http://www.brentcrowley.com/" target="_new">homepage</A>
<font color=red>AIM BrentUnitedMem

 

[Rugger]

I learn a little more everyday - that was a great, brief description!

I've been trying to get a better hold on this concept and recently wrote AMD about the Winchester core downclocking issue. I got this response from AMD Tech Svc Ctr:

The limitation of the memory controller is based on the ranks of the memory. Any DIMM setup over 4 ranks is recommended to run at 333MHz by AMD. 4 sticks of memory can be used with 4 sticks of single rank memory. However, only 2 sticks of memory that are dual rank is recommended to run 400MHz.

Questions:
1. Is a side of a memory module only considered a rank if it has memory chips on it? That's how I interpret/read your response and the info I got from AMD.
2. Do the most common memory configs have one logical bank to each physical rank? Is that the most efficient config or is it more efficient to split the banks onto different ranks?
3. What's the easiest way to determine if a memory module is SS or DS?

__________________________________________________
<font color=red>You're a boil on the arse of progress - don't make me squeeze you!</font color=red>

 

[BrentUnitedMem]

1. Is a side of a memory module only considered a rank if it has memory chips on it? That's how I interpret/read your response and the info I got from AMD.

Single rank modules have chips on one side. Many PCBs do not support the soldering of chips on two sides. Thus the PCB can be designed differently with this in mind.

2. Do the most common memory configs have one logical bank to each physical rank? Is that the most efficient config or is it more efficient to split the banks onto different ranks?

Normally 1 rank = 1 bank. So that is why people often confuse RANK/BANK. The wiring of most PCBs is designed for 8 chips per rank. And in this case, the 8 chip rank equals 1 BANK.

It is common for chips to be x8 or x16 bits wide, either 32M or 64M in depth. The logical partition for any binary system follows base 2 values. And so a PCB can have 1, 2, 4, 8, or 16 slots for chips etc...

8 chip-slots seems to be a good number for the PCB. There are some older PCBs with slots for 16 chips per RANK. And notebook PCBs are designed for 4 chip-slots per RANK.

Of course memory chips can be made smaller, so can the PCBs. And certainly they are for some technologies like cell phones, PDA, hand held electronics etc.

The trouble is, once a technology gains momentum, that momentum dictates future technologies as well, because it is too expensive to make changes in the middle (take a look at how expensive DDR2 is for example). For DDR memory modules, they are still taking form factors that were used in early SDRAM systems; because the standards are in place and easy to follow.

If your design calls for a 128-bit data bus, where the module has to be single sided, then you will end up with 1 rank, 2 banks, where each bank is organized into a single 64-bit data bus. This is not common, but it can be done.

For dual-channel configurations, the channels are divided necessarily by BANK, but not necessarily by RANK.
note:
It is possible to run a single-sided module in dual-channel if the RANK is divided into 2 BANKs. You just need a 128-bit channel per rank, 64-bit channel per bank. And also you need a chipset that will recogize the logical partition of BANKS.
example:
***PCB DESIGN***
-9 sockets total. No soldering on the opposite side
-BANK0 = slots 0 - 3
-BANK1 = slots 5 - 8
-slot4 is for the ECC chip.

***CHIP CONFIGURATION***
-8 chips total: (64Mx16) each

***BANK CONFIGURATION***
-4 chips per bank.
- 64M depth
- x16 data bus
-COMBINED = x16 x 8 chips = 64-bit data bus

***MODULE SPECIFICATION***
-Two banks each 64-bits wide
-Total memory size: 2GB.

Is this module configuration being mas-produced: no
Is it possible to build: yes

Theoretically, the configuration that offers the best performance would be a very wide memory bus with a shallow memory delth. 1Mx32 for example would have a high performance value. But since 1Mx32 has a particularly high real-estate value, it is not a cost effective design. And so the standards are set for cost/performance in mind.

The analogy would be between:
1. A very tall building with many floors
vs.
2. A large area one story building with many rooms.
Where the performance is a measure of how fast people can get to their desk. Of course it's quicker in the one-story building, but as you know it's much cheaper to build up. Same is true for electronic components.

3. What's the easiest way to determine if a memory module is SS or DS?

Look at chips on the PCB. If there are chips on both sides of the PCB you can be certain it's DS. Chips on one side is a SS module.

<font color=green>*****
"Memory with lifetime warranty? So, whose lifetime is that?"
<A HREF="http://www.brentcrowley.com/" target="_new">homepage</A>
<font color=red>AIM BrentUnitedMem

 

[Rugger]

Thanks! Lots of great info that I will continue to digest.

Look at chips on the PCB. If there are chips on both sides of the PCB you can be certain it's DS. Chips on one side is a SS module.

:lol: I do know that much, but what if you don't have the module and need to determine SS/DS from the companys product description?

__________________________________________________
<font color=red>You're a boil on the arse of progress - don't make me squeeze you!</font color=red>

 

[BrentUnitedMem]

The product descriptions are usually vague and don't tell you if they are SS or DS.

However, if you know the module's component configuration you can find the number of sides given the size of memory.

example of 512MB SS & DS:
1. 512MB,64Mx64 (32Mx8 chip configuration)
2. 512MB,64Mx64 (64Mx8 chip configuration)

Both are popular configurations. And both the module configurations are 64Mx64.

In fact, all 512MB modules are organized as 64Mx64. =(64x64)/8bitsPerByte = 512MB

You'll have to distinguish the RANKS by chip configuration.

QUICK EQUATION:
(MEMORY SIZE)/(CHIP CONFIGURATION) = # RANKS

example above:
1. 512/(32x8) = 2 ranks
2. 512/(64x8) = 1 rank

The reason this works is because you also have to multiply by 8 chips/rank and divide by 8 bits/Byte, which leaves you with ranks as the final unit.

<font color=green>*****
"Memory with lifetime warranty? So, whose lifetime is that?"
<A HREF="http://www.brentcrowley.com/" target="_new">homepage</A>
<font color=red>AIM BrentUnitedMem

 

[Rugger]

Have to add that little equation to my list of "neat little things to know"

__________________________________________________
<font color=red>You're a boil on the arse of progress - don't make me squeeze you!</font color=red>

 

[cbocchi]

hello everybody
what i'd like to know is: would the differences here explained create a compatibility problem? i have a hp compaq nx9020, with 512MB RAM, and i want to upgrade it to 1GB... and i have found two different 512 MB memories, which both fit perfectly the specs, but are different:
the first:
1x 512MB, 2 Ranks, 32Mx16 double-sided (8 Chips) 64Mx64

the second:
1 x 512MB (=512MB) 2 Ranks, 128Mx8 double-sided (16 Chips) 256Mx64

this is what's written in each one's specs

i don't know what's on my notebook, but even so, is there a "wrong" type in my case? could the difference matter, or it's just an internal efficiency issue?

thank you in advance
carlo