RAM question

[Riddler356]

I was wondering if anyone could lead me to a good source to explain about the PC3 thing I keep seeing with the ram, like "32GB (4x8GB) DDR3 1866 MHZ (PC3 15000)" or "32GB (4x8GB) DDR3 1600 MHZ (PC3 12800)" I am thinking of upgrading my RAM but I want to know more about that PC3 thing, when I tried upgrading my laptop it was not compatible and had to return the RAM, I will be ordering online and do not want to have to return. I know I can just look up if it is compatible or not, which I will, but I just want to know what the PC3 thing means, and how compatibility works with it.

 

[acidydragon]

It refers to the speed, let me try to find something.

(It doesn't relate to compatibility.)

 

This explains all things RAM. (A long read, but informative)

http://www.hardwaresecrets.com/article/Understanding-RAM-Timings/26

[Ryan Leech]

PC3 means DDR3

[Riddler356]

I am posting this in the appropriate location which i just found

[TheNinjaNextDor]

"Lets look at a RAM module marketed as PC3 6400:

This is about the slowest RAM you can find but I chose it for simplicity purposes.

Now, lets define something real quick. Clock Speed: the operating speed of a computer or its microprocessor, defined as the rate at which it performs internal operations and expressed in cycles per second (megahertz).

Lets define one more thing: Double Data Rate(DDR): It is an advanced version of SDRAM, a type of computer memory. DDR-SDRAM, sometimes called "SDRAM II," can transfer data twice as fast as regular SDRAM chips. This is because DDR memory can send and receive signals twice per clock cycle.

With that out of the way, lets start at PC1-#### and work our way up to PC3-#### and the example up there to break down how these numbers work.

DDR
This nice, slow RAM has a 100MHz Memory Clock speed, meaning it can process 200 Million operations per second. Remember, since we're talking about DDR-SDRAM, the data rate is doubled (essentially 100 MHz * 2). Though it has a clock speed of 100 MHz, for marketing purposes, this will be marketed at 200 MHz (or DDR-200), it's effective clock based on its "Double Data Rate".

Now, the Module Name (PC-####) is based on transfer rate and is actually the PC sped rating. You're going to multiply the effective clock speed by 8, the width (in Bytes) of all DDR SDRAM sticks. In the example above, you'd be taking the 200 * 8 = 1600. Slap a PC in front of that and you have PC1600.

Why is 8 the multiplyer you ask? Modern DRAM is 64 "bits" wide. Bit's are usually convered into Bytes and since there are 8 bits in a Byte, divide 64 by 8 and you get 8. The 64-bit width converts into 8-bytes (your multiplier). 

DDR 2

When we're talking about DDR 2, it's twice as fast as DDR as it clock doubles the I/O circuits on the chips, speeding up the input/output and adding special buffers. 

So that same 100 MHz clock speed translates into (100 MHz * 2) 2 = 400 MHz (or DDR2-400). Multiply that by 8 and (and slap a PC2 in front) you have PC2-3200.

DDR3

DDR3 doubles the buffer of DDR2 from 4-bits to 8-buts, giving it a bandwidth boost. There are also some other features thrown in there that I wont get into.

So that same 100 MHz clock speed translates into ((100 MHz * 2) 2)2 = 800 MHz (or DDR3-800). Multiply that by 8 and (and slap a PC3 in front) you have PC3-6400.

That should give you a basic understanding of how these numbers work. The bottom line doesn't seem to matter to me as I'm always looking for the fastest my board supports (and I can afford) so the "how it works" matters little to me."

 

I searched for it

[Riddler356]

Its posted in the appropriate area sorry for posting it in the wrong place.

[JohnnyGrey]

I believe the PC3 and the numbers after it are just another way of stating the speed. the DDR3 and 1600mhz are what's important.

 

"The number following each is usually the effective clock rate:

e.g. DDR2-800 has a raw memory clock rate of 400 MHz

that transmits data twice per tick -- hence the "double data rate".

 

 

A second convention has developed, which simply multiplies

that effective clock rate by 8 bytes per tick:

thus, 800 MHz x 8 bytes per tick = 6,400 Megabytes per second."

 

Both are a different way of saying the same thing. 1600mhz will always equate to PC3-12,800.

[RWT98]

I am posting this in the appropriate location which i just found

@MG2R he can move it to the right location 

[Glenwing]

It's an alternate way of describing the type and speed of RAM.  DDR3 1600 can also be written as PC3 12800, or DDR3 1866 as PC3 15000, etc.

[Riddler356]

@MG2R he can move it to the right location 

Well a thanks to @MG2R for doing that.

[MG2R]

Well a thanks to @MG2R for doing that.

I think that Glenwing did it this time

 

If you need something moved, you can simply report it and asking for a move in the report

[Riddler356]

I think that Glenwing did it this time

 

If you need something moved, you can simply report it and asking for a move in the report

Thank you for the info, and I guess whoever moved it thank you.