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  What does the PCxxxx mean when buying RAM 
 
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Nathan Daniels May 15, 2007, 06:47am EDT Reply - Quote - Report Abuse
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Is it some strange measurment of speed or is it a form factor? If it is speed, can any computer take any number?


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-Patton
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Shadow_Ops_Airman1 May 15, 2007, 07:00am EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM

AMD Athlon XP-M 2500+ (133x14= 1867MHz) (209x11= 2299MHz)
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Dublin_Gunner May 15, 2007, 07:32am EDT Reply - Quote - Report Abuse
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Edited: May 15, 2007, 07:38am EDT

 
>> Re: What does the PCxxxx mean when buying RAM
Theoretical bandwidth limit.

i.e. PC3200 runs at 400Mhz (DDR) or 200Mhz real.

200Mhz*(64[bits transferred per clock] / 8[bits per byte])*2[DDR] = 3200 MegaBytes p/s


**edited to include proper calculation

For those feeling mathematically challenged, you can pf course change the 200Mhz value to 400Mhz for DDR, and exclude the last 2x multiplication.

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_MD_ May 15, 2007, 10:08am EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
DublinGunner said:
Theoretical bandwidth limit.

i.e. PC3200 runs at 400Mhz (DDR) or 200Mhz real.

200Mhz*(64[bits transferred per clock] / 8[bits per byte])*2[DDR] = 3200 MegaBytes p/s

Thanks. good and detailed info.


For those feeling mathematically challenged, you can pf course change the 200Mhz value to 400Mhz for DDR, and exclude the last 2x multiplication.

LOL

___________________MD_____________________
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Archangel May 15, 2007, 11:25am EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
HorsePower!!!!!

_MD_ May 15, 2007, 11:58am EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
PC = Polycarbonate with various valences.
Sometimes known as Phosphatidylcholine
Or in very rare cases Pachyonychia Congenita with various classification numbers:
Pachyonychia congenita (PC) is a rare form of hereditary palmoplantar keratoderma (PPK). Müller made the first documented observation in 1904 (Müller, 1904). The next reports were published in 1905 by Wilson (Wilson, 1905) and in 1906 by Jadassohn and Lewandowsky (Jadassohn, 1906). In the dermatologic literature, PC is better known as Jadassohn-Lewandowsky syndrome.

Various classifications for PC have been proposed. Currently 2 distinct syndromes of PC are recognized: (1) PC-1, or the Jadassohn-Lewandowsky type, which is designated as Mendelian Inheritance in Man (MIM) entry 167200 (McKusick, 1994), and (2) PC-2, or the Jackson-Lawler type, which is designated as MIM entry 167210.
http://www.emedicine.com/derm/topic812.htm

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Nathan Daniels May 15, 2007, 02:13pm EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
Well that answers the first half of my question. Now can I use a PC2700 int a computer that has a PC3200 already in it?

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"The more we sweat in peace, the less we bleed in war."
-Patton
CrAsHnBuRnXp May 15, 2007, 02:24pm EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
Nathan Daniels said:
Well that answers the first half of my question. Now can I use a PC2700 int a computer that has a PC3200 already in it?

Yes, but the PC3200 ram will only run at the PC2700 speeds.

FordGT90Concept May 15, 2007, 02:30pm EDT Reply - Quote - Report Abuse
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Edited: May 16, 2007, 06:23am EDT

 
>> Re: What does the PCxxxx mean when buying RAM
DublinGunner said:
200Mhz*(64[bits transferred per clock] / 8[bits per byte])*2[DDR] = 3200 MegaBytes p/s


// Fomula
bandwidth = chip speed per second (aka hertz) * transfers per hertz (or simply transfers times seconds) * width (in bits) per second * bytes per 8 bits * number of buses

// DDR, unsolved.
x = 200 M/s * 2 s * 64 b/s * B/8 b * 1
http://img170.imageshack.us/img170/9970/formularr7.png

// We multiply the first two to eliminate the second and get number of transfers made
x = 400 M * 64 b/s * B/8 b * 1

// Now we multiply the middle two to eliminate bits leaving bytes per second.
x = 400 M * 8 B/s * 1

// Get the product of the of transfers with the amount trasferred to get the bandwidth.
x = 3200 MB/s * 1

// Multiply by the number of busses (connections between the memory and memory controller) to get the sum of the sticks input/output bandwidth.
x = 3200 MB/s

DDR doesn't exist in mathematics, only it's value which represents transfers per cycle which is given the same as transfers * seconds.

Bits and hertz cancel out.

Hz = per Second.


DDR2 has four transfers per second because it has double the buses of DDR:
x = 200 M/s * 2 s * 64 b/s * B/8 b * 2
x = 400 M * 64 b/s * B/8 b * 2
x = 400 M * 8 B/s * 2
x = 3200 MB/s * 2
x = 6400 MB/s

DDR3 has eight transfers per second because it has double the buses of DDR2:
x = 200 M/s * 2 s * 64 b/s * B/8 b * 4
x = 400 M * 64 b/s * B/8 b * 4
x = 400 M * 8 B/s * 4
x = 3200 MB/s * 4
x = 12800 MB/s

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_MD_ May 15, 2007, 02:58pm EDT Reply - Quote - Report Abuse
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Edited: May 15, 2007, 02:59pm EDT

 
>> Re: What does the PCxxxx mean when buying RAM
From here on, a little correction...

FordGT90Concept said:
DDR2 has four transfers per second because it has double the buses of DDR:
x = 200 MHz * (64 b/s / 8 B/b) * 4
x = 200 MHz * 8 B/s * 4
x = 3200 MB/s * 4 --> should be 1600MB/s * 4 or if you say double the speed of DDR then 3200*2
x = 6400 MB/s


DDR3 has eight transfers per second because it has double the buses of DDR2:
x = 200 MHz * (64 b/s / 8 B/b) * 8
x = 200 MHz * 8 B/s * 8
x = 6400 MB/s * 8 --> should be 1600MB/s * 8 or if you say double the speed of DDR2 then 6400*2
x = 12800 MB/s


:cool:

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FordGT90Concept May 15, 2007, 03:18pm EDT Reply - Quote - Report Abuse
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Edited: May 15, 2007, 03:18pm EDT

 
>> Re: What does the PCxxxx mean when buying RAM
Opps. I am good at making mistakes. :(

But not afraid to fix them. :)

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Dublin_Gunner May 16, 2007, 05:03am EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
FordGT90Concept said:
DublinGunner said:
200Mhz*(64[bits transferred per clock] / 8[bits per byte])*2[DDR] = 3200 MegaBytes p/s

x = 200 MHz * (64 b/s / 8 B/b) * 2
x = 200 MHz * 8 B/s * 2
x = 1600 MB/s * 2
x = 3200 MB/s

DDR doesn't exist in mathematics, only it's value which represents Transfers per Second (T/s).

Bits cancels out.

Hz = Cycles per Second


DDR2 has four transfers per second because it has double the buses of DDR:
x = 200 MHz * (64 b/s / 8 B/b) * 4
x = 200 MHz * 8 B/s * 4
x = 1600 MB/s * 4
x = 6400 MB/s


DDR3 has eight transfers per second because it has double the buses of DDR2:
x = 200 MHz * (64 b/s / 8 B/b) * 8
x = 200 MHz * 8 B/s * 8
x = 1600 MB/s * 8
x = 12800 MB/s


MHz on all the above are given using the chip clockspeed--not the I/O bus speed which is a sum of all the buses.



I included the parenthesis to show what the values were that are used.

Obviously DDR doesnt exist in Maths, its an electronics term. BTW, DDR is not designed to represent tranfers per second, its there to indicate that there are 2 transfers per clock, on the rising and falling edges of the clock cycle wave.


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FordGT90Concept May 16, 2007, 05:14am EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
DublinGunner said:
Obviously DDR doesnt exist in Maths, its an electronics term. BTW, DDR is not designed to represent tranfers per second, its there to indicate that there are 2 transfers per clock, on the rising and falling edges of the clock cycle wave.

I knew something was missing because something has to cancel out the Hz. That would be another one of my mishaps...

DDR is represnted by the units as 2/Hz, DDR2 as 4/Hz, and DDR3 as 8/Hz.

Correcting...

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Dublin_Gunner May 16, 2007, 05:16am EDT Reply - Quote - Report Abuse
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Edited: May 16, 2007, 05:17am EDT

 
>> Re: What does the PCxxxx mean when buying RAM
lol

We'll have a maths debate up and running soon!

DDR is represnted by the units as 2/Hz, DDR2 as 4/Hz, and DDR3 as 8/Hz.


Actually its Hz*2, Hz*4, Hz*8 etc

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FordGT90Concept May 16, 2007, 06:14am EDT Reply - Quote - Report Abuse
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Edited: May 16, 2007, 07:09am EDT

 
>> Re: What does the PCxxxx mean when buying RAM
Hertz means "per second" so 1/Hz is the same as 1/(1/s) is the same as 1s. All in the same. I finally got my equation written that covers all the units and accounts for SDR through DDR3. :D

Oh, and I think I turn this into an article for future reference with color coding and all the fancy crap we all love. Prevents me from making more silly mistakes. :)


Oh, and I don't think anyone mentioned this. PC#### on DDR is the theoretical peak bandwidth. PC### on SDRAM is the clock speed. Theoretical peak bandwidth varies depending on the bitrate (4-bit/s, 8-bit/s, or 16-bit/s).

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Dr. Peaceful May 16, 2007, 01:34pm EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
DublinGunner said:

Theoretical bandwidth limit.
i.e. PC3200 runs at 400Mhz (DDR) or 200Mhz real.

200Mhz*(64[bits transferred per clock] / 8[bits per byte])*2[DDR] = 3200 MegaBytes p/s


Further clarifications:
DDRx-xxxx is the specification identifier for a memory chip, where xxxx represent the
effective clock speed.
PCx-xxxxx is the specification identifier for a DIMM stick, where xxxxx represent the
theoretical bandwidth (rounded sometimes).

Effective clock speed = memory clock x IO clock ratio x dual rate
- for DDR = mem clock x 1 x 2 = mem clock x 2^1
- for DDR2 = mem clock x 2 x 2 = mem clock x 2^2
- for DDR3 = mem clock x 4 x 2 = mem clock x 2^3

Theo. bandwidth (DIMM) = Effective clock speed x 64 bits transfer rate / 8 bits per byte

DDR-333
mem clock = 333 / 2^1 = 166.5 Mhz
theo. bandwidth = 333 x 64/8 = 2664 = ~2700
So the DIMM is called PC-2700.

DDR2-800
mem clock = 800 / 2^2 = 200 Mhz
theo. bandwidth = 800 x 64/8 = 6400
So the DIMM is called PC2-6400.

DDR3-1600
mem clock = 1600 / 2^3 = 200 Mhz
theo. bandwidth = 1600 x 64/8 = 12800
So the DIMM is called PC3-12800.

A DDR3-1600 is actually running at the same mem speed as a DDR-400, just more
prefetch buffers.

Nathan Daniels May 16, 2007, 07:35pm EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
good lord. I like physics and all but damn! I just wanted to know what it meant, not how it is found. I don't need a very high PCxxxx because the only reason I am buying RAM is to take the load off my page file. Besides, I doubt a human can tell the difference between PC2700 and PC3200.

--------
"The more we sweat in peace, the less we bleed in war."
-Patton
Gerritt May 16, 2007, 08:13pm EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
Depending on your system the difference between DDR2700 and DDR4800 can be VERY significant.
I'm pretty sure that all systems that support DDR cap out at DDR 3200 un-OCed, but DDR 2700 can cause a major bottleneck to systems supporting dual memory busses.
I'd go with DDR3200 memory (which is cheap) in an older AMD system or DDR2-800 in a newer INTEL system as minimums.
Just me though....
Gerritt

Ad Astra Per Aspera
(A rough road leads to the Stars)
We all know what we know, and everyone else knows we are wrong.
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Nathan Daniels May 16, 2007, 09:14pm EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
Mine only supports up to 2700

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"The more we sweat in peace, the less we bleed in war."
-Patton
Shadow_Ops_Airman1 May 16, 2007, 09:15pm EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
Dual Channel works with PC 2100 DDR aswell.

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Dublin_Gunner May 16, 2007, 09:39pm EDT Reply - Quote - Report Abuse
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>> Re: What does the PCxxxx mean when buying RAM
Brandon R. said:
Dual Channel works with PC 2100 DDR aswell.


That would depend on the motherboard / chipset. not the ram modules.

Lancool PC K62
Phenom II x3 @ 3.5Ghz
4GB DDR2-800
ASUS GTX570 DirectCU II

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