# what is PC2 DDR ?

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I know a bit about what DDR2 is..  and different notch position, not
compatible with DDR.
But i'm puzzled over PC2.

I once suspected that PC2 was DDR2.
I'm sure i've often seen PC2 DDR2

But I just saw some RAM in a laptop that said PC2 but also said DDR.

## Re: what is PC2 DDR ?

I suspect you have seen something like PC2700 and assumed it is PC2 700,
whereas it is actually PC 2700. I shall explain...

DDR stands for Double Data Rate. DDR2 is Double Data Rate (2x). EG "DDR
266", "DDR 333", "DDR2 553" etc.

A 'PC' rating is also a measure of speed of memory - PC 2700, PC 3500 etc.

With DDR, the number following DDR or DDR2 is a measure of speed of a memory
chip in ticks per second. It is the quantity of transfers the memory is
capable of per second. DDR333 runs at 166MHz and does 2 transfers per
second, therefore the number is 2x166=333. DDR2 533 runs at 133 MHz and does
4 transfers per second so number is 4x133 = 533.

With the PC rating, the number is the amount of MegaBytes the memory can
transfer in a second. PC 2700 can transfer 2700MB/s

PC2100: 266Mhz
PC2700: 333Mhz
PC3200: 400Mhz
PC3500: 433Mhz
PC3700: 466Mhz
PC4000: 500Mhz
PC4200: 533Mhz

Hope that clears thing up
GT

## Re: what is PC2 DDR ?

absolutely right!!
thanks!

I shouldn't have made that mistake. It said PC2100.  DDR 266 (so
133Mhz).
133*16~=2100.

But since it said DDR, it had to be PC. Not PC2

I goess there is no such thing as PC2 100

I'm not up on PC2 speeds.. But I know that with PC amounts, they went
PC 66, PC 100, maybe even PC133 and PC150 (for the bus), Then they
came up with DDR. What was the lowest speed they made DDR at ?

With DDR,  PC became redefined, to be followed by bandwidth amount
(actual bus speed * 16).   And in the DDR notation, (DDR 266, - noting
that one doesn't write Mhz after effective speed..)

It was PC 2100, 'cos  DDR 266.  (actual speed 133Mhz, effective speed
266).   133*16~=2100

What are the ranges of PC2 numbers? I guess they don't start as low as
100.

I remember the the EDO RAM with no clock, speed measured in
nanoseconds. In the days of the P120.  (for those that don't recall.
Pentium 1, 120MHz !).

Was that EDO RAM immediately followed by SDRAM . Such as PC 66.

thanks, I knew most of that, about DDR, though not at the top of my
head. I didn't know much about DDR2, but you've filled me in. it's
times 4.. I recall reading it sent once during the rise and once
during the fall of the FSB's clock's signal, as well as the peek and
the trough of the wave. So 4 times in a clock cycle.

(peak and trough of wave, being, high school physics terminology!)

## Re: what is PC2 DDR ?

There is no PC2. There is PC2100, PC2700, etc. There is DDR, DDR2 and DDR3.

## Re: what is PC2 DDR ?

if there is no PC2 then what is this?

google PC2 5300 DDR2, there's DDR2 PC5400 too
there's PC2 4200 too

and they are on ebay too.

it does seem to me , - i haven't researched it thoroughly though -
that when ram is specified, so, in the terminology.  DDR and PC go
together.
But for DDR2, it can be written with PC or with PC2. Both give google
results.

So , with DDR2, there does appear to be a thing as PC2.. Is it the
same as PC ?

TIA

## Re: what is PC2 DDR ?

On Tue, 19 Jun 2007 12:14:33 -0700,
wrote:

There is much confusion amongst those who don't
differentiate terms as they should merely repeating them
across similar *concepts*.

DDR, DDR2, DDR3 are the technologies the chips use.
Once those chips are integrated onto a particular PCB, that
PCB with a certain # of pins, shape/size to meet a
form-factor,  it's then PC2 nnnn, or with further qualifiers
of not for desktop use such as PC2 5300 SODIMM for a
notebook.

## Re: what is PC2 DDR ?

jameshanley39@yahoo.co.uk wrote:

The place to chase down labeling information, is jedec.org, the standards
body. For example, this is a sample of a document discussing DDR2:

The naming convention is PC2-wwww, as in PC2-4200, for DDR2.

Paul

## Re: what is PC2 DDR ?

you must be an alien, how did you find that?!
There are over a hundred documents on DDR, and it only displays 10 at
a time and it isn't as quick as google at going from one set of 10 to
the next(of course, google also lets you display 100 at a time), and
they're pdfs, not html files you can go back and forth between
quickly !!

I looked for an equivalent document for DDR, but didn't find one. I
searched for keyword "product label" in the "Document search". Since
that expression appeared on the document that you found.

according to the standards, is it the case that in terminology, DDR
goes with PC and DDR2 with PC2 ?

Looking at the jedec site, given that you describe it as the place to
chase down labelling information, I figured that if I search for
"label" i'd find lots of info related to labelling of different
computer components. But all I found was DDR2.
Nothing on labelling of DDR, nothing on the old 72pin EDO RAM..
Nothing on labelling of any computer component that I could recognise.
Except DDR2 !

I thought I might find something on what i'd heard.. that in a phrase
like "DDR 266",   the 266 should not be followed by MHz. (even though
it's a [M]hz speed - albeit an "effective speed")  .  I did find the
DDR spec, but nothing on that.  I wondered if a similar standard
applied to FSB, and whether it's FSB 266 or 266 FSB.. Mhz or not. But
I found no entry for FSB on jedec.

thanks for the tip on jedec, I guess it's useful if you know how to
make use of it!!

## Re: what is PC2 DDR ?

jameshanley39@yahoo.co.uk wrote:

I don't use the JEDEC built-in search engine. I use this, setting the
domain to jedec.org . The search term was "ddr2 label" without quotes.

Good luck finding labeling info for older tech :-) I don't expect
that will be quite as easy.

Paul

## Re: what is PC2 DDR ?

On Tue, 12 Jun 2007 07:17:02 -0700,
wrote:

PC66 was unofficial, at the time memory was typically called
66MHz.  PC100 and PC133 are valid but PC150 was a made-up
term by companies wishing to denote their claim that the
memory could do 150MHz... on a board spec'd for 133MHz
memory bus.

DDR started at PC1600, IIRC.

Actually it was never in DDR notation, DDR was to denote the
FSB speed and the memory was assumed to be at the same clock
rate, but was always correctly called PC(nnnn).

## Re: what is PC2 DDR ?

DDR 200..  yeah, you're prob right.  (1600/16=100. 100Mhz bus)

i'm not sure what you mean by memory (bus) assumed to be at the same
clock rate as the FSB. I guess know what you mean.. That somehow when
selling the RAM they sassume the user will run the FSB at the speed of
the memory bus. Or, he'll run the memory bus at the speed of the FSB,
and buy RAM for that speed for his memory bus.

I still don't see the significance. I guess marketting the RAM ,
you're saying they say the RAM is for a certain speed FSB.  Amd they
mean memory bus.  Or they say it's for a certain speed memory bus, and
some users wouldn't know that they could run that RAM even though
their FSB is set higher or lower than that speed.

If they need to sell the RAM based on the FSB speed, then they'd use
some way of telling the user what FSB speed to use/have.  Or what
memory bus speed to have/use.   So if they didn't use DDR notattion,
what notation did they use? no notation at all?

Hasn't DDR always been followed by effective speed, not actual speed.
Effective speed doesn't really correlate anyway

There were the chipsets for the P4 and the chipsets for the Athlon
XP,

The effective speed of the FSB used with the P4 , was 4 times the
actual speed, 'cos the P4 was "quad pumped". Quad pumped the fsb.

So an equal (actual) bus speed, and fsb speed. 133Mhz.
Would've been  e.g. DDR 266 (133*2) and an FSB of effective speed of
533(133*4).  A 533 FSB and DDR 266 ar every different numbers..

If same actual speed is assumed, then using effective speeds to market
the RAM, and assuming the same actual speed of memory bus and FSB,
just doesn't make sense. THankfully, the concepts can't be blurred
together ! ' cos the numbers are different !

With the Athlon XP, if the memory bus and FSB were at the same 'actual
speed', then the effective speeds would've been the equal too ,
double.

.

## Re: what is PC2 DDR ?

On Tue, 12 Jun 2007 14:06:32 -0700,
wrote:

yes

The significance is merely that this is how they spec it,
and it avoids any confusion by not using the term that
denotes a DDR FSB speed since some FSB are not DDR even if
the memory bus is.

I'm not saying some "didn't" use it, but the proper
convention was the PC(nnnn) which did still correspond to a
max memory bus speed capability.

## Re: what is PC2 DDR ?

It was a typo and incorrect.  No such animal.

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DaveW