CAS 2 vs. CAS 3 speed differences in RAM with Athlon 64?

Hello.

I am going to upgrade my old gaming box to an Athlon 64 system. I
noticed the memory CAS speeds. Does CAS 2 (faster) and CAS 3 (slower)
make any big speed differences for 1 GB of PC3200 RAM on a Socket 754
ATX motherboard with an AMD Athlon 64 3000+/2.0 Ghz to 3400+ 2.4 Ghz
(both with 512 KB socket and 754 CPU)? CAS 2 is expensive so... I am
wondering if getting 3 is really worth the price. I am mainly gaming,
watching movies, using the Internet, etc. Gaming is the big one to
note.

You can see my current Athlon XP 2200+ system at
http://alpha.zimage.com/~ant/antfarm.../computers.txt ... I will be
replacing the motherboard (ASUS K8V SE Deluxe or a MSI K8T Neo F...),
CPU, RAM, and sound card (getting an Audigy 2).

Thank you in advance.
--
"Oh, look what Kyle got me, it's a red Mega... Ants in the pants? Ants
in the pants?! Ants in the Pants?!! ..." --Eric Cartman in South Park's
Damien Episode (Season 1; Episode 8)
/\___/\
/ /\ /\ \ Phillip (Ant) @ http://antfarm.ma.cx & http://aqfl.net
| |o o| | E-mail: NT or
\ _ / Nuke ANT from e-mail address if your e-mail was returned.
( )

The CAS ratings are latency cycles. What this means is how many clock ticks
before the memory can read/right again. For CAS 2, this is two mhz, for CAS
3 this is 3mhz. In theory, this calculates to CAS 3 being 30% slower than
CAS 2. Now you know why CAS 2 has a premium on it.

For gaming, if frames per second are your main concern, then you need CAS 2.


<> wrote in message
news:asudnawOzsnnkNPcRVn-...
> Hello.
>
> I am going to upgrade my old gaming box to an Athlon 64 system. I
> noticed the memory CAS speeds. Does CAS 2 (faster) and CAS 3 (slower)
> make any big speed differences for 1 GB of PC3200 RAM on a Socket 754
> ATX motherboard with an AMD Athlon 64 3000+/2.0 Ghz to 3400+ 2.4 Ghz
> (both with 512 KB socket and 754 CPU)? CAS 2 is expensive so... I am
> wondering if getting 3 is really worth the price. I am mainly gaming,
> watching movies, using the Internet, etc. Gaming is the big one to
> note.
>
> You can see my current Athlon XP 2200+ system at
> http://alpha.zimage.com/~ant/antfarm.../computers.txt ... I will be
> replacing the motherboard (ASUS K8V SE Deluxe or a MSI K8T Neo F...),
> CPU, RAM, and sound card (getting an Audigy 2).
>
> Thank you in advance.
> --
> "Oh, look what Kyle got me, it's a red Mega... Ants in the pants? Ants
> in the pants?! Ants in the Pants?!! ..." --Eric Cartman in South Park's
> Damien Episode (Season 1; Episode 8)
> /\___/\
> / /\ /\ \ Phillip (Ant) @ http://antfarm.ma.cx & http://aqfl.net
> | |o o| | E-mail: NT or
> \ _ / Nuke ANT from e-mail address if your e-mail was returned.
> ( )

DDStech wrote:

> The CAS ratings are latency cycles. What this means is how many clock ticks
> before the memory can read/right again. For CAS 2, this is two mhz, for CAS
> 3 this is 3mhz.

You were right when you said clock ticks. That is not 2, or 3, 'MHz' however.

> In theory, this calculates to CAS 3 being 30% slower than
> CAS 2. Now you know why CAS 2 has a premium on it.

If CAS delay were the only thing to memory access that would be right but,
in reality, that occurs once per data stream so the one 'difference' is
spread over multiple reads making it relatively minor in the total picture,
say a few percent.

>
> For gaming, if frames per second are your main concern, then you need CAS 2.
>
>
> <> wrote in message
> news:asudnawOzsnnkNPcRVn-...
>
>>Hello.
>>
>>I am going to upgrade my old gaming box to an Athlon 64 system. I
>>noticed the memory CAS speeds. Does CAS 2 (faster) and CAS 3 (slower)
>>make any big speed differences for 1 GB of PC3200 RAM on a Socket 754
>>ATX motherboard with an AMD Athlon 64 3000+/2.0 Ghz to 3400+ 2.4 Ghz
>>(both with 512 KB socket and 754 CPU)? CAS 2 is expensive so... I am
>>wondering if getting 3 is really worth the price. I am mainly gaming,
>>watching movies, using the Internet, etc. Gaming is the big one to
>>note.
>>
>>You can see my current Athlon XP 2200+ system at
>>http://alpha.zimage.com/~ant/antfarm.../computers.txt ... I will be
>>replacing the motherboard (ASUS K8V SE Deluxe or a MSI K8T Neo F...),
>>CPU, RAM, and sound card (getting an Audigy 2).
>>
>>Thank you in advance.
>>--
>>"Oh, look what Kyle got me, it's a red Mega... Ants in the pants? Ants
>>in the pants?! Ants in the Pants?!! ..." --Eric Cartman in South Park's
>> Damien Episode (Season 1; Episode 8)
>> /\___/\
>>/ /\ /\ \ Phillip (Ant) @ http://antfarm.ma.cx & http://aqfl.net
>>| |o o| | E-mail: NT or
>> \ _ / Nuke ANT from e-mail address if your e-mail was returned.
>> ( )
>
>
>

Can you explain the difference? The clock cycle is in mhz. Perhaps I am
jumping to oonclusions here.

However, there is a huge difference between cas2 and cas3 memory settings.
It is easily noticed by the human eye. Windows snap open alot quicker,
programs pop up faster. Games run noticibly faster.


"David Maynard" <> wrote in message
news:...
> DDStech wrote:
>
>> The CAS ratings are latency cycles. What this means is how many clock
>> ticks before the memory can read/right again. For CAS 2, this is two mhz,
>> for CAS 3 this is 3mhz.
>
> You were right when you said clock ticks. That is not 2, or 3, 'MHz'
> however.
>
>> In theory, this calculates to CAS 3 being 30% slower than CAS 2. Now you
>> know why CAS 2 has a premium on it.
>
> If CAS delay were the only thing to memory access that would be right but,
> in reality, that occurs once per data stream so the one 'difference' is
> spread over multiple reads making it relatively minor in the total
> picture, say a few percent.
>
>>
>> For gaming, if frames per second are your main concern, then you need CAS
>> 2.
>>
>>
>> <> wrote in message
>> news:asudnawOzsnnkNPcRVn-...
>>
>>>Hello.
>>>
>>>I am going to upgrade my old gaming box to an Athlon 64 system. I
>>>noticed the memory CAS speeds. Does CAS 2 (faster) and CAS 3 (slower)
>>>make any big speed differences for 1 GB of PC3200 RAM on a Socket 754
>>>ATX motherboard with an AMD Athlon 64 3000+/2.0 Ghz to 3400+ 2.4 Ghz
>>>(both with 512 KB socket and 754 CPU)? CAS 2 is expensive so... I am
>>>wondering if getting 3 is really worth the price. I am mainly gaming,
>>>watching movies, using the Internet, etc. Gaming is the big one to
>>>note.
>>>
>>>You can see my current Athlon XP 2200+ system at
>>>http://alpha.zimage.com/~ant/antfarm.../computers.txt ... I will be
>>>replacing the motherboard (ASUS K8V SE Deluxe or a MSI K8T Neo F...),
>>>CPU, RAM, and sound card (getting an Audigy 2).
>>>
>>>Thank you in advance.
>>>--
>>>"Oh, look what Kyle got me, it's a red Mega... Ants in the pants? Ants
>>>in the pants?! Ants in the Pants?!! ..." --Eric Cartman in South Park's
>>> Damien Episode (Season 1; Episode 8)
>>> /\___/\
>>>/ /\ /\ \ Phillip (Ant) @ http://antfarm.ma.cx & http://aqfl.net
>>>| |o o| | E-mail: NT or
>>> \ _ / Nuke ANT from e-mail address if your e-mail was returned.
>>> ( )
>>
>>
>>
>

> However, there is a huge difference between cas2 and cas3 memory settings.
> It is easily noticed by the human eye. Windows snap open alot quicker,
> programs pop up faster. Games run noticibly faster.

Are you sure you didn't just have window animation turned off when you
were running CAS2? Because I could barely tell the difference at all.
Benchmark improvements were almost in the noise. IMHO, CAS2 is not
worth the price premium.

Wow, 30% slower? That's a big number! Thanks for the comments!


In comp.os.linux.hardware DDStech <> wrote:
> The CAS ratings are latency cycles. What this means is how many clock ticks
> before the memory can read/right again. For CAS 2, this is two mhz, for CAS
> 3 this is 3mhz. In theory, this calculates to CAS 3 being 30% slower than
> CAS 2. Now you know why CAS 2 has a premium on it.

> For gaming, if frames per second are your main concern, then you need CAS 2.

> <> wrote in message
> news:asudnawOzsnnkNPcRVn-...
> > Hello.
> >
> > I am going to upgrade my old gaming box to an Athlon 64 system. I
> > noticed the memory CAS speeds. Does CAS 2 (faster) and CAS 3 (slower)
> > make any big speed differences for 1 GB of PC3200 RAM on a Socket 754
> > ATX motherboard with an AMD Athlon 64 3000+/2.0 Ghz to 3400+ 2.4 Ghz
> > (both with 512 KB socket and 754 CPU)? CAS 2 is expensive so... I am
> > wondering if getting 3 is really worth the price. I am mainly gaming,
> > watching movies, using the Internet, etc. Gaming is the big one to
> > note.
> >
> > You can see my current Athlon XP 2200+ system at
> > http://alpha.zimage.com/~ant/antfarm.../computers.txt ... I will be
> > replacing the motherboard (ASUS K8V SE Deluxe or a MSI K8T Neo F...),
> > CPU, RAM, and sound card (getting an Audigy 2).
> >
> > Thank you in advance.
--
"Oh, look what Kyle got me, it's a red Mega... Ants in the pants? Ants
in the pants?! Ants in the Pants?!! ..." --Eric Cartman in South Park's
Damien Episode (Season 1; Episode 8)
/\___/\
/ /\ /\ \ Phillip (Ant) @ http://antfarm.ma.cx & http://aqfl.net
| |o o| | E-mail: NT or
\ _ / Nuke ANT from e-mail address if your e-mail was returned.
( )

In comp.os.linux.hardware Lachoneus <> wrote:
> > However, there is a huge difference between cas2 and cas3 memory settings.
> > It is easily noticed by the human eye. Windows snap open alot quicker,
> > programs pop up faster. Games run noticibly faster.

> Are you sure you didn't just have window animation turned off when you
> were running CAS2? Because I could barely tell the difference at all.
> Benchmark improvements were almost in the noise. IMHO, CAS2 is not
> worth the price premium.

Hmmm... not 30% speed difference? OK, I really need to know if CAS 2 is
really worth buying for major speed difference. 30% is a lot. If it is
5%, I would just get CAS 3 and save my money.
--
"Oh, look what Kyle got me, it's a red Mega... Ants in the pants? Ants
in the pants?! Ants in the Pants?!! ..." --Eric Cartman in South Park's
Damien Episode (Season 1; Episode 8)
/\___/\
/ /\ /\ \ Phillip (Ant) @ http://antfarm.ma.cx & http://aqfl.net
| |o o| | E-mail: NT or
\ _ / Nuke ANT from e-mail address if your e-mail was returned.
( )

DDStech wrote:

> Can you explain the difference? The clock cycle is in mhz. Perhaps I am
> jumping to oonclusions here.

Well, even if it could be expressed in Mhz, 2 or 3 is way off no matter how
you look at it. Take a 100Mhz FSB. 1 'clock' represents '100 Mhz'. 2 would
then be half that speed, or '50 Mhz'. (I'm using SDR PC100 SDRAM here for
simplicity's sake). The number is obviously larger the faster the FSB is,
so there's no way we're going to come around to '2 or 3 MHz'.

However, 'MHz' refers to a repetitive, cyclic, thing and the CAS '2 clock
ticks' doesn't repeat every '2 clock ticks' (which would be needed to claim
it's '50 MHz'). It occurs at the beginning of a burst read and then again
before the next burst. The repetition rate, which one might say is a 'MHz'
number, is, then, more related to the number of bytes in the data stream
than it is to whether it's CAS 2 or 3. To make matters even more
complicated, there are other delays besides simply CAS (why you see SDRAM
specs with those three numbers. e.g. 3-2-2 [for CAS 3])

Let's take a simplified example for a read without precharge. The delay
before read is CAS plus Trcd, 3+2, 5 clocks. Then a 4 clock data read.
That's 9 clocks. At 100MHz FSB that's 90ns which translates to 11.1 Mhz, if
it repeated over and over.

However, the repetition depends on there being constant reads, that the
selected bank doesn't change, in which case the extra 2 (or 3) clock
precharge time must be added, and we're ignoring things like bank
interleaving and command overlap.

In other words, it's gets rather complicated to do simple calculations like
"2 is 33% faster than 3" and have much meaning. Note that in our simplified
example, going from CAS 3 to CAS 2 memory lowers the clocks needed from 9
to 8; roughly 11% better, not 33%. But, as noted, that doesn't take into
account other memory cycles, such as the 2 clock precharge.

And then, the main memory access is being L2 cached, so that it's from the
L2 that the processor really reads, and that tends to mask 'improvements'
in the main memory access times since that is, after all, the purpose of L2
cache to begin with: to minimize the effect of main RAM delays.

>
> However, there is a huge difference between cas2 and cas3 memory settings.
> It is easily noticed by the human eye. Windows snap open alot quicker,
> programs pop up faster. Games run noticibly faster.

I seriously doubt that whatever difference you think you're seeing is
because of CAS 2 vs 3. Odds are something else changed at the same time.


> "David Maynard" <> wrote in message
> news:...
>
>>DDStech wrote:
>>
>>
>>>The CAS ratings are latency cycles. What this means is how many clock
>>>ticks before the memory can read/right again. For CAS 2, this is two mhz,
>>>for CAS 3 this is 3mhz.
>>
>>You were right when you said clock ticks. That is not 2, or 3, 'MHz'
>>however.
>>
>>
>>>In theory, this calculates to CAS 3 being 30% slower than CAS 2. Now you
>>>know why CAS 2 has a premium on it.
>>
>>If CAS delay were the only thing to memory access that would be right but,
>>in reality, that occurs once per data stream so the one 'difference' is
>>spread over multiple reads making it relatively minor in the total
>>picture, say a few percent.
>>
>>
>>>For gaming, if frames per second are your main concern, then you need CAS
>>>2.
>>>
>>>
>>><> wrote in message
>>>news:asudnawOzsnnkNPcRVn-...
>>>
>>>
>>>>Hello.
>>>>
>>>>I am going to upgrade my old gaming box to an Athlon 64 system. I
>>>>noticed the memory CAS speeds. Does CAS 2 (faster) and CAS 3 (slower)
>>>>make any big speed differences for 1 GB of PC3200 RAM on a Socket 754
>>>>ATX motherboard with an AMD Athlon 64 3000+/2.0 Ghz to 3400+ 2.4 Ghz
>>>>(both with 512 KB socket and 754 CPU)? CAS 2 is expensive so... I am
>>>>wondering if getting 3 is really worth the price. I am mainly gaming,
>>>>watching movies, using the Internet, etc. Gaming is the big one to
>>>>note.
>>>>
>>>>You can see my current Athlon XP 2200+ system at
>>>>http://alpha.zimage.com/~ant/antfarm.../computers.txt ... I will be
>>>>replacing the motherboard (ASUS K8V SE Deluxe or a MSI K8T Neo F...),
>>>>CPU, RAM, and sound card (getting an Audigy 2).
>>>>
>>>>Thank you in advance.
>>>>--
>>>>"Oh, look what Kyle got me, it's a red Mega... Ants in the pants? Ants
>>>>in the pants?! Ants in the Pants?!! ..." --Eric Cartman in South Park's
>>>> Damien Episode (Season 1; Episode 8)
>>>>/\___/\
>>>>/ /\ /\ \ Phillip (Ant) @ http://antfarm.ma.cx & http://aqfl.net
>>>>| |o o| | E-mail: NT or
>>>> \ _ / Nuke ANT from e-mail address if your e-mail was returned.
>>>> ( )
>>>
>>>
>>>
>
>

DDStech <> wrote:
> The CAS ratings are latency cycles. What this means is how many clock
> ticks before the memory can read/right again. For CAS 2, this is two
> mhz, for CAS 3 this is 3mhz. In theory, this calculates to CAS 3
> being 30% slower than CAS 2. Now you know why CAS 2 has a premium on
> it.
> For gaming, if frames per second are your main concern, then you need
> CAS 2.

No chance. CAS stands for Column Address Strobe, and its latency is the
number of cycles it takes to activate it. If you picture RAM as a grid, then
you will have the memory arranged in rows and columns. Similarly the RAS is
the Row Address Strobe, with its own latency timing.

Due to the mainly linear nature of memory accesses, you will only need to
activate the CAS only once in awhile and keep it open, while you cycle
through the memory using the RAS. This is known as a burst transfer. Really,
RAS is the more important measure of the speed of RAM, because it's done so
much more often. But RAS timings don't really change from module to module,
it's always stuck at about 3 cycles in DDR-RAM. So the only timing that
might be slightly better or worse is the CAS timing, so that's what they
advertise. Really, CAS timing is sort of a measurement of what kind of a
delay you can expect for a burst of data to begin coming to you after you've
told it to start, since CAS is one of the first activities done.

Now a DDR-200 (aka PC1600) runs at 100Mhz, DDR-266 (PC2100) runs at 133Mhz,
DDR-333 (PC2700) runs at 166Mhz, and DDR-400 (PC3200) runs at 200Mhz. CL3
would mean 3 cycles for CAS, and CL2 would mean 2 cycles. So a DDR-200 CL2
module would have a CAS latency time of 2/(100) = 50ns; while a DDR-400 CL3
would have a CAS latency of 3/(200) = 15ns. So a DDR-400 even with a CL3 has
considerably lower latency than a CL2 DDR-200.

So yes, CAS latency does make a small difference, but we're only talking
about nanoseconds at the beginning of a burst.

Yousuf Khan

DDStech <> wrote:
> Can you explain the difference? The clock cycle is in mhz. Perhaps I
> am jumping to oonclusions here.
>
> However, there is a huge difference between cas2 and cas3 memory
> settings. It is easily noticed by the human eye. Windows snap open
> alot quicker, programs pop up faster. Games run noticibly faster.

Did you make the observations of the RAM on the same machine, or is this an
observation based on comparing two separate machines (i.e. one running CAS2
and the CAS3, obviously)?

Yousuf Khan