I emailed Crucial today - got a response hours later (great turn-around)
Quote:
Thank you for contacting Crucial regarding your Apple Mac Pro. We currently do not have the 1GB fully buffered DIMMs available for the Mac Pro. We anticipate availability within the next week or two, so please continue to check back with us.
Ouch. $199 at Crucial for a 1gb kit (2x512mb), and I just paid $270 at Ramjet for the same kit. The killer is that I won't even have the machine for another month.
Ouch. $199 at Crucial for a 1gb kit (2x512mb), and I just paid $270 at Ramjet for the same kit. The killer is that I won't even have the machine for another month.
Yes, compared to others the Crucial price looked good so I bought some. Last week I bought 1gb kit (2x512MB) from Ramjet and they have performed flawlessly (no heat or noise increases and no EEC errors). Before I bought, the Ramjet folks assured me that their memory met all the Apple requirements and, to this point, I have no reason to doubt their claim.
The Mac Pro requires fully-buffered ECC, right? I can't sell the gig that comes with it and put in cheaper, faster, but more error-prone unbuffered stuff?
The Mac Pro requires fully-buffered ECC, right? I can't sell the gig that comes with it and put in cheaper, faster, but more error-prone unbuffered stuff?
What makes the Mac Pro memory performance so average then?
I think it's because of the additional bus between the memory and the system. Each memory stick has it's own memory bus hidden behind the FB-DIMM controller.
What makes the Mac Pro memory performance so average then?
I didn't mean to be so flippant with the ECC comment.
FB-DIMMs have higher latency because there's some intelligence out on the DIMM, and they transmit serially. There are many reasons the industry will eventually have to move to serial RAM for everything. For one, serial means less traces on the motherboard, which means motherboards are less expensive.
The main reason is that it is very hard to drive a bunch of parallel lines very fast without skewing the results (due to capacitance) between the lines. (I.e., some bits arrive sooner than others.) Serial solves this problem.
So, in the long run, FB-DIMMs trade latency for bandwidth. Many applications are latency sensitive, so the Mac Pro suffers on those. Bandwidth-hungry applications that can deal with latency will scream.
Note that you can improve the latency by using all the channels in the memory controller, which is why it's better to have four 512MB DIMMs than two 1GB DIMMs.
I made the ECC comment because I can't imagine a server-class machine without some kind of memory error detection.
Thanks, that's what I suspected was true (greater bandwidth but greater latency) but I didn't know that the buffering didn't really tie into it.
However, now that I know more about serial RAM, can I get an answer as to whether I can use unbuffered memory for lower expense? I mean, am I wrong that all Macs up to this point have used unbuffered memory? My G5 was stable enough for me, that's why I'm wondering.
I think the market is too small to explore those sorts of niches now. I mean, right now 90% of FB-DIMMs are gonna go into workstations or servers that would want ECC. When more of the world moves to FB-DIMMs, that may be more of an option - but by then FB-DIMM prices will come down naturally.
I think the market is too small to explore those sorts of niches now. I mean, right now 90% of FB-DIMMs are gonna go into workstations or servers that would want ECC. When more of the world moves to FB-DIMMs, that may be more of an option - but by then FB-DIMM prices will come down naturally.
Reason I was wondering was because there were a ton on Newegg that were unbuffered...
Thanks, that's what I suspected was true (greater bandwidth but greater latency) but I didn't know that the buffering didn't really tie into it.
However, now that I know more about serial RAM, can I get an answer as to whether I can use unbuffered memory for lower expense? I mean, am I wrong that all Macs up to this point have used unbuffered memory? My G5 was stable enough for me, that's why I'm wondering.
The buffering is inherent to the FB-DIMM standard. It doesn't necessarily have anything to do with stability. What buffering does is allow DIMMS to be chained into larger banks with more slots because standard unbuffered memory often can only drive so many memory chips. Mac Pro doesn't even stretch this capability. It's probably only using it because that's all the Intel workstation chipsets offer right now.
Error correction is something different. What that does is add another assurance that your data doesn't get corrupted when it is in memory.
Comments
Thank you for contacting Crucial regarding your Apple Mac Pro. We currently do not have the 1GB fully buffered DIMMs available for the Mac Pro. We anticipate availability within the next week or two, so please continue to check back with us.
Ouch. $199 at Crucial for a 1gb kit (2x512mb), and I just paid $270 at Ramjet for the same kit. The killer is that I won't even have the machine for another month.
Yes, compared to others the Crucial price looked good so I bought some. Last week I bought 1gb kit (2x512MB) from Ramjet and they have performed flawlessly (no heat or noise increases and no EEC errors). Before I bought, the Ramjet folks assured me that their memory met all the Apple requirements and, to this point, I have no reason to doubt their claim.
The Mac Pro requires fully-buffered ECC, right? I can't sell the gig that comes with it and put in cheaper, faster, but more error-prone unbuffered stuff?
People make non-ECC FB-DIMMs?
*shudder*
WELL I DON'T KNOW! And ECC seems to make latency go through the ceiling for little tangible gain outside of high-precision science.
For FB-DIMM, the latency has little to do with ECC.
For standard DIMMs, ECC latency is generally one additional cycle, hardly what I would consider "through the roof".
What makes the Mac Pro memory performance so average then?
I think it's because of the additional bus between the memory and the system. Each memory stick has it's own memory bus hidden behind the FB-DIMM controller.
This page describes the memory system:
http://www.anandtech.com/mac/showdoc.aspx?i=2811&p=4
What makes the Mac Pro memory performance so average then?
I didn't mean to be so flippant with the ECC comment.
FB-DIMMs have higher latency because there's some intelligence out on the DIMM, and they transmit serially. There are many reasons the industry will eventually have to move to serial RAM for everything. For one, serial means less traces on the motherboard, which means motherboards are less expensive.
The main reason is that it is very hard to drive a bunch of parallel lines very fast without skewing the results (due to capacitance) between the lines. (I.e., some bits arrive sooner than others.) Serial solves this problem.
So, in the long run, FB-DIMMs trade latency for bandwidth. Many applications are latency sensitive, so the Mac Pro suffers on those. Bandwidth-hungry applications that can deal with latency will scream.
Note that you can improve the latency by using all the channels in the memory controller, which is why it's better to have four 512MB DIMMs than two 1GB DIMMs.
I made the ECC comment because I can't imagine a server-class machine without some kind of memory error detection.
However, now that I know more about serial RAM, can I get an answer as to whether I can use unbuffered memory for lower expense? I mean, am I wrong that all Macs up to this point have used unbuffered memory? My G5 was stable enough for me, that's why I'm wondering.
can I get an answer as to whether I can use unbuffered memory for lower expense?
it is not possible.
I think the market is too small to explore those sorts of niches now. I mean, right now 90% of FB-DIMMs are gonna go into workstations or servers that would want ECC. When more of the world moves to FB-DIMMs, that may be more of an option - but by then FB-DIMM prices will come down naturally.
Reason I was wondering was because there were a ton on Newegg that were unbuffered...
Unheatsinked too, but whatever.
Thanks, that's what I suspected was true (greater bandwidth but greater latency) but I didn't know that the buffering didn't really tie into it.
However, now that I know more about serial RAM, can I get an answer as to whether I can use unbuffered memory for lower expense? I mean, am I wrong that all Macs up to this point have used unbuffered memory? My G5 was stable enough for me, that's why I'm wondering.
The buffering is inherent to the FB-DIMM standard. It doesn't necessarily have anything to do with stability. What buffering does is allow DIMMS to be chained into larger banks with more slots because standard unbuffered memory often can only drive so many memory chips. Mac Pro doesn't even stretch this capability. It's probably only using it because that's all the Intel workstation chipsets offer right now.
Error correction is something different. What that does is add another assurance that your data doesn't get corrupted when it is in memory.
Well, I bit the bullet with Crucial's 2x 512 MB setup. I'll take some pictures to show you the sink if anyone is interested.
Please do. Some of the purported heat sinks on 3rd party RAM are laughably inadequate. Show us just how big yours are.
Please do. Some of the purported heat sinks on 3rd party RAM are laughably inadequate. Show us just how big yours are.
Either that or Apple's are an overkill to reduce fan noise.
Either that or Apple's are an overkill to reduce fan noise.
I'd rather overkill and overbuilt to just getting by.