[PEHowland]

Apple's web site claims that the new G5 iMac supports dual channel memory providing the two modules are identical. However, this implies more than the modules having just the same size (eg. 512MB) - the configuration (eg. 64Mx8) and the timings (eg. CAS latency, RAS-to-CAS delay, etc) also probably need to be the same.

It would be useful if new iMac owners could take the back off their iMac and provide details of the memory chip mmanufacturer and part number. This would allow us to figure out the specifications of the chip and hence buy compatible memory from a 3rd party supplier that would allow dual channel operation.

Perhaps new iMac owners could respond to this thread with the following details:

- iMac type (eg. 17" 1.8GHz, etc)
- Apple installed memory size (eg. 1 x 256MB, 2 x 512MB, etc)
- Chip details (eg. Samsung KH560838E-TCCC)

Then we can figure out the exact specifications and so allow people to buy compatible 3rd party memory for dual-channel use in advance.

Thanks in advance.

Paul

[PEHowland]

No new owners checked out their memory yet?

[kcmac]

This is what is on the base 256 that I removed.

MTBVDDT3264AG-40BG4 200433 CBNBM2M012
COUNTRY OF ORIGIN SINGAPORE
PC3200U-30331-A1
256MB, DDR, 400, CL3

By the way. If you want to buy this chip, PM me. I will be happy to sell it.

Edit:

I bought 2 sticks of 512 from 18004memory.com. They are a brand named Princeton. They are CL3. (I had to look this up on the Princeton site.) I purhased the Powermac G5 400 DDR because it was cheaper than the same ram listed for the iMac.

Really makes a huge difference in how this iMac works. No beach balls. Apps open pretty much instantly. Even Word 2004 which grinds on my 12" PB.

[PEHowland]

Ah ha! Thanks. A quick Google reveals this link. So this memory module is made by Crucial:

Crucial Technology
PC3200U-30331-A1
MT8VDDT6464AG-40BC1
CCTAGA3013 200407
CT6464Z40B.8T
42545

Speed type: PC 3200, 200 MHz (DDR400)
Chip capacity: 8x 512 Mbit, 5 sn
Sides: single
SPD: 200 MHz 3.0-3-3-8, 166 MHz 2.5-3-3-7, 133 MHz 2.0-2-2-6

[kcmac]

pehowland,

The sticks I purchased are made by Princeton. Limited specs I have found at the Princeton site are

512MB 400Mhz. CL3 184PIN (32X8)

How does that compare? They seem to work very well.

[alternate_bit]

using powermac ram? doesn't the iMac require SDRAM?

[PEHowland]

Originally posted by kcmac:
pehowland,

The sticks I purchased are made by Princeton. Limited specs I have found at the Princeton site are

512MB 400Mhz. CL3 184PIN (32X8)

How does that compare? They seem to work very well.

It's probably identical. Obviously the bus speed is the same, 400MHz, and the Column Address Strobe (CAS) latency is the same, 3. These are the key parameters. The only difference mught be in the other timings - the Crucial memory is fairly standard in terms of timings. You can get faster, eg. this but I don't know what are the fastest timings supported by the G5 chipset, so faster timings may be irrelevant.

[PEHowland]

Originally posted by alternate_bit:
using powermac ram? doesn't the iMac require SDRAM?

Powermac RAM is SDRAM. DDR-SDRAM. Same as the iMac.

[alternate_bit]

reheheally? interesting. how long has powermac ram been sdram?

[PEHowland]

Originally posted by alternate_bit:
reheheally? interesting. how long has powermac ram been sdram?

Since at least the G3

[kcmac]

Yes, it is the same. I called several memory places to find out. It is interesting that they have added a slight premium to the iMac memory pricing. Get the Powermac G5 version for the best price if you care about such things.

When I check System profiler, it says 1 gig ram instead of 1024 ram. I found this a little odd though. Anyone else seen this with 2 sticks of 512?

Runs great though. That's really what matters.

[PEHowland]

Originally posted by kcmac:

When I check System profiler, it says 1 gig ram instead of 1024 ram. I found this a little odd though. Anyone else seen this with 2 sticks of 512?

2x512 = 1GB. Remember that in computing, 1K=1024B, 1M=1024K and 1G=1024M.

[pliny]

Originally posted by PEHowland:
Apple's web site

....

(cut for brevity)

where else have you found info at apple about this?

[kcmac]

Originally posted by pliny:
(cut for brevity)

where else have you found info at apple about this?

Here

Here

"Additional DIMMs can be installed. The combined memory of all of the DIMMs installed is configured as a contiguous array of memory. The throughput of the 400 MHz memory bus is dependent on the DIMMs installed. If only one DIMM is installed, the memory bus is 64-bit. If two non-identical DIMMs are installed, there are two 64–bit memory buses. If two identical DIMMs are installed, the memory bus is 128-bit. Identical DIMM pairs have the same size and composition and provide the fastest and most efficient throughput."

[alternate_bit]

d'oh i was thinking of SODIMM... laptop RAM. didn't the old imac use laptop ram? so this mac doesn't?
man i'm confusing myself here, heheh.

[PEHowland]

Originally posted by alternate_bit:
d'oh i was thinking of SODIMM... laptop RAM. didn't the old imac use laptop ram? so this mac doesn't?
man i'm confusing myself here, heheh.

No, the new iMac uses identical memory to the current Powermacs - PC3200 184-pin DDR400 CAS Latency 3 memory.

The issue here is that PC3200 DDR can come in many different chip configurations (how the bits are organized on the chip - you'll see it described as 64Mx4, etc) and with different timing capabilities - CAS is the key timing parameter, but there are others, and these are often harder to find out. It seems that Crucial memory shipping with the iMac uses 3.0-3-3-8 timings. So, to be sure that dual channel will work with the shipping memory if you want to add one extra stick, you need to get memory that is PC3200 with 3.0-3-3-8 timings (and the same size as the installed memory).

The numbers refer to the number of cycles used for CAS latency, RAS to CAS latency, RAS precharge, and cycle time (TRAS). They all deal with the accessing of information on the RAM. Faster timings mean fewer cycles and hence better performance.

[alternate_bit]

Excellent information. I'll have to bookmark this for when I order my iMac. Thanks.

[MrMiyagi]

"If two identical DIMMs are installed, the memory bus is 128-bit. Identical DIMM pairs have the same size and composition and provide the fastest and most efficient throughput."

Does this really matter? If the iMac has only a 2048 MB maximum of RAM, then you don't really need 128 bit addressing. 32 bits is good enough isn't it?

2^32 = 4,294,967,296 (4,096MB)

Please tell me why i'm wrong.

Cheers!

[Al G]

I guess technically speaking, you're not wrong, it's just that you're talking about something completely different.

Apple doesn't say anything about addressing. What it says is matched DIMMs increase the width of the memory bus from 64-bit to 128-bit. It's about throughput not address space.

[MrMiyagi]

Originally posted by Al G:
I guess technically speaking, you're not wrong, it's just that you're talking about something completely different.

Apple doesn't say anything about addressing. What it says is matched DIMMs increase the width of the memory bus from 64-bit to 128-bit. It's about throughput not address space.

Yeah, but what does that matter if you're using a 64 bit processor? You can only work with 64 bits at a time, no?

[PBG4 User]

Originally posted by MrMiyagi:
Yeah, but what does that matter if you're using a 64 bit processor? You can only work with 64 bits at a time, no?

The whole idea behind a wide RAM buss is to keep the CPU fed with data. Yes, the processor only works with 64 bits at a time, but if it wastes cycles waiting for data from main RAM then those cycles are wasted (NOP).

Trust me, like the old Pontiac commercial says, "E Aho La Ula" (wider is better).

[Calli46]

Well, I read this thread and couldn't find an answer to the (my) following problem.

I had an iMac G5 (1.6 GHz educ model) ordered by my school. Everything in it is standard, even the 256 MB Ram. I want to add some more HP to the beast, namely boost the memory to 512 MB with 2 identical chips and get a 128 bit bus. OTOH I could buy and add a 512 MB chip to get a total of 768 MB.

Question : which way to go ? 512 MB would optimize the I/O to/from memory but 768 MB would give more space in memory for disk caching, keeping more apps in memory without going to virtual RAM.

What is your advice on this ? Should I go for 768 MB or 512 MB with a larger bus ?

TIA

[PEHowland]

Originally posted by Calli46:
Well, I read this thread and couldn't find an answer to the (my) following problem.

I had an iMac G5 (1.6 GHz educ model) ordered by my school. Everything in it is standard, even the 256 MB Ram. I want to add some more HP to the beast, namely boost the memory to 512 MB with 2 identical chips and get a 128 bit bus. OTOH I could buy and add a 512 MB chip to get a total of 768 MB.

Question : which way to go ? 512 MB would optimize the I/O to/from memory but 768 MB would give more space in memory for disk caching, keeping more apps in memory without going to virtual RAM.

What is your advice on this ? Should I go for 768 MB or 512 MB with a larger bus ?

TIA

Almost certainly 768MB is better than 2x256MB. The performance boost in practice from dual-channel memory is only a few percent. The performance boost from virtual memory (ie. disk) to real memory is massive. It depends on exactly how many apps you will be running at once, and how memory intensive they are, but if you're close to filling 512MB you'd be far better off with 768MB single channel. You could always replace the original 256MB with another 512MB stick at a later date, to get 2x512MB dual-channel.