iMac G5 Developer Note available

Apple has now published the Developer Note for the new G5 iMac.

There are a few interesting things in the note that weren't known previously:

1) The iMac G5 supports dual-channel memory:

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.

This means that if you install two identical DIMMS, you get twice the theoretical throughput. It also means the system bus speed may become the bottleneck.

2) The iMac G5 may support DDR333:

The RAM expansion slots accept 184-pin DDR SDRAM DIMMs that are 2.5 volt, unbuffered, 8-byte, nonparity, and DDR400-compliant (PC3200). The iMac G5 only supports DIMMs up to 1.25” in height...

DDR266 (PC2200) or slower DIMMs do not work in the iMac G5 computer.

If the iMac G5 does support DDR333, then it would support dual-channel DDR333. Theoretically, in this configuration memory bandwidth would still be faster than system bus bandwidth, at least in ideal conditions. Theory aside, support for dual-channel DDR333 would make DDR333 memory in an iMac G5 a reasonable compromise for those on a budget and who already have DDR333 memory.

3) The iMac G5 uses a 90 nm system controller:

The processor bus is an up to 600 MHz bus connecting the processor to the U3L IC. The bus has 32-bit wide data running in both directions. The processor has 42-bit wide addresses.

The iMac G5 system controller is built with 90-nanometer SOI technology.

One wonders if this was one reason for the new iMac's delay.

Steve Jobs back at work

c|net reports that Steve Jobs is already back at Apple, albeit part time for now. He should be back full-time by the end of September.

It sounds like his pancreatic neuroendocrine tumour was indeed low risk. That's great if true.

We wish him well.

iMac G5 best seller at Apple Store

Even though the iMac G5 is not even shipping yet, it is now the number one best seller at the Apple Store, beating out even the iPod and iPod mini. In fact, no other computer is on Apple's top ten list.



This is very good news for Apple. One can only hope that the sales continue to be good in a few months, after the initial pent up demand is satisfied. I suspect that in the revision B G5 iMac, Apple will update the CPU, and more importantly the GPU, to try to ensure continued strong sales.

Freescale to unveil new G4 MPC7448 in September

Freescale will be unveiling the details about its new G4 MPC7448 CPU at SNDF 2004 Europe at the end of this month. This chip is the evolution of Freescale's tried-and-true G4 744x line. It appears to be a lower power version, possibly due to a die shrink.

Note that this chip announcement is in addition to the planned October announcement of Freescale's next-generation chip line, the e600. Unlike the G4 744x, the e600 will offer support for dual cores and an integrated memory controller.

While not as advanced as the e600, the G4 MPC7448 will still likely be very important to Apple. Apple has already stated that there will be no G5 PowerBook in 2004 and it is possible that Apple will release another G4 PowerBook this year based off the MPC7448. This chip will likely have a much faster time to market than the e600, and will have low power requirements perfect for a new Apple laptop update.

VT supercomputer uses 2.3 GHz Xserves

According to USA Today, Virginia Tech's new supercomputer cluster is composed of G5 Xserves running at 2.3 GHz.

The 2.3 GHz speed does seem curious though, for a few reasons:

First, no such 2.3 GHz Xserve is sold to the general public, but it is technically feasible. The Power Macs do use a 2.5 GHz G5 (although fairly hot), and IBM has already announced an IBM G5 supercomputer with 2.2 GHz G5 970FX chips, using its IBM eServer JS20 blade server system.

Second, although Apple already sells 2.0 and 2.5 GHz machines, they sell nothing in between. That's a pretty big gap to leave empty. This does make one wonder if Apple was hoarding 2.3 GHz chips for a specific purpose (like making supercomputers), or perhaps that Apple was simply underclocking 2.3 GHz capable chips for use as 2.0 GHz chips in Xserves (at a time when yields of high speed G5 chips were too low to support high volume 2.3 GHz sales).

Third, this might suggest an imminent release of 2.3 GHz G5 Xserves to the public. The G5 Xserve was first announced in January, and although only recently has Apple caught up with orders, it has already been 9 months since the announcement. One would expect a speedbump to the Xserve soon, possibly at or before MacWorld in January 2005, and 2.3 GHz would be the perfect speed for that announcement from both from the technical and marketing points of view.

Finally, back when the G5 2.0 GHz Xserves were first announced, Apple Canada had an advertisement which indicated the Xserves were at 2.3 GHz:



The ad was later corrected, but it does seem (especially if the USA Today article is correct) that Apple may have originally planned to release 2.3 GHz Xserves right from the outset, but had to change its plans even after some of the Xserve advertising material had already been completed.

iMac G5 user upgradable parts

Apple has released a new document about the upgradability of the new iMac G5:

Think you need a new part? You can replace many of your iMac G5's parts yourself.

The iMac G5 is designed to make it easy for you to install replacement parts if you need to. The parts you can install yourself are:

AirPort Extreme Card
Memory - DDR 400 MHz (PC3200) SDRAM
Hard drive
Optical drive
Power supply
LCD display
Modem card
Mid-plane assembly (contains the main logic board, the G5 processor, fans, NVIDIA graphics processor, and so forth).

This is very interesting and good news. Essentially, the entire new iMac G5 is user replaceable. The new iMac's design is a far cry from that of the previous iMacs, which were essentially black box designs with very limited user upgradability.

This potentially addresses the issue of the iMac G5's less than stellar GPU. For some users, the GPU is the unit's Achilles heel and the various Mac enthusiast sites are full of comments lamenting Apple's decision not to offer higher speed GPU options. The possibility of a future GPU upgrade can help future-proof the machine (as would a CPU upgrade). However, it sounds like a GPU (or CPU) upgrade may require the replacement of the entire mid-plane assembly in the iMac G5. If true then one wonders if these components will be widely available, and even if available, how expensive they would be.