DIY repair site iFixit has pulled apart the new 21.5" iMac that Apple began shipping yesterday. While the exterior and much of the interior remains largely the same, a few differences have been discovered—including the fact that the GPU is now on a potentially upgradable, removable board.
Like previous generations of aluminum iMacs, the front glass panel is held in with magnets; behind it is the LCD panel screwed into the chassis. iFixit noted that the LG panel in its sample of the 21.5" iMac is identical to the previous generation.
Underneath the panel, it's possible to access the hard drive and optical drive. iFixit said that the space underneath the optical drive is where the optional secondary SSD boot volume would go; it's only an option on the higher-end 21.5" and 27" iMac models, however. Given the overall layout, iFixit gave these iMacs a 7 out of 10 reparability rating, and said that most users should be able to swap LCD panels and drives with relative ease. Getting the LCD and glass panel back in without getting dust stuck somewhere in between, though, is a challenge.
Removing the logic board revealed the main differences between the new and previous-generation iMac. An Intel Thunderbolt controller—slightly different from the one used in the latest MacBook Pros—powers the new Thunderbolt port that replaces the Mini-DisplayPort of the previous model. The GPU is on a separate daughter card as it was with the last generation iMacs, so a GPU failure won't require an entire logic board replacement as some earlier iterations did. Don't expect to find replacement GPUs at NewEgg, however—the daughter card uses the MXM form-factor (see update below) and is generally hard to find.
The iMac's GPU is on a swappable card instead of being soldered directly to the logic board. That makes repairs easier, but the MXM connector is fairly rare outside of OEM parts, so off-the-shelf swaps may not be possible.
The Intel Sandy Bridge processor is also replaceable, but doing so voids the iMac's warranty. iFixit discovered when removing the large heatsinks for the CPU and GPU that both had "proper amounts of thermal paste applied," as opposed to the "absurd amounts" that appeared to be slapped on the latest MacBook Pros.
Other sources have revealed some additional details about the iMac's hardware. According to OWC, the iMac's three internal SATA ports are only 3Gbps, 2.0 ports. This is oddly in contrast to the latest MacBook Pros, which have 6Gbps SATA 3.0 ports. For hard drives this isn't much of an issue, but the latest generation SSDs can take advantage of the additional bandwidth.
OWC has also noted that the 21.5" iMac can only use a maximum of 4GB SO-DIMMs, for a total of 16GB of RAM, while the 27" iMac can use 8GB SO-DIMMs for a total of 32GB of RAM. The 8GB SO-DIMMs still cost about 15 times as much as more common 4GB SO-DIMMs, but if money is no object, you can have an iMac with 32GB of RAM at a roughly $3,000 premium.
The new iMacs also use an as-yet-unreleased Intel Z68 controller, which 9to5 Mac noted includes support for Intel's Smart Response Technology. The controller allows an SSD to act as a high-speed cache for a traditional hard drive, combining the performance of an SSD for often used files with the high capacity of a spinning platter. Adding the secondary SSD option on build-to-order iMacs adds about a month to the expected ship date, which 9to5 Mac speculated means Apple is waiting on a supply of "Larsen Creek" SSDs from Intel that work with the hybrid technology.
The latest iMacs now have an ambient light sensor to the left of the FaceTime HD camera.
Finally, MacGeneration revealed that the iMacs have a new ambient light sensor, which can be configured to automatically adjust backlight brightness based on ambient lighting conditions. This is similar to the ambient light sensors used in current MacBook Pros as well as Apple's iOS devices.
UPDATE: As noted in the comments, the GPU is not on a proprietary daughter card as we first suspected, but on what appears to be an MXM (Mobile PCI Express Module) form factor card. Originally developed by NVIDIA, this form factor is also used in a number of larger Windows laptops to allow the GPU to be swapped for different parts. However, availability of MXM-based GPUs seems scarce, mostly relegating the MXM card to a repairman's convenience. Furthermore, GPUs destined for iMacs typically use incompatible firmware compared to parts used in Windows laptops, though evidence in recent Snow Leopard and Lion releases suggests Mac OS X can now support standard firmware AMD Radeon GPUs.
UPDATE 2: OWC confirmed that a firmware update for the latest iMacs released on May 5 enables 6Gbps SATA 3 capabilities on the two main SATA ports on the iMac logic board. The port reserved for the optical drive remains at 3Gbps.
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Like previous generations of aluminum iMacs, the front glass panel is held in with magnets; behind it is the LCD panel screwed into the chassis. iFixit noted that the LG panel in its sample of the 21.5" iMac is identical to the previous generation.
Underneath the panel, it's possible to access the hard drive and optical drive. iFixit said that the space underneath the optical drive is where the optional secondary SSD boot volume would go; it's only an option on the higher-end 21.5" and 27" iMac models, however. Given the overall layout, iFixit gave these iMacs a 7 out of 10 reparability rating, and said that most users should be able to swap LCD panels and drives with relative ease. Getting the LCD and glass panel back in without getting dust stuck somewhere in between, though, is a challenge.
Removing the logic board revealed the main differences between the new and previous-generation iMac. An Intel Thunderbolt controller—slightly different from the one used in the latest MacBook Pros—powers the new Thunderbolt port that replaces the Mini-DisplayPort of the previous model. The GPU is on a separate daughter card as it was with the last generation iMacs, so a GPU failure won't require an entire logic board replacement as some earlier iterations did. Don't expect to find replacement GPUs at NewEgg, however—the daughter card uses the MXM form-factor (see update below) and is generally hard to find.
The iMac's GPU is on a swappable card instead of being soldered directly to the logic board. That makes repairs easier, but the MXM connector is fairly rare outside of OEM parts, so off-the-shelf swaps may not be possible.
The Intel Sandy Bridge processor is also replaceable, but doing so voids the iMac's warranty. iFixit discovered when removing the large heatsinks for the CPU and GPU that both had "proper amounts of thermal paste applied," as opposed to the "absurd amounts" that appeared to be slapped on the latest MacBook Pros.
Other sources have revealed some additional details about the iMac's hardware. According to OWC, the iMac's three internal SATA ports are only 3Gbps, 2.0 ports. This is oddly in contrast to the latest MacBook Pros, which have 6Gbps SATA 3.0 ports. For hard drives this isn't much of an issue, but the latest generation SSDs can take advantage of the additional bandwidth.
OWC has also noted that the 21.5" iMac can only use a maximum of 4GB SO-DIMMs, for a total of 16GB of RAM, while the 27" iMac can use 8GB SO-DIMMs for a total of 32GB of RAM. The 8GB SO-DIMMs still cost about 15 times as much as more common 4GB SO-DIMMs, but if money is no object, you can have an iMac with 32GB of RAM at a roughly $3,000 premium.
The new iMacs also use an as-yet-unreleased Intel Z68 controller, which 9to5 Mac noted includes support for Intel's Smart Response Technology. The controller allows an SSD to act as a high-speed cache for a traditional hard drive, combining the performance of an SSD for often used files with the high capacity of a spinning platter. Adding the secondary SSD option on build-to-order iMacs adds about a month to the expected ship date, which 9to5 Mac speculated means Apple is waiting on a supply of "Larsen Creek" SSDs from Intel that work with the hybrid technology.
The latest iMacs now have an ambient light sensor to the left of the FaceTime HD camera.
Finally, MacGeneration revealed that the iMacs have a new ambient light sensor, which can be configured to automatically adjust backlight brightness based on ambient lighting conditions. This is similar to the ambient light sensors used in current MacBook Pros as well as Apple's iOS devices.
UPDATE: As noted in the comments, the GPU is not on a proprietary daughter card as we first suspected, but on what appears to be an MXM (Mobile PCI Express Module) form factor card. Originally developed by NVIDIA, this form factor is also used in a number of larger Windows laptops to allow the GPU to be swapped for different parts. However, availability of MXM-based GPUs seems scarce, mostly relegating the MXM card to a repairman's convenience. Furthermore, GPUs destined for iMacs typically use incompatible firmware compared to parts used in Windows laptops, though evidence in recent Snow Leopard and Lion releases suggests Mac OS X can now support standard firmware AMD Radeon GPUs.
UPDATE 2: OWC confirmed that a firmware update for the latest iMacs released on May 5 enables 6Gbps SATA 3 capabilities on the two main SATA ports on the iMac logic board. The port reserved for the optical drive remains at 3Gbps.
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