iMac SO-DIMMs!

SO-DIMMs listed on this page are appropriate for installation in the original M6709LL/A and M6709LL/B iMac-series only, not the later iMac, iMac DV, and iMac DV Special Edition, which accept standard PC100 SDRAM DIMMs like other Power Macintosh G3. If you are uncertain which memory to install in your iMac, look for the manufacturing date on the rear: iMacs built prior to October, 1999 typically accept SO-DIMMs.

If you are in doubt about your ability to handle sensitive electronic components, please contact your local authorized Apple dealer for professional assistance. Note that installing memory in the iMac, particularly in the lower factory slot, is a non-trivial exercise that should only be attempted by competent upgraders. For the fearless, step-by-step guidance is depicted in the Apple iMac Developer Note, the iMac2Day Visual Guide to RAM and VRAM Upgrades, and the Apple Technical Information Library (TIL) article "iMac: Installing Memory." We emphasize that damage inflicted during an install by a non-Apple Authorized technician is not warranted by Apple. Do not void your warranty!


Technical Comments

Note: All 144-pin SDRAM SO-DIMMs ("small outline") listed on this page are high-quality 3.3-volt, self-refreshing, JEDEC-standard (MO-190) 64-bit devices, with a speed of 100MHz/10ns or faster.

All 144-pin SGRAM SO-DIMMs ("small outline") video memory upgrades listed on this page are high-quality 3.3v, JEDEC-standard (MO-190) 64-bit SGRAM devices with a speed of 100MHz/10ns or faster, identical to video memory upgrades used in Apple Beige G3 Power Macintosh.

The Apple iMac has two SDRAM expansion slots and one SGRAM video memory expansion slot. As the Grackle IC memory controller and PCI bridge on the iMac logic board supports only linear memory organization, no benefit accrues from installing SDRAM SO-DIMMs in matched pairs, and SO-DIMMs (installed in any density, in either slot, and in any order) are addressed as a contiguous memory array. No SDRAM main memory is soldered on the iMac logic board, and at least one SDRAM SO-DIMM must be installed for the machine to boot. Two MBs of SGRAM video memory are soldered on the main logic board, upgradeable to 4MB via the installation of a 2MG SGRAM SO-DIMM, or 6MB via the intallation of a 4MB SGRAM SO-DIMM.

It must be noted that installing additional SGRAM video memory will not appreciably accelerate 2D video performance in the iMac; it will, however, enable the ATI Rage IIc graphics controller to display richer color depths, up to millions at the highest resolution (1024 x 768) of the built-in display. Installing additional video memory up to the maximum of 6MBs will directly benefit QuickDraw3D applications, improving the speed of their performance, and enabling richer textures.

iMac Video Display Resolutions and Pixel Depths
Resolution	Vertical Rate	Pixel Depth (2MB)	Pixel depth (4MB)
640 x 480	117.233Hz	32-bit	32-bit
800 x 600	94.97Hz	32-bit	32-bit
1024 x 768	75.03Hz	16-bit	32-bit

Note: 16-bits = "thousands" of colors, while 32-bits = "millions" of colors. If you are using Internet Explorer and the above table is blank, simply "windowshade" the page to view the contents. This phenomenon is due to a bug in the way IE draws tables. Netscape Navigator, all versions, works properly.


Additional Comments

Although Apple technical documents state that the densest SDRAM SO-DIMM currently supported by the iMac main logic board is a two-banked 64MB piece, the same source states, "Future devices with higher density may allow expansion beyond the 128MB limit," with the primary limiting factor being SO-DIMM physical size. Testing has demonstrated that configurations of 256MB are easily attainable in these two-slot machines using two 128MB SDRAM SO-DIMMs, and 384MB using a 2.0-inch 256MB SDDRAM DO-DIMM in the top slot, and a 1.5-inch or smaller 128MB SDRAM SO-DIMM in the lower slot. Fortunately, the top memory expansion slot can accommodate a 2.0-inch SO-DIMM, while only the bottom memory slot requires a 1.5-inch SO-DIMM device. At this time, MacGurus ships both 1.5-inch (or smaller) and 2.0-inch SO-DIMMs which are appropriate for use in the lower or upper memory expansion slot in the iMac respectively, and which handily support the iMac's 66MHz main logic board bus speed.

While chip-sets vary in accordance with market conditions, all memory on this page is fully compliant with (or exceeds) Apple specifications described in the Developer Note Apple iMac Computer, and the Apple Technical Information Library (TIL) article "iMac: Type of Memory to Order to Upgrade RAM and VRAM." and is warranted to work error-free for the lifetime of the machine. Due to their 1.5-inch form factor, SO-DIMMs in densities of 128MB or less will work in either the upper or the lower factory memory expansion slot, while 256MB SO-DIMMs must be used only in the upper memory expansion slot due to their 2.0-inch form factor.


The DIMMs on this page are specifically designed to support revision A,B,C, and D iMac systems. These are the first generation iMacs with tray-loading CD-ROM drives and NO Airport or FireWire.