Power Mac 8600-series

Motherboard Diagram by MacGurus
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The PowerPC 604e-based-Power Mac 8600 boasts a unique logic board (aka "Nitro") in the Power Mac lineup, with eight (8) DRAM DIMM slots and a 64-bit data bus which widens to 128-bits when interleaved. This computer requires either 5-volt, 64-bit, 168-pin fast-paged mode (FPM) 70ns DIMMs, in 2k or 4k refresh, or 5-volt, 64-bit, 168-pin Extended Data Out (EDO) 60ns DIMMs. As these machines typically ship with 32MB EDO DRAM (either a single 32MB DIMM in slot B4 or a pair of 16MB DIMMs in slots A4 & B4), MacGurus recommends the installation of EDO memory, despite the fact that no performance benefit accrues through its use.

Note: MacGurus reccomends the use of 168-pin, 5v EDO 64-bit, 2k refresh, 60ns DIMMs in this machine. EDO DIMMs are engineered to higher tolerances, and are more compatible with G3 processor upgrades. The two types of RAM can be mixed in a machine.

Since no DRAM is soldered to the logic board of the 8600-series, these Power Macs require at least one DIMM to be installed for the computer to boot. DIMMs may be installed in any slot, in any order, although a performance boost of 10-15% results from installing matching pairs of high-quality DIMMs in pairs, in corresponding slots (A4-B4, A3-B3, A2-B2, A1-B1), as a consequence of interleaving. Apple specs state that the maximum amount of usable memory is 512MB, in the form of eight (8) 64MB DIMMs, although greater configurations are theoretically conceivable through the use of 128MB DIMMs.

Like other Power Macs of its generation, the 8600-series does not require DIMMs to be installed in pairs. In contrast to the 7200-series, however, the 8500's HammerHead ASIC memory controller does support memory interleaving, utilizing a 128-bit memory path. When purchasing memory for this computer, consequently, it is best to purchase DIMMs in matching pairs, to ensure that chipsets, densities, and speeds, all correspond. Disparate pieces may interleave, especially if they are of high quality and well within Apple specifications, but chances are enhanced if differences between DIMMs are minimized.

It should be stressed that it is, indeed, permissible to mix and match EDO and FPM DIMMs in these computers, as the HammerHead ASIC treats both types of memory as FPM: for this reason no performance benefit is derived through the exclusive use of EDO memory. Nonetheless, MacGurus recommends the exclusive use of EDO DIMMs in the 8600-series, and we further advise that pieces be matched in terms of chipset and density.

On a side note, it is worth noting that the 8600-series can accommodate DIMMs up to 1.255 inches in height; previous Power Macs required DIMMs no taller than 1.100 inches, in accordance with the smallest dimensions permitted by JEDEC specification MO-161. The curious can consult Power Macintosh 7300/7600/8600/9600: New Features (20789) in the Apple Technical Information Library.

One of the strengths of the 8600-series architecture is that it accepts L2 cache DIMMs in capacities of 256k, 512k, or 1MB, in contrast to the 9500 Tsunami motherboard, which is limited to 512k soldered L2 cache. It should be noted that most shipping 1MB L2 DIMM cache is compatible with the 50MHz bus speeds found in the 200MHz versions of these computers; faster processors, and faster bus speeds, however, remain untested. Intriguingly, Apple technical documents, (TIL-#14750), state that the 8600-series can accommodate L2 sizes up to 4MBs; no compatible commercial L2 of this size has ever been manufactured, however, and no supporting data is available.

The 8600-series also boasts fast 64-bit video circuitry which enables both video capture and printing to video tape, as well as support for simultaneous use of NTSC/PAL monitors off the computer's RCA or S-Video jacks.

NTSC/PAL monitors can be used at the same time as the computer's main display (by definition the one attached to the logic board video port, although like other Power Macs, the 8600 can drive additional displays off third party PCI video cards, for a contiguous desktop of extended size) through the addition of two standard 112-pin 70ns VRAM DIMMs to its stock configuration. The 8600 typically ships with two (2) of its four (4) VRAM slots filled.

Details can be found in articles Power Mac 8500 Display Video On TV (TECHINFO-0018559), and Power Mac 7500 8500 Max Color (TECHINFO-0018358) in the Apple Technical Information Library (TIL).

Specifications
Logic Board RAM None
Supported DIMMs 32MB, 64MB, 128MB
Number DIMM Slots Eight (8)
Supported VRAM 112-pin 70ns VRAM DIMM: 1024k
Number VRAM Slots Four (4)
L2 Cache Supported L2 DIMM: 256k, 512k, 1MB
DIMM Type 168-pin, 64-bit, 5-volt buffered EDO, 60ns or faster

As noted, the 8600-series have four (4) 1MB VRAM DIMM slots on the logic board, and typically ship with two (2) slots filled. When two additional 1MB VRAM DIMMs are installed, the maximum capacity of 4MBs on-board VRAM is achieved.



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