The PowerPC 604-based-Power Mac 9500 boasts a whopping twelve (12) DRAM DIMM slots, a HammerHead ASIC memory controller, 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) 60ns DIMMs, or 5-volt, 64-bit, 168-pin extended data out (EDO) 60ns DIMMs , with either 2k or 4k refresh. The Power Mac 9500 typically ships with 16MB or 32MB of RAM (either a single 16MB or 32MB DIMM in slot B4 or a pair of 8MB or 16MB DIMMs in slots A4 & B4).
Note: While no performance benefit accrues through the use of EDO memory in this machine, and it is indeed permissible to mix EDO with FPM memory on their logic boards, MacGurus advises utilizing matched pairs of EDO DIMMs. For more information on using either EDO or FPM DIMMs in your 9500 consult the 'support' section of the FPM and EDO RAM pages.
As there is no DRAM soldered to the logic board (aka "Tsunami"), the 9500-series requires that at least one DIMM be installed for the computer to boot. DIMMs may be installed in any slot, in any order, although a performance boost of approximately 5-15% results from installing matching pairs of high-quality DIMMs in pairs, in corresponding slots (A6-B6, A5-B5, A4-B4, etc.), as a consequence of interleaving.
Apple's technical documentation and hardware manuals are contradictory when recommending which slots to use and in which order when installing DIMM pairs, and questions asking whether to begin with the high DIMM slots (i.e. A6-B6), or the low slots (i.e. A1-B1) are perennial favorites on the Mac-related newsgroups on Usenet and the various Mac-specific mailing lists on the internet. As of this writing, the consensus appears to be in favor of beginning with the high slots, A6-B6, proceeding in sequence to the lower numbered slots, and we here at MacGurus have proceeded in this way with hundreds of Power Macs without adverse consequence. Our hardware hacking confirms that interleaving does appear to succeed regardless of start point in those Power Macs that support it, however, with the hard rule appearing to be that DIMM pairs should be installed with the greatest density pieces first, progressing down to pairs of the lowest density, regardless of whether A6-B6 or A1-B1 is the first pair.
It also seems very clear that interleaving requires L2 cache to be present, and works best in cases where the DIMM pairs in question have been selected with some care, and the software in use has been written to exploit interleaving. When purchasing memory for this computer, it is best to purchase DIMMs in matching pairs, to ensure that chipsets, density, addressing modes, refresh rate and speed 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. The Power Macintosh Memory FAQ has some bearing on these issues, while those with an inexhaustible thirst for detail may mine Apple's pertinent Developer's Technotes with some profit, particularly the classic TN1055: SIMMs to DIMMs: Making Sense Out of Memory Expansion for the Power Macintosh - 7/96.
The maximum amount of usable memory in the 9500-series is 768MB, in the form of twelve (12) 64MB DIMMs, although theoretical configurations utilizing 128MB DIMMs up to 1,536MB are conceivable. Please see articles Power Mac Interleaving Performance Gain (TECHINFO-0018870) and Power Mac 9500 Series Memory Q & A (TECHINFO-0018196) in Apple's Technical Information Library (TIL) for more information.
One of the great flaws of the 9500-series Tsunami architecture is that its 512k L2 cache is soldered onto the logic board, with no L2 DIMM slot available for further expansion. After the debut of the Power Computing Power Tower Pro 225 in August, 1996, it is clear that the accelerating clock speeds of the PowerPC 604e processor absolutely mandate larger L2 cache sizes.
Specifications Logic Board RAM None Supported DIMMs 32MB, 64MB, 128MB Number DIMM Slots Twelve (12). Supported VRAM 2MB upgrade module from ATI in some variants. Number VRAM Slots None. Some variants shipped with a 64-bit ATI video card. L2 Cache Supported 512k soldered on logic board. DIMM Type 168-pin, 5v EDO 64-bit, 2k refresh, 60ns.
As noted, the 9500-series have no VRAM slots on the logic board, and no on-board video circuitry, the intent being that end-users should purchase accelerated third-party video cards. Some variants of the 9500 include a 2MB 64-bit video card from ATI, which can be expanded to 4MB with the installation of a 2MB VRAM Upgrade Module.