Power Computing PowerWave-series


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The PowerPC 604-based-Power Computing PowerWave boasts eight (8) 168-pin DRAM DIMM slots, a HammerHead ASIC memory controller, and a 64-bit data bus which widens to 128-bits when interleaved. This computer requires 5-volt, 64-bit, 168-pin fast-paged mode (FPM) 70ns or 60ns DIMMs, with 2k refresh, and typically shipped with 16MB RAM (either a single 16MB in slot B4 or a pair of 8MB DIMMs in slots A4 & B4). Unlike other Tsunami-based logic boards, the PowerWave bizarrely does not tolerate EDO DRAM, and Power Computing has stressed its endorsement of FPM memory only in this machine.

As there is no DRAM soldered to the logic board (aka "Tsunami"), the PowerWave-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 (A4-B4, A3-B3, A2-B2, 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. A4-B4), 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, A4-B4, 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 A4-B4 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 maximum amount of usable memory in the PowerWave-series is 512MB, in the form of eight (8) 64MB DIMMs, although theoretical configurations utilizing 128MB DIMMs up to 1024MB 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. Fortunately, Power Computing departed from the Apple design, utilizing a standard socketed L2 cache DIMM which is upgradable to a maximum of 1MB. PowerLogix RapidCache is recommended..

Specifications
Logic Board RAM		None
Supported DIMMs		32MB, 64MB, 128MB
Number DIMM Slots		Eight (8).
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		1MB.
DIMM Type		168-pin, FPM 64-bit, 2k or 4k refresh, 70ns or faster.

^*Note: MacGurus is indebted to our esteemed client Derek Brumley for clarifying that PCC PowerWave 120 & PowerWave 150 clones do indeed require L2 cache DIMMs rather than the L2 cache SIMMs their logic board masking suggests. We are uncertain whether this incorrect masking affects all PCC motherboards of this type or merely a specific range of serial numbers. Further clarification is most welcome.

As noted, the PowerWave-series has 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 PowerWave included a 2MB or 4MB 64-bit video card from ATI, the 2MB version of which can be expanded to 4MB with the installation of a 2MB VRAM Upgrade Module.