Specifications

Processor familyPowerPC 970 / 970FX / 970MP, 1.6–2.7 GHz, single, dual, or dual dual-core
Architecture64-bit big-endian PowerPC (ppc64)
EnclosureAnodized-aluminium tower, shared across all four generations
MemoryDDR, later DDR2; up to 16 GB on the Late 2005 Quad
NetworkingGigabit Ethernet on every generation; a second port on Late 2005
CoolingAir, except the liquid-cooled Dual 2.5, Dual 2.7, and Quad 2.5 GHz
Operating system rangeMac OS X 10.2.7 through 10.5.8; 10.5 Leopard is the last PowerPC-supported release
ProducedJune 2003 – August 2006

The rows above are the facts that hold across the whole line. The unit in the lab is now known: a Late 2005 PowerMac11,2, the single-socket dual-core 970MP at 2.3 GHz on PCI Express — the row set in bold in the table below. The rest of the per-generation detail stays on the page as reference, since “Power Mac G5” names four machines and the contrast is what makes the identification mean anything.

By generation

GenerationReleasedProcessorModel identifierBus and slotsCooling
Power Mac G5 (Mid 2003)Jun 2003Single or dual PowerPC 970, 1.6–2.0 GHzPowerMac7,2AGP 8X Pro + PCI or PCI-XAir
Power Mac G5 (Late 2004)Jun 2004 (dual); Oct 2004 (single 1.8)Single or dual PowerPC 970FX, 1.8–2.5 GHzPowerMac7,3 (dual); PowerMac9,1 (single 1.8)AGP 8X Pro + PCI or PCI-XAir, except liquid on Dual 2.5 (the first liquid-cooled Mac)
Power Mac G5 (Early 2005)Apr 2005Dual PowerPC 970FX, 2.0–2.7 GHzPowerMac7,3AGP 8X Pro + PCI or PCI-XAir, except liquid on Dual 2.7 (Panasonic loop)
Power Mac G5 (Late 2005 / Quad)Oct 2005Dual-core, or two dual-core, PowerPC 970MP, 2.0–2.5 GHzPowerMac11,2PCI Express (2× x4 + 1× x8/x16, no AGP)Air, except liquid on Quad 2.5

A few points a table flattens:

Single-source and unverified figures

Sources: Apple’s four Power Mac G5 technical-specifications pages (Mid 2003, Late 2004, Early 2005, Late 2005), read in full and cross-checked against EveryMac’s per-model pages and Wikipedia’s specifications table; the operating-system range against Wikipedia’s supported-OS table and the general record of 10.5 Leopard as PowerPC’s last release; the liquid-cooling and leak detail against EveryMac’s dedicated FAQ and Wikipedia’s defects section. Links are on the overview.