HP's Z tower range runs from a compact single-socket machine to a dual-socket workstation with four graphics slots. The number in the name tracks expansion capacity, not speed — a well-specified Z4 will outrun a poorly specified Z8 on most single-threaded work.
The tier ladder
| Model | Sockets | DIMM slots, one CPU | DIMM slots, two CPUs | DIMMs per channel | Graphics slots | PCIe slot positions | Max internal drives | Power supply options |
|---|---|---|---|---|---|---|---|---|
| Z2 Tower G9 | One | 4 | Not applicable | 2 | 2 | 4 | 2 | 350W, 500W, 700W |
| Z4 G4 | One | 8 | Not applicable | 4 | 2 | 5 | 2 | 465W, 750W, 1000W |
| Z6 G4 | One or two | 6 | 12 | 6 | 2 | 6 | 2 | 700W, 1000W |
| Z8 G4 | One or two | 12 | 24 | 6 | 4 | 7 | 4 | 1125W, 1450W |
Reading the ladder
The Z2 Tower G9 is the compact tier
Four DIMM slots at two per channel, two graphics slots, four PCIe positions and two internal drives. It suits single-application engineering and design work where the chassis has to be small and quiet, and where one GPU is enough.
The Z4 G4 doubles memory slots, and has a board question attached
Eight DIMM slots at four per channel and five PCIe positions. The important detail for anyone buying used is that the Z4 G4 shipped on three different boards — Xeon W-21xx, Xeon W-22xx and Core X — and a processor from one family will not fit another. The unit decides the upgrade path, not the model name.
There is also a slot caveat: on some Core X configurations, slot 5 has no data connection. If a full card layout is planned, confirm the processor variant and slot order first.
The Z6 G4 looks like a step backwards on memory until you add the second processor
With one processor the Z6 G4 has six DIMM slots — fewer than the Z4 G4's eight. That is not a downgrade. It runs six DIMMs per channel and is designed around a second processor, at which point it reaches twelve slots. A single-processor Z6 G4 is a partially populated machine by design.
The Z8 G4 is the only tier that changes graphics and storage
Four graphics slots rather than two, seven PCIe positions, four internal drives, and 24 DIMM slots with both processors fitted. Its 1125W and 1450W power supplies are the only ones in the family sized for multi-GPU work.
The same rule applies as on the Z6: the headline 24 slots require two processors. With one, it is twelve.
Choosing by workload
- Single-application CAD and design, small footprint — Z2 Tower G9.
- General engineering, one or two cards, room to grow — Z4 G4, with attention to which board variant you are buying.
- Memory-bound or thread-bound work — Z6 G4 with both processors fitted, for six-channel memory across twelve slots.
- Rendering, GPU compute, multi-GPU — Z8 G4, the only tier in the family with four graphics slots and power supplies to match.
What these figures describe
The table sets out what each platform supports as a design, drawn from HP's published QuickSpecs. It does not describe what is fitted to a particular refurbished unit. Board variant, processor count and populated slots vary unit by unit.
Where to go next
- Z4 G4, Z6 G4 and Z8 G4 compared side by side
- Z4 G4, Z6 G4 and Z8 G4 specifications
- HP Z2 Tower G9 and HP Z840
- HP Z8 G4 compared with the Dell Precision 7920
- Browse refurbished HP Z workstations
- Check memory options with the RAM Advisor
Hardware bought from TekBoost carries our standard 3-year warranty with Next Business Day part replacement, subject to the terms, exclusions and conditions on that page. If you would rather describe the workload than pick a model, request a quote.
If the work is CAD or BIM
Most workstation purchases in this range are driven by a specific application rather than by a model preference. Our CAD guide sets out what AutoCAD, Revit and similar workloads actually need — clock speed against core count, professional graphics, memory and storage — and compares Autodesk’s stated requirements with what works in practice.