The Z4 G4, Z6 G4 and Z8 G4 are HP's three tower workstation tiers from the same generation. As with most workstation families, the tier is really a decision about processor sockets and memory slots — and on the Z4 G4 there is a second decision, about which board variant you are buying, that is easy to miss on the used market.
Specification comparison
| HP Z4 G4 | HP Z6 G4 | HP Z8 G4 | |
|---|---|---|---|
| Form factor | Tower | Tower | Tower |
| Processor sockets | One | One or two | One or two |
| Memory technology | DDR4 | DDR4 | DDR4 |
| DIMM slots, one processor | 8 | 6 | 12 |
| DIMM slots, two processors | Not applicable | 12 | 24 |
| DIMMs per channel | 4 | 6 | 6 |
| PCIe slot positions | 5 | 6 | 7 |
| Graphics slots | 2 | 2 | 4 |
| Maximum internal drives | 2 | 2 | 4 |
| Power supply options | 465W, 750W or 1000W | 700W or 1000W | 1125W or 1450W |
| Board variants | Xeon W-21xx, Xeon W-22xx, and Core X | Single tower board | Single tower board |
How to choose
The Z4 G4 has three different boards, and they are not interchangeable
This is the single most useful thing to know about buying a used Z4 G4. The platform shipped with a Xeon W-21xx board, a later Xeon W-22xx board, and a Core X board. A processor from one family will not work on another family's board, so the CPU you can fit is decided by the unit you buy, not by the model name.
There is also a slot caveat specific to this platform: on some Core X configurations, slot 5 has no data connection. If you are planning a card layout that uses every position, confirm the processor variant and the slot load order before ordering.
Apart from that, the Z4 G4 is the straightforward single-socket tier: eight DIMM slots across four DIMMs per channel, two graphics slots, two internal drives.
The Z6 G4 is the odd one on memory, and it is worth understanding why
The Z6 G4 has fewer DIMM slots than the Z4 G4 with one processor fitted — six against eight. That looks like a downgrade and is not. The Z6 G4 runs six DIMMs per channel and expects a second processor to reach its real capacity of twelve slots. A single-processor Z6 G4 is a partially populated machine by design.
If you are buying a Z6 G4 with one processor and comparing it to a Z4 G4 on memory capacity alone, the Z4 will look better. Add the second processor and the picture reverses.
The Z8 G4 is the only one that changes the graphics and storage picture
Four graphics slots against two, seven PCIe positions against five, four internal drives against two, and 24 DIMM slots with both processors fitted. It also carries the only power supplies in the family sized for multi-GPU work, at 1125W and 1450W.
The same rule as the Z6 applies more sharply here: 24 DIMM slots need two processors. A single-processor Z8 G4 has twelve.
What these figures describe
The table sets out what each platform supports as a design, drawn from HP's published QuickSpecs for these models. It does not describe what is fitted to any particular refurbished unit. Board variant, processor count and populated slots vary unit by unit on the used market — which is exactly why the Z4 G4 board question matters.
Where to go next
- HP Z4 G4 specifications and options
- HP Z6 G4 specifications and options
- HP Z8 G4 specifications and options
- Which HP Z workstation is right for your work?
- Browse refurbished HP Z workstations
- Check memory options for these platforms 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.