IBM 9856-42H
The 9856-42H machine type is the IBM Power L1124, the Linux-first 4U Power 11 system, with IBM i and AIX capped at 25 percent of activated cores.
The 9856-42H is the machine type of the IBM Power L1124, the 4U Linux-first Power 11 system. It matches the 9824-42A S1124 on chassis, memory, storage and core count, and posts 25,718 CPW per core. The difference that decides whether you can buy it is a licensing cap, not a specification.
On the 9856-42H, IBM i and AIX are limited to 25 percent of activated cores. On a 60-core system that is 15 cores of IBM i, maximum, no matter what the hardware could do. That cap is the entire buying decision. Estates that are overwhelmingly Linux with a small IBM i remnant fit this machine type well and pay less for it. Anything else belongs on the S1124.
IBM 9856-42H datasheet
IBM Power L1124 (9856-42H) published specifications
| Specification | Value |
|---|---|
| Machine type-model | 9856-42H |
| Generation | IBM Power 11 |
| Sockets | 2 |
| Maximum cores | 60 in the DCM configuration |
| Memory | 64 GB to 8 TB DDR5 across 32 DDIMM slots |
| Internal storage | 244.8 TB NVMe (16x 15.3 TB) or 102.4 TB (16x 6.4 TB) |
| PCIe | 4 direct slots, Gen4 x16 or Gen5 x8 mix |
| I/O expansion | 1 NED24 drawer and 2 Gen4 I/O drawers (24 slots each) |
| CPW per core | 25,718 |
| Operating system posture | Linux-first. IBM i and AIX limited to 25 percent of activated cores |
Figures are the published maximums for this machine type. A specific installed system is defined by its processor feature code and activated core count, not by the machine type alone.
Processor feature codes for the 9856-42H
L1124 processor options
| Feature | Cores | Clock (GHz) | CPW |
|---|---|---|---|
| EP4C | 16 or 32 | 3.4 ... 4.2 | 433,000 / 823,000 |
| EP4B | 24 or 48 | 3.05 ... 4.15 | 1,118,500 at 48 cores |
| EP4J | 30 or 60 | 2.8 ... 3.95 | 1,345,900 at 60 cores |
These features mirror the S1124 EP3X, EP3H and EP3Y options at the same core counts and clocks, under different part numbers. They are not interchangeable between the two machine types.
The 25 percent cap is on activated cores, not installed cores. Activating more cores raises the IBM i ceiling proportionally, which is a different lever from a hardware upgrade and worth modeling separately.
How to confirm you have a 9856-42H
From IBM i
DSPSYSVAL QMODEL returns the model portion and DSPSYSVAL QPRCFEAT returns the processor feature code. Together those two values identify a 9856-42H build exactly, which is more than the L1124 name alone tells a vendor.
From AIX, Linux or VIOS
lsconf reports the machine type and model on the first lines of output. prtconf gives the same alongside processor implementation and clock speed.
From the HMC
Managed system properties shows the machine type-model and serial together, plus installed against activated cores. This is the view to screenshot when requesting a quote.
From the bezel
The 9856 prefix marks the Linux-focused L-series; the equivalent S1124 is 9824-42A. Both are 4U with sixteen NVMe bays, so the machine type on the label is the only reliable way to tell them apart.
Next steps for a 9856-42H
The feature codes sit alongside their S-series counterparts on the Power 11 CPU page, with the full listing at IBM Power L1124. If the IBM i share of the workload is above a quarter, price the 9824-42A S1124 instead.