The collaboration between Arm and IBM is thus steering toward hybrid mainframe cores. This was confirmed last week at the Hot Chips conference.
The initial announcement, made in April, could leave room for doubt. It did not rule out the emulation option, nor the possibility of using distinct cores.
We are ultimately looking at a dual-ISA processor, with 11 cores capable of natively executing both z/Architecture instructions and AArch64.
Logical partitions backed by KVM/OpenShift virtualization allow threads to run Arm and s390x, in parallel with z/OS. Context switching is claimed to be a nanosecond affair, according to IBM*.
A 5.7 GHz Mainframe Processor
No commercialization date has been announced yet. If we look at the pace at which IBM typically refreshes its mainframe processors, a 2028 timeframe could be anticipated.
The current z17 is built on 5 nm, with 8 “Telum II” cores at 5.5 GHz, a DPU and a lighter version of Spyre accelerators (24 TOPS). Its likely successor is on 2 nm. It houses two Spyre units — focused on fraud detection across transactions. Its 11 cores (12 including a spare, it seems) run at 5.7 GHz. They fully implement the Arm v9.3 specification.
The Arm and z/Architecture decoders are separated. The switching between Arm’s little-endian mode (storing the least significant byte at the lowest memory address) and the big-endian approach of the latter (most significant byte at the lowest address) is entirely handled at the hardware level.
The Linux Kernel Patched in Parallel
In parallel with the April announcement, IBM had begun patching the Linux kernel to enable a common KVM layer. Work continues, with close to 300 patches proposed at the latest tally.
Big Blue says it targets 99.999999% availability on the mainframes that will carry this hybrid processor. To accommodate Arm-based applications, it has other arguments, including closer alignment with critical data and the unification of the execution environment (starting with security guarantees).
* It is said that this factor would have jeopardized, in the 1990s, the launch of another IBM-made hybrid processor. Specifically, the PowerPC 615, which included an x86 core. Microsoft’s reluctance to develop a Windows version running in PowerPC mode apparently also played a role.
Further Reading:
Claude Code, the end of mainframes? IBM cries foul at conflation
Mainframe modernization: IBM wins in court against LzLabs
Gravity, the throughline of Santander’s shift from mainframe to cloud
The datacenter, the ideal backdrop for Arm’s first CPU
Windows on Arm: NVIDIA joins the fray
