IBM Sub-Capacity PVU Licensing:
Rules, Virtualisation & Reducing Exposure

IBM Sub-Capacity PVU Licensing: The Core Mechanism

IBM Processor Value Unit (PVU) licensing has two modes: full capacity and sub-capacity. Under full-capacity licensing, every physical processor core on every server where IBM software is installed must be licensed — regardless of whether a VM is using 2 vCPUs or the host has 128 physical cores. Under sub-capacity licensing, only the virtual cores allocated to the VMs running IBM software need to be licensed. For most enterprise virtualised environments, the difference between these two positions is enormous. A 128-core x86 ESXi host running IBM WebSphere on a 4-vCPU VM would cost 8,960 PVUs (128 × 70) at full capacity versus 280 PVUs (4 × 70) at sub-capacity — a 97% reduction in licence requirement. This is why IBM ILMT compliance is not optional for enterprises running IBM software in virtualised environments.

IBM introduced sub-capacity licensing specifically to support virtualised environments, but the mechanism came with firm conditions: customers must use IBM's approved tracking tool, run it correctly, and report sub-capacity consumption quarterly. IBM's licence compliance team treats any gap in ILMT coverage as grounds to revert sub-capacity consumption to full physical host capacity — and they apply this retroactively, potentially covering the entire period ILMT was not operating correctly. Our IBM ILMT sub-capacity advisory covers the technical requirements in full detail.

Eligible Virtualisation Technologies for Sub-Capacity

Not every hypervisor qualifies for IBM sub-capacity PVU licensing. IBM maintains a published list of Eligible Virtualisation Technologies, which currently includes VMware vSphere (ESXi), IBM PowerVM on POWER servers, IBM z/VM on mainframe systems, Red Hat KVM (on supported Linux distributions), and Microsoft Hyper-V. Each platform has specific configuration requirements that must be met for sub-capacity eligibility to apply. For VMware environments, ILMT must have read access to vCenter to track VM migrations between ESXi hosts — without this, any VM migration results in peak PVU being calculated at the highest host capacity the VM touched, not the allocated vCPU count.

Platforms that are explicitly not eligible for sub-capacity include Oracle VM Server and most cloud provider native hypervisors (where IBM has separate cloud licensing terms that do not use PVU sub-capacity). Enterprises running IBM software on AWS, Azure, or Google Cloud need separate licensing guidance — the sub-capacity PVU rules do not apply in the same way, and IBM's cloud licensing terms vary by product. For deeper analysis of IBM Db2 licensing including cloud deployment metrics, see our dedicated guide.

How PVU Tables Work and Why They Matter

IBM assigns a PVU value per processor core based on the processor family. x86 processors (Intel, AMD) are assigned 70 PVU per core. IBM POWER8 and POWER9 processors are assigned 120 PVU per core. IBM POWER10 processors introduced in 2021 are also 120 PVU per core. IBM z (mainframe) processors have their own PVU values under IPLA (IBM Passport Advantage) terms. IBM updates the PVU table periodically — typically when new processor families are released — and ILMT must be running the current catalogue version to correctly classify new hardware. Running an outdated PVU table is a compliance risk: a new Intel Sapphire Rapids processor not yet in an old ILMT catalogue could be classified incorrectly, generating an undercount that IBM auditors would identify and convert to full-capacity liability.

The PVU table also affects the economics of cloud migration. When IBM software moves from on-premises x86 (70 PVU/core) to an IBM Cloud bare metal server running POWER (120 PVU/core), the PVU cost per vCPU increases by 71% — a factor many enterprises fail to model during cloud migration planning. This PVU table complexity is one reason IBM has introduced VPC (Virtual Processor Core) licensing via Cloud Pak as a simpler alternative metric: 1 VPC = 1 virtual core, regardless of processor type. For enterprises considering this transition, our IBM Db2 licensing guide covers the PVU-to-VPC economics in detail, and booking a call with our team allows us to model the exact cost impact for your estate.

Legitimate Strategies to Reduce PVU Exposure

Sub-capacity PVU exposure can be reduced through a combination of workload placement decisions, VM right-sizing, and licence consolidation — all within IBM's rules. The most impactful strategies involve ensuring that IBM software VMs run on physically separate hosts from non-IBM workloads wherever possible, so that the ILMT-tracked host pool contains only the servers actually running IBM software. This reduces the peak PVU calculation by limiting the VM migration footprint.

VM right-sizing is equally important. IBM calculates sub-capacity PVU based on the maximum vCPU allocation to IBM software VMs at any point during the reporting quarter — not the average. Many enterprises provision IBM software VMs with 16 vCPUs because the application team requested it, but performance analysis shows the workload only utilises 6 vCPUs at peak. Reducing the vCPU allocation from 16 to 8 on a 70 PVU/core x86 host saves 560 PVUs per VM per quarter — at IBM's enterprise pricing, that represents a material annual saving.

The PVU-to-VPC Transition: When Sub-Capacity PVU Stops Being the Right Answer

IBM's long-term licensing direction is clearly away from PVU and towards VPC (Virtual Processor Core) via Cloud Pak and IBM Software subscription offerings. Several IBM products — including IBM Db2, IBM MQ, and WebSphere Liberty — are now available under VPC pricing through Cloud Pak for Data, Cloud Pak for Integration, and related bundles. VPC is architecturally simpler than PVU sub-capacity: 1 VPC = 1 virtual core, no PVU table, no hypervisor-specific rules, no ILMT requirement for VPC-licensed products. Download our IBM sub-capacity advisory guide for a full comparison of PVU sub-capacity versus VPC Cloud Pak economics.

However, the VPC transition is not universally cheaper. IBM has removed volume discount structures from some PVU product lines as it pushes customers to Cloud Pak, meaning that customers renewing PVU licences in 2025–2026 sometimes face 10–20% higher unit costs than their previous agreements. Enterprises need to model their specific workload requirements against both PVU sub-capacity and VPC Cloud Pak pricing before committing to a transition. Redress has conducted over 120 PVU-to-VPC cost modelling exercises for enterprise clients, and the outcome is not always lower cost under VPC — it depends significantly on the number of IBM products in use, the degree of bundling, and the enterprise's growth trajectory. To assess your specific situation, contact our IBM advisory team for a confidential review.