Virtualisation
What is vCPU?
A vCPU is a virtual processor presented to a guest, backed by scheduling time on a physical core or thread. The decisive question is whether the backing thread is shared with other tenants or reserved. A dedicated vCPU has no other tenant scheduled against it; a shared one competes, producing steal time.
Why vCPU matters
The decisive question is whether the backing thread is shared with other tenants or reserved. A dedicated vCPU has no other tenant scheduled against it; a shared one competes, producing steal time.
vCPU in practice
When you're running a server, vCPU is what your workload actually consumes. You look at steal time first: if it's consistently above a few percent, your vCPUs are shared and other tenants are eating your cycles. You might bump vCPU count to fix latency, but watch whether the problem is contention, not cores. Getting it wrong means paying for scheduling time that isn't yours, and your application suffers stalls you can't explain.
What people get wrong about vCPU
A common error is treating vCPUs as if they were physical cores with guaranteed speed. In a KVM environment, each vCPU is backed by a host thread, and on a shared host, that thread competes. People assume more vCPUs always help, but if the backing thread is contended, you get steal time. The correction: check steal time before scaling vCPU count.
vCPU — common questions
How many vCPUs do I need?
It depends on your workload. For a busy web server, start with two and watch CPU steal time. If steal stays low and you're still capped, add vCPUs. On our KVM plans, you can increase CPU and RAM with a short reboot, so you can adjust without a rebuild.
Can I change vCPU count later?
Yes, on your existing server you can increase CPU with a short reboot, and disk grows online. Moving down a tier requires a rebuild rather than a live migration, so it's better to start small and scale up.
Where vCPU comes up
- What is CPU steal time and why does it matter? Steal time is the percentage of time your virtual CPU was ready to run but the hypervisor gave the physical core to someone else. It appears as the "st" co…
- How much does a VPS cost? A usable VPS starts at about $4 a month for 1 vCPU, 1 GB of RAM and 20 GB of NVMe storage. A production instance with dedicated cores, 8 GB of RAM and 160 …
- What is the cheapest VPS that is actually usable? About $4 a month buys 1 vCPU, 1 GB of RAM and 20 GB of NVMe on real KVM virtualisation. That is genuinely enough for a WireGuard VPN, a DNS resolver, a Tor…
- What is the best VPS setup for a beginner? Start with 2 vCPU, 4 GB of RAM and Ubuntu 24.04 LTS in the region closest to you. Ubuntu has the largest body of tutorials, which matters more than any spe…
- How many visitors can a VPS handle? A well-configured 2 vCPU / 4 GB instance serves a static site to millions of monthly visits, a cached WordPress site to roughly 300,000, and an uncached dy…
- What is the difference between shared and dedicated vCPU? A shared vCPU is scheduled against other tenants, so under contention your process waits — visible as steal time. A dedicated vCPU is a physical thread res…
More from virtualisation
- KVM
- KVM is full hardware virtualisation built into the Linux kernel, giving each guest its own kernel and hardware-enforced isolation from other tenants.
- OpenVZ
- OpenVZ is container-based virtualisation in which every instance shares the host kernel, so guests cannot load kernel modules or run a different operating system.
- LXC
- LXC is Linux-native containerisation that isolates processes with namespaces and cgroups while sharing the host kernel.
- Hypervisor
- A hypervisor is the software layer that creates and runs virtual machines, allocating physical CPU, memory and IO between them.
- Nested virtualisation
- Nested virtualisation lets a virtual machine itself run virtual machines, by exposing the processor virtualisation extensions to the guest.
- cloud-init
- cloud-init is the standard mechanism for configuring a virtual machine on first boot, using metadata supplied by the platform.