Q&A: Why is My Virtual Machine so Slow?

Why is my virtual machine so slow

Virtual machines are useful. They are used by many professionals from a wide variety of fields. Cybersecurity experts use virtual machines to find vulnerabilities in a software system. And many Software developers use them to test their applications on different platforms and operating systems.

But as useful as they are, they can be very problematic at times. Of course, virtualization is a resource-intensive process and the Guest OS won’t ever be as snappy as a host machine. But sometimes they can be really, really slow.

Why is Your Virtual Machine so Slow?

Virtual machines can run slow for a lot of reasons. Here are some common culprits:

1. The host isn’t capbale enough

The first thing you want to check is your host machine. Maybe it isn’t just powerful enough to run the VMs smoothly.

Virtualization is a resource-intensive task. A virtual machine requires a lot of RAM to run, and constantly uses the host‘s resources. So a high-performance host machine is necessary to run VMs smoothly.

There are mainly three resources a VM uses: The CPU, memory, and secondary storage. Virtual machines demand a lot of processing power. You want a fast multi-core processor to run them. They also require a lot of free memory to run smoothly. Shortage of free memory is often responsible for lags and slowdown in virtual machines.

And then you need a fast SSD with high Read/Write speed. Any operating system performs I/O operations on a regular basis. So if you run a VM from an HDD (which is way slower than SSDs), it may run very slow.

You can check the task manager to see how much resource the VM is using.

You can see resource usage of the Virtualbox process in Windows Task Manager
The Virtualbox process in Windows Task Manager

If you see that any of the three resources are almost used up by the VM, the culprit is the host machine.

2. The Virtual Machine is Badly Configured

Another common cause for a slow VM is bad configuration. You need to configure your VM program (also called a hypervisor) properly to maximize performance. You don’t necessarily have to reconfigure everything.

Another mistake people make is that they allocate too much system resource to the VM. This limits the host’s performance, which in turn slows down the VM. To ensure this isn’t the case, find a sweet spot between your guest’s requirements and the amount recommended by your VM program.

Ram Aloocation on Virtualbox.
Virtualbox Memory allocation window. The green part of the bar is what you can safely allocate.

3. The VM software isn’t functioning properly

The VM application can sometimes cause slowdowns. Sometimes a particular OS isn’t fully compatible with your VM software. Some hypervisors play better on one OS than another.

You could just try another VM program to see if the problem gets solved. Here are a few you can try:

  1. VMware
  2. VirtualBox
  3. Parallels Desktop
  4. QEMU

Upgrade your hardware to speed up VM

If you found that the host isn’t just capable enough, upgrading your hardware is the best solution.

Virtual machines are resource-intensive. They require a lot of RAM, use the CPU constantly, and make a lot of I/O requests. For a smooth experience, there isn’t just an alternative to upgrading hardware.


The host’s memory size plays an integral part in VM performance. If you have very little memory, your guest OS will definitely run slow. You want to at least meet the minimum requirement of the guest OS without taking too much from the host.

A good rule of thumb is to allocate one-third of the host’s memory to the VM. You also don’t want to allocate too much, or you may slow the host down.


The clock speed and the number of threads in a CPU can affect VM speed. The higher, the better. Both AMD and Intel processors are great for virtual machines, with fast clock speeds and higher core counts. But we recommend AMD since their CPUs have more threads.

Disk Usage

If you’re running the VM from an HDD and it runs slow, check the disk speed first. Hard drives aren’t great for operating systems, their high I/O latency slows the system down. A solid-state drive or an SSD is more suited to run operating systems.

SSDs offer higher data transfer rates, and their I/O latency is very low. They can significantly enhance VM performance due to their remarkably fast access speeds.


Virtual machines come in handy in different situations. But a slow VM can be more painful than useful. Especially if you are a professional, it can highly affect your creativity and productivity.

Did our solutions work? Let us know in the comments.

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