# Type 1 hypervisor

> Source: Courseiva IT Certification Glossary — https://courseiva.com/glossary/type-1-hypervisor

## Quick definition

A Type 1 hypervisor is software that installs directly onto a computer's hardware, like a bare metal server. It allows you to run multiple virtual machines, each with its own operating system, by managing the hardware resources directly. Unlike Type 2 hypervisors, it does not need a regular operating system like Windows or Linux underneath it. This makes it very efficient and stable, which is why data centers and cloud providers prefer it.

## Simple meaning

Imagine you own a large apartment building. The building itself is the physical server hardware. A Type 1 hypervisor is like the building's central management system that controls everything: electricity, water, heating, and access to each apartment. It does not need a separate manager living in the building to tell it what to do. Instead, it controls everything directly from the building's core systems.

Now, each apartment in the building is a virtual machine. Each tenant (operating system) can live in their own apartment, decorate it however they want, and run their own appliances (applications). The central management system (the hypervisor) makes sure that no tenant uses more than their fair share of electricity or water. If one tenant tries to run a huge air conditioner that would blow a fuse, the management system steps in and limits their power usage.

In the IT world, a Type 1 hypervisor works the same way. It sits directly on top of the server hardware, managing the CPU, memory, storage, and network connections. It creates isolated environments (virtual machines) and allocates resources to each one. Because there is no middle layer (like a regular operating system), the hypervisor can use the hardware very efficiently. This is why cloud giants like Amazon Web Services, Microsoft Azure, and Google Cloud use Type 1 hypervisors for their virtual servers. It gives them maximum performance, security, and the ability to move virtual machines between physical servers without any downtime.

## Technical definition

A Type 1 hypervisor, also known as a bare-metal hypervisor, is a virtualization layer that runs directly on the physical hardware of a host machine without an underlying operating system. It acts as a lightweight operating system that manages hardware resources and provides isolated execution environments called virtual machines (VMs). Unlike Type 2 hypervisors, which run as applications on top of an existing OS, Type 1 hypervisors have direct access to the hardware components such as the CPU, memory, storage controllers, and network interface cards.

The architecture of a Type 1 hypervisor consists of a small microkernel that handles CPU scheduling, memory management, and interrupt handling. It uses hardware-assisted virtualization technologies like Intel VT-x and AMD-V to improve performance and isolation. The hypervisor exposes virtualized hardware interfaces to each guest VM, which includes virtual CPUs (vCPUs), virtual memory, virtual disks, and virtual network adapters. The hypervisor's scheduler allocates physical CPU time slices to each vCPU, often using techniques like proportional fairness or credit-based scheduling to ensure fair resource distribution.

Memory management in Type 1 hypervisors involves shadow page tables or hardware-based nested page tables (Intel EPT or AMD NPT) to translate guest virtual addresses to physical addresses efficiently. The hypervisor also implements device emulation or paravirtualized drivers to allow guest operating systems to interact with hardware. For example, VMware ESXi uses the VMkernel as its core, while Microsoft Hyper-V uses a similar microkernel approach on Windows Server. KVM (Kernel-based Virtual Machine) in Linux is also considered Type 1 because it turns the Linux kernel into a hypervisor via a kernel module.

In real IT implementations, Type 1 hypervisors are deployed in server clusters within data centers. They support features like live migration (moving a running VM from one physical host to another without downtime), high availability (restarting VMs on another host if one fails), and resource pools. They also integrate with storage area networks (SAN) and virtual local area networks (VLANs) for scalable infrastructure. Security is enforced through hypervisor-level firewalls, role-based access control, and secure boot processes for VMs. Understanding these technical details is critical for IT professionals managing cloud and virtualized environments, especially when troubleshooting performance issues or planning capacity.

## Real-life example

Think of a large office building with multiple tenants. The building itself is the physical server hardware. The Type 1 hypervisor is the building's property management system that controls all the core infrastructure: elevators, HVAC system, electrical panels, and security gates. The management system runs directly on the building's central control panel, not on some external office computer. It does not need a building superintendent's desktop PC to function.

Each tenant leases an office suite, which is like a virtual machine. The tenant can bring in their own furniture, computers, and phone systems (their operating system and applications). The property management system ensures that each tenant gets their fair share of electricity, cooling, and elevator usage based on their lease agreement (resource allocation). If one tenant tries to run a massive data center that would overload the building's power grid, the management system has the authority to limit their power draw or even shut them off.

Now, imagine the building has an emergency. A fire alarm goes off. The property management system can automatically shut down power to certain areas, lock doors, and notify the fire department. In the same way, a Type 1 hypervisor can handle hardware failures by automatically restarting failed VMs on a different physical server. It can also move a tenant's entire office (a running VM) to a different floor (another server) without the tenant even noticing, because the hypervisor can migrate the VM live while it is still running.

This direct control over the building's infrastructure is what makes Type 1 hypervisors so efficient and reliable. They do not have to go through a middleman (a host operating system) to manage hardware, so they can respond faster and use resources more effectively. This is exactly why data centers use them: they need maximum performance and stability for critical applications like web servers, databases, and email systems.

## Why it matters

In practical IT, the choice between Type 1 and Type 2 hypervisors has significant implications for performance, security, and management. Type 1 hypervisors are the backbone of modern data centers and cloud computing. When you spin up a virtual server on AWS EC2 or Microsoft Azure, you are almost certainly running on a Type 1 hypervisor like KVM (used by AWS) or Hyper-V (used by Azure). This matters because these environments need to support thousands of customers securely and efficiently.

From a performance perspective, Type 1 hypervisors introduce very little overhead because they control hardware directly. This means virtual machines can achieve near-native performance, which is critical for resource-intensive applications like databases, big data analytics, and real-time processing. For example, a SQL Server database running in a VM on VMware ESXi can achieve throughput that is 90-95% of what it would be on bare metal. This efficiency directly affects the bottom line: organizations can consolidate more workloads onto fewer physical servers, saving on hardware, power, and cooling costs.

Security is another major advantage. Since there is no general-purpose operating system beneath the hypervisor, the attack surface is much smaller. The hypervisor itself is a minimal codebase with fewer vulnerabilities. Each VM is isolated from others by the hypervisor, preventing a compromised guest from accessing another guest's memory or storage. This isolation is foundational to multi-tenant cloud environments where one customer's VM must not be able to read another's data.

Management and automation are also key. Type 1 hypervisors come with centralized management tools like VMware vCenter, Microsoft System Center, or Proxmox VE. These tools allow administrators to monitor all hosts, migrate VMs, balance loads, and apply patches across the entire virtual infrastructure from a single pane of glass. Without Type 1 hypervisors, modern cloud computing as we know it would not be possible.

## Why it matters in exams

Type 1 hypervisors are a core topic in several major IT certification exams, including CompTIA A+, CompTIA Network+, CompTIA Server+, CompTIA Cloud+, Microsoft Azure Administrator (AZ-104), VMware VCP, and the AWS Certified Solutions Architect exams. In each of these, the concept appears in different forms, and exam candidates must understand both the definition and the practical implications.

For CompTIA A+ (220-1101), Type 1 hypervisors appear in the virtualization and cloud computing domain. You might be asked to differentiate between Type 1 and Type 2 hypervisors. A typical question could be: 'Which hypervisor type runs directly on server hardware and is commonly used in data centers?' The correct answer is Type 1. You might also be asked to identify examples: VMware ESXi, Microsoft Hyper-V, and Citrix XenServer are Type 1; Oracle VirtualBox and VMware Workstation are Type 2.

In CompTIA Cloud+ (CV0-003), the concept goes deeper. The exam covers hypervisor selection based on workload requirements, performance considerations, and management features. You might face a scenario where a company needs to consolidate 20 physical servers into a virtualized environment with high availability and live migration. The correct solution would involve deploying a Type 1 hypervisor like VMware ESXi with vSphere HA and vMotion. The exam could also ask about resource allocation: 'Which hypervisor feature allows a VM to use more CPU than its allocated limit temporarily?' The answer is CPU overcommitment, a feature better supported by Type 1 hypervisors.

For the Azure Administrator (AZ-104) exam, while Azure uses Hyper-V as its underlying hypervisor, the exam focuses on managing VMs, not the hypervisor itself. However, understanding that Azure runs on a Type 1 hypervisor helps you grasp concepts like reserved instances, VM sizes, and availability sets. The exam might ask about VM placement and redundancy, and knowing that the hypervisor handles fault domains can be useful.

VMware VCP (VCP-DCV) exam questions go very deep. You might be asked about the VMkernel architecture, how it handles network I/O, or how to configure a hypervisor for NUMA (Non-Uniform Memory Access) alignment. The exam tests your ability to configure ESXi hosts, set up networking, and troubleshoot performance issues related to hypervisor overhead.

Across all these exams, the key is to remember that Type 1 hypervisors are optimized for production environments. They provide better performance, security, and scalability than Type 2. Exam questions often try to trap you by mixing up features or by giving scenarios where a Type 2 hypervisor might be appropriate (like a developer testing a VM on their laptop). Always think about whether the scenario involves a data center or a personal workstation.

## How it appears in exam questions

Exam questions about Type 1 hypervisors typically fall into several categories: definition, comparison, scenario-based, and troubleshooting. In definition questions, you might see something like: 'Which of the following best describes a Type 1 hypervisor?' The answer will emphasize that it runs directly on the host hardware without an underlying operating system. The distractors might describe Type 2 hypervisors or other virtualization concepts.

Comparison questions are very common. You could be asked to pick the correct statement about Type 1 versus Type 2 hypervisors. For example: 'A Type 1 hypervisor has lower overhead than a Type 2 hypervisor because it does not rely on a host OS for hardware access.' This is true. Another question might ask about security: 'Which hypervisor type provides stronger isolation between VMs?' The answer is Type 1, because it has a smaller attack surface and direct hardware control.

Scenario-based questions are where you really need to think. Imagine this: 'A company is planning to virtualize its production database servers. They need maximum performance and the ability to migrate VMs between physical hosts without downtime. Which hypervisor type should they choose?' The answer is Type 1, specifically one that supports live migration like VMware ESXi. Another scenario: 'A software developer wants to run a Linux VM on their Windows laptop for testing. Which hypervisor type is most appropriate?' The answer is Type 2, like VirtualBox, because it is easier to set up and does not require bare-metal installation.

Troubleshooting questions might ask about performance issues. For example: 'A virtualization administrator notices that VMs respond slowly during peak hours. The hypervisor is a Type 1. What could be the issue?' Possible answers could include CPU overcommitment, memory ballooning, or storage I/O contention. The question might require you to identify that the hypervisor's resource scheduling is being overwhelmed, and the solution could be to reduce the number of VMs per host or increase hardware resources.

Some exams include configuration questions. For example: 'An administrator needs to configure a new ESXi host. Which of the following is required for the installation?' The answer might be a bootable USB drive with the ESXi ISO, or understanding that the hypervisor needs direct hardware access and cannot be installed on top of Windows. Other questions might ask about supported file systems: 'Which file system is typically used by Type 1 hypervisors for storing virtual machine files?' The answer could be VMFS (VMware) or NTFS (Hyper-V).

Finally, some questions test your knowledge of related technologies. For instance: 'What is the purpose of Intel VT-x in a Type 1 hypervisor?' The answer is hardware-assisted virtualization, which improves performance by offloading certain tasks to the CPU. By understanding these question patterns, you can prepare to answer confidently.

## Example scenario

You are the IT administrator for a medium-sized company called TechVille Inc. The company runs several critical business applications: an email server, a customer database, a web server for the company website, and a file server. Currently, each application runs on its own physical server. That means you have four separate machines taking up rack space, consuming electricity, and generating heat. The CEO wants to reduce costs and improve efficiency.

You propose moving all four servers into a virtualized environment using a Type 1 hypervisor. You purchase a single powerful physical server with 32 CPU cores, 256 GB of RAM, and 10 TB of storage. You install VMware ESXi directly onto the server's hard drive. This is your Type 1 hypervisor. Once it is running, you create four virtual machines. You configure one VM with 8 vCPUs and 64 GB of RAM for the database server. Another VM gets 4 vCPUs and 32 GB of RAM for the email server. The web server and file server get smaller allocations. You install Windows Server on each VM and then restore the applications from backups.

Now, the magic of the Type 1 hypervisor becomes clear. The hypervisor manages the physical resources directly. If the web server suddenly gets a huge spike in traffic due to a marketing campaign, the hypervisor can dynamically give it more CPU time from the shared pool (if you have configured resource scheduling to allow bursting). If the database server VM crashes, the hypervisor can automatically restart it on the same host without needing any manual intervention. If you need to perform maintenance on the physical server, you can use live migration to move all four VMs to another ESXi host in your cluster while they are still running. Users experience zero downtime.

This scenario shows how a Type 1 hypervisor solves real business problems: it reduces hardware costs, improves resource utilization, simplifies management, and increases availability. Without the hypervisor, you would need four times the hardware and would struggle to maintain uptime during maintenance windows.

## Common mistakes

- **Mistake:** Thinking a Type 1 hypervisor needs a host operating system like Windows or Linux to run on.
  - Why it is wrong: A Type 1 hypervisor is designed to run directly on the bare metal hardware. Installing it on top of an OS defeats its purpose and introduces overhead and compatibility issues.
  - Fix: Remember that Type 1 is 'bare-metal.' It boots directly on the server hardware, just like an operating system, but it is much smaller and purpose-built for virtualization.
- **Mistake:** Confusing Type 1 hypervisors with Type 2 hypervisors, especially by labeling VMware Workstation as Type 1.
  - Why it is wrong: VMware Workstation is a Type 2 hypervisor because it runs as an application on top of a host OS (Windows or Linux). VMware ESXi is Type 1 because it runs directly on hardware.
  - Fix: Know the examples: Type 1 = ESXi, Hyper-V (when installed as server role), XenServer, KVM. Type 2 = VirtualBox, VMware Workstation, Parallels Desktop.
- **Mistake:** Believing that Type 1 hypervisors are only for large data centers and not relevant for small businesses.
  - Why it is wrong: While large data centers popularized them, small businesses can also benefit from Type 1 hypervisors on a single server to consolidate workloads, reduce costs, and simplify backup.
  - Fix: Think of Type 1 hypervisors as a tool for any environment where reliability and resource efficiency matter, even if it is just a few VMs on one server.
- **Mistake:** Assuming that all Type 1 hypervisors support the exact same features, like live migration or high availability.
  - Why it is wrong: Features vary by vendor and licensing. For example, basic Hyper-V does not include live migration without System Center; VMware vMotion is included in higher vSphere editions.
  - Fix: When studying, learn the features of each Type 1 hypervisor separately, especially for exam scenarios that compare functions like live migration, snapshots, and clustering.
- **Mistake:** Thinking that Type 1 hypervisors are inherently more secure than Type 2 in every way.
  - Why it is wrong: While Type 1 has a smaller attack surface, security still depends on proper configuration, patching, and isolation policies. A misconfigured Type 1 can be vulnerable.
  - Fix: Focus on best practices: keep the hypervisor updated, restrict management access, use network segmentation, and enable secure boot for VMs.

## Exam trap

{"trap":"Mixing up Type 1 and Type 2 by saying 'Hyper-V is Type 2 because it runs on Windows.'","why_learners_choose_it":"Learners see Hyper-V as a Windows feature that requires the Windows OS, so they assume it is a Type 2 hypervisor. They do not realize that Hyper-V replaces the Windows kernel with its own hypervisor when enabled, making it Type 1.","how_to_avoid_it":"Understand that Hyper-V, when the Hyper-V role is installed, turns the Windows Server OS into a partition running on top of the hypervisor. The hypervisor itself boots first and loads the parent partition. This makes it a Type 1 hypervisor. In contrast, VirtualBox or VMware Workstation run as applications under the existing OS, which is Type 2."}

## Commonly confused with

- **Type 1 hypervisor vs Type 2 hypervisor:** A Type 2 hypervisor runs as a software application on top of an existing host operating system. It has higher overhead because hardware requests go through the host OS. Type 1 runs directly on hardware with no host OS, giving better performance and security. (Example: Using VMware Workstation on a Windows laptop to run a Linux VM is Type 2. Using VMware ESXi on a dedicated server is Type 1.)
- **Type 1 hypervisor vs Containerization (Docker):** Containers share the host OS kernel and do not require a hypervisor for isolation. They are lighter and start faster than VMs, but they cannot run different operating systems on the same host. Type 1 hypervisors run full VMs with separate kernels. (Example: If you need to run a Linux app on a Linux server and want minimal overhead, use Docker containers. If you need to run Windows and Linux side by side on the same hardware, use a Type 1 hypervisor.)
- **Type 1 hypervisor vs Bare-metal server:** A bare-metal server is a physical server with no virtualization layer. The OS runs directly on the hardware. A Type 1 hypervisor also runs directly on hardware, but it enables multiple VMs, while bare-metal runs a single OS. (Example: Renting a dedicated server from a hosting provider where you install Windows directly is bare-metal. Using the same server with VMware ESXi to run multiple VMs is Type 1 hypervisor.)
- **Type 1 hypervisor vs Virtual machine monitor (VMM):** A VMM is the core component of a hypervisor that manages the virtual machines. The term 'hypervisor' is often used interchangeably with VMM, but technically the hypervisor includes both the VMM and management tools. Type 1 hypervisors have their own VMM built in. (Example: VMware ESXi's VMM is the part that schedules vCPUs and manages memory. The full hypervisor includes the VMkernel and management interfaces.)

## Step-by-step breakdown

1. **Hardware Preparation** — The physical server is prepared with compatible hardware: CPU that supports virtualization extensions (Intel VT-x/AMD-V), sufficient RAM, storage, and network interfaces. BIOS settings must enable virtualization technology. This step ensures the hypervisor can directly access hardware features.
2. **Hypervisor Installation** — The Type 1 hypervisor software (e.g., VMware ESXi ISO) is installed directly onto the server's local storage or booted from a USB drive. During installation, the hypervisor creates its own partition and file system (e.g., VMFS) without needing a host OS. The server reboots into the hypervisor.
3. **Resource Pool Initialization** — After booting, the hypervisor detects all hardware components: CPU cores, RAM modules, storage controllers, and network adapters. It creates a resource pool that will be shared among virtual machines. The hypervisor's microkernel initializes device drivers and interrupt handlers.
4. **Virtual Machine Creation** — An administrator uses a management tool (e.g., vSphere Client or Hyper-V Manager) to define a new VM. They specify virtual hardware: number of vCPUs, amount of virtual RAM, virtual disk size, and network settings. The hypervisor allocates the specified resources from the pool and creates a configuration file (e.g., .vmx for ESXi).
5. **Guest OS Installation** — The VM is powered on, and it boots from an ISO image or installation media. The guest operating system (e.g., Windows Server, Ubuntu) is installed inside the VM. The hypervisor emulates virtual hardware (network card, disk controller) that the guest OS sees as real devices.
6. **Resource Scheduling and Management** — Once VMs are running, the hypervisor's scheduler distributes CPU time slices and memory pages to each vCPU and guest. It uses algorithms like credit-based or weighted fair queuing to enforce resource limits and shares. The hypervisor also handles I/O requests from guests by forwarding them to physical devices or emulating them.
7. **Ongoing Maintenance and Migration** — Administrators can perform live migration (vMotion) to move a running VM to another physical host without downtime. The hypervisor copies memory pages to the destination while the VM runs, then switches over seamlessly. This enables hardware maintenance, load balancing, and disaster recovery.

## Practical mini-lesson

Let us dive into the practical side of Type 1 hypervisors. If you are an IT professional managing virtualized infrastructure, you need to understand how these hypervisors work in the real world, not just for exams.

First, consider installation. Most Type 1 hypervisors are deployed from a bootable ISO or USB drive. For example, to install VMware ESXi, you boot the server from the ESXi installer. The installer detects storage devices and offers to install on the first disk it finds. It is critical to verify that the server hardware is on the vendor's Hardware Compatibility List (HCL). If the storage controller or network card is not supported, the hypervisor may not boot or may have limited features. After installation, you configure the management IP address so you can connect via a client or web browser.

Once the hypervisor is running, you connect to it using a management interface. For ESXi, that is the vSphere Client or the web interface. From there, you create datastores (VMFS volumes) on your storage. You can use local disks, iSCSI SAN, or NFS storage. Datastores hold VM files like virtual disks (.vmdk), configuration files, and snapshots. You need to plan storage layout carefully: separate fast SSD storage for performance-critical VMs and larger spinning disks for less demanding workloads.

Creating a VM is straightforward, but there are configuration pitfalls. For instance, if you allocate too many vCPUs to a VM (more than the physical cores), the hypervisor will overcommit CPU resources. While this is allowed, it can cause performance contention. A practical rule is to not allocate more than 2-3 vCPUs per physical core for production workloads. Memory is another concern. Hypervisors use transparent page sharing (TPS) or memory ballooning to reclaim unused memory from VMs, but overcommitting memory can lead to swapping and poor performance. Always monitor memory usage with tools like esxtop or vCenter performance charts.

Networking in hypervisors is a topic on its own. You create virtual switches (vSwitch) that connect VMs to physical network adapters. You can configure VLANs, team multiple NICs for redundancy, and set up traffic shaping. A common mistake is placing all VMs on one virtual switch without proper segmentation, which can cause broadcast storms or security issues. Best practice is to isolate management traffic, VM traffic, and storage traffic onto different VLANs or separate physical NICs.

What can go wrong? A lot. If your storage has high latency, VMs will feel sluggish even if CPU and RAM are fine. If you lose a network connection to the storage, VMs may crash or become read-only. Hypervisor crashes are rare but can happen due to faulty hardware or driver issues. Always keep the hypervisor patched and run hardware diagnostics regularly. Also, never forget to back up VM configurations and use features like snapshots before making changes, but be aware that long-lived snapshots degrade performance.

In production, you typically have multiple hypervisor hosts managed as a cluster. This allows features like Distributed Resource Scheduler (DRS) which automatically balances VMs across hosts based on load. High Availability (HA) monitors hosts and restarts VMs on other hosts if one fails. Understanding these practical aspects will make you a better administrator and help you pass certification exams that require real-world judgment.

## Memory tip

Think 'Bare Metal Boss', Type 1 hypervisor is the boss that commands hardware directly, no middle manager OS needed.

## FAQ

**What is the difference between Type 1 and Type 2 hypervisors?**

Type 1 hypervisors run directly on the hardware with no host OS, giving better performance and security. Type 2 hypervisors run as applications on top of a host OS, which adds overhead but is easier to set up on personal computers.

**Is Microsoft Hyper-V a Type 1 or Type 2 hypervisor?**

Hyper-V is a Type 1 hypervisor. When you enable the Hyper-V role on Windows Server, it installs a hypervisor layer that boots before the parent partition, making it bare-metal.

**Can I run a Type 1 hypervisor on my laptop?**

Technically, some laptops support it, but it is not practical because it would replace your existing OS. For laptops, Type 2 hypervisors like VirtualBox are the right choice.

**What is live migration and which hypervisors support it?**

Live migration moves a running VM from one physical host to another with zero downtime. VMware vSphere (with vMotion), Microsoft Hyper-V (with System Center), and KVM all support it.

**Do I need a license for Type 1 hypervisors?**

Some are free (VMware ESXi free edition, Proxmox VE, KVM), while others require paid licenses for advanced features like live migration or high availability (VMware vSphere, Hyper-V in Server Standard).

**What hardware requirements does a Type 1 hypervisor have?**

The server must have a CPU with virtualization extensions (Intel VT-x or AMD-V), enough RAM and storage for the VMs, and compatible network and storage controllers. Check the vendor's HCL.

**Can Type 1 hypervisors run on ARM processors?**

Yes, some Type 1 hypervisors support ARM, such as KVM on ARM64 hardware. However, most enterprise hypervisors (ESXi, Hyper-V) primarily target x86 architectures.

## Summary

Type 1 hypervisors are the backbone of modern data center virtualization and cloud computing. They run directly on the physical hardware of a server, without needing a separate operating system beneath them. This bare-metal approach gives them superior performance, security, and resource efficiency compared to Type 2 hypervisors. They are used by major cloud providers like AWS, Azure, and Google Cloud to offer virtual servers to millions of customers.

For IT certification candidates, understanding Type 1 hypervisors is essential. Whether you are studying for CompTIA A+, Network+, Cloud+, Azure Administrator, or VMware VCP, you will encounter questions that test your knowledge of hypervisor types, features, and real-world application. Common exam traps include confusing Hyper-V as Type 2, misunderstanding the role of the host OS, and mixing up virtualization with containerization.

The key takeaway for exams is to remember that Type 1 hypervisors are designed for production environments where performance, stability, and isolation are critical. They support enterprise features like live migration, high availability, and centralized management. When you see a scenario involving data center consolidation, virtualized servers, or cloud infrastructure, think Type 1 hypervisor. With the right understanding, you can confidently answer definition, comparison, and scenario-based questions on your certification exam.

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Practice questions and the full interactive page: https://courseiva.com/glossary/type-1-hypervisor