Sometimes people mistakenly use "Gen1" and "Gen2" when talking about VMware, usually in the context of importing VMs from Hyper-V or nested virtualization. In Hyper-V "Gen1" and "Gen2" are Microsoft Hyper-V virtual machine generation types. Here’s the breakdown: In Hyper-V Generation 1 (Gen1) * Emulates legacy BIOS-based boot (MBR partition). * Uses IDE controllers for the virtual hard disks. * Supports older guest operating systems (e.g., Windows Server 2008, 2012). * Doesn’t support Secure Boot or UEFI features. * Better for compatibility when the guest OS doesn’t support UEFI. Generation 2 (Gen2) * Uses UEFI firmware (GPT partition support). * Boots directly from SCSI virtual disks. * Supports Secure Boot, PXE boot via synthetic network adapter. * No floppy drives or legacy hardware. * Recommended for newer OS versions (Windows Server 2012 R2 and later). In VMware VMware does not have "Gen1" or "Gen2" labels, but the concept maps like this: Gen1 ===== VM configured with BIOS firmware (in VM options). Gen2 ===== VM configured with EFI / UEFI firmware. When creating or editing a VM in VMware: * BIOS Mode → Use when migrating older OS that require MBR boot. * EFI / UEFI Mode → Use for modern OS, Secure Boot, and GPT partitioning. When to choose in VMware: Use BIOS if: * OS only supports legacy BIOS boot. * You’re importing a Gen1 Hyper-V VM. Use UEFI if: * OS supports it (modern Windows/Linux). * You want Secure Boot or GPT. * You’re importing a Gen2 Hyper-V VM.