QCOW is a file format for disk images used by QEMU virtualization software. It was developed by Fabrice Bellard. QCOW uses a disk storage optimization strategy that delays allocation of storage until needed. This reduces file size. Three versions exist: qcow, qcow2 and qcow3. These use the extensions .qcow, .qcow2 and .qcow3.
QEMU differs from other virtualization software. Other software assigns fixed disk space, where part can remain unused. QCOW uses a “delay allocation” strategy for storage. It allocates storage as needed. This reduces file size.
QCOW allows running multiple operating systems on one physical machine. It is an emulator and virtualization solution. QCOW files contain disk images for guest operating systems. Files can be compressed with zlib and encrypted with AES.
QEMU
VirtualBox
KVM