Your A2 Hosting account comes pre-configured with PHP accelerator OPcache. External tests have shown OPcache offers up to 50% faster PHP processing! While some users prefer accelerators like eAccelerator or xCache, we've found the largest performance boost with OPcache. OPcache is available by default with PHP 5.5, while APC is available on previous PHP versions.
Similarly, in the case of VPS, there are several users that are using the same server but they are isolated from each other. It means that no one will be affected by how much resources another is using. You will get the speed and security that you need without compromise. It is almost a perfect scenario because you will get the benefits of a private server with shared cost of services.
Shared hosting is cheap and allows you to install any gallery platform you wish if a hosting plan meets its requirements. But be careful and study your hosting provider’s Acceptable Use Policy thoroughly. The truth is, that even if they claim unlimited storage with their plans, they don’t want you to use much of it. On the contrary, they secretly hope that you will use less and they can host many other clients on the same server. For that reason, hosting providers usually put limitations on their policies (e.g. “no more than 10 GB for images,” etc.). So don’t be convinced that you have unlimited storage without first checking your shared hosting provider's policies or you will find your account suspended someday.
Similarly, in a real dedicated server, you will pay for the entire server that is not shared with anyone else. You will get complete control over all services. Unfortunately, it is also the most expensive hosting option and needs some technical expertise to manage. It is commonly used by those who have websites with specific scenarios, most commonly extremely high traffic and tight security requirements.
Operating System virtualization refers primarily to Type-2 hypervisors like KVM or platforms like OpenVZ & Virtuozzo that share the Linux kernel (+ drivers) between partitions on the same web server hardware. This form of VPS is common in managed cloud plans where the web hosting company provides a custom web server stack software such as LAMP/LEMP pre-installed on a VM partition. Multiple customers can share a single dedicated or rackmount server with better security, file isolation, database, and programming language extension support than shared hosting provides, as well as having access to a higher level of web server resources when processing scripts like PHP, Python, or Node.js code. Some forms of OS virtualization will also permit Windows, Linux, & BSD to be installed on the same physical hardware.
If you are familiar with hosting control panels, shell commands, and you have basic server administration and troubleshooting skills, then unmanaged VPS is the way to go. Note that while you purchase self managed VPS, you should be capable of managing applications, software, services installed on your VPS. Also, you must know installation/uninstallations, resource monitoring, server performance tweaking and troubleshooting of any technical issues.