What is VPS ?

A Virtual Private Server shares its resources with multiple users providing fully functioning Web Server that resides within the same physical location of a true Web Server, multiple virtual servers can reside on a single Web Server, it allow hosting a number of sites simultaneously, each with a unique domain name and IP address, VPS are independent with their own operating system and resources.

What is Burstable Memory

Each Virtual Private Server has a guaranteed amount of RAM, your host always guaranteed a certain amount of system resources, as the usable memory, out of the memory available in VPS. Burstable memory set a maximum limit for the memory available  so in case if the guaranteed memory is exhausted, the users of VPS can use the memory up to the limit of burstable memory, for example if the guaranteed memory of a VPS is 512mb and the burstable memory limit is 1024 mb, the users can use the remaining 512MB RAM once their guaranteed memory is completely used up.

This is possible only if the host server has that much memory available with it, however it is always best not to use the burstable memory unless it is emergency.Bursted memory are not guaranteed but it can be allocated to any VPS that may need it as long as it is available on the box at that time. So as long as those resources are available, as a user you can be able to go over that limit of guaranteed RAM.

While looking for VPS server you should make proper analysis of the memory availability considering the VPS provider that work to make sure that an ample amount of burst resources are always available on each host machine. In case if your VPS constantly requires greater resources than your allocated guarantees memory, you should upgrade your account.