There are several variables that decide how many JBE (jazz build engines) you'll need for your project. For example, the length of the build and the number of builds you'll have to run in a day are probably the aspects that will decide on the # of JBEs needed.

You can run several JBEs on the same machine, as long as you've carefully scripted the build scripts such that they don't step on each other (eg, paths and root directories in which code is loaded, etc).

Cheers,
Jean-Michel

Note also that JBE runs as a client of the Jazz server, it's not itself a server (the terminology gets confusing because the machines on which builds run are often called build servers).

I wouldn't recommend running JBE on the same machine as the Jazz server, since you don't want builds taking cycles away from regular server operations.

As JM says, you can run multiple JBEs on the same machine, but it takes some care, e.g. if a build definition is supported by two or more build engines that run on the same machine, its load directory needs to be configured carefully to avoid collisions, e.g. specify ${buildResultUUID} as part of the load directory, but then this will consume more disk space than always using the same load directory for each build.