This property affects the operation of the Input method. When your application collects/retrieves data from the receive buffer (See the Input method) it will return a maximum of this many bytes for each .Input operation.
The default for this property is 0 (zero). If this property is set to 0 then the Input method will retrieve ALL bytes from the receive buffer.
Leave this at default zero unless you really need to receive fixed length packets or single characters/bytes.
In MSComm32 this property, the number of bytes/characters to receive, is a 16bit integer. In .Net this is defined as a short integer. If programming in VB.Net you can pretty much ignore that fact and just treat it as an integer like any other. But if programming in C#, a stronger typed language, you'll need to be aware that a cast to (short) may be required if you process values as int. That was also the case with MSComm32 so we've kept the same type.