What are the similarities between a process and a thread?

Answer 1

Thread and Process both do the same thing. ie. parallel jobs done on a CPU. The thread is under the process's control, ie. the programmer can control the thread regard to its priority, memory etc. I am not very sure about multi-threading and process-control under Windows. We have a process control system running on a 8086 based system. It is of Siemens make. It supports 64 threads which are called Tasks in their terminology. Initiation of task, suspending the task, readying the task etc is under the control the program, ie user software. In another computer Data General's M-600, we had multiple processes (max 64), each having a logical address space of 64 kilo bytes. Under each process we can have multiple tasks (I think max 32 tasks). The task control block is in the program's memory space. Intertask communication is pretty simple here. Sharing memory between tasks is simple as the entire memory of the process is under the control of the process. I have used a muti-tasking program under windows. One task continuously communicates with a groupp of microprocessor based controlers over RS-485, and another task processes the read data and does display, storage etc. The program was written in VC++(6.0) . Here the sharing of memory is easy as the entire memory of the process is shared between the tasks(threads). But VB uses something called compartmental multi-threading, meaning each thread has its own compartment of resources.

Answer 2

both process and thread are independent sequence of execution