opencl code concept

hello everyone,I am new to OpenCL.I have a few questions about work items.I am trying to find the sum of an array.I am trying to compute the sum by dividing the array into several parts and each work item will sum up a part of the array.suppose I have 20 elements in the array and I have 4 work items.So I want each work item to get 5 elements each and then they will compute the sum of each part using a loop but all the work items will work simultaneously so that I have the sum of the 4 parts after 4 time units.So I want to know how many work items can work parallely in my computer?Please help.

It varies, but some devices are capable of running hundreds or thousands of work items in parallel. You should design kernels to be launched over thousands or millions of work items to best utilize the hardware.

use clGetDeviceInfo to get CL_DEVICE_MAX_WORK_ITEM_SIZES