What is the meaning of handle in relation to computers?

Answer 1

A handle provides the means by which we can refer to an object by a virtual memory address rather than its physical address. There are only 4 gigabytes of physical addresses available on a 32-bit system, where each address refers to a single byte of memory. However, not all 32-bit systems have a full complement of 4 gigabytes of physical memory. So, when a memory request is made but there is insufficient physical memory available to meet the request, objects that are already allocated may be moved out of memory and stored in a hard-disk file, thus freeing the physical memory to meet the allocation request. Any object that was moved out of memory can be moved back into memory when it is needed, however there is no guarantee that the object will exist at the same address it was originally allocated, because if the object that currently resides at that address is in use it cannot be moved out. Thus, an object's physical address may change at any time.

When we make a memory request, the operating system returns the start address of the allocation, allowing us to refer to the allocation. However, if that address can change at any time we would not be able to refer to the objects stored within that allocation because we'd still be referring to the original location. To get around this, the operating system returns a virtual address rather than a physical one. The operating system maintains a table of these virtual addresses and maps them to physical addresses. As objects are swapped to and from physical memory, the operating system updates the table accordingly. In this way, we can refer to objects through their virtual addresses and the operating system will translate those addresses into physical ones.

A virtual address is, therefore a handle; it allows us to "hold" our memory allocations by referring to objects through their virtual addresses.