User space is the address space of the virtual memory of the operating system allocated to user programs, in contrast to the kernel space , which is reserved for the kernel of the operating system , its extensions, and possibly some device drivers . In English-language computer literature, the term often used to refer to a collection of applications that run in user space.
Each process in user space is usually executed in its own area of virtual memory , and in the absence of an obvious need, it cannot gain access to the memory used by other processes. This approach is basic to ensure the memory protection of most modern operating systems, and a kind of "foundation" for ensuring access rights . Depending on privileges, a process may request the kernel to map part of the address space of another process to its own, as, for example, debuggers do. Programs can also request for themselves the area of shared memory in conjunction with other processes.
Some experimental operating systems use a different approach - for all software products, a single address space is used , taking into account the fact that the implementation of a virtual machine ensures the impossibility of random access - applications simply cannot get references to objects to which they do not have access [1] , this approach has been used in operating systems such as JXOS , Unununium , Phantom OS , Microsoft Singularity .
An important element in the design of system software is a solution for implementation in kernel space or user space. In particular, in UNIX systems, before the advent of FUSE technology in the 2000s, when mounting a file system, it was required that its code run in kernel space, due to which, for example, only the superuser could mount the CD .