Hyper-threading (officially Hyper-Threading Technology, and abbreviated HT Technology, HTT or HT) is Intel's term for its simultaneous multithreading implementation in its Atom, Intel Core i3/i5/i7, Itanium, Pentium 4 and Xeon CPUs.
Hyper-threading is an Intel-proprietary technology used to improve parallelization of computations (doing multiple tasks at once) performed on PC microprocessors. For each processor core that is physically present, the operating system addresses two virtual processors, and shares the workload between them when possible. Hyper-threading requires not only that the operating system support multiple processors, but also that it be specifically optimized for HTT, and Intel recommends disabling HTT when using operating systems that have not been optimized for this chip feature.
Non-intel processors can have more than 2 threads per core... there have been 8 threaded multi-core cpu's for years...
In computer science, a thread of execution is the smallest unit of processing that can be scheduled by an operating system. It generally results from a fork of a computer program into two or more concurrently running tasks. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process. Multiple threads can exist within the same process and share resources such as memory, while different processes do not share these resources. In particular, the threads of a process share the latter's instructions (its code) and its context (the values that its variables reference at any given moment). To give an analogy, multiple threads in a process are like multiple cooks reading off the same cook book and following its instructions, not necessarily from the same page.
On a single processor, multithreading generally occurs by time-division multiplexing (as in multitasking): the processor switches between different threads. This context switching generally happens frequently enough that the user perceives the threads or tasks as running at the same time. On a multiprocessor or multi-core system, the threads or tasks will actually run at the same time, with each processor or core running a particular thread or task.
Many modern operating systems directly support both time-sliced and multiprocessor threading with a process scheduler. The kernel of an operating system allows programmers to manipulate threads via the system call interface. Some implementations are called a kernel thread, whereas a lightweight process (LWP) is a specific type of kernel thread that shares the same state and information.
Programs can have user-space threads when threading with timers, signals, or other methods to interrupt their own execution, performing a sort of ad-hoc time-slicing.
Threads differ from traditional multitasking operating system processes in that:
Edited by LiNERROR - 7/24/11 at 12:17am
- processes are typically independent, while threads exist as subsets of a process
- processes carry considerable state information, whereas multiple threads within a process share state as well as memory and other resources
- processes have separate address spaces, whereas threads share their address space
- processes interact only through system-provided inter-process communication mechanisms.
- Context switching between threads in the same process is typically faster than context switching between processes.