<processor, programming> (Or "virtual mode" or "virtual 8086 mode") An operating mode provided by the Intel 80386 and later processors to allow real mode programs to run under operating systems which use protected mode. In this sub-mode of protected mode, an operating environment is created which mimics the address calculation in real mode. In virtual 86 mode the segment MMU is practically turned off and the segment registers exhibit the same behaviour as in real mode. The paged MMU, however, still operates. This means that the one megabyte address space of real mode can be remapped in four kilobyte pages to anywhere in the 32 bit physical address space. Each page can be protected separately from read or write accesses. Virtual mode is handled on a per-task-basis, so each exception (from protection violations or interrupts) switches the processor back into protected mode. It is therefore possible to have multiple tasks in virtual mode which run concurrently under the control of an operating system which runs in protected mode. Most operating system services in MS-DOS systems are called by software interrupts, which are a kind of exception. If an MS-DOS application runs in virtual mode under the control of a protected mode operating system, each call to MS-DOS causes a switch to protected mode. The operating system emulates the MS-DOS service and switches back to the application in virtual mode. From the viewpoint of the application nothing differs from real mode. Microsoft Windows, Windows NT, and OS/2 use this feature to implement "DOS-boxes" in which both MS-DOS and real mode application programs can run.

In the 80386 microprocessor and later, virtual 8086 mode (also called virtual real mode, V86-mode, or VM86) allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running a protected mode operating system. It is a hardware virtualization technique that allowed multiple 8086 processors to be emulated by the 386 chip.

In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking designed to increase an operating system's control over application software.

An operating mode of Intel 80x86 processors. The opposite of real mode. The Intel 8088, Intel 8086, Intel 80188 and Intel 80186 had only real mode, processors beginning with the Intel 80286 feature a second mode called protected mode. In real mode, addresses are generated by adding an address offset to the value of a segment register shifted left four bits. As the segment register and address offset are 16 bits long this results in a 20-bit address. This is the origin of the one megabyte (2^20) limit in real mode. There are 4 segment registers on processors before the {Intel 80386}. The 80386 introduced two more segment registers. Which segment register is used depends on the instruction, on the addressing mode and of an optional instruction prefix which selects the segment register explicitly. In protected mode, the segment registers contain an index into a table of segment descriptors. Each segment descriptor contains the start address of the segment, to which the offset is added to generate the address. In addition, the segment descriptor contains memory protection information. This includes an offset limit and bits for write and read permission. This allows the processor to prevent memory accesses to certain data. The operating system can use this to protect different processes' memory from each other, hence the name "protected mode". While the standard register set belongs to the CPU, the segment registers lie "at the boundary" between the CPU and MMU. Each time a new value is loaded into a segment register while in protected mode, the corresponding descriptor is loaded into a descriptor cache in the (Segment-)MMU. On processors before the Pentium this takes longer than just loading the segment register in real mode. Addresses generated by the CPU (which are segment offsets) are passed to the MMU to be checked against the limit in the segment descriptor and are there added to the segment base address in the descriptor to form a linear address. On a 80386 or later, the linear address is further processed by the paged MMU before the result (the physical address) appears on the chip's address pins. The 80286 doesn't have a paged MMU so the linear address is output directly as the physical address. The paged MMU allows for arbitrary remapping of four klilobyte memory blocks (pages) through a translation table stored in memory. A few entries of this table are cached in the MMU's Translation Lookaside Buffer to avoid excessive memory accesses. After processor reset, all processors start in real mode. Protected mode has to be enabled by software. On the 80286 there exists no documented way back to real mode apart from resetting the processor. Later processors allow switching back to real mode by software. Software which has been written or compiled to run in protected mode must only use segment register values given to it by the operating system. Unfortunately, most application code for MS-DOS, written before the 286, will fail in protected mode because it assumes real mode addressing and writes arbitrary values to segment registers, e.g. in order to perform address calculations. Such use of segment registers is only really necessary with data structures that are larger than 64 kilobytes and thus don't fit into a single segment. This is usually dealt with by the huge memory model in compilers. In this model, compilers generate address arithmetic involving segment registers. A solution which is portable to protected mode with almost the same efficiency would involve using a table of segments instead of calculating new segment register values ad hoc. To ease the transition to protected mode, Intel 80386 and later processors provide "virtual 86 mode". (1995-03-29)

Airplane mode (also known as aeroplane mode, flight mode, offline mode, or standalone mode) is a setting available on smartphones and other portable devices. When activated, this mode suspends the device's radio-frequency (RF) signal transmission technologies (i.

Eighty-six or 86 is American English slang used to indicate that an item is no longer available, traditionally from a food or drinks establishment; or referring to a person or people who are not welcome in the premises. Its etymology is unknown but seems to have been coined in the 1920s or 1930s.

Virtual hosting is a method for hosting multiple domain names (with separate handling of each name) on a single server (or pool of servers). This allows one server to share its resources, such as memory and processor cycles, without requiring all services provided to use the same host name.

A virtual event is an online event that involves people interacting in a virtual environment on the web, rather than meeting in a physical location. Virtual events are typically multi-session online events that often feature webinars and webcasts.

virtual host

<networking> Most computers on the Internet have a single IP address; however, often via special kernel patches, a given computer can be made to respond to several IP addresses and provide different services (typically different Web services) on each. Each of these different IP addresess (which generally each have their own hostname) act as if they were distinct hosts on distinct machines, even though they are actually all one host. Hence, they are virtual hosts. A common use is when an {Internet Service Provider} "hosts" World-Wide Web or other services for several of their customers on one computer but giving the appearence that they are separate servers. (1997-09-11)