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The 8086 ( also called iAPX 86 ) is a 16-bit microprocessor chip designed by Intel between early 1976 and mid-1978, when it was released.
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8086 and also
Microprocessors such as the Intel 8008, the direct predecessor of the 8080 and the 8086, used in early personal computers, could also perform a small number of operations on four bits, such as the DAA ( Decimal Add Adjust ) instruction, and the auxiliary carry ( AC / NA ) flag, which were used to implement decimal arithmetic routines.
Both the architecture and the physical chip were therefore developed rather quickly by a small group of people, and using the same basic microarchitecture elements and physical implementation techniques as employed for the slightly older 8085 ( and for which the 8086 also would function as a continuation ).
The legacy of the 8086 is enduring in the basic instruction set of today's personal computers and servers ; the 8086 also lent its last two digits to later extended versions of the design, such as the Intel 286 and the Intel 386, all of which eventually became known as the x86 family.
However, IBM already had a history of using Intel chips in its products and had also acquired the rights to manufacture the 8086 family.
Multiply and divide also showed great improvement being several times as fast as on the original 8086 and multi-bit shifts were done almost four times as quickly as in the 8086.
The 8086 was introduced during 1978 as a fully 16-bit extension of Intel's 8-bit based 8080 microprocessor and also introduced memory segmentation to overcome the 16-bit addressing barrier of such designs.
The term x86 derived from the fact that early successors to the 8086 also had names ending with " 86 ".
The original line was equipped with the Intel 8088 CPU, which was later extended to faster clock speeds and also the 8086 and 80286 processors.
In real mode, code may also modify the CS register by making a far jump ( or using an undocumented instruction on the 8086 or 8088 )< ref > must be used with extreme care and has limited usefulness, because it immediately changes the effective address that will be computed from the instruction pointer to fetch the next instruction.
With the introduction of the 80386, the memory management features were enhanced to allow the system to be shifted into protected mode but also allowing the addresses to be configured in a virtual 8086 mode so that the extended memory could be mapped into addressing frames and accessible to real-mode programs such as MS-DOS.
It uses an Intel 8086 central processing unit that operates at 5MHz, which also the 8086 gave rise to the x86 architecture of Intel's future processors.
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.
Identification can be generally done also using cpuid instruction, whereas result value of 2nd bit ( bit no. 1, 0x2 in value ) in EDX register represents support of Enhanced Virtual 8086 mode.
Earlier versions of QRAM also supported the older 8086 and 8088 CPUs.
Olivetti also sold quasi-portable 8086 / 8088-based PCs with an integrated keyboard and one or two integrated 3. 5 " floppy disk drives, running DOS 3. 27, an Olivetti OEM version of PC-DOS 3. 20 with minor improvements.
The PRO was never widely accepted as an office personal computer, nor as a scientific workstation, where the market was also headed to Intel 8086, or alternately to Motorola 68000-based computers.
8086 and called
Microsoft bought 86-DOS, adapted it for computers using the Intel 8086 and 8088 processors, and called it MS-DOS ; IBM sold it for the IBM PC as PC DOS.
8086 and iAPX
The 8086 project started in May 1976 and was originally intended as a temporary substitute for the ambitious and delayed iAPX 432 project.
8086 and 86
It was superseded by NetWare 86, which was written for the Intel 8086 processor, in 1985.
8086 and is
( Another reference is that the PCI Vendor ID for Intel devices is 8086 < sub > h </ sub >.
As the original implementation of the 32-bit extension of the 8086 architecture, the 80386 instruction set, programming model, and binary encodings are still the common denominator for all 32-bit x86 processors, this is termed x86, IA-32, or i386-architecture, depending on context.
x86 is a series of computer microprocessor instruction set architectures based on the Intel 8086 CPU.
80186 CPUs and earlier, back to the original 8086, have only one operational mode, which is equivalent to real mode in later chips.
Since a primary design specification of x86 microprocessors is that they are fully backwards compatible with software written for all x86 chips before them, the 286 chip was made to start in ' real mode ' – that is, in a mode which turned off the new memory protection features, so that it could run operating systems written for the 8086 and the 80186.
There is a small difference though: the resulting physical address is no longer truncated to 20 bits, so real mode pointers ( but not 8086 pointers ) can now refer to addresses between 100000 < sub > h </ sub > and 10FFEF < sub > h </ sub >.
The existence of is probably an accident, as it follows a pattern of PUSH and POP instruction opcodes for the four segment registers on the 8086 and 8088 .</ ref >).
Virtual 8086 mode is designed to allow code previously written for the 8086 to run unmodified and concurrently with other tasks, without compromising security or system stability.
Virtual 8086 mode, however, is not completely backwards compatible with all programs.
The Intel 8088 and 8086 were the first CPUs to have an instruction set that is now commonly referred to as x86.
The modern x86 instruction set is a superset of 8086 instructions and a series of extensions to this instruction set that began with the Intel 8008 microprocessor.
The six byte long queue was chosen because the maximum number of bytes required for any instruction in 8086 is this long.
) C9h is an invalid opcode on the 8088 / 8086, and it will cause an INT 6 exception in v86 mode since the 386.
This is the full 8086 / 8088 instruction set, but most, if not all of these instructions are available in 32-bit mode, they just operate on 32-bit registers ( eax, ebx, etc.
The most common problem by running 8086 code from protected mode is memory addressing which is totally different between protected mode and real mode.
Support for Virtual 8086 mode is not available in x86-64 Long Mode, although it is still present on 64-bit capable processors running in 32-bit protected mode.
8086 and 16-bit
On June 28, 1984 Compaq released the Compaq Deskpro, a 16-bit desktop computer using an Intel 8086 microprocessor running at 7. 14 MHz.
However, the 8086 design was expanded to support full 16-bit processing, instead of the fairly basic 16-bit capabilities of the 8080 / 8085.
It had an 8-bit external data bus instead of the 16-bit bus of the 8086.
Following the same tradition, modern 64-bit x86 processors are able to run most programs written for older chips, all the way back to the original 16-bit 8086 of 1978.
It was based on the Intel 8086 and, like it, had a 16-bit external data bus multiplexed with a 20-bit address bus.
Konix wanted the machine to use a 16-bit processor, so the Z80 was removed and replaced with an 8086 processor.
* CPU: 16-bit 8086 processor ( running at 6 MHz )
Arriving late to the 16-bit arena afforded the new processor more transistors ( roughly 40000 active versus 20000 active in the 8086 ), 32-bit macroinstructions, and acclaimed general ease of use.
Until release 2. 0 in April 1992, OS / 2 ran in 16-bit protected mode and therefore could not benefit from the Intel 80386's much simpler 32-bit flat memory model and virtual 8086 mode features.
The SL series enjoyed a modest, yet appreciable, performance increase over the earlier 8088-based Tandy 1000's, owing to the 8086 processor's 16-bit bus coupled with a slightly higher clock speed.
In this context, the term came about because DOS, Microsoft Windows and OS / 2 were originally written for the 8088 / 8086 and / or 80286, 16-bit microprocessors with a segmented address space where programs had to switch between segments to reach more than 64 kilobytes of code and / or data.
Generation 1 68000 CPUs primarily competed against the 16-bit 8086 / 8088 and 80286.
The extended 8 KB version was then generalized into BASIC-80 ( 8080 / 85, Z80 ), and ported into BASIC-68 ( 6800 ), BASIC-69 ( 6809 ), and MOS Technology 6502-BASIC ( unfortunately spilling over to 9 KB, in an era when 8 KB ROM chips were standard ), as well as the 16-bit BASIC-86 ( 8086 / 88 ).
The 8088 and 8086 both used a 20-bit address bus and 16-bit internal registers but while the 8086 had a 16-bit data bus, the 8088, intended as a low cost option for embedded applications, had an 8-bit data bus.
His second book, Zen of Assembly Language ( 1990 ), focused on writing efficient assembly code for the 16-bit 8086 processor, but was released after the 80486 CPU was already available.
This problem arises because x86-64 processors in long mode do not support the virtual 8086 mode used to run 16-bit code in IA-32 processors.
The original Intel 8086 ( Intel's first 16-bit microprocessor ) was an exception to this rule which implemented a segmented memory model, because it provided an easy form of memory management with flexible page boundaries for early operating systems such as DOS and allowed access to an address space greater than what would otherwise be available with its 16-bit addressing.
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