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Intel 8086
Central processing unit

Produced: From 1978 to 1990s
Manufacturer: Intel
Max CPU clock: 5 MHz to 10 MHz
Instruction set: x86-16
Package: 40 pin DIP

The 8086[1] is a 16-bit microprocessor chip designed by Intel and introduced on the market in 1978, which gave rise to the x86 architecture. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. An instruction set is a list of all the instructions and all their variations that a processor can execute See also X86 assembly language The generic term x86 refers to the most commercially successful Instruction set architecture in the history of Personal In Microelectronics, a dual in-line package (DIP, sometimes called a DIL package is an electronic device package with a rectangular housing and two parallel rows A microprocessor incorporates most or all of the functions of a Central processing unit (CPU on a single Integrated Year 1978 ( MCMLXXVIII) was a Common year starting on Sunday (link displays the 1978 Gregorian calendar) See also X86 assembly language The generic term x86 refers to the most commercially successful Instruction set architecture in the history of Personal Intel 8088, released in 1979, was essentially the same chip, but with an external 8-bit data bus (allowing the use of cheaper and fewer supporting logic chips[2]), and is notable as the processor used in the original IBM PC. The Intel 8088 is an Intel X86 Microprocessor based on the 8086, with 16- Bit registers and an 8-bit external Data bus Year 1979 ( MCMLXXIX) was a Common year starting on Monday (link displays the 1979 Gregorian calendar) In Computer architecture, a bus is a subsystem that transfers data between computer components inside a Computer or between computers

Contents

History

Background

In 1972, Intel launched the 8008, the first 8-bit microprocessor[3]. Year 1972 ( MCMLXXII) was a Leap year starting on Saturday (link will display full calendar of the Gregorian calendar. The Intel 8008 was an early byte-oriented Microprocessor designed and manufactured by Intel and introduced in April 1972 It implemented an instruction set designed by Datapoint corporation with programmable CRT terminals in mind, that also proved to be fairly general purpose. An instruction set is a list of all the instructions and all their variations that a processor can execute Datapoint Corporation, originally known as Computer Terminal Corporation (CTC, was a computer company based in San Antonio Texas, United States. A computer terminal is an electronic or electromechanical hardware device that is used for entering data into and displaying data from a Computer or a Computing The device needed several additional ICs to produce a functional computer, in part due to its small 18-pin "memory-package" which prevented a separate address bus (Intel was primarily a DRAM manufacturer at the time). Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside

Two years later, in 1974, Intel launched the 8080[4], employing the new 40-pin DIL packages originally developed for calculator ICs to enable a separate address bus. Year 1974 ( MCMLXXIV) was a Common year starting on Tuesday (link will display full calendar of the 1974 Gregorian calendar. The Intel 8080 was an early Microprocessor designed and manufactured by Intel. In Microelectronics, a dual in-line package (DIP, sometimes called a DIL package is an electronic device package with a rectangular housing and two parallel rows A calculator is device for performing mathematical calculations distinguished from a Computer by having a limited problem solving ability and an interface optimized for interactive It had an extended instruction set source (not binary) compatible with the 8008 and also included some 16-bit instructions to make programming easier. In Computer software, an application binary interface ( ABI) describes the low-level interface between an application program and the Operating system The 8080 device, often described as the first truly useful microprocessor, was nonetheless soon replaced by the 8085 which could cope with a single 5V power supply instead of the three voltages of earlier chips. The Intel 8085 is an 8-bit Microprocessor introduced by Intel in 1977 [5] Other well known 8-bit microprocessors that emerged during these years were Motorola 6800 (1974), Microchip PIC16X (1975), MOS Technology 6502 (1975), Zilog Z80 (1976), and Motorola 6809 (1977), as well as others. The 6800 is an 8-bit Microprocessor produced by Motorola and released shortly after the Intel 8080 in late 1974 PIC is a family of Harvard architecture Microcontrollers made by Microchip Technology, derived from the PIC1640 originally developed by General Instrument The MOS Technology 6502 is an 8-bit Microprocessor that was designed by Chuck Peddle for MOS Technology in 1975 The Zilog Z80 is an 8-bit Microprocessor designed and sold by Zilog from July 1976 onwards The Motorola 6809 is an 8-bit (arguably an 8/ 16-bit) Microprocessor CPU from Motorola, introduced circa 1979

The first x86 design

The 8086 was originally intended as a temporary substitute for the ambitious iAPX 432 project in an attempt to draw attention from the less-delayed 16 and 32-bit processors of other manufacturers (such as Motorola, Zilog, and National Semiconductor) and at the same time to top the successful Z80 (designed by former Intel employees). The Intel iAPX 432 was Intel 's first 32-bit Microprocessor design introduced in 1981 as a set of three Integrated circuits The iAPX 432 was intended Motorola Inc ( is an American, multinational Fortune 100, Telecommunications company based in Schaumburg Illinois. Zilog Inc, often seen as ZiLOG (the official company denotation in 1998 through Jun 2007 is a manufacturer of 8-bit, 16-bit, 24-bit National Semiconductor ( is a Semiconductor manufacturer specializing in analog devices and subsystems headquartered in Santa Clara, California, The Zilog Z80 is an 8-bit Microprocessor designed and sold by Zilog from July 1976 onwards Both the architecture and the physical chip were therefore developed quickly (in a little more than two years[6]), using the same basic microarchitecture elements and physical implementation techniques as employed for the one year earlier 8085, which it would also function as a continuation of. In Computer engineering, microarchitecture (sometime abbreviated to µarch or uarch is a description of the Electrical circuitry of a Computer, Central The Intel 8085 is an 8-bit Microprocessor introduced by Intel in 1977 Although not directly source compatible, it was designed so that assembly language for the 8085, 8080, or 8008 could be automatically converted into equivalent (sub-optimal) 8086 source code, usually with little or no hand-editing, i. See the terminology section below for information regarding inconsistent use of the terms assembly and assembler e. the programming model and instruction set was (loosely) based on the 8085. However, the 8086 design was expanded to support full 16-bit processing instead of the fairly basic 16-bit capabilities of the 8080/8085.

8086 was implemented[7] using a mix of random logic and microcode and was designed using depletion load nMOS circuitry using around 20,000 active transistors (29,000 counting all ROM and PLAs sites). Microprogramming (ie writing microcode) is a method that can be employed to implement Machine instructions in a CPU relatively easily often using less In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals A programmable logic array (PLA is a programmable device used to implement combinational Logic circuits. It was soon moved to Intels new refined nMOS manufacturing process called HMOS (later to HMOS-II and III) originally developed for manufacturing of fast static RAMs. HMOS, high-performance n-channel MOS, also called depletion-load NMOS, is a Digital circuit style which uses n-type MOSFETs to implement Static random access memory (SRAM is a type of Semiconductor memory where the word static indicates that unlike ''dynamic'' RAM (DRAM, it does not [8] The chip measured 33mm² and minimum feature size was 3. 2μm.

While less known than the 8088 chip, the legacy of the 8086 is enduring; references to it can still be found on most modern computers in the form of the Vendor entry for all Intel device IDs which is "8086". It also lent its last two digits to Intel's later extended versions of the design, such as the 286 and the 386, all of which eventually became known as the x86 family. The Intel 286, introduced on February 1, 1982, (originally named 80286, and also called iAPX 286 in the programmer's manual See also X86 assembly language The generic term x86 refers to the most commercially successful Instruction set architecture in the history of Personal

Details

Buses and operation

All internal registers as well as internal and external data buses are 16 bits wide, firmly establishing the "16-bit microprocessor" identity of the 8086. A 20-bit external address bus gives a 1 MB (segmented) physical address space (220 = 1,048,576). 16-bit I/O addresses give 64 KB of separate I/O space. (216 = 65,536). The control pins carry the essential signals for all external operations.

The data bus was multiplexed with the address bus, this was only slightly diminishing performance however, as other factors, more important for this particular chip, shadow this design choice; transfers of 16 (or 8) bit quantities are done in a four-clock memory access cycle. For multiplexing in electronics and signal processing see Multiplexer. 8086 instructions varied from 1 to 6 bytes. Therefore, fetch and execution were concurrent (as it remains in today's x86 designs): The bus interface unit feeds the instruction stream to the execution unit through a 6 byte prefetch queue (a form of loosely coupled pipelining), speeding up operations on register and immediates, while memory operations unfortunately became slower (4 years later, this performance problem was fixed with the 80186 and 80286). In Computer science, concurrency is a properties of system in which several Computational processes are executing at the same time and potentially interacting In Computing, a pipeline is a set of data processing elements connected in series so that the output of one element is the input of the next one In Computer architecture, a processor register is a small amount of storage available on the CPU whose contents can be accessed more quickly than storage In Mathematics, an operand is one of the inputs (arguments of an Operator. The 80186 is a Microprocessor that was developed by Intel circa 1982. The Intel 286, introduced on February 1, 1982, (originally named 80286, and also called iAPX 286 in the programmer's manual The performance gain over the 8080 and 8085 resulting from the full (instead of partial) 16-bit architecture, the operand versus operation orthogonalizations, and other enhancements, were still fairly significant, despite cases where the older chips may be faster (see below). In Mathematics, an operand is one of the inputs (arguments of an Operator. In Linear algebra, orthogonalization is the process of finding a set of Orthogonal vectors that span a particular subspace.

The maximum linear address space is limited to 64 KB, simply because internal registers are only 16 bits wide. Programming over 64 KB boundaries involves adjusting segment registers (see below) and is therefore fairly awkward (and remains so until the 80386). Some control pins have more than one function depending upon whether the device is operated in the "min" or "max" mode. The former is intended for small single processor systems whilst the latter is for medium or large systems using more than one processor. The processor had some new instructions (not present in the 8085) to better support stack based high level programming languages such as Pascal and C; some of the more useful ones were push immed, push mem-op, and ret size (several others would be added in the subsequent 80186, 80286, and 80386 designs).

Registers and instructions

The 8086 has eight (more or less general) 16-bit registers including the stack pointer, but excluding the instruction pointer, flag register and segment registers. In Computer architecture, a processor register is a small amount of storage available on the CPU whose contents can be accessed more quickly than storage Stacks in computing architectures are regions of memory where data is added or removed in a Last-In-First-Out manner Four of them could also be accessed as eight 8-bit registers (see picture).

Due to a compact encoding inspired by 8085 and other 8-bit processors, most instructions were one-address or two-address operations which means that the result were stored in one of the operands. At most one of the operands could be in memory, but this memory operand could also be the destination, while the other operand, the source, could be either register or immediate. A single memory location could also often be used as both source and destination which, among other factors, further contributed to a rather small executable code footprint, comparable to most eight bit machines.

Although the degree of orthogonality between registers and operations were greater than in 8085, it was still low, and registers were also sometimes used implicitly by instructions. In Mathematics, two Vectors are orthogonal if they are Perpendicular, i While perfectly sensible for the assembly programmer, this complicated register allocation for compilers compared to more regular contemporary 16- and 32-bit processors (such as VAX or 68000); on the other hand, compared to contemporary 8-bit processors (such as 8085 or 6502), it was significantly easier to generate code for the 8086 design.

As mentioned above 8086 also featured 64 KB of 8-bit (or alternatively 32 K-word or 16-bit) I/O space. In Computing, input/output, or I/O, refers to the communication between an Information processing system (such as a Computer) and the outside A 64 KB (one segment) stack growing towards lower addresses is supported by hardware; 2-byte words are pushed to the stack and the stack top (bottom) is pointed out by SS:SP. In Computer science, a stack is an Abstract data type and Data structure based on the principle of Last In First Out (LIFO Hardware is a general term that refers to the physical artifacts of a Technology. There are 256 interrupts, which can be invoked by both hardware and software. In Computing, an interrupt is an asynchronous signal from hardware indicating the need for attention or a synchronous event in software indicating the need for a change The interrupts can cascade, using the stack to store the return address. In postal Mail, a return address is an explicit inclusion of the address of the person sending the message

Segmentation

There were also four segment registers that could be set from index registers. x86 memory segmentation refers to the implementation of Memory segmentation on the X86 architecture. The segment registers allowed the CPU to access one mebibyte + 64 KiB - 16 bytes of memory in an odd way. A mebibyte (a contraction of me ga bi nary byte) is a unit of Information or Computer storage, abbreviated MiB. A kibibyte (a contraction of ki lo bi nary byte) is a unit of Information or Computer storage, established by the International Rather than just supplying missing bytes, as in most segmented processors, the 8086 shifted the segment register left 4 bits and added it to the offset address, thus:

physical address = segment×16 + offset

The physical memory address was therefore 20 bits wide (while both segment and offset were 16 bits). As a result of this scheme, segments overlapped, making it possible to have up to 4096 different pointers addressing the same location. While acceptable, and even useful, for assembly language programming (where control of the segments was complete) it caused confusion and was considered poor design by most people, forcing entirely new concepts (near and far keywords) into languages such as Pascal and C; data and/or code could be managed within near 16-bit segments, or a large data structure (or many and/or large procedures) could be accessed by far pointers (32-bit segment:offset pairs) reaching the full physical address space. See the terminology section below for information regarding inconsistent use of the terms assembly and assembler tags please moot on the talk page first! --> In Computing, C is a general-purpose cross-platform block structured

Although this scheme made expanding the address space to more than 220 bytes more difficult, it was nevertheless soon expanded by a new MMU-controlled addressing scheme in the 80286's protected mode. A memory management unit ( MMU) sometimes called paged memory management unit ( PMMU) is a Computer hardware component responsible for handling The Intel 286, introduced on February 1, 1982, (originally named 80286, and also called iAPX 286 in the programmer's manual In computing protected mode, also called protected virtual address mode, is an operational mode of X86 -compatible Central processing units (CPU Later, and on top of this, 80386 expanded the whole general purpose registers set (and hence, the offsets) to 32 bits, thereby enabling a linear addressing range of 232 bytes (with a total range of 236). However, those chips were, for a long period of time, often used in real mode, remaining compatible with older OSes. Real mode, also called real address mode, is an operating mode of 80286 and later X86 -compatible CPUs.

In a similar way, early programs could ignore the segments, and just use plain 16-bit addressing, which allowed 8-bit software to be easily ported to the 8086. Eight-bit CPUs normally use an 8-bit data bus and a 16-bit address bus which means that their Address space is limited to 64 KBs This is not a "natural The authors of MS-DOS took advantage of this by providing an Application Programming Interface very similar to CP/M. MS-DOS (short for M icro' s' oft D isk O perating S ystem is an Operating system commercialized by Microsoft. CP/M (Control Program for Microcomputers is an Operating system originally created for Intel 8080 / 85 based Microcomputers by Gary Kildall This was important when the 8086 was new, because it allowed many existing CP/M applications to be quickly made available on the new platform, which greatly eased the transition. CP/M (Control Program for Microcomputers is an Operating system originally created for Intel 8080 / 85 based Microcomputers by Gary Kildall

Performance

Execution times for typical instructions (in clock cycles):

Timings are best case, depending on prefetch status, instruction alignment, and other factors. 

MOV reg,reg: 2, reg,im: 4, reg,mem: 8+EA, mem,reg: 9+EA,  mem,im: 10+EA cycles
ALU reg,reg: 3, reg,im: 4, reg,mem: 9+EA, mem,reg: 16+EA, mem,im: 17+EA cycles

JMP reg: 11, JMP label: 15, Jcc label: 16 (cc = condition code)

MUL reg: 70. . 118 cycles
IDIV reg: 101. . 165 cycles

EA: time to compute effective address, ranging from 5 to 12 cycles.

As can be seen from these tables, operations on registers and immediates were fast (between 2 and 4 cycles), while memory-operand instructions and jumps were quite slow; jumps took more cycles than on the simple 8080 and 8085, and the 8088 (used in the IBM PC) was additionally hampered by its narrower bus. The Intel 8080 was an early Microprocessor designed and manufactured by Intel. The Intel 8085 is an 8-bit Microprocessor introduced by Intel in 1977 The reasons why most memory related instructions were so slow were threefold:

It should be noted, however, that the memory access performance was drastically enhanced with Intel's next generation chips; the 80186 and 80286 both had address calculation in hardware, saving many cycles; 80286 also had separate (non-multiplexed) address and data buses. The 80186 is a Microprocessor that was developed by Intel circa 1982. The Intel 286, introduced on February 1, 1982, (originally named 80286, and also called iAPX 286 in the programmer's manual The Intel 286, introduced on February 1, 1982, (originally named 80286, and also called iAPX 286 in the programmer's manual

Floating point

The 8086/8088 could be connected to a mathematical coprocessor to add floating point capability. In Computing, floating point describes a system for numerical representation in which a string of digits (or Bits represents a Real number. The Intel 8087 was the standard math coprocessor, operating on 80-bit numbers, but manufacturers like Weitek soon offered higher performance alternatives. The 8087 was the first math Coprocessor for 16 bit processors designed by Intel (the I8231 was older but designed for the 8 bit Intel 8080) Weitek Corporation was a former Chip -design company that originally concentrated on Floating point units for a number of commercial CPU designs

Chip versions

The clock frequency was originally limited to 5 MHz (IBM PC used 4. 77 MHz, 4/3 the standard NTSC color burst frequency), but the last versions in HMOS were specified for 10 MHz. In Composite video, colorburst is a signal used to keep the Chrominance subcarrier synchronized in a Color television signal HMOS, high-performance n-channel MOS, also called depletion-load NMOS, is a Digital circuit style which uses n-type MOSFETs to implement HMOS-III and CMOS versions were manufactured for a long time (at least a while into the 1990s) for embedded systems, although its successor, the 80186/80188, has been more popular for embedded use. Complementary metal–oxide–semiconductor ( CMOS) (pronounced "see-moss" siːmɔːs ˈsiːmɒs is a major class of Integrated circuits CMOS technology An embedded system is a special-purpose Computer system designed to perform one or a few dedicated functions often with Real-time computing constraints The 80186 is a Microprocessor that was developed by Intel circa 1982. The Intel 80188 is a version of the Intel 80186 microprocessor with an 8 bit external Data bus, instead of 16 bit

Derivatives and clones

OKI M80C86A QFP-56
OKI M80C86A QFP-56

Compatible and, in many cases, enhanced versions were manufactured by Fujitsu, Harris/Intersil, OKI, Siemens AG, Texas Instruments, NEC, and AMD. ( is a Japanese electronics company founded (as Meikosha Ltd in January 1881 by Kibataro Oki A QFP or Quad Flat Package is an Integrated circuit package with leads extending from each of the four sides is a Japanese company specializing in Semiconductors Computers ( Supercomputers Personal computers, servers, Telecommunications Harris ( Na Hearadh in Scottish Gaelic nə hɛɾəɣ is the southern part of the largest island of the Western Isles of Scotland or Outer Intersil Corporation specializes in the design and manufacture of high-performance analog Semiconductors for four high-growth markets — Communications Computing High End ( is a Japanese electronics company founded (as Meikosha Ltd in January 1881 by Kibataro Oki Texas Instruments ( better known in the electronics industry (and popularly as TI, is an American company based in Dallas, Texas, USA is a Japanese multinational IT company headquartered in Minato Tokyo, Japan. For example, the NEC V20 and NEC V30 pair were hardware compatible with the 8088 and 8086, respectively, but incorporated the instruction set of the 80186 along with some (but not all) of the 80186 speed enhancements, providing an drop-in capability to upgrade both instruction set and processing speed without manufacturers having to modify their designs. NEC V20 (μPD70108 was a processor made by NEC that was a reversed-engineered, pin-compatible version of the Intel 8088 with an Instruction Such relatively simple and low power 8086-compatible processors in CMOS are still used in embedded systems.

The electronics industry of the Soviet Union was able to replicate the 8086 through both industrial espionage and reverse engineering. The Union of Soviet Socialist Republics (USSR was a constitutionally Socialist state that existed in Eurasia from 1922 to 1991 The resulting chip, K1810BM86, was pin-compatible with the original Intel 8086 and had the same instruction set. This IC was the core of Soviet-made PC-compatible ES1840 and ES1841 desktops. However, in hardware these computers had significant differences from their authentic prototypes (respectively PC and PC/XT): the K1810BM86 was a copy from Intel 8086, not Intel 8088, and the data/address bus circuitry was designed independently of original Intel products.

Notable bugs

8086/8088 CPUs produced prior to 1982 had a severe interrupt bug. IBM provided an upgrade free of charge to affected PCs. Processors remaining with original 1979 markings are quite rare; they have become collectors' items.

Microcomputers using the 8086

Notes and references

  1. ^ Microprocessor Hall of Fame. Southampton ( IPA /ˌsaʊθˈhæmptən/ is the largest city in the county of Hampshire, on the south coast of England Intel. Retrieved on 2007-08-11. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 2492 BC - Traditional date of the defeat of Bel by Hayk, progenitor and founder of the Armenian nation
  2. ^ It also permitted cheap 8080-family chips to be used (such as the 8254 CTC, 8255 PIO, and 8259 PIC which were used in the IBM PC design). The Intel 8255 (or i8255) Programmable Peripheral Interface chip is a peripheral chip originally developed for the Intel 8085 microprocessor In addition, it made PCB layout simpler and boards cheaper, as well as demanding fewer (1 or 4-bit wide) DRAM chips.
  3. ^ using enhancement load pMOS logic
  4. ^ using enhancement load nMOS logic
  5. ^ made possible with depletion load nMOS logic (the 8085 was later made using HMOS processing, just like the 8086)
  6. ^ Two years from idea to product was considered fast for a complex design (almost no CAD-tools were used)
  7. ^ 8086 used less microcode than many competitors designs, such as the MC68000 and others
  8. ^ Fast static RAMs (as fast as bipolar) in MOS technology was an important product for Intel during this period.

See also

External links

The IBM Personal Computer XT, often shortened to the IBM XT or simply XT, was IBM's successor to the original IBM PC. See also X86 assembly language The generic term x86 refers to the most commercially successful Instruction set architecture in the history of Personal
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