Intel 80286

related topics
{system, computer, user}
{math, number, function}
{film, series, show}
{work, book, publish}

The Intel 80286[1] (also called iAPX 286), introduced on February 1, 1982, was a 16-bit x86 microprocessor with 134,000 transistors. Like its contemporary simpler cousin, the 80186, it could correctly execute most software written for the earlier Intel 8086 and Intel 8088.[2] It was employed for the IBM PC/AT, introduced in 1984, and then widely used in most PC/AT compatible computers until the early 1990s.

Contents

History

After the 6 and 8 MHz initial releases, it was subsequently scaled up to 12.5 MHz. (AMD and Harris later pushed the architecture to speeds as high as 20 MHz and 25 MHz, respectively.) On average, the 80286 had a speed of about 0.21 instructions per clock.[3] The 6 MHz model operated at 0.9 MIPS, the 10 MHz model at 1.5 MIPS, and the 12 MHz model at 1.8 MIPS.[4]

Design

The 80286's performance per clock cycle was more than twice that of its predecessors, the Intel 8086 and Intel 8088. In fact, the performance increase per clock cycle of the 80286 over its immediate predecessor may be the largest among the generations of x86 processors. Calculation of the more complex addressing modes (such as base+index) had less clock penalty because it was performed by a special circuit in the 286; the 8086, its predecessor, had to perform effective address calculation in the general ALU, taking many cycles. Also, complex mathematical operations (such as MUL/DIV) took fewer clock cycles compared to the 8086.

Having a 24-bit address bus, the 286 was able to address up to 16 MB of RAM, in contrast to 1 MB that the 8086 could directly access. While DOS could utilize this additional RAM (extended memory) via BIOS call (INT 15h, AH=87h), or as RAM disk, or emulation of expanded memory, cost and initial rarity of software utilizing extended memory meant that 286 computers were rarely equipped with more than a megabyte of RAM. Additionally, there was a performance penalty involved in accessing extended memory from real mode, as noted below.

The 286 was designed to run multitasking applications, including communications (such as automated PBXs), real-time process control, and multi-user systems.

Full article ▸

related documents
Telephony Application Programming Interface
Motorola 6809
Mbox
Audio signal processing
Cambridge Z88
Channel access method
ACCESS.bus
Asynchronous communication
S-100 bus
Sideband
Break key
Motorola 68020
Digital image processing
Heterodyning
Very-large-scale integration
Game Boy Advance
Apple IIe Card
Real Time Streaming Protocol
Broadband
Intel 8086
Real-time operating system
EPROM
Noise
8P8C
Wide area network
Web service
Duron
Protocol stack
Chaffing and winnowing
PDP-1