Intel 80286

  • Intel
  • AMD
  • IBM
  • Harris ( Intersil )
  • Siemens AG
  • Fujitsu

The Intel 80286 microprocessor was a company Intel, the 8086 came as the successor to the market on February 1, 1982. The 286 - like the 80286 is often called (voiced Zweisechsundachtziger ) - was first installed in office microcomputer systems, running under Unix. In 1984 the company launched the successor to the IBM PC XT IBM, the IBM PC AT, out, on 80286 - based. Almost exclusively through AT computers and their replicas found the 80286 distribution.

Protected Mode

Regarding his instruction set of the 80286 is backwards compatible with the 8086, but he had an additional operating mode: protected mode. The 8086 for backward-compatible mode of operation was called real mode. The term Real fashion was so familiar that even to this day often over the 8086 and whose brother is 8088 words simplistic, they would run mode in the Real, because was in real mode the 80286 almost completely software compatible with the 8086 - including the restriction to 1 MiB address space.

The protected mode, however, allows to address up to 16 MiB via the 24 -bit address bus. However, the restriction to a maximum of 64 KiB large segments remained in this mode - all address registers were still only 16 bits wide. However, a segment could be placed on virtually any address in the 24 -bit address space. Only in this way opened up for program code of the entire address space. Due to the memory management possibility of Protected mode is a virtual memory of just 1 GiB ( 16383 segments max. 64 KiB) available.

The Protected Mode supported multitasking, memory protection and additional options not available in real mode extensions. Although the Protected Mode was more difficult to program than the real fashion, he offered a number of advantages and new opportunities. The developers of Intel believed that old programs that adhered to certain rules, would run unchanged in the new mode. In practice, however, showed that due to many problems with the PC architecture and the operating system MS- DOS almost no real mode programs in protected mode were run. Bill Gates described the 80286 as mindless chip as the CPU could not process multiple MS -DOS programs simultaneously in a Windows environment. This was only made possible in the successor 80386 for its own operation mode, the Virtual 8086 Mode got.

Although the CPU could relatively easily be switched to protected mode - the way back, however, was only possible via a reset or by using an undocumented command ( LOADALL 0x0F05 - invite all processor registers from memory). There has been much speculation why Intel is no easier opportunity arose from protected mode to real mode return - the most frequently cited reasons are:

  • Intel looked to protected mode as such superior that no one in the real mode would want to return.
  • A corresponding instruction was provided, but did not do work properly and was shut down shortly before launch.
  • A design flaw on the microarchitecture of the 80286 have a trouble-free switching back does not allow without profound changes to this.
  • The implementation of the instruction was simply forgotten.

Siemens CPU 80286

Harris 80286-16 in the PLCC socket

IBM 80286 8 MHz in the PGA package

Memory Extender

1987, with Windows 2.1, Microsoft Corporation realized for the first time a so-called memory extender, which took the 80286 protected mode to help. With such memory can DOS would extenders memory above the 1 MB limit and the high memory, the so-called extended memory to be used.

1988, this access has been standardized. The standard was called XMS. The memory extender were called XMS Extender. The most famous among them was from 1990 with DOS 5.0 HIMEM.SYS extender included.

DOS extender and Windows

From 1990, then DOS - Extender to improve the utilization of the protected mode of the 80286 came - and 80386 processors.

Until Windows 3.0, the real mode of the PC / XT ( 8086/88 ) was supported until Windows 3.1, the standard mode (ie the 16- bit protected mode ) of the AT ( 80286 ). Windows 3.11 or Windows 95 but ran only in extended mode (that is, 32- bit protected mode ), which requires a 80386 processor or higher.

Architecture

  • Max Addressable Memory: 16 MiB
  • Processing width: 16 bits
  • Data bus: 16 bits
  • Address bus: 24 bit

Specifications

  • L1 cache: No
  • L2 cache: No
  • Design: PGA, PLCC or 68-pin LCC
  • Operation voltage ( Vcore ): 5 V
  • Release Date: 1982
  • Manufacturing Technology: 1.5 micron
  • The size: 47 mm ² with 134,000 transistors
  • Clock rates: 4 MHz (This version was only available for a short time. External clock was 8 MHz. )
  • 6 MHz
  • 8 MHz
  • 10 MHz
  • 12 MHz
  • 16 MHz
  • 20 MHz ( only Harris CS80C286 -20 and AMD -20 N80L286 (?) )
  • 25 MHz (only Harris CS80C286 -25)

Peripheral Devices

  • Intel 82284: Clock
  • Intel 82288: Bus Controller
  • Intel 82289: bus arbiter
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