In 1982, Intel introduced the Intel 80286 processor, normally abbreviated as 286. The first CPU behind the original IBM PC AT (Advanced Technology), it did not suffer from the compatibility problems that damned the 80186 and 80188. Other computer makers manufactured what came to be known as IBM clones, with many of these manufacturers calling their systems AT-compatible or AT-class computers. When IBM developed the AT, it selected the 286 as the basis for the new system because the chip provided compatibility with the 8088 used in the PC and the XT. Therefore, software written for those chips should run on the 286.
The 286 chip is many times faster than the 8088 used in the XT, and at the time it offered a major performance boost to PCs used in businesses. The processing speed, or throughput, of the original AT (which ran at 6MHz) is five times greater than that of the PC running at 4.77MHz. The die for the 286 is shown in Figure 1.1
Figure 1.1 - 286 processor die. Photograph used by permission of Intel Corporation.
Faster Then The 8088
The 286 was faster than the 8088 for two reasons: it required only 4.5 cycles to perform the average instruction (versus 12 on the 808x processors), and handled data in 16-bit chunks. The 286’s real mode imitates an 808x processor, and the protected mode can access memory larger than 1MB. The 286 also supports multitasking.