INTEL

Meanwhile, the 386 has an architecture of 32-bit registers with an address bus is also 32 bits (addresses up to 4 Gigabytes = 4096 Mb) and possible modes of operation: real mode (Windows 8086), the protected Mode (relatively compatible with the 286), a proprietary protected mode allows' At last - break the barrier of traditional segments and "virtual 86" mode, in which you can emulate the simultaneous operation of several 8086. again, all modes are incompatible and require a specific operating system: if you can forgive the loss of manufacturer support the advanced mode 286 versus 8086, due to logical technological evolution, you can not say same 386 compared to 286: it had not been necessary to add a new protected mode if it had been better constructed the 286 just a couple of years ago. Normally, the 386 typically operate in real mode (due to DOS) so multitasking and memory management capabilities are not exploited. Moreover, although you can use the 32-bit registers in real mode, this is not usually done-for compatibility with previous ones processors which input is throwing away 50% of the processing capacity of the chip, though fortunately these processors typically work at frequencies of 16-20 MHz (obsolete) and usually from 33 to 40 MHz. 

The 386sx is a variant of the 386 at the hardware level, but compatible software. Basically, it's a 386 with a data bus only 16 bits-more slowly, having to make two passes for 32 bits- data. In fact, it could have been perfectly designed to maintain compatibility with the 286 hardware, but probably prevented the manufacturer for commercial reasons. 

The 486 differs from the 386 in the integration on a single chip of 387 coprocessor has also improved the speed of operation: 25 MHz version doubles in real terms to a 386-25 MHz equipped with the same cache size. 486SX version no difference in the size of the bus, also of 32 bits, but in the absence of 387 (which may be added externally). 486 versions are also available with 16-bit buses, the first manufacturer of these chips, called 486SLC has been Cyrix. A trend started by the 486 was to double the speed of the internal clock (say 33 to 66 MHz) but in communications with external 33 MHz buses are respected This streamlines the implementation of longer instructions. Lowest DOS, the overall system performance can be considered practically double. DX2 are chips (also a variant at 50 MHz: 25 x 2). The culmination of this technology comes from the hand of a 75/100 MHz DX4 (25/33 x 3).