Features of 80186, 80286, 80386 and 80486 Microprocessor:

Let us discuss the Features of 80186 Microprocessor, Features of 80286 Microprocessor, Features of 80386 Microprocessor, Features of 80486 Microprocessor one by one

Features of 80186 Microprocessor:

In 1982, the 80186 microprocessor was developed by Intel. This is an improved 8086 with several common functions built in blocks such as clock generator, system controller, interrupt controller, DMA controller, and timer/counter. This processor has 8 new instructions and executes instructions faster than the 8086. Just like the 8086 processor, it has a 16-bit external data bus. It is also available with an 8-bit external data bus, and then the processor name is 80188 microprocessor. The initial clock frequency of the 80186 and 80188 is about 6 MHz. Generally, these processors are used as embedded processors and also used as the CPU of personal computers.

The second generation of the 80186 family, such as the 80C186/C188 processors, have been developed by Intel in 1987. The 80186 was redesigned as a static, stand-alone module known as the 80C186 Modular Core and its pin configuration is compatible with the 80186 family. The high-performance CHMOS III pro­cess allowed the 80C186 to operate at twice the clock rate of the NMOS 80186, but this processor consumes less than one-fourth the power.

The 80C186 Modular Core family was further developed and the 80C186XL processor was developed in 1991. The 80C186XL/C188XL is a higher performance and lower power replacement for the 80C186/C188.

The 80186 and 80188 processor series are generally intended for embedded systems such as modems, public and private PBX switching systems, cellular phones, etc. The architecture of 80186 can also be found in many real-time environments such as robotics, automation industry, measurement control systems, sensors and test equipment’s, fax machines, copiers, printers and medical equipment. Therefore, Intel 80186 proces­sor family, 80186, 80C186XL, 80C186EA/EB/EC, have been accepted in a wide range of applications.

Features of 80286 Microprocessor:

The Intel 80286 was introduced in early 1982. This is also known as iAPX 286 and it is an x86 I6-bit micro­processor with 134,000 transistors. It was the first Intel processor that could run all the software written for its predecessor. It was widely used in IBM PC compatible computers such as IBM PC/AT during the mid 1984 to early 1990s.

Initially, 80286 was released with 6 MHz and 8 MHz, it was subsequently scaled up to 12.5 MHz. The 80286 had an average speed of about 0.21 instructions per clock. The 6 MHz model usually operated at 0.9 MIPS, the 10 MHz model at 1.5 MIPS, and the 12 MHz model at 1.8 MIPS.

The 80286’s performance is more than twice that of its predecessors, i.e., Intel 8086 and Intel 8088 per clock cycle. The 80286 processors have a 24-bit address bus. Therefore, it is able to address up to 16 MB of RAM, whereas the 8086 could directly access up to 1 MB. The 80286 CPU was designed to run multitasking applications. digital communications, real-time process control systems, and multi-user systems.

This processor is the first x86 processor, which can be used to operate in protected mode. The protected mode enabled up to 16 MB of memory to be addressed by the on-chip linear memory management unit (MMU) with 1 GB logical address space. The memory management unit is able to provide some degree of protection from applications writing outside their allocated memory zones. But the 80286 could not revert to the 8086 compatible real mode without resetting the processor.

80286 is a high-performance 16-bit microprocessor with on-chip memory management and protection capabilities. Actually, this processor has been designed for a multi-user as well as a multitasking system. Usually, the 80286 processor is booted in real mode, and thereafter it works in protected mode by software command. But it is not possible to switch the 80286 from protected mode to real mode. To shift from pro­tected mode to real mode, 80286 microprocessors must be reset. The 80286 with 8 MHz clock provides up to 6 times higher than the 5 MHz 8086.

There is no on-chip clock generator circuit in 80286. Therefore, an external 82284 chip is required to generate the external clock. The 80286 has a single CLK pin for single-phase clock input. Usually, the exter­nal clock is divided by 2 internally to generate the internal clock. The 82284 provides the 80286 RESET and READY signals.

The 80286 operates in two different modes such as real mode and protected mode. The real mode is used for compatibility with existing 8086/8088 software base, and the protected mode is used for enhanced system level features such as memory management, multitasking, and protection.

The 80286 is the first advanced microprocessor with memory management and protection abilities.

Features of 80386 Microprocessor:

The concepts of memory management, privilege and protection was introduced with 80286. The 16-bit word length of 80286 provides limitations on its operating speed. But for advanced applications, technology demanded high-speed machines with more powerful instruction sets incorporating all the features of 80286. Subsequently, a CPU with a 32-bit word size and higher operating frequency and high speed of operation, has been developed to overcome all the limitations of 80286. The new processor is called the 80386 processor. This is the third-generation processor and is introduced by Intel in 1985. The Features of 80386 Microprocessor are as follows:

  • The 80386 is a 32-bit microprocessor that can support 8-bit, 16-bit and 32-bit operands. It has 32-bits registers, 32-bits internal and external data bus, and 32-bit address bus.
  • Due to its 32-bit address bus, the 80386 can address up to 4GB of physical memory. The physical memory of this processor is organized in terms of segments of 4 GB size at maximum.
  • The 80386 CPU is able to support 16k number of segments and the total virtual memory space is 4 giga bytes x 16k = 64 terrabytes.
  • Another Features of 80386 Microprocessor has a 16-byte prefetch queue.
  • It is manufactured by Intel using 0.8-micron CHMOS technology.
  • It is available with 275k transistors in a 132-Pin PGA package.
  • It operates at clock speeds of 16 MHz to 33 MHz.
  • This Features of 80386 Microprocessor has memory management unit with a segmentation unit and a paging Unit.
  • It operates in real, protected and virtual real mode. The protected mode of 80386 is fully compatible with 80286.
  • The 80386 instruction set is upward compatible with all its predecessors.
  • The 80386 can run 8086 applications under a protected mode in its virtual 8086 mode of operation.
  • The 80386 processor supports Intel 80387 numeric data processor.

Features of 80486 Microprocessor:

Due to the increasing demand for inure sophisticated processing capability in advanced applications, the 80387 numeric data processors became compulsory for processors. Subsequently, the designers developed a new processor after incorporating the floating-point unit inside the CPU itself. The Intel 80486 is the first processor with an in-built 80387 floating-point unit and it is developed in 1989 using CHMOS IV technology.

The features of the 80486 processor are given below:

  • It has complete 32-bit architecture which can support 8-bit, 16-bit and 32-bit data types.
  • 8 KB unified level 1 cache for code and data has been added to the CPU. In advanced versions of the 80486 processor, the size of level 1 cache has been increased to 16 KB.
  • The 80486 is packaged in a 168-pin grid array package. The 25 MHz, 33 MHz, 50 MHz and 100 MHz ( DX-4) versions of 80486 are available in the market.
  • Execution time of instructions is significantly reduced. Load, store and arithmetic instructions are executed in just one cycle when data already exists in the cache.
  • Intel 80486 operates at much faster bus transfers.
  • This processor retains all complex instruction sets of 80386, and more pipelining has been intro­duced to improve performance in speed.
  • Floating-point unit is integrated with 80486 processor. Hence the delay in communications between the CPU and FPU has been eliminated and all floating-point instructions are executed within very few CPU cycles.
  • For fast execution of complex instructions, the 80486 has a five-stage pipeline. Two out of the five stages are used for decoding the complex instructions and the other three stages are used for execution.
  • Clock-doubling and clock-tripling technology has been incorporated in faster versions of Intel 80486 CPU. These advanced i486 processors can operate in existing motherboards with 20-33 MHz bus frequency, while running internally at two or three times of bus frequency.
  • Power management and System Management Mode (SMM) of 80486 became a standard feature of the processor.

The different variations of 80486 processors are manufactured, but two most common versions are 80486DX with integrated FPU and 80486SX without integrated FPU. The Intel 80486 microprocessor was developed for speeds up to 100 MHz. AMD486 produced at 120 and 133 MHz versions of the 80486, and also manufactured in small quantities the 150 MHz and possibly 166 MHz versions.