LECTURE-1

8086 PROCESSORS: Historical background, The microprocessor-based personal computer

system, 8086 CPU Architecture, Machine language instructions, Instruction execution timing.

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Historical Background:

The first general-purpose, programmable electronic computer system was developed in 1946 at

the University of Pennsylvania. This first modern computer was called the ENIAC (Electronics

Numerical Integrator And Calculator).

Basically the microprocessors capacity can be analyzed with respect to their data handling

capability and accordingly they have been evolved as listed.

4-Bit Microprocessors, 8-Bit Microprocessors, 16-Bit Microprocessors, 32-Bit Microprocessors and 64-Bit Microprocessors etc.,

4-BIT MICROPROCESSORS: The Intel 4004 & 4040:

With the invention of integrated circuit technology in 1959, Intel introduced the world’s first

microprocessor, a 4-bit Intel 4004 microprocessor in the year 1971. It addresses a mere 4096

4-bit wide memory locations and clocks at 740KHz. The 4004 instructions set contained only 45

instructions. It was fabricated with the P-channel MOSFET technology. Later Intel introduced

4040, an updated version of 4004, which operated at higher speed, although it lacked

improvements in word width and memory size.

8-BIT MICROPROCESSORS: The Intel 8080 & 8085:

8080 address more memory and execute additional instructions, but it executed them 10

times faster than 8008.

The 8080 was compatible with TTL, whereas the 8008 was not directly compatible.

The 8080 also addressed four times more memory (64 Kbytes) than the 8008 (16

Kbytes).

Intel corporation introduced 8085, an updated version of 8080. Although only slightly more

advanced than an 8080 microprocessor, the 8085 executed software at an higher speed. The

main advantages of the 8085 were its internal clock generator, internal system controller, and

higher clock frequency. This higher level of component integration reduced the 8085‟s cost and

increased its usefulness.

16-BIT MICROPROCESSORS: The Intel 8086, 8088, 80186 and 80286.

The 8086 & 8088 microprocessors

The Intel released 16-bit microprocessors 8086 & 8088, which executed instructions in as little

as 400ns (2.5 MIPS). The 8086 & 8088 addressed 1 Mbytes of memory, which was 16 timers

more memory than the 8085. 8086/8088 have a small 6-byte instruction cache or queue that pre-

fetched a few instructions before they were executed, which leads to the faster processing.

8086/8088 has multiply and divide instructions which were missing in 8085. These

microprocessors are called as CISC (Complex Instruction Set Computers) because of the

number and complexity of the instructions. The 16-bit microprocessor also provided more

internal register storage space that the 8-bit microprocessor. Applications such as spread sheets,

word processors, spelling checkers, and computer-based thesauruses on personal computers are

few developed using 8086/8088 microprocessors.

The 80186 & 80188 microprocessors:

INTEL 80186 & 80188 Introduced in 1982. They were 16-bit µPs. Clock speed was 6 MHz.

80188 was a cheaper version of 80186 with an 8- bit external data bus. They had additional

components like Interrupt Controller , Clock Generator, Local Bus Controller and Counters .

The 80286 microprocessor: Even the 1 M-byte memory on 8086/8088 found limited for the advanced applications. This led Intel to introduce the 80286 microprocessor. 80286 follow 8086‟s 16-bit architecture, except it

can address 16 M-byte memory system. The instruction set was similar to 8086 except few

instructions for managing extra 15 Mbytes of memory. The clock speed of 80286 was increased,

so it executed some instructions in as little as 250 ns (4 MIPS).

The 32-bit Microprocessors: The Intel 80386 & 80486

The 80386 Microprocessor:

The 80386 is the Intel‟s first 32-bit microprocessor. The 80386 has 32-bit data bus and a 32-bit

memory addresses. The 80386 was available in different versionsas 80386 DX , 80386 SX ,

80386 SL , which vary in the amount of memory they address. Applications that require

Graphical User Interface (GUI) were using the 80386 microprocessors. Even applications which

involve floating-point numbers were using the 80386 microprocessors. The 80386 included a

memory management unit that allowed memory resources to be allocated and managed by the

operating system. Intel 80386 became the best selling microprocessor in history.

The 80486 Microprocessor:

The 80486 has 80386 like microprocessor, an 80387 like numeric co-processor, and an 8 Kbyte

cache memory integrated in it. Most of the instructions in 80486 can be executed in a single

clock instead of two clocks compared to 80386. the average speed improvement of instructions

was about 50% over the 80386 that operated at the same clock speed. It had five different

versions- 80486 DX , 80486 SX , 80486 DX2 , 80486 SL and 80486 DX4

The Pentium Microprocessor:

The Pentium microprocessor was introduced late in 1993 with higher speeds compared to

80486. in Pentium cache size was increased to 16 Kbytes from the 8K cache found in the basic

version of 80486. After Pentium, many versions were introduced, like Pentium Pro, Pentium II,

Pentium III , Pentium IV ,Pentium dual core, Core i2, i3, i5 and i7 with higher capacities and

speed.