What Is i386 Architecture?

by Kristopher Gray

The Intel 80386 was a 32-bit computer processor more commonly known as the i386 or the 386. The i386 was backward compatible with hardware that targeted earlier x86 chips. The i386 was also the first consumer processor to support 4 gigabytes of memory. The low price of the i386 made possible the growth of the personal computer market.

History

Intel introduced the x86 line of microprocessors in 1978 with the Intel 8036. A microprocessor is the heart of a computer--it performs math and logic operations. Intel released the successor to the 8036 in 1982, when it introduced the 80286 microprocessor. The 80286 was the first processor to feature "protected mode," which allowed an operating system to use more memory than the computer actually had. However, the 80286 was not backward compatible with 8086 hardware.

Launch

Intel released the third generation of the x86 line in 1985, when it introduced the i386 microprocessor. The i386 addressed the problems of the 80286 microprocessor. Most notably, the i386 included backward compatibility for 8086 hardware. The i386 also expanded the capabilities of the "protected mode" feature introduced by the 80286. The i386's low price helped launch the personal computer industry. Variations of the i386 remained in production until 2007, almost 22 years after it was first introduced.

Hardware Architecture

The i386 sported 32-bit memory registers, capable of handling 32-bit instructions. Memory registers store the instructions sent to a computer processor and any data referenced by those instructions. A computer processor with large memory registers can store more operations and operate on more data than a processor with smaller memory registers. The 32-bit memory architecture of the i386 increased the amount of accessible memory to 4 GB. However, not all versions of the i386 supported 4 GB of memory.

80386 Protected Mode

Protected mode, also known as "protected virtual address mode," is a feature of x86 computer processors that provides numerous memory-management functions. Protected-mode features include virtual memory, multitasking, and memory paging. These features made it possible for an operating system to use more memory than the computer actually had. Intel introduced protected mode with the 80286 processor, the immediate predecessor of the i386. The i386 added several features to protected mode: paging, 32-bit virtual address space (an address for data stored in the computer's memory), protected mode toggling and a virtual 8086 mode for compatibility with older hardware. To maintain compatibility with older hardware and software, the i386 processor only entered protected mode after the system software explicitly enabled protected mode.

Variations

The standard i386 model was the i386DX. Intel first released the i386DX in October 1985. The first version of the i386DX operated at 12 megahertz. Later versions of the i386DX could operate at speeds up to 33 MHz. Intel released the i386SX in June 1988. The i386SX was a budget version of the i386. The first version of the i386SX operated at 16 MHz, while later versions operated at speeds up to 33 MHz. The i386SX used a 16-bit external data bus, which transfers data between computer components. This provided compatibility with 16-bit hardware, but made 32-bit memory usage slower. The i386SX was limited to 16 megabytes of RAM. Intel released a mobile version of the i386SX, the i386SL, in 1990. The i386SL sported more transistors than other i386 chips. However, the i386SL had a fixed memory cache of 16 to 64 kilobytes. It also had a fixed processor speed of 25 MHz.

About the Author

Kristopher Gray began writing in 2009. He has experience in computer programming, trial practice and civil law practice. He writes law and technology articles for eHow. Gray has a law degree from Case Western Reserve University and a Bachelor of Arts in cognitive science from University of California-Berkeley.

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