The Intel 80386 microprocessor is a landmark in computing history, being the first 32-bit processor in the CISC x86 family. Released by Intel in 1985, it ushered in a new era for the PC platform, introducing several innovations that shaped the future of personal and professional computing.
Key Features of the Intel 80386
- Initial Speed: 12 MHz
- Number of Transistors: Approximately 275,000
- Internal Architecture: 32-bit word operation
- Data and Address Bus: 32 bits
Technological Advancements
The Intel 80386 introduced several significant improvements over its predecessors:
Protected Mode:
- Efficient use of protected mode, virtual memory, and multitasking.
- Ability to switch freely between real mode and protected mode, facilitating the execution of programs that required the benefits of protected mode.
New Architecture:
- The 32-bit architecture allowed the 80386 to access up to 4 GB of RAM, a massive leap compared to the limitations of previous processors.
Introduction of the 386 SX:
- To overcome the high cost of the 386 DX, Intel released the 386 SX, a lower-cost version that used a 16-bit bus, making systems more affordable for the market.
The Protected Mode and Its Advantages
Although protected mode had been used since the 80286, the 80386 was the first to allow efficient switching between real mode and protected mode. Programs running on DOS could switch to protected mode to leverage its benefits and return to real mode for using DOS routines, transparently to the user. This was made possible through the DOS Protected Mode Interface (DPMI).
Example of Operation:
- Mode Switching: When a program needed to execute a DOS routine, it invoked the DPMI, which switched the processor to real mode, executed the command, and returned to protected mode.
Architecture and the Introduction of the 386 SX
The original 386 featured a 32-bit data and address bus, enabling it to access 4 GB of RAM. Due to the high cost of 386 DX-based systems, Intel launched the 386 SX, which operated internally with 32 bits but used a 16-bit bus to communicate with memory and peripherals.
Peripheral Compatibility:
- The 386 SX’s architecture allowed the reuse of peripherals from 286 boards, making 386 SX-based systems much more affordable.
Memory Limitation:
- Using a 24-bit addressing scheme, the 386 SX could directly access up to 16 MB of RAM, which was more than sufficient at the time.
Cache and Performance
To solve the issue of wait cycles caused by the speed difference between the processor and memory chips, 386 motherboards were equipped with cache memory. This extremely fast memory stored the most recent data and instructions, drastically reducing the processor’s wait time.
Cache Effectiveness:
- The high cache hit rate meant that the processor found the required data in the cache most of the time, significantly boosting efficiency.
ISA and EISA Bus
386 systems used the 16-bit ISA bus at 8 MHz for peripheral installation. Some advanced boards incorporated the 32-bit EISA bus, which increased bandwidth but did not match the data demands of faster processors.
EISA Limitations:
- The 8 MHz frequency was insufficient for the 33 MHz processors released in 1989, necessitating a more efficient bus that was only introduced with the VESA Local Bus (VLB) on 486 processors.
Conclusion
The Intel 80386 was a breakthrough in computing, marking the era of 32-bit processing and laying the groundwork for modern operating systems. Its advanced architecture, ability to switch between modes, and introduction of cache memory set new standards for performance and efficiency, paving the way for future innovations in the computing industry.
FAQ
- What is the Intel 80386 microprocessor?
- The Intel 80386 is a 32-bit microprocessor from the CISC x86 family, released in 1985. It was the first 32-bit processor for the PC platform, introducing many technological innovations.
- The Intel 80386 is a 32-bit microprocessor from the CISC x86 family, released in 1985. It was the first 32-bit processor for the PC platform, introducing many technological innovations.
- What were the key innovations of the Intel 80386?
- The 80386 introduced several innovations, such as the ability to operate in protected mode, support for virtual memory, efficient multitasking, and the introduction of a 32-bit data and address bus.
- The 80386 introduced several innovations, such as the ability to operate in protected mode, support for virtual memory, efficient multitasking, and the introduction of a 32-bit data and address bus.
- What was the initial speed of the Intel 80386?
- The Intel 80386 was initially released with a speed of 12 MHz.
- The Intel 80386 was initially released with a speed of 12 MHz.
- How many transistors did the Intel 80386 have?
- The 80386 microprocessor contained approximately 275,000 transistors.
- The 80386 microprocessor contained approximately 275,000 transistors.
- What is the protected mode in the Intel 80386?
- Protected mode allows the processor to access virtual memory and perform efficient multitasking. It also allows switching freely between real mode and protected mode, providing greater flexibility for programs.
- Protected mode allows the processor to access virtual memory and perform efficient multitasking. It also allows switching freely between real mode and protected mode, providing greater flexibility for programs.
- What’s the difference between the 386 DX and the 386 SX?
- The 386 DX has a 32-bit data and address bus, while the 386 SX, a lower-cost version, uses a 16-bit bus but operates internally with 32 bits. The 386 SX was designed to be more affordable and compatible with 286 peripherals.
- The 386 DX has a 32-bit data and address bus, while the 386 SX, a lower-cost version, uses a 16-bit bus but operates internally with 32 bits. The 386 SX was designed to be more affordable and compatible with 286 peripherals.
- What was the maximum memory the Intel 80386 could access?
- The 386 DX could access up to 4 GB of RAM, while the 386 SX, using 24-bit addressing, could directly access up to 16 MB of RAM.
- The 386 DX could access up to 4 GB of RAM, while the 386 SX, using 24-bit addressing, could directly access up to 16 MB of RAM.
- Did the Intel 80386 have an integrated floating-point unit (FPU)?
- No, the Intel 80386 did not have an integrated floating-point unit. Motherboards for the 386 included a socket for an arithmetic coprocessor like the Intel i387 to perform real-number operations.
- No, the Intel 80386 did not have an integrated floating-point unit. Motherboards for the 386 included a socket for an arithmetic coprocessor like the Intel i387 to perform real-number operations.
- What is cache memory, and why was it important in the 80386?
- Cache memory is a fast static memory that stores recently accessed data and instructions. In the 80386, the cache helped minimize wait cycles, improving the processor’s efficiency by reducing the time spent waiting for slower RAM.
- Cache memory is a fast static memory that stores recently accessed data and instructions. In the 80386, the cache helped minimize wait cycles, improving the processor’s efficiency by reducing the time spent waiting for slower RAM.
- What types of buses were used in systems based on the 80386?
- 386 systems primarily used the 16-bit ISA bus at 8 MHz. Some advanced boards featured the 32-bit EISA bus, which doubled the bandwidth for data flow but was not widely adopted due to its high cost.
- 386 systems primarily used the 16-bit ISA bus at 8 MHz. Some advanced boards featured the 32-bit EISA bus, which doubled the bandwidth for data flow but was not widely adopted due to its high cost.
- What is the VESA Local Bus (VLB)?
- The VESA Local Bus (VLB) is a high-speed bus introduced for use with 486 processors. It was developed to overcome the limitations of the ISA and EISA buses by providing faster communication between the processor and peripherals.
- The VESA Local Bus (VLB) is a high-speed bus introduced for use with 486 processors. It was developed to overcome the limitations of the ISA and EISA buses by providing faster communication between the processor and peripherals.
- How did the Intel 80386 contribute to the evolution of operating systems?
- The Intel 80386 enabled the development of operating systems capable of taking advantage of its advanced features, such as multitasking and virtual memory. Examples include OS/2 2.0 (1992) and Windows NT 3.1 (1993), both of which leveraged the 80386’s capabilities.
- The Intel 80386 enabled the development of operating systems capable of taking advantage of its advanced features, such as multitasking and virtual memory. Examples include OS/2 2.0 (1992) and Windows NT 3.1 (1993), both of which leveraged the 80386’s capabilities.
- Why was the 386 SX a commercial success?
- The 386 SX was a commercial success due to its lower cost and compatibility with 286 peripherals, making systems based on it more affordable and accessible to a broader range of users.
- The 386 SX was a commercial success due to its lower cost and compatibility with 286 peripherals, making systems based on it more affordable and accessible to a broader range of users.
- What memory modules were used during the 80386 era?
- During the 80386 era, the commonly used memory modules were 30-pin SIMMs, which could transfer 8 bits per clock cycle. To provide the 32-bit data needed for the processor, memory modules were installed in multiples of four.
- During the 80386 era, the commonly used memory modules were 30-pin SIMMs, which could transfer 8 bits per clock cycle. To provide the 32-bit data needed for the processor, memory modules were installed in multiples of four.
- How did the 80386’s 32-bit architecture influence computing?
- The 32-bit architecture of the 80386 allowed for the development of more complex and efficient software and operating systems, supporting greater memory capacity and multitasking, and laying the foundation for future innovations in computing.
- The 32-bit architecture of the 80386 allowed for the development of more complex and efficient software and operating systems, supporting greater memory capacity and multitasking, and laying the foundation for future innovations in computing.
