The 80386 Microprocessor Architecture & Features

The 80386 Microprocessor Architecture & Features – The 80386 microprocessor is the first 32-bit microprocessor. The designers of the 80386 microprocessor have tried to overcome the limitations of the 80286 microprocessor, such as a 16-bit word length, limitations of operating speed, less powerful instruction set according to new technology.

Architecture of 80386 Microprocessor

The architecture of the 80386 microprocessor is shown in Figure 1. It contains the following six functional units:

1. Bus Interface Unit – Interfaces 80386 with external devices and is responsible for external operations.
2. Code Prefetched Unit – Contains a prefetched queue in which instruction bytes fetched by the BIU are stored.
3. Instruction Unit – Decodes the instructions received from the prefetched queue and stores them in the three instructions decoded queue.
4. Segment Unit – Allows the use of two address components: segment and offset addresses.
5. Paging Unit – Organizes the physical memory in terms of pages of 4K bytes each.
6. Execution Unit – Executes the instructions.

Features of the 80386 Microprocessor

The 80386 microprocessor is available in two different versions: 80386 SX and 80386DX. The 80386SX is the economical version of the 80386, having 32-bit internal architecture but haing 16 bit data bus and a 24-bit address bus. The 80386DX is a full 32-bit internal architecture with a 32-bit data and address bus.

The 80386 microprocessor has the following salient features:

1. The 80386 microprocessor is the first 32-bit microprocessor.
2. The 80386 microprocessor supports 16K number of segments, and thus the total virtual memory space is 4G byte X 16K = 64 Terra bytes.
3. Virtual memory, paging, and four levels of protection are supported by the memory management section of the 80386 microprocessor.
4. The 80386 microprocessor contains a total of eight debug registers (DR0 – DR7) for hardware debugging and control.
5. The 80386 microprocessor is compatible with the math coprocessor 80387, and the couplet 80386 – 80387 provides a high-speed processing environment.