Microprocessor - 80486
Posted by Harisinh | Posted in | Posted on 4:32 AM
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The 80486s were not groundbreaking in terms of a radically different design philosophy, like the 80386. It did have four new features that made the 80486 about twice as fast as the fastest 80386. The most talked about new features were a built-in cache, (when the processor speeds reached the 20-25 MHz vicinity, reasonably priced DRAM memory could no longer be accessed with zero wait bus cycles) and a built-in math co processor (increased the throughput for floating point operations). On average, the math co processor built into the 80486 yielded three times the greater performance than external 80387 Numeric Processing Unit (NPU). The speed difference between the 80386 and the 80486 made the Graphical User Interface (GUI) practical for everyday use.
A concept which is known as, Unified Internal Code/Data Cache is used in 80486. It incorporates the advantage of the external cache coupled with the fact that every time a memory request is fulfilled by the internal cache, one less bus cycle results. In addition, the access of data is much faster since the only delay would be to look up the data/code and to deliver it to the internal requester. This also frees up the bus for other bus masters. The address bus in 486 is bi-directional because of the presence of cache memory inside 486 (to enable cache invalidation). It also supports burst type of bus cycle which saves time during floating point operand fetch as well as cache memory fill.
Internal data conversion logic for both 8-bit subsystem and 16-bit subsystems; dynamic bus sizing supporting 8, 16 and 32 bit cycles. The 386 does not support direct interfacing of 8 bit subsystem. An external logic is needed for this purpose. The 486 incorporates several features in order to simplify the debugging process. The on-chip debugging aids of 486 are of three types: Breakpoint instruction, Single-set capability by Trap and Code and data breakpoint capability by means of debug register.
The 486 also has a parity generator and parity checker inside it, providing parity logic for Data bus ne parity bit for each data byte. This offers better reliability. It consists of 1.2 million transistors and could run at clock rates of 50MHz.
Mircoprocessor - 80486
The 80486s were not groundbreaking in terms of a radically different design philosophy, like the 80386. It did have four new features that made the 80486 about twice as fast as the fastest 80386. The most talked about new features were a built-in cache, (when the processor speeds reached the 20-25 MHz vicinity, reasonably priced DRAM memory could no longer be accessed with zero wait bus cycles) and a built-in math co processor (increased the throughput for floating point operations). On average, the math co processor built into the 80486 yielded three times the greater performance than external 80387 Numeric Processing Unit (NPU). The speed difference between the 80386 and the 80486 made the Graphical User Interface (GUI) practical for everyday use.
A concept which is known as, Unified Internal Code/Data Cache is used in 80486. It incorporates the advantage of the external cache coupled with the fact that every time a memory request is fulfilled by the internal cache, one less bus cycle results. In addition, the access of data is much faster since the only delay would be to look up the data/code and to deliver it to the internal requester. This also frees up the bus for other bus masters. The address bus in 486 is bi-directional because of the presence of cache memory inside 486 (to enable cache invalidation). It also supports burst type of bus cycle which saves time during floating point operand fetch as well as cache memory fill.
Internal data conversion logic for both 8-bit subsystem and 16-bit subsystems; dynamic bus sizing supporting 8, 16 and 32 bit cycles. The 386 does not support direct interfacing of 8 bit subsystem. An external logic is needed for this purpose. The 486 incorporates several features in order to simplify the debugging process. The on-chip debugging aids of 486 are of three types: Breakpoint instruction, Single-set capability by Trap and Code and data breakpoint capability by means of debug register.
The 486 also has a parity generator and parity checker inside it, providing parity logic for Data bus ne parity bit for each data byte. This offers better reliability. It consists of 1.2 million transistors and could run at clock rates of 50MHz.
Mircoprocessor - 80486
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