This Archaic Processor Influences Our Modern Processors Architecturally. But How?
Channel: Tech. Inc
Date: 2019-08-22

The I486 was the original saving grace from Intel whose creation and success has a lasting effects on our  modern processors. In this video I will explain you what made it such a commercial success.

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Transcript:
The Intel 486 was the predecessor of the original Pentium processor. It might be obscured with the modern 
Hot and flashy processor. but it was one of the processor that held most of our memories from 80's



The I486 was essentially an high performance follow up to the i386, It focused more on improving the the total performance of the processor 
rather than improving clock speed. as a result it's lowest clock speed was 16Mhz of clock speed, just 4 MHz higher than the i386 
all the while achieving the Intel's goal of 2 to 3x performance from i386


The i486 had several new instructions introduced like XADD,BSWAP, CMPXCHG, INVD, WBINVD and INVLPG. 
The i486 has a on chip shared 8 KB on-chip Ram cache that stores recent data. now this would like a oddly specific detail I'm talking about, but the thing is 
the i386 and previous processors didn't have an on die cache, only a small storage line for storing instruction. instead it used a separate chip
for cache that is embedded on the motherboard it worked on and the cache was SLOW

The 486 also had an more powerful external bus which contacted with other parts of computer like ram. The bus had a new burst mode to access memory and transfer the
data to the cache line, this method was quite fast. The i486 could transfer 16 bytes within 5 cycles of the processor while the i386 required 8 cycles to do the same thing


The 386 had no such internal cache but supported a slower off-chip cache (which was not a level 2 cache because there was no internal level 1 cache on the 80386).
An enhanced external bus protocol to enable cache coherency and a new burst mode for memory accesses to fill a cache line of 16 bytes within 5 bus cycles.
 The 386 needed 8 bus cycles to transfer the same amount of data.

The i486 also had an integrated FPU and like the cache part, 
the I386 lacked this and instead used an i387 co processor to do arithmetic or emulated the arithmetic operation with software when the co processor did not exist , which was really slow.
with all of this we can really say that the processor's performance was sure improved enormously. The Instruction performance was increased through a tight pipeline, allowing it to be about twice as fast as the i386 clock for clock. 

The 1980's was quite a phase for desktop computers or just processors in general. For starters, the 80's era touted RISC architecture as the future of all computing
with  MIPS, SPARC and ARM were dominating the headline all the time.

RISC architecture is more of a diet instruction set. A instruction set is all the commands that a processor can understand of. RISC architecture have a small 
and a basic instruction set and follows the "less is more" ideology from minimalism and requires complex process to be broken into smaller basic instructions 
to work on it. while CISC has a more redundant instruction so that it doesn't have to spend time and memory to break up small tasks. each have their own advantages and neither one of them is a clear cut
faster than the other

Now, as i said RISC is getting more hype and people are not liking the CISC architecture. Even Intel had introduced the i860, a RISC based processor along with a 
separate RISC team which was internally competing with the company's CISC, Along with this. the  increased market demands made the CISC team know that 
the processor had to be executed flawlessly, the Team Could not afford delays and bugs. Samples of i486 were scheduled to be released in Q3 of 1989. However the team just barely beat the announced 
shipping date with production starting at late September to early October.


 don't get me wrong,the CISC team didn't create the i486 flawlessly,there were several bugs in the FPU of 486,
Chips with the B4-Mask revision and earlier were affected (SX249). However these bugs were relatively minor,

The 80486 was a success in the market and secured CISC as the backbone of personal computing.
  Today, the CISC x86 ISA is still used, alongside the greats of RISC as well.