Originally posted by: walla
What is the architectural difference among 386/486/586, x86? In other words, what is the significance of these labels.
Also, what is the significance of Intel's P3/P4 label, and what will mark the arival of a P5?
Yes, I do realize that there is a progression in performance...but I am looking for a more "highly-technical" answer
386/486/586:
There's not much functional difference between these. In fact, until the arrival of x86-64, we're basically still using the '386 software architecture. Hardware wise though, there are great performance improvements through new core technologies.
Before the '386 there were the 8086 and 80286, or '286 for short. These though, are quite different!
8086 was a 16 bit CPU with a segmented real (direct) addressing scheme for 1MB. 64KB segments. No protected memory or virtual address space. An address corresponded directly to a byte in physical ram.
'286 was a 16-bit CPU with 16-bit segmented protected memory addressing (for maximum 64MB? I think?). '286 protected mode is not compatible with 8086 code, 'real mode'. But the '286 could still switch mode to 'real mode' to execute 8086 code.
The '386 then, was the first 32-bit CPU for the "Wintel" PC. '386 introduced 32-bit addressing and linear, flat virtual space, rather than segmented. As the '286, the '386 could also dumb down to 'real mode' to run 8086 programs. It could also, importantly, run 8086 code in a virtual mode, while still staying in a protected address space. The virtual flat address space for the 386 was now 4GB.
All the features of the '386 weren't really used until the advent of Win95 and Linux. So the revolution you saw then, were hardware wise prepared for, already with the '386. Even if most people were on the Pentium or at least the '486, by then.
'486 was basically a faster '386. It introduced the famous 'pipelining' with a 5-stage pipe. This allowed the '486 to finish instructions in less clock cycles than the '386. The '486DX also integrated the FPU inside the CPU. So we can say that it introduced the '87 FP extension to the instruction set. This had been an optional external coprocessor, the '387, before.
'586, this is the Pentium. Intel got tired of other manufacturers calling their CPU's 486, 586, so the wanted a proprietary name that they protect. So they dropped the numbering scheme.
Pentium did some more and better pipelining, prefetching and caching than the '486. It also introduced a complete PC architecture technology package, consisting of our now wellknown and familiar PCI, Northbridge, Southbridge and 64-bit memory bus (previously 32-bit).
The performance boost of the Pentium was pretty dramatic. And it came at a critical time, when many believed the future was RISC and that the '86 PC was dead in the water. I'm sure it was cold shower for Apple, Motorola and their PowerMac. Later Pentiums introduced the MMX extension.
Next would logically be the "Hexium". However, Intel wanted to keep and take advantage of the "Pentium" trademark. So it became the PentiumPro instead. Same ideas as Pentium, Just more and better of everything. This is actually the base for most wellknown Intel CPUs: PentiumII included MMX and was produced in a cheapified 'slot' package (due to the way the L2 cache was made, it was actually cheaper that way, for a while). PentiumIII introduced the SSE extension, but is basically the same core. Somewhere then the PentiumIII also went back to socket and onchip L2 cache. The PentiumIIIe also had full speed L2 cache. This versatile and successful core is also said to be the starting point for the PentiumM, desktop derivatives, and quite possible also for Intel's future new main x86-64 CPU ("Conroe"? early 2006?), which could possibly become marketed as the 'Pentium5'.
Pentium4 is a completely different animal. In fact two different main CPU cores are marketed as Pentium4. Both the original Willamette/Northwood, and now the Prescott. I might have been that the Prescott should have been the Pentium5. However, since it failed to achieve better performance, it might have been one reason it retained the 'Pentium4' market name.
Anyway, all Pentium4s use what Intel call the 'Netburst' architecture, And are designed with reaching highest possible clockrate as the primary goal. Nevermind actual performance.
Willamette/Northwood is notable because it introduced the SSE2 extension.
Prescott is notable because it will introduce the new 64-bit software architecture, x86-64 aka EM64T.
I hope someone else makes a neat table of buswidth's, clocks and caches, for you, because I'm tired now.
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