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87 votes
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How much better was DEC Alpha than contemporaneous x86?

The Alpha team set out to create a high-performance architecture, planned to last for 25 years and allow for 1000-performance increase over those 25 years. So they placed some long bets, starting with ...
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82 votes

Were there 8086 coprocessors other than the 8087?

Not all of the original co-processors were for floating point math. Intel itself offered an I/O coprocessor for the 8088 and 8086 called the 8089. Part of the reason it didn't do as well as the 8087 ...
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75 votes
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Intel CPU bug in the '90s

I suspect your teacher was referring to the FDIV Pentium bug, which led to a large outcry in the media at the time and for which Intel issued a recall. This bug caused floating-point division to ...
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57 votes

How much better was DEC Alpha than contemporaneous x86?

Stephen Kitt has done what seems to me an excellent job of outlining features and when they were introduced. I'll take a slightly different tack, instead picking a single point in time, and pointing ...
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55 votes

What was the last x86 CPU that did not have the x87 floating-point unit built in?

As far as I’m aware, the last FPU-less x86-compatible CPU which could still be considered general-purpose is the Vortex86SX, released in 2007 and still available now. This is a Pentium-class CPU, ...
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53 votes
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The start of x86: Intel 8080 vs Intel 8086?

8086 was designed to make asm source porting from 8080 easy (not the other direction). It is not binary compatible with 8080, and not source-compatible either. 8080 is not an x86 CPU. 8080 is a ...
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46 votes
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Is it true that Pentium III was faster than its successor Pentium 4?

Clock to clock Tualatin Pentium 3 was a lot faster (i.e. a P3 got more done in each clock cycle than a P4). High-end Pentium 3 is available at 1.4 GHz while low-end Pentium 4 is 1.5 GHz so if you ...
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45 votes
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What's the relationship between early 90s Pentium microprocessor and today's Intel designs?

My approximate version: Prior to the Pentium, Intel CPUs were pipelined: different parts of the CPU would simultaneously be working on different operations, but the different parts were designed to ...
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45 votes
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Why did Intel abandon unified CPU cache?

I’m not sure the separate cache was “obviously better” back when the Intel designers were working on the 80486, at least, not to the designers in question. But “better” might not even have been much ...
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44 votes
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Did any notable product use Intel's first RAM?

It might be important to know that the 3101 was neither a genuine Intel development, nor intended as a RAM - at least not in a way we see RAM today. After all, what use could there be in 1970 for a ...
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40 votes
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Are MS-DOS and Windows 9x vulnerable to Meltdown?

The Meltdown attack is about figuring out what's in protected memory (typically, kernel memory) by arranging for it to be speculatively read, and then looking for residual side effects after the ...
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39 votes

Were people building CPUs out of TTL logic prior to the 4004, 8080 and the 6800?

It was very common to build CPUs out of TTL logic prior to the 4004, 8080 and the 6800. This was the standard way to build later minicomputers. Examples are the Data General NOVA, Xerox Alto and TI-...
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33 votes

Which Linux or BSD distributions do still support i386, i486 or i586 CPUs?

Slackware still claims to support 486s: Below is a list of minimum system requirements needed to install and run Slackware. 486 processor 64MB RAM (1GB+ suggested) About 5GB+ of hard disk space for ...
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33 votes
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Why was segment register value scaled by such a small factor of 16 on i8086?

Wikipedia says: According to Morse et al.,.[5] the designers actually contemplated using an 8-bit shift (instead of 4-bit), in order to create a 16 MB physical address space. However, as this would ...
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33 votes
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Why are the Intel 8080's rotate instructions called opposite to intuition?

What historical reason is there for these instructions being called that? "Historical Reason" is the right key word here, as ... TL;DR: It's Piled Up Heritage The 8080 inherited the ...
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32 votes
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Why did Socket 3 have more pins than needed for the 486?

The extra pins were forward-planning, on both Socket 2 and Socket 3. Most of the extra pins are used for power (Vcc) and ground (Vss), which is useful to provide more power to a CPU. The other pins ...
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30 votes
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Should 486s have a heatsink?

It depends on the airflow in your computer. You can run even a 100 MHz 486DX4 without a heatsink or fan, if your PSU’s fan (or another fan) pulls enough air over it; they commonly used heatsinks ...
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29 votes

80286 can switch from real mode to protected mode - but why not back?

My guess is that it was merely a design decision based upon the assumption that once a protected mode OS is started, there is no need to go back. Most microprocessors at that time already booted in ...
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29 votes

Which Linux or BSD distributions do still support i386, i486 or i586 CPUs?

I have had great success with Gentoo Linux on the earliest generation of Intel 80486 processors, though I had to patch it (below). It works on the later ones too (486DX2 and 486DX4, both clock ...
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28 votes

Intel CPU bug in the '90s

Stephen Kitt has already provided a good answer regarding the FDIV bug. I'll fill in some details about Intel employing logicians: Because of this bug, Intel had to replace a lot of processors, which ...
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  • 381
27 votes

Which Linux or BSD distributions do still support i386, i486 or i586 CPUs?

Linux still supports the 80486 SX: the SX was simply a DX without the FPU, and the FPU emulation code is still present (Processor type and features->Math emulation). Finding a distro is a bit ...
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27 votes
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What are these weird long ISA slots on this 386 board? (not VLB)

I found this page on the motherboard, which says they are some sort of "32-bit external memory card." What are these slots? They are exactly that, memory expansion. This is a rather early ...
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  • 173k
26 votes
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Were people building CPUs out of TTL logic prior to the 4004, 8080 and the 6800?

Here is an homebrew / educational computer made of LSI / MSI chips : http://www.kenbak-1.net/index.htm Designed in 1971 256 bytes of memory made of MOS shift registers.
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26 votes
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Why is the 8254's default rate 18.2 Hz?

The first CGA PCs used a single clock from which they derived all their timings. To allow for NTSC output, the main clock had to run at a multiple of the colour subcarrier frequency; the main clock ...
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26 votes

Were there 8086 coprocessors other than the 8087?

Alan Cox mentions in this post having seen a hard drive interface that plugged into the 8087 socket (for computers with no expansion slots). I've checked various issues of Amstrad PC magazine. PPC ...
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26 votes
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Intel processor transistor type evolution

Here’s the list of main technologies used: 4004: 10µm PMOS; 4040: 10µm PMOS; 8008: 10µm PMOS; 8080: 6µm NMOS (faster than PMOS, and TTL-compatible); 8085: 3.2µm NMOS, then HMOS (“H” variants); 8086: ...
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25 votes

The start of x86: Intel 8080 vs Intel 8086?

To supplement @PeterCordes's excellent answer, I thought it would be worth going into the details of exactly how close to source code compatible the two processors are -- for example, how easy would ...
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  • 12.4k
25 votes

Is it true that Pentium III was faster than its successor Pentium 4?

The very earliest, slowest-clocked, Pentium 4 chips were slower than the fastest Pentium IIIs of the time. The PIII was available at 1GHz when the Pentium 4 was introduced, and a 1.5GHz P4 was about ...
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