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33 votes
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Why did the 8087 need a special socket?

But why was the 8087 designed such that it needed a special socket? Because the 8087 is a processor EXTENSION, not another CPU. The 8087 has, except for a few lines, exactly the same signals and ...
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18 votes
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Which x87 first acquired the ability to flush denormal to zero?

Full disclosure: I worked on the x87 FPU of a 486-class CPU at a math-coprocessor company in the early 1990s and thereafter worked at AMD, where I was on the 3DNow! design team and the design team for ...
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17 votes
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x87 trigonometric instructions

The tan(x) function has a period of π radians, with asymptotes at ±π/2; it effectively calculates sin(x)/cos(x), and the latter goes to zero at those points. So a function which evaluates properly ...
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14 votes

x87 trigonometric instructions

The restrictions on the range of arguments the transcendental instructions are able to handle is a direct result of hardware resource limitations in these early floating-point units. The primary ...
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14 votes
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What was the performance penalty for denormal inputs on 80s-era FPUs?

The MC68882 was relatively well-regarded among 1980s FPUs. Digging out accurate timing information takes some effort, but it appears that handling denormalised values was only moderately burdensome ...
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6 votes

Why did the 8087 need a special socket?

The socket was 'special' only in the sense that its only purpose was to accept an 8087; it wasn't an unusual component. Adding this socket would be significantly cheaper than adding what would come ...
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6 votes
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How did databases use the 8087?

You need to understand that using the 8087 was effectively "free" for the developers and for the users. You linked in a floating point library that determined the existence of the 8087, and ...
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5 votes
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What were the most common applications of the 8087?

Without detailed sales and usage figures, “the most common” is probably impossible to answer, and even considering only the 8087, the answer depends on “when” — reasons to buy 8087s changed as ...
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2 votes

How did databases use the 8087?

Many database programs, including later versions of dBase and Paradox, provided features beyond simple database table storage lookup. They could generate tables dynamically, and also had programming ...
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1 vote

x87 trigonometric instructions

I remember that FPTAN didn't give the actual tg(x), but two results and you had to divide one by another in order to get tg(x) (and they were not sin(x) and cos(x) as one would hope). Probably that'...
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