> Also, the arbitrary "Oh, and the registers are 80 bits wide" is also just one of those weird "Where did that number come from?".

One of the features that was advertised (mentioned in the iAPX 86, 88, 186 Microprocessors Part II book (July 1984)) was the ability to do exact arithmetic on integers up to 2^64, which is possible due to the 64-bit mantissa used in the 80-bit format.

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mortja 6 hours ago | parent [-]

So in a sense the 8087 was the first 64 bit CPU?

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matja 6 hours ago | parent | next [-]

I wouldn't say so, because it was a co-processor: e.g., it depended on the 8086 to even generate addresses for memory operations.

I think the IBM 7030 Stretch CPU (from 1964) would be a likely contender for being one of the first 64-bit CPUs.

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kens 5 hours ago | parent | prev [-]

The Cray-1 (1976) was probably the first 64-bit CPU.

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kragen 5 hours ago | parent [-]

https://en.wikipedia.org/wiki/64-bit_computing#64-bit_data_t... names Stretch from 01961 as the first natively 64-bit CPU, but maybe there are some that are even older?

	▲	kens 5 hours ago \| parent [-]
		I forgot about the IBM 7030 Stretch (1961), which was also 64 bits. The NORC (Naval Ordnance Research Calculator) (1954) had 16 decimal digits, which is sort of 64 bits.