C8087-4 Specs

gekaufman · Joined: 08 Dec 2014 Posts: 385 Location: New Hampshire, USA

Anyone know the frequency rating of the C8087-4?

Thanks!

- Gary

CPUShack · Posted: Thu Dec 18, 2014 1:32 pm Post subject:

Should be 4MHz (like the D8086-4)

gekaufman · Joined: 08 Dec 2014 Posts: 385 Location: New Hampshire, USA

Hope that's not the case, as I'd actually like to use one with a 8mhz system Sad

It always seems to be listed as an OEM/TRAY part, but I can't ever find the speed listed.

Thanks!

CPUShack · Posted: Thu Dec 18, 2014 2:04 pm Post subject:

frag_ · Joined: 17 Nov 2008 Posts: 4015 Location: Estonia

There are only two speed grades for this package (the earliest one):
4 (C8086-4) and 5 (C8086) MHz unfortunately.
Faster ones (D8086-1) was produced later.

CPUShack · Posted: Thu Dec 18, 2014 2:12 pm Post subject:

Yup preliminary (1979) datasheet lists the 8086-4 as 4MHz (the 8087 will be the same)

By 1986 none of the -4s were available for sale

gekaufman · Joined: 08 Dec 2014 Posts: 385 Location: New Hampshire, USA

Thanks for checking. Guess it won't do well in my CompuPro 8086 8mhz S-100 board!

Robev · Joined: 10 Mar 2006 Posts: 3693 Location: New Zealand

Qwerty · Joined: 20 May 2005 Posts: 3141 Location: Germany

As far as I know, a 8087 FPU doesn't run at full frequency of the host 8088. I think there is a 1/2 divider. Correct me if I'm wrong.

frag_ · Joined: 17 Nov 2008 Posts: 4015 Location: Estonia

8087 has the same clock frequency as the main CPU, unlike 287.
And another difference - 8087 (and 80187) shares the system bus with CPU unlike later FPUs.

rjluna2 · Joined: 27 Oct 2014 Posts: 1302 Location: Hiram, GA, USA

CPUShack · Posted: Sat Mar 28, 2015 2:52 pm Post subject:

8087 runs the off the exact same clock as the host processor.

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