Date   : Tue, 10 Apr 1990 03:00:15 EDT
From   : dg%pallio.UUCP@XAIT.Xerox.COM (David Goodenough)
Subject: Why Bother With CP/M?

A couple of points:
> According
> to a test done by a friend of mine (also reachable through this common
> account; email to Dent / cs2591aq@carina.unm.edu) the Z80a at 4MHz does
> a MIP.

Only assuming it's executing single byte instructions. Something like

       ld      a,(0x1234)

takes 13 T states, so those done repeatedly would only achieve 1/3 MIP.
On average, I'd guess it'd hit about 1/2 MIP doing _REAL_ work, although
some instructions ('inc (ix + dd)' or 'call xxxx') really hog CPU T states.

On the other side though, it still chugs along nicely: a 4MHz Z80 can
do the CRC and data transfer to keep an Xmodem transfer going at up to
about 22000 BPS, and that's doing the CRC the hard way (i.e. bit banging),
with a table driven CRC, it'd probably exceed 38400 BPS.

Now, why do _I_ bother with CP/M: One reason is that you gotta keep it
small: 57K of TPA can vanish in a real hurry. Keeping it small usually
means keeping it simple, and simple programs are easier to write and
maintain.
-- 
       dg@pallio.UUCP - David Goodenough               +---+
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