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From: kludge@gitpyr.UUCP (Scott Dorsey)
Newsgroups: net.arch
Subject: Re: Re: Addressing modes
Message-ID: <1468@gitpyr.UUCP>
Date: Tue, 25-Feb-86 15:09:12 EST
Article-I.D.: gitpyr.1468
Posted: Tue Feb 25 15:09:12 1986
Date-Received: Fri, 28-Feb-86 04:51:28 EST
References: <187@anwar.UUCP> <1441@gitpyr.UUCP> <890@umn-cs.UUCP>
Reply-To: kludge@gitpyr.UUCP (Scott Dorsey)
Organization: Georgia College Of Universal Knowledge
Lines: 22

In article <890@umn-cs.UUCP> crickman@umn-cs.UUCP (Robin Crickman) writes:
>How about a conditional SKIP instruction (if TRUE, skip the next opcode, else 
>execute it), which was the only kind of conditional instruction on the pdp-8?
>I believe the pdp-8 used the sort of jump described above.  Was it a RISC 
>machine?  It certainly had a reduced instruction set!
>
>John Hasler (guest of ...ihnp4!umn-cs!crickman)

   My HP-34C calculator has just that instruction.  Seems a little better
than a short branch, but not all that much.  Conditional branches are probably
faster, even if they require a larger word.  Most branches tend to be short, and
I suspect you'd wind up using a lot of (execute this branch if true) instructions.
I wouldn't call the PDP-8 a RISC machine, but then, what do you call a machine
that can't add?

-------
Disclaimer: Everything I say is probably a trademark of someone.  But
            don't worry, I probably don't know what I'm talking about.

Scott Dorsey
ICS Programming Lab, Georgia Insitute of Technology, Atlanta Georgia, 30332
...!{akgua,allegra,amd,hplabs,ihnp4,seismo,ut-ngp}!gatech!gitpyr!kludge