Xref: utzoo comp.sys.ibm.pc.programmer:388 comp.sys.ibm.pc:46350
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!srhqla!demott!kdq
From: kdq@demott.COM (Kevin D. Quitt)
Newsgroups: comp.sys.ibm.pc.programmer,comp.sys.ibm.pc
Subject: Re: How is a 68000 as fast as an 80386??
Message-ID: <70@demott.COM>
Date: 14 Mar 90 03:35:59 GMT
References: <908@tijc02.UUCP>
Reply-To: kdq@demott.COM (Kevin D. Quitt)
Followup-To: comp.sys.ibm.pc.programmer
Distribution: na
Organization: DeMott Electronics Co., Van Nuys CA
Lines: 43

In article <908@tijc02.UUCP> rdo031@tijc02.UUCP (Rick Odle           ) writes:

>  The 680x0 family architecture ALWAYS
>fetches long word addresses (32 bits), so the most fair comparision
>is the x86 large model.

    WRONG! The 680x0 family fetches on 16bit word addresses.  The 68020
and later are more efficient on long-word fetches, but can execute from
odd-byte addresses.

> On the other hand, the segmented architecture
>lends itself to being able to develop position independent code easier.

    TRY AGAIN! In 68K assembly language, you have to go out of your way to
generate absolute addresses - some assemblers even flag them as errors!
Every compiler in existence uses PC relative addressing - it's faster
code and smaller.  It's the segmented architecture that makes PIC
(position independent code) difficult.  How do you jump or call out of
your segment without specifying absolute segments, or going through
gymnastics to calculate things in your code? In a segmented
architecture, only trivial (<64K) programs can be easily be made PIC. 

    There are no advantages to the segmented architecture when the
segment registers are available to user level code.  If the segment
registers are available to the operating system only and the segments
are sufficiently large, then they're a pretty good (i.e.  low overhead)
way to handle simple memory management schemes.  Memory management
belongs to the operating system, not to user code.  Unfortunately, the
segments on the x86 are so small that the user is burdened with the
extra effort (except for 386 native mode, where generally the ignored). 

    I really don't mean to start a religeous war - I regularly use most
members of both families.  But let's get the facts right.

-- 

Kevin D. Quitt                          Manager, Software Development
DeMott Electronics Co.                  VOICE (818) 988-4975
14707 Keswick St.                       FAX   (818) 997-1190
Van Nuys, CA  91405-1266                MODEM (818) 997-4496 Telebit PEP last
34 12 N  118 27 W                       srhqla!demott!kdq   kdq@demott.com

  "Next time, Jack, write a God-damned memo!" - Jack Ryan - Hunt for Red Oct.