The Importance of Terminology's Quality

[Arne Vajhøj]

Paul Wallich wrote:
> Martin Gregorie wrote:
>> On Fri, 22 Aug 2008 22:56:09 +0000, sln wrote:
>>> On Thu, 21 Aug 2008 09:11:48 -0500, rpw3 at rpw3.org (Rob Warnock) wrote:
>>>> sln at netherlands.com> wrote:
>>>> *IS* raw machine code, *NOT* assembler!!
>>> [snip]
>>>
>>> I don't see the distinction.
>>> Just dissasemble it and find out.
>>>
>> There's a 1:1 relationship between machine code and assembler. Unless 
>> its a macro-assembler, of course!
>>  
>>> Each op is a routine in microcode.
>>> That is machine code. Those op routines use machine cycles.
>>>
>> Not necessarily. An awful lot of CPU cycles were used before microcode 
>> was introduced. Mainframes and minis designed before about 1970 didn't 
>> use or need it and I'm pretty sure that there was no microcode in the 
>> original 8/16 bit microprocessors either (6800, 6809, 6502, 8080, 
>> 8086, Z80 and friends).
>>
>> The number of clock cycles per instruction isn't a guide either. The 
>> only processors I know that got close to 1 cycle/instruction were all 
>> RISC, all used large lumps of microcode and were heavily pipelined.
>>
>> By contrast the ICL 1900 series (3rd generation mainframe, no 
>> microcode, no pipeline, 24 bit word) averaged 3 clock cycles per 
>> instruction. Motorola 6800 and 6809 (no microcode or pipelines either, 
>> 1 byte fetch) average 4 - 5 cycles/instruction.
> 
> One problem with this discussion is that the term "microcode" isn't 
> really well-defined. There's the vertical kind, the horizontal kind, 
> with and without internal control-flow constructs, and then there are 
> various levels of visibility to the user -- see e.g. the pdp-8 manual, 
> where "microcoding" is used to mean piling the bits for a bunch of 
> instructions together in the same memory location, which works fine as 
> long as the instructions in question don't use conflicting sets of bits.

I thought microcode was relative well defined as being the software
used to implement instructions that were not fully implemented in
hardware.

http://en.wikipedia.org/wiki/Microcode does not make me think otherwise.

Arne