Microprogramming: History and Evolution - Edwardbosworth.com
Microprogramming: History and Evolution - Edwardbosworth.com
Microprogramming: History and Evolution - Edwardbosworth.com
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Side–Effects of <strong>Microprogramming</strong><br />
It is a simple fact that the introduction of microprogramming allowed the development of<br />
Instruction Set Architectures of almost arbitrary <strong>com</strong>plexity.<br />
The VAX series of <strong>com</strong>puters, marketed by the Digital Equipment Corporation, is usually<br />
seen as the ―high water mark‖ of microprogrammed designs. The later VAX designs<br />
supported an Instruction Set Architecture with more than 300 instructions <strong>and</strong> more than<br />
a dozen addressing modes.<br />
When examining the IA–32 Instruction Set Architecture, we may not a number of<br />
instructions of significant <strong>com</strong>plexity. These were introduced to support high–level<br />
languages (remember the ―semantic gap‖). It was later discovered that these were rarely<br />
used by <strong>com</strong>pilers, but the ―legacy code‖ issue forced their retention.<br />
It is now the case that the existence of these instructions in the IA–32 ISA required that<br />
part of the control unit be microprogrammed; a hardwired control unit would be too<br />
<strong>com</strong>plex. The ghost of the Intel 80286 still haunts us.
Change language