Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!unmvax!ncar!boulder!sunybcs!bingvaxu!leah!itsgw!steinmetz!davidsen
From: davidsen@steinmetz.ge.com (William E. Davidsen Jr)
Newsgroups: comp.arch
Subject: String length hardware
Message-ID: <13121@steinmetz.ge.com>
Date: 13 Feb 89 14:47:29 GMT
References: <8882@alice.UUCP>
Reply-To: davidsen@kbsvax.steinmetz.UUCP (William E. Davidsen Jr)
Organization: General Electric CRD, Schenectady, NY
Lines: 31

In article <8882@alice.UUCP> dmr@alice.UUCP writes:

>Originally, I believe, there were no operators for accessing
>individual characters in a compact string, though they were
>added later.

  The GE line had support for true string descriptors as early as the
625 (~1962?). There was a "tally word" mechanism which consisted of a
starting address (word), a starting address (char in word), a count for
string size (12 bits), and a bit for 6 or 9 bit bytes.

  This could be used by instructions with modifiers, as below:
	LDA	STR1,CI		; Character indirect
	STA	STR2,SC		; store, move the starting address
				; forward one byte, and decriment the 
				; size by one.
	LDQ	STR3,SCR	; Move the address back one, etc.

  While the 600 line didn't have bytes addressing, they did have the
tally mechanism, which could emulate a stack in 6 or 9 bit bytes, or any
number of words up to (I believe) 64 (might be 63).

  Perhaps when the 68/xxx series replaced the 645 direct byte addressing
was added, I got away from Multics about the end of the 645 era, when GE
decided to sell the computer operation and put the money into nuclear
development, since computers would never be a mass produced item.

-- 
	bill davidsen		(wedu@ge-crd.arpa)
  {uunet | philabs}!steinmetz!crdos1!davidsen
"Stupidity, like virtue, is its own reward" -me