31 Jan
2011
31 Jan
'11
4:19 p.m.
From: Chuck Guzis
Sent: Monday, January 31, 2011 3:30 PM
On 31 Jan 2011 at 14:30, Rich Alderson wrote:
> From: Chuck Guzis
> Sent: Monday, January 31, 2011 2:13 PM
>> When it comes to variable-length instructions,
I'm surprised that no
>> one mentioned the IBM 1401, particularly in its ability to "chain"
>> instructions.
> The instructions on the 1401 are 1 character long,
that is, 6 bits.
> Or have I misunderstood the discussion so far. I
thought we were
> talking about different operations being effected by different lengths
> of bits as the op codes.[1]
Are we talking about instructions themselves, or their
operands?
[snip long discussion of 1401, which was my first computer 42 years ago]
Have I missed a third category of "variable
length"?
I don't know. Have you? Eric Smith wrote the following:
From: Eric Smith
Sent: Saturday, January 29, 2011 12:32 PM
Tony Duell wrote:
> Are you implying that the data registers should be variable length, or
> that a variable number of bits should be used in each instruction?
The only processor I've ever seen for which
instructions are a variable
number of bits (not bytes or words) is the Intel iAPX 432. For the
release 1 GDP, instructions ranged from 6 to 344 bits long.
commenting on Tony Duell's followup to Dwight Elvey's message:
> From: dwight elvey
> Sent: Friday, January 28, 2011 8:54 PM
> I always thought is would be fun to make a
variable
> bit serial computer. Many operations only need a single bit
> while the single bit ALU could operate on data, like
> adding, one bit at a time and use any length one wanted.
Notice that Dwight is talking about variable numbers of *bits* in the
instruction (by which I think he means "op code"), and Tony and Eric
both appear to at elast wonder if that's what he means.
Rich Alderson
Vintage Computing Sr. Server Engineer
Vulcan, Inc.
505 5th Avenue S, Suite 900
Seattle, WA 98104
mailto:RichA at vulcan.com
mailto:RichA at LivingComputerMuseum.org
http://www.LivingComputerMuseum.org/