AMD bit-slice machines

[Lyle Bickley]

On Saturday 31 December 2005 08:19, Jan-Benedict Glaw wrote:
> On Sat, 2005-12-31 09:10:35 -0700, e.stiebler <emu at ecubics.com> wrote:
> > Richard wrote:
> > >This is really interesting!  I had no idea that DEC used them for some
> > >of their processors -- personally I find that fascinating as I always
> > >pictured DEC as a "NIH" shop.
> >
> > The am2901 is just a chip. The smarts are in the microcode ;-)
>
> Is there some really interesting documentation available for these
> chips and maybe some microcode for some really simple task?  I'd like
> to really understand how bit-slice CPUs do work to form something like
> a VAX CPU.

The 11/34A used AM2901 bit slices in it's FP implementation - and the 
microcode listings are available for both the FP and non-FP microcode of the 
11/34A.

If you are interested in more detail on DEC's use of bit slices, look at Part 
IV "Evolution of Computer Building Blocks" in "Computer Engineering", by 
Moore, Mudge and McNamara. (Every DEC affectionado ought to own and read this 
book cover-to-cover - multiple times ;-)

Here's an excerpt:

Page 436 "BIT-SLICES (Fractional Register Level Modules) as building 
blocks" ...

"Today, these components are the dominant mainstream building blocks and have 
been in a variety of applications. For example, the 4 bit wide AM2901 slice 
was used in 1976 to implement the 64 bit wide data path of the Floating-Point 
Processor for the PDP-11/34, and bit-slices are not the technology of choice 
for mid-range PDP-11 processors."

"The building blocks available in 1978 are reasonably represented by the 
following" (abbreviated):

1. "Datapath slice: A 4-bit wide slice containing arithmetic and logic unit, 
16 registers in a two-port file, data buses, shifter, and multiplexers (the 
AM2901)."

2. "Microprogram control unit. (AM2909: 4 bits wide or AM2911: 12 bits wide.)"

3. "Interrupt processing unit. (AM2914)"

4. "Interface circuits. (AM2917)"

In the same book, Chapter 19, the CMU PDP-11 is described in detail - a PDP-11 
architected using Intel/Signetics 3000 bit slices. Covered in this chapter is 
the design, architecture, implementation, benchmarks and costs associated 
with the project. Bottom-line: The cost of the CMU bit-slice PDP-11 was $1076 
in single unit quantity - and estimated to be $419 in quantities of 100+ 
(1976 dollars). The system was benchmarked to be about twice the speed of an 
LSI-11 and half the speed of an 11/40.

Cheers,
Lyle
-- 
Lyle Bickley
Bickley Consulting West Inc.
Mountain View, CA
http://bickleywest.com

"Black holes are where God is dividing by zero"