Bit-slice parts are parts that are meant to be stacked together to
create a larger function.  They generally came 4 bits wide.  If you
wanted a 24 bit ALU you would line up six of these 4 bit ALU chips.
They would have pins for the appropriate carries and borrows so they
would work together.  You could make a CPU of whatever width your data
required.

A Google search of "bit slice chips" will give lots more info.

Sherpa Doug

> -----Original Message-----
> From: Sean H. Breheny [mailto:shb7@CORNELL.EDU]
> Sent: Wednesday, April 10, 2002 10:59 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Scratchbuilt computer?
>
>
> I'm not familiar with "bit-slice parts". What are these?
>
> It would be a lot easier if you built your own CPU using an
> FPGA. That way,
> you would eliminate the need to buy all the various different logic
> functions and assemble them, you could make changes just by
> editing your
> file in the design software, AND if you have decent software,
> you could
> even simulate part or all of your design and see what is going on for
> debugging purposes.
>
> We did this for a simple 8 bit CPU way back in our first
> class on logic
> design. It was fun and not all that difficult. You might even
> be able to
> build something useful that you would want to use later on!
>
> Sean
>
> At 09:22 AM 4/10/02 -0400, you wrote:
> >Douglas Butler wrote:
> >>If you can still get the parts, it might be fun to build your own
> >>bit-slice CPU.  Design and build the registers, ALU, instruction
> >>decoders, etc. yourself.  My friend did this in 1982 as his senior
> >>project in college.  He used 4 bit bit-slice parts to make
> a 36 bit CPU.
> >>  The logic was static so he could single step the clock phases for
> >>debugging.  I think his max clock speed was about 100kHz.
> It could do a
> >>36x36 multiply in the blink of an eye - if you didn't blink
> too fast!
> >
> >Neat idea - but I think all those parts are made of unobtanium now.
> >Bit-slice CPUs have certainly gone the way of the dodo. Even a lot of
> >the MSI TTL stuff that you would have used in a CPU design -
> ALUs and so
> >forth - have been discontinued. (You might be able to make
> replacements
> >for some of the functions out of PALs.) Bipolar PROMs -
> another mainstay
> >of such designs - are history, too, though CMOS parts have
> gotten fast
> >enough that they might be able to fill in - or, if not, you could use
> >SRAM that was loaded from ROM at boot time.
> >
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