[Info-vax] Further on the PDP-10 [was Re: Hard links on VMS ODS5 disks]

[Rich Alderson]

jgd at cix.co.uk (John Dallman) writes:

> In article <kifmjpF4bvU2 at mid.individual.net>, bill.gunshannon at gmail.com
> (bill) wrote:

>> I would love to see what the performance would be for any of these
>> processors [DEC-10, DEC-20] made with today's tech.  I think even 
>> without growing memory size they would be more than adequate and
>> probably a lot better than some of the Windows Servers running
>> applications today.

> What sort of thing would you want to use them for? I don't know the
> architecture well, but they seem to be limited to 30-bit addressing of
> their 36-bit words. That's more or less 4GB, which will do for many
> things, but there doesn't seem to be any obvious advantage of the
> architecture that would make doing an commercial implementation
> worthwhile. 

An embedded processor which can run a fully capable operating system is
extremely useful.  Len Bosack, cofounder of cisco systems, was never happy that
they were limited to the capabilities of the M68K processor family.

> If you were keen, you could do an FPGA version: some Amiga fans have done
> that for the Motorola 68000 family. http://www.apollo-core.com/

The original product from XKL was the Toad-1 system.[1] The CPU was based on an
Altera part programmed in PALASM to provide a microcode engine.  The TOAD-2
processor in their Darkstar optical routers is built around a Xilinx part using
VHDL.

There are also a couple of hobbyist FPGA implementations of the KA-10
processor, using Verilog.

> The painful part is the character size: 6-bit characters aren't adequate
> for lots of modern work. Using 8-bit characters is probably best. That
> wastes four bits per word, but allows you to use UTF-8 and communicate
> with other kinds of machine.

The byte size on a PDP-10 is defined in the byte pointer (so not equivalent to
an integer).  The standard character set in DEC's systems, all the way back to
the PDP-6 in 1964, is 7-bit ASCII, with 5 characters per word.  The extra bit
was even used by the editor to mark line numbers in test files; the assembler
and various compilers ignored words so marked.

As noted elsewhere, the C compiler uses 9 bit bytes.

The UTF-9 and UTF-18 encodings were proposed by our late friend Mark Crispin,
and rejected by the Unicode editors because he was the proposer.

[1] "ToaD" was the codename Bosack gave to his proposal for a -10 on a desk
    when he was an engineer in DEC's Large Systems group.  The original
    business plan for cisco Systems was to build the ToaD; they built
    networking gear, beginning with the Massbus-Ethernet Interface Subsystem
    (MEIS)[2] and continuing on to terminal interface processors (TIPs) and
    routers.

[2] The Stanford developed Ethernet interface for the KL-10, available years
    before the NIA-20 which came out of the cancelled Jupiter project.  The
    MEIS was more featureful than the eventual Digital product.

-- 
Rich Alderson					  news at alderson.users.panix.com
      Audendum est, et veritas investiganda; quam etiamsi non assequamur,
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									--Galen