The DSD-880 I had offered earlier has been claimed.
Thanks much.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Bruce Lane, Owner and head honcho, Blue Feather Technologies
http://www.bluefeathertech.com // E-mail: kyrrin(a)bluefeathertech.com
Amateur Radio: WD6EOS since Dec. '77 (Extra class as of June-2K)
"I'll get a life when someone demonstrates to me that it would be
superior to what I have now..." (Gym Z. Quirk, aka Taki Kogoma).
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
>2) The physical address to write it to.
>
>To get the first may involve calculating the parity bits based on the
raw
>data word. This, agreed, takes some time, so the parity bit is available
>later than the data.
>
>To get the second involves an MMU-type operation. We have to map the
>program-generated virtual address to a physical address. This will also
>take some time, so the relocated address is available some time after
the
>virtual address.
Usually the physical address is the only one we talk of at the memory
pins
and any virtualization, mapping and all is prior history.
>We then have to apply the address to the memory. Probably in 2 parts,
row
>and column. Until both parts have been applied to the memory, in general
>the state of the data lines is irrelevant. Again, strobing in the
address
>in two parts takes time.
Usually the address for the memory preceeds the data. If the system
expects
DRAM it's often far earlier to permit the MUX operation.
However, in the PC world where the conversation started considerations
of MMUs and the like were limited to the older 286s as the 386 class
and later were alrady delivering physical addresses to the memory
subsystem.
>Now, suppose the parity calculation takes p ns. Now, if the parity
>generator circuit can get the raw data more then p ns before the address
>can be got into the RAM, then the parity logic is not slowing things
down
>at all. The parity bit is available before the RAM can use it anyway.
Save for that is speculative as most cpus deliver data AFTER the address
of in coincidence at best. Even then it's meaningless as the timing
relative
to what ever strobes declare the address valid and qualify the data read
or write.
One generalization that has mostly held true for most years is that
memory (at the system level) usually slower than cpu. This leads to
things like pipelining, caching and burst mode(block) transfers to get
stuff in and out of the finite bandwith resource. That consideration
was as true for the PDP-8 as latest PentIV/1.4G. It's also true that
things like DMA and video(bit blitters) are also competing for
the same ram bandwith.
Allison
To make up for my blunder (too much Canadian on an empty stomach
interferes with the keyboard-mashing apparatus), can anyone give or point
me to some solid information on the aforementioned machine? All I can find on
the Web is pretty vague. Also , it looks like only 7 or so were actually
built. Were they all eventually turned into Toyotas, or does anything remain
of them anywhere?
Thanks,
jbdigriz
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
>I see what you're saying, but I don't think it's as simple as that.
>
>After all, in a reasonably complex system you're going to want to write
a
>given word to a given address. The address is probably going to have to
>be relocated by some kind of MMU, and then applied to the DRAM in 2
>halves. And while the address is being processed in this way, it's
Parity is either in parallel or downstream of the MMU. Also the
parity is always applied at the byte level so for 72pin and larger
simms there are two (or more) bytes to apply parity to.
>possible that the data is already 'available', so the partity bit could
>be calculated at the same time. Then it doesn't take any longer to
>calculate and store parity -- in a sense the critical path could be the
>address relocation.
Still no. Parity is calculted from the data and by default has
some inherent propagation delay associated with the logic.
For example the old and venerable 74180 that delay is 10s
of nS (about 40 from the 1985 databooks) LATER than the
the data.
>It depends -- a lot -- on the design of the entire machine.
While there may be exceptions parity is generally downstream
and part of the memory system rather than CPU. The expections
are some of the big iron that had parity on all data as part of the cpu.
>So I guess that it might well be the case that parity memory _for a
>particular machine_ might have to use faster chips than non-parity
memory,
>and this might be one reason why they're so much more expensive. But
it's
>certainly not the case that all memory modules that store a parity bit
are
>faster than non-parity modules.
They are expensive if only for they are Nbits wider (more rams).
Allison
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
>> Is it? Someone also told me that parity was usually faster, though.
True?
>
>There's no reason at all why parity memory should be faster than
>non-parity memory. Parity memory just stores a parity bit for each byte
The assumption is that parity is available at the ram at the time of
write
and while true it was calculated some where.
Parity can only be calculated (simple combinational logic with attendant
delays) at the time of a wirte so the write must for a given ram speed
take longer. So if you want the parity to fit in a given memory write
cycle time you must use faster ram.
>of normal data, so you can detect (but not recover from) some memory
errors.
There is also ECC ram, those are slower (over all) as the ECC bits have
to be
calculated. Expensive, errors are caught and recovery is possible.
Allison
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
>> That would be interesting. You could use duct tape to attach a
soldering
>> iron to the board so it would generate the same heat that 512MB does
:-)
>
>Many a true word is spoken in jest.
;)
>I've seen PCBs in some systems that are nothing more than an array of
>high-power resistors connected between (one of?) the supply lines and
>ground. Said PCBs are generally fitted if a particular option
(consisting
>of a PCB containing logic chips, etc) is not installed. And the only
>purpose of the board of resistors is to load the PSU so that it stays in
>regulation -- the load of the rest of the machines (without the optional
>logic board) is not enough for the PSU to remain happy.
The best known and classic is Microvax2000 diskless systems. The
disks of the day were 30W loads and if they were not used there was
a board (array of resistors). The matching tape (TK50..) used the same
box, PS and the resistor array to load it.
Allison
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
>Perhaps somebody could expain the aims of this hobby of ours. Is it to :
>
>Obtain as many machines as possible without caring what they are
>
>Obtain as many of particular types of 'interesting' (to you) machines
>
>Getting (again) the machine that you 'used as a kid' and enjoying those
>ancinet games again (say)
>
>Getting machines that you dreamed of owning many years ago and could
>never aford back then
>
>Getting machines that have particular hardware (or software) features
>that you find interesting, whether or not you've ever heard of the
>machine before
>
>Preserving a piece of computer history
>
>Programming a machine that is really simple enough to fully understand
>
>Repairing a machine that's built from parts you can get and understand
>
>Learning about the operation of a computer by understanding a processor
>at gate level
>
>
>I guess for me it's many of the above and more besides.
Amen..
... and not every machine I have is for the same set or subset of
reasons.
Some I hack for the hardware, some represent MY history, other computing
history and the handfull that were out of my reach when new.
>But most of those 'reasons for the hobby' don't depend on getting a
>bargain, and thus it's not unsporting/against the aims of the hobby to
>pay for a machine.
Generally, though dropping a bomb for a given machine like a ceratin rare
painting or other object is as much personal as business.
>OK, I know most of us (myself included) can't afford to spend as much
>money as we'd like on this hobby, and we'd love it if the machines were
>free... However, it wouldn't bother me to spend say \pounds 100.00 on a
>machine of particular interest to me, knowing that I would get at least
>that much enjoyment/education from programming it, repairing it,
learning
>about it, etc. And I don't thing that's against the aims of the hobby.
That is the clearest explanation I've read.
Allison
In a message dated 1/26/01 9:39:33 PM Eastern Standard Time,
spectre(a)stockholm.ptloma.edu writes:
<< > Let me cheer you up, $515 for 128MB kit for an AlphaStation 500/333, or
> Sparc 5 RAM 32MB $50-100, or Sparc 20 RAM at about $1.50-2.00 per MB. Of
> course it's the AlphaStation RAM I need the most followed by at least a
> couple sticks of 64MB Sparc 20 RAM. BTW, the Sparc RAM prices listed above
> take eBay into account on the low end! Then there is the 8MB VSIMM I want
> for my Sparc 20, it's about $240.
Oh, I do sympathise :-) Remember the Apple Network Server that I was trying
to get parity FPM for? $500 for 64MB.
I'm going to throw in the towel and just stick non-parity in it. That's what
everyone seems to be doing these days with ANSes. But I would really love
that extra security that parity affords, unless someone wants to convince me
that parity is not all that useful in memory? (I'd love to be convinced since
you will save me around $300.)
>>
well, its my understanding that all that parity memory will do for you is
stop processing when getting a memory error unlike standard memory which will
supposedly keep going. The ECC memory I have in my IBM PS/2 95 can fix on the
fly if one bit gets out of order as far as i know.
www.nothingtodo.org
CC to port-vax and classiccmp.
I'll be hauling a goodly amount of stuff to the upcoming Puyallup
electronics swap this year (Saturday, March 10th, Puyallup Fairgrounds,
WA), but I've also got some stuff that I know would probably never sell.
With that in mind, I'd like to offer the following to the listmembers.
Two complete VCB02 video subsystems, including board sets, cab kits,
monitors (VR290's if I'm not mistaken), keyboards, 'hockey-puck' rodents,
and cabling. These are out of MicroVAX II's.
A MicroVAX 2000 "Lunchbox" system. This is one that I kitted out to do
low-level formats on RD52 and RD53 drives in the form of adding a
longer-than-normal flat cable so the drive could be placed outside the box
and still remain connected.
I'm pretty sure I have a couple of BA23 boxes I can part with.
A DSD-880 floppy/hard drive subsystem with manuals, diag diskettes, and at
least one Qbus controller. I may or may not still have a Unibus controller
for it as well. Note that this is the only piece I'm going to ask for
actual money on (see below).
I know I have some MicroVAX II CPU/Memory board sets. I can probably stand
to get rid of them.
Various other bits and pieces that I have yet to go through. Possibly a
VAXStation 3100, probably a DECStation RISC box as well. I've yet to look.
I would far rather see this stuff go to good homes than see it scrapped,
but I know it's sometimes hard to put a price on things. With that in mind,
here's how I'm going to work it.
The only piece from this list that I'm going to ask for actual money on is
the DSD-880, mainly because it's complete right down to the rack slides,
and was known to be fully functional when removed from service about two
years ago. I would like to ask $50 or best offer for it.
As for the rest of the stuff, it's going up as "Free to good home, but
donations to the 'Classic Collecting Fund' will not be refused." ;-)
Pickup would be in Kent, WA, southeast of Seattle by about 30 or so miles.
I would greatly prefer not to ship anything due to other time-constraining
activities like school, running a side business, etc.
Get in touch with me if anything looks tempting. Thanks much.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Bruce Lane, Owner and head honcho, Blue Feather Technologies
http://www.bluefeathertech.com // E-mail: kyrrin(a)bluefeathertech.com
Amateur Radio: WD6EOS since Dec. '77 (Extra class as of June-2K)
"I'll get a life when someone demonstrates to me that it would be
superior to what I have now..." (Gym Z. Quirk, aka Taki Kogoma).
Don't know how on-topic it is for port-vax, but...
Added to the 'Available' list in my previous message: An ApplicationDEC
433MP box in great shape. I had it running NetBSD for a little while, so I
know it works. It is one of many things that I Just Don't Need right now.
Thanks.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Bruce Lane, Owner and head honcho, Blue Feather Technologies
http://www.bluefeathertech.com // E-mail: kyrrin(a)bluefeathertech.com
Amateur Radio: WD6EOS since Dec. '77 (Extra class as of June-2K)
"I'll get a life when someone demonstrates to me that it would be
superior to what I have now..." (Gym Z. Quirk, aka Taki Kogoma).
