The biggest problem that I see here is that Bob wants to be able to use
this OS on systems that have as little as 16k words but still use LARGE
modern drives.
--
I have been thinking about this a LOT lately relating to using older
CPUs with few or none of the original peripherals, and it may make
sense, since you're building an IDE interface anyway, to build a
file level interface onto the card, rather than talking to the drive
as an unstructured block device. The idea I've been toying with is
building an interface card like this with a local processor, disc,
ethernet, etc. and using it in conjuction with a remote system that
would provide the console / debugging UI / shared peripherals for
a bunch of different processors that I have.
This would also reduce the in-core footprint of the OS, since
the file system (and networking in my case) is handled on the
interface card.
>From: Joe <rigdonj(a)cfl.rr.com>
>
>At 11:18 AM 7/28/03 -0700, Patrick wrote:
>>> > I agree that it's simple, but not that it's efficient. For small micros,
>>> > finding the first "0" bit in an arbitrarily long bit string takes a few
>>> > cycles.
>>>
>>> You would just look for the first byte that is not a 255.
>>
>>That's absolutely true, you can do that, and from there it's fairly
>>straightforward. But here's what I'm thinking. Let's say you have just a
>>1.44MB floppy, with a 512 byte sector size. A convenient allocation size
>>might be one sector, because you can easily fit the total number of
>>allocation units (2880) into a 16-bit unsigned integer (that which is used
>>in the file link blocks). That takes about 360 bytes to store on disk,
>>which fits nicely into a single sector as well. So far, so good.
>>
>>But now let's say you go to an 80MB partition with 512 byte sectors. You
>>then have approximately 163,840 allocation units (not discounting any space
>>used for boot and other common structures). That's too many for a 16-bit
>>word, so you decide to make your allocation units four sectors. That means
>>you have 40,960 allocation units, each of which is 2K in size. Your
>>free-space bitmap, then, would be 5,120 bytes, which takes 10 sectors or 3
>>allocation units to store depending on your implementation choices, but
>>let's just go with the smaller 10-sector size.
>>
>>I'm thinking about two things: first, trying to keep the entire volume
>>bitmap in memory chews up almost 5K of RAM, and that's probably not good for
>>an 8-bit machine, at least, it's not sufficiently memory-efficient, IMO.
>>Second, if you decide then that you'll only deal with one sector of it at a
>>time to save RAM, you may have to read-then-write juggle those ten sectors a
>>lot. If you do a linear search for a free block, it may be that you can rip
>>through the 255-valued bytes quickly, but they have to be in RAM, so you may
>>have to do several reads to find what you want, which saps time.
>
>
> I wonder if it really would sap a lot of time. Modern IDE drives have
>large cache buffers so I would think that system could very likely read the
>data from the buffer. I'm thinking that as slow as these old systems are
>and as fast as the modern drives are that it would be better to use a
>simple and fast algorithim even if it means more drive accesses.
>
> Joe
>
As I recall, Bob is looking to put this onto some old HP hardware.
Dwight
We at Robins AF BASE are in need of a copy of a 09877-10002 Tape Binary
Duplicator Tape. I just did a Google search for this part number and
recieved the following. Do you still have these? Any help would be
appreciated. Thanks, Doyle Bullock
Eureka!
Joe cctech(a)classiccmp.org <mailto:cctech%40classiccmp.org>
Sun Feb 9 16:04:30 2003
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Well I didn't find the Holy Grail but this is close! I went to a hamfest
today and in a box of junk I found the operating program for the HP 9877
Mass Memory unit! That's the box that has up to four tape drives installed
and was used to mass duplicate HP 9825 tapes at the HP factory. The 9877 is
a rare bird and was only offered to the public for one year (1979 IIRC) but
I've got two of the 9877s, Tony D has one and NASA KSC has one but NO ONE
has been able to locate the operating program for it till now. The tape
APPEARS to be in good condition but you know how HP tapes are :-(
The full name of the tape is "Duplicator 9825A/9877" and it's part number
is 09877-10002.
Other INTERESTING finds (in the same box no less!) were a new DC-300A
tape (as used on the IBM 5100 and Tektronix 4051), a Plot 50 tape and Plot
50 Backup tape and an Alignment tape. All three are for the Tektronix 4051
computer.
Wahoo! A good ClassiComp day!
Joe
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> I was just looking at the schematics for the display/control
board
> for the Altair 8800 and saw that there is a 1702 EPROM on the board.
The
> lowest 4-bits of the EPROM's address bus are connected to a 7493
binary
> counter and the highest 4-bits are connected directly to the address
bus.
>
> What's the purpose of the EPROM? Did the front panel have some
> intelligence?
I'm pretty sure that you're looking at an Altair 8800B front panel
schematic. I believe those were software controlled front panels. The
8800 and 8800a had no EPROMs on the front panel - just TTL and the
switches, LEDs, etc.
Erik Klein
www.vintage-computer.com/vcforum
The Vintage Computer Forum
Do you have any Sharp EA-850B (black) or EA-850C (color) pens available for
sale? If so how many do you have and how much would you like for some?
TIA Tom Lake
Bob:
I don't know the exact Altair model the schematics relate to, but
it's not the turnkey model. The ROM socket appears on the display/control
board schematic, which has the front panel switches and LEDs. The Altair
Turnkey would, I believe, have a different board in it called the Turnkey
Module or something like that.
If you want to see the schematic, go to my Altair32 Emulator page
and look on the technical links page for the ZIP file containing scans of
the schematics. I do not have an Altair, and I got these schematics from
another source. The only designation on the page is "Figure 3-16;
Display/Control Schematic (sheet 1 of 3)".
The URL is
http://highgate.comm.sfu.ca/~rcini/classiccmp/Altair32.htm
I've had these schematics for a while, but I never looked at them
that closely.
Rich
-----Original Message-----
From: Kapteyn, Rob [mailto:kapteynr@cboe.com]
Sent: Monday, July 28, 2003 2:37 PM
To: cctalk(a)classiccmp.org
Subject: RE: ROM on Altair front panel board
Which version Altair ?
The original Altair has no ROM anywhere.
I think you are looking at the "turn-key" version.
It has no switches for manual intervention, so it would have to have some
intelligence,
in the form of a boot-loader.
I have never worked with a turn-key version, so I am not sure.
-Rob
-----Original Message-----
From: Cini, Richard [mailto:RCini@congressfinancial.com]
Sent: Monday, July 28, 2003 12:15 PM
To: CCTech (E-mail)
Subject: ROM on Altair front panel board
Hello, all:
I was just looking at the schematics for the display/control board
for the Altair 8800 and saw that there is a 1702 EPROM on the board. The
lowest 4-bits of the EPROM's address bus are connected to a 7493 binary
counter and the highest 4-bits are connected directly to the address bus.
What's the purpose of the EPROM? Did the front panel have some
intelligence?
Rich
Which version Altair ?
The original Altair has no ROM anywhere.
I think you are looking at the "turn-key" version.
It has no switches for manual intervention, so it would have to have some intelligence,
in the form of a boot-loader.
I have never worked with a turn-key version, so I am not sure.
-Rob
-----Original Message-----
From: Cini, Richard [mailto:RCini@congressfinancial.com]
Sent: Monday, July 28, 2003 12:15 PM
To: CCTech (E-mail)
Subject: ROM on Altair front panel board
Hello, all:
I was just looking at the schematics for the display/control board
for the Altair 8800 and saw that there is a 1702 EPROM on the board. The
lowest 4-bits of the EPROM's address bus are connected to a 7493 binary
counter and the highest 4-bits are connected directly to the address bus.
What's the purpose of the EPROM? Did the front panel have some
intelligence?
Rich
>From: spc(a)conman.org
>
>It was thus said that the Great Bob Shannon once stated:
>>
---snip---
>
> It also depends upon the size of the disk you are going to use---up to a
>few meg in size the MS-DOS FAT system (12 or 16 bit variants) will probably
>be the best bet---well documented with the ability for interoperability
>between most systems.
>
> -spc (my two bits worth ... )
>
Hi Bob
If you absolutely must start with a FAT system I think that
you should use a DOS like FAT. This makes things easy to
move from machine to machine. The 12 bit FAT is a little clumsy
so I'd suggest the 16 bit as the easier to deal with.
Dwight
