View Full Version : Bits 483

November 15th, 2009, 01:34 AM
I have acquired a BITS 483 8K (bit or byte I don't know--it doesn't say, but I suspect *bit*) core-memory system (including schematics and some spare boards) with it's punched-paper-tape reader, in what might be it's original washing-machine-sized rackmount cabinet. There is some rust on the cabinet itself, and scuffing all about; is missing the cover on a couple of the lights/switches on the front.

It does power on, but as I don't really have any experience with using it, and at the moment have no manual for it, I can't program it, and have no programs on tape for it either.

I've done quite a lot of searching around, and have yet to find another example of one or any info about them anywhere. Anyone here seen one before?





Dwight Elvey
November 15th, 2009, 07:00 AM
It sure looks like an entire computer, not just
a core memory. The front panel isn't to clear
but it does look like what you'd expect to see
on a front panel.

Dwight Elvey
November 15th, 2009, 07:14 AM
I was right. It is a computer. See stuff at:


It is interesting that it is a variable word length computer
as well. Cool find.
You definately want to see if you can get it running.

November 15th, 2009, 08:56 AM
Wow, that's a find! Probably one of the last variable-word length systems made. Brutally simple instruction set, but still more complex than the PDP-8.

Basically, memory-to-memory operation, with the accumulator occupying the top 256 bytes of memory.

9 bit word length (8 bits + word mark)

You're fortunate enough to have the 8K model, which allows for running of some more interesting programs.

According to the description, the logic appears to be commodity TTL, which is a good thing if you're going to restore it.

I hope you can find some maintenance manuals for it.

November 15th, 2009, 02:24 PM
It certainly seems to be an interesting unit! I've never seen another; I've been to a few electronics graveyards and seen quite a lot of different parts and manuals my dad used to bring home from Control Data, Xerox, Honeywell, as he worked at each in turn.

I did know it was the "whole" computer; I'm just not good at speaking clearly when I try to keep things short. ;) (I tend to post walls of text, but try not to do that if possible). I'm only a couple of years older than this computer, and we both probably operate as fast and as well. :)

Thanks very much for the link to the other manuals; I'll see if I can eventually scan in the schematics to offer to that site owner. They are old (and aged) purple-mimeograph reproductions on size D paper, so every page is at least 4, probably 6 scans, and there are almost 50 sheets.

An interesting part of the schematics is the pencilled-in notes and schematic alterations on at least one page that I recall (power reg board, I think). They don't appear to be in the same hand as the several pages that are not stencil-created, so I don't know who might have added them, but they appear a professional hand.

I can't remember now what is in the parts box, but at least one board looked like a spare core board; it's possible there are still programs in it. I don't know if any of them work.

If I had time to restore it, I would. I probably have enough spare parts! Right now I have a lot on my plate, starting with my electric-assist semi-recumbent cargo bike project (http://electricle.blogspot.com), which is done as much as possible (almost entirely so far) from recycled parts, up to taking care of the 4 dogs plus the 9 puppies of the St Bernard rescue that came to me pregnant. :roll: (http://kyuuut.blogspot.com)

Thanks to a friend that had to move but couldn't take the stuff with him, I've got a whole bunch of other "vintage" equipment of various types; mostly test equipment, including some Nixie stuff (mostly HP) that still works. I use one of the Sorenson lab power supplies to charge my e-bike. ;) If it was light enough, I'd be sorely tempted to use one of the Nixie voltmeters on the bike simply for it's appearance. :) I do use the Tek 531A scope fairly frequently. There's some pics of some of it at http://flickr.com/photos/amberwolf

There is also a TI scientific desktop calculator (forgot the model) that came from ASU's labs. It's larger than most cash registers were even ten or fifteen years ago. ;) It works, too, though it is missing the fuse holder cap.

Less interesting is a VAX 4000-300; just the main unit. It turns on, but I have no idea if it is working as it should.

Also, I guess the reason I was having such trouble finding info is that I somehow managed to add an "S" on the end of the name. :( I have no idea why, but in my original notes I wrote down off the stickers and schematics to locate info from, I wrote it as BITS instead of BIT. I'm surprised I didn't change 483 to 486, too! :oops: I wish I could fix the title of the thread. :(

November 15th, 2009, 03:18 PM
Of course, searching for the RIGHT name, "BIT 483" finds a LOT of references. :roll:

I like the "and walk out with a little computer under your arm" part. HAHA. This thing weighs so much I doubt I could actually lift it by myself; I have to use a furniture dolly to move just the main rack unit around, separate from the rack it was mounted in!


November 15th, 2009, 03:26 PM
You didn't happen to get any software with it, did you?

On some of these older less-common systems, the software can be much harder to find than the hardware...

November 15th, 2009, 06:55 PM
I wish. :( No, just the schematics, computer, punchtape reader, and spare boards.

November 15th, 2009, 07:45 PM
Argh! :( That's too bad. Unless your friend happens to have a few rolls of punched tape for your treasure, any programs will be seat-of-the-pants. CHM has an assembly language manual for it, however, so you might scavenge a few sample programs if you're lucky.

The last two variable-word-length machines I programmed were the IBM 1401 and the 1620. Very different in many respects, but a lot of fun.

The BIT 483 seems to have an upper limit of 256 bytes for the length of a word. The 1620's limit was about 20,000 digits.

November 16th, 2009, 11:55 AM
9 bit word length (8 bits + word mark)

I noticed the 'word mark'. What kind of things would one use this for. Is it used as a flag for conditional jumps, etc?

November 16th, 2009, 01:22 PM
I don't find any reference to an operating system of any kind or a boot ROM. Does one have to load in a bootstrap loader from the front switches and load utilites from the paper tape for everything? How does the ASR-33 serial interface come to life? It mentions a channel "C" bus for serial comm which I take to be a TTY/UART hardware, but where are the software drivers for it?

I vaguely remember the Data General Nova where from a cold start, one entered and ran a very short machine language 'bootstrap loader'of a few words into memory and it woke up the disk and loaded RDOS. Does this thing have something equivalent?

This looks like a wonderful machine but without a little existing software like Chuck says, it would be hard to do anything except blink the lights.

Dwight Elvey
November 16th, 2009, 01:26 PM
I noticed the 'word mark'. What kind of things would one use this for. Is it used as a flag for conditional jumps, etc?

It is used to determine the size of the value in bytes. When doing an operation,
such as add, it would continue the add+carry until it got to the mark.
I didn't read the instruction manual closely but I assume there
are some restrictions to input and output sizes.
It wouldn't make sense to add two 4 bytes values and put the
result into a 1 byte result. Would one save the high byte or the low byte?

November 16th, 2009, 04:52 PM
Addressing of variable length fields is done by the address of the low-order byte. When performing an arithmetic operation, the length of the accumulator must be at least as long as the operand; if it's shorter, the operand is extended with zeroes. (I'm simplifying a bit, as there are "reverse" operations also, such as subtract the accumulator from the operand in memory (the accumulator is not changed)).

If the operand field has more bytes than the accumulator, the operation terminates when the wordmark in the accumulator is encountered and overflow is set depending on whether or not a carry/borrow is generated. As far as I can tell, no error condition is set if no carry is generated; the operation simply terminates.

A curious aspect is the operation of the decimal instructions. Each byte is assumed to contain a 4-bit BCD value. The other 4 bits are ignored. If a byte whose low-order 4 bits contains 0A through 0F, it's skipped over as if it isn't present. This allows for the inclusion of characters such as comma (hex 2C) and decimal point (hex 2e) when doing decimal arithmetic.

November 16th, 2009, 05:09 PM
I don't find any reference to an operating system of any kind or a boot ROM. Does one have to load in a bootstrap loader from the front switches and load utilites from the paper tape for everything? How does the ASR-33 serial interface come to life? It mentions a channel "C" bus for serial comm which I take to be a TTY/UART hardware, but where are the software drivers for it?

The literature claims availability of disk and tape drives as I/O devices, but I suspect that many installations were largely paper tape or card. Like the PDP-8L, you could load either an assembler or FORTRAN compiler (USA BASIC FORTRAN, which is very simple dialect--for example, only arithmetic IF is supported).

I think the closest contemporary system to this machine would be a PDP-8/L, as no mention is made of memory greater than 8K in the documentation, although it seems that up to a shade under 64K was theoretically possible. One thing that makes this sort of ugly is the 256 byte page size. Reminds me of some modern microcontrollers.

May 2nd, 2011, 11:31 AM
I just noticed (5/2011) this thread about the BIT 483 computer, a rather unique variable-word-length system of discrete ICs once made by Business Information Technologies of Natick, MA. (It was the successor to the BIT480). In the mid 1970s the firm closed down and its remaining inventory was acquired by TriTek electronic surplus resellers in Phoeniz, AZ. Running across their advertisement, I arranged for acquisition of all remaining working computer inventory by various educational instituitions in and around Minnesota. I went to Arizona to inspect the computers and deliver them, and I personally ended up with the spare parts and all the documentation, including engineering diagrams and plans, etc. I was told that this included all rights to the systems, 'patents and copyrights if any', but I never pursued that aspect of the purchase. I developed some expertise in the BIT 483, organized a small group of BIT483 enthusiasts in Minneapolis, and made a couple more working computers from the spare parts and used these systems for a few years in an educational computer group I myself was then organizing. (I even received a birthday cake that year in the shape of a BIT480; it was supposed to be a BIT483 but my ladyfriend did not know the difference!)
In 1978 I moved east and carried with me the remaining spare parts and documentation. I stored these largely in an old truck I had parked in a field with permission of the owner, but might well have removed some of these to a storage unit I maintained. Some years later I found that the truck and its contents had been removed and disappeared; apparently the field had been sold and no one claimed to know to reach me to move the truck. It is possible, however, that I still have some parts or documentation for these systems in my storage unit. I have visited it very rarely in some years, but hope to clean it out this summer or as soon as time and energy allow. I will gladly donate to wheresoever they might be useful any BIT483 parts or documentations I might run across. Interested parties may email me - I believe this forum will pass along emails to me.

May 2nd, 2011, 02:10 PM
I noticed the 'word mark'. What kind of things would one use this for. Is it used as a flag for conditional jumps, etc?

No, the word mark indicates the high-order byte of a word in the case of the BITS. Words are addressed by the low-order byte and grouped into a "word" until a byte with a wordmark is discovered (high-order byte). In the BITS system, a word can be anywhere between 1 and 256 bytes in length; there are rules for combining unequal length operands.

In a way, this is closer to the way humans work with numbers. If, for instance you want to add 13 to 4567, you write:


and not


In the late 50's and early 60's, variable word length IBM systems were quite common--the 1401 and 1620 are two examples. There are several nuances that the Bits machine doesn't employ, such as record marks (special-value characters that serve to group up one or more words) and use of the word mark to indicate other things, such as sign (if the low order character has a word mark set, the word is negative; a 2 character word is therefore the minimum size) or indirect addressing (address->address->address->address...). The maximum word size on the 1620 was 20,000 decimal digits.

That's not to say that these things were fast, however...