31
votes
Accepted
Why user-assembled kits?
Back in the 80s, it was an industry and market very different from today's PC world.
The audience were mainly do-it-yourself people who wanted to create things, and to understand how they worked. So, ...
- 2,410
31
votes
Why user-assembled kits?
I believe that your presumption is incorrect:
The vendor, having no way of knowing whose fault this is, has to take
the machine back and try to debug it.
The vendors did not have to take the machine ...
- 3,057
28
votes
Accepted
How did the Altair 8800 front panel load the program counter?
Just about a week ago, I encountered the same question as I was thinking about the idea of building a front panel for my homebrew computer, but I didn't understand how could one "move" the CPU to ...
- 3,264
26
votes
Accepted
Test emulated 8080 CPU without an OS?
I'm actually not aware of any major 8080 test suites; everything I've ever found has been for the Z80 rather than its parent.
That aside, I'd heavily suggest you don't discard the CP/M solutions you'...
- 38.2k
26
votes
Accepted
When did the Altair move ROM to the top of memory?
It didn't move anything. There is no ROM at the beginning of memory. As the system did not include any code in ROM at all by default, ROMs were optional and usually placed at the end of memory. ROM is ...
- 37.2k
26
votes
Accepted
Did anyone ever put half a megabyte of memory in an Altair?
Did anyone ever put that much memory in an Altair, IMSAI or other 8080/Z80 S-100 bus machine?
Has been done a lot of times. Remember, S100 has been used all the way thru the 1980s into the 1990s. RAM ...
- 236k
22
votes
Accepted
How did Altair 8800 interrupts work?
I feel like I'm fundamentally misunderstanding something very important here, but the manual isn't much help.
Yes, looks quite like it.
The Altair is a very basic 8080 computer, so any handling is ...
- 236k
19
votes
Why user-assembled kits?
if every machine will be sold preassembled, the vendor can invest in things like wave soldering equipment that can do the job much more efficiently than a user doing it once on the kitchen table
I ...
18
votes
Why 18 expansion slots on the Altair 8800?
The Altair 8800 had a backplane with 18 connectors for S-100 cards.
To start with, the genuine Altair had a 4 slot backplane, or 'Expander Board' as they called it. To cite their advertizement:
The ...
- 236k
16
votes
Did anyone ever put half a megabyte of memory in an Altair?
If you count Altair clones, yes. For the original Altair 8080, quite
possibly (if the PSU was capable of powering eight of the IMSAI memory
boards along with the CPU and I/O boards) and for the ...
- 28k
15
votes
Accepted
How many cards could you put on an S-100 bus?
The standard (IEEE 696) is available here
Section 1.1 defines the scope of the standard as
Data exchanged among the devices is digital.
A maximum of 22 devices are interconnected.
The total ...
- 6,696
14
votes
Why user-assembled kits?
Many early computers were sold as self-assembly kits
Not really. There is a visibility bias. Kits were simply more visible than ready made machines.
Kits were simply the best way to fill pages of ...
- 236k
13
votes
Accepted
Why did the Altair use 100-pin edge connectors?
As Wikipedia says (S-100 bus):
"(Author) then looked for an inexpensive source of connectors, and he
came across a supply of military surplus 100-pin edge connectors. The
100-pin bus was created ...
- 5,605
12
votes
Why did the Apple III have more heating problems than the Altair?
The absence of a fan was only part of the problem. (By the way, the Apple II also did not have a fan). [1] describes it like this:
Those that did work initially often failed after minimal use thanks ...
- 30.5k
11
votes
Was natural convection ever a consideration in orienting expansion cards?
Simply put, for most of the PC's history, either the components were roughly uniform in their power consumption (with the major offenders typically being the 12V motors in disk drives, rather than ...
- 16.9k
11
votes
Accepted
What additional hardware was required for BASIC on an Altair 8800?
Lately I found myself wondering what hardware was required for the Altair to get BASIC up and running.
Basically
Cage
CPU-Card with 1 KiB RAM
4 KiB RAM Card
Serial Interface
To have some space for ...
- 236k
10
votes
Accepted
Why is the original Altair BASIC (for the 8080 CPU) source code not available on-line?
The original code was sold to MITS before it was even completed and teams from MITS and Micro-Soft both worked on it simultaneously. Bill and Paul both moved to Albuquerque to continue work. It was ...
10
votes
Accepted
Why did the Apple III have more heating problems than the Altair?
TL;DR: Basic Design
Altair excels in thermal over the Apple III by two several basic points:
Less Power to be Removed
More Volume to Handle the Heat Transport
Better Airflow to Remove Heat
Power ...
- 236k
9
votes
Accepted
How did the Altair ensure that the −5 V supply was the first connected and last disconnected?
Never used nor saw an Altair so I might be completely wrong in here. However this doc for some Altair 8800 contains the circuits (at the end)...
The power supply is divided to 2 zones. one with ...
- 7,354
8
votes
Accepted
Why did the SWTPC 6800 Computer System not take off?
TL;DR:
SWTPC and their 6800 system did sell quite well and over a longer time than all of its competition. The question is rather why do most people only know MITS/Altair, which I'd say is rather a ...
- 236k
7
votes
How did the Altair 8800 front panel load the program counter?
How exactly does it load the program counter, given that there's no obvious way to tell the CPU to do this without excecuting instructions to do so?
Seams like you know it already :))
Does it ...
- 236k
7
votes
Why 18 expansion slots on the Altair 8800?
so there is likely some other reason.
This pre-supposes some sort of rationality in the early PC industry - I'm not sure that was really the case :-) I suspect it wasn't chosen, based on the history ...
- 5,047
7
votes
What is the format of the packets on an Altair 8K BASIC 3.2 Tape?
I'll answer my question.
There are some basic things you'd need to know in order to pull bytes in from an original Altair 8K BASIC cassette tape.
In my case I wanted to decode the tape to a file and ...
- 1,129
6
votes
Accepted
Was natural convection ever a consideration in orienting expansion cards?
The main means of thermal dissipation are convection and radiation (and flow). Convection is used always and independent of orientation. Board setup of the era have been made in any direction.
Putting ...
- 236k
6
votes
Accepted
Single-stepping the Altair 8800
It has a button on the front panel to single-step the CPU one instruction at a time... Except that, on closer inspection, that's not actually what it does.
Exactly, and it's not what the button is ...
- 236k
6
votes
Test emulated 8080 CPU without an OS?
You can find some Intel 8080 CPU tests on this website. These can be run with no OS, just a minimal support framework described below:
These binaries should be loaded to memory starting at 0x0100, ...
- 2,810
6
votes
How did the Altair ensure that the −5 V supply was the first connected and last disconnected?
It looks like the Altair 8800 didn’t have any provisions to ensure -5V was available first (but see @Spektre’s answer and the note below).
I found a schematic of the Altair 8800 CPU board power supply ...
- 1,463
5
votes
Why user-assembled kits?
At the time the numbers of unit made were was smaller than today, and technology for assembly electronics was way less advanced than today.
Was a labour-intensive process so shifting the work to the ...
5
votes
Why user-assembled kits?
The difference is the 2 years from 1975 to 1977 (when the Apple and TRS-80 came out). A 1975 Altair was programmed in opcodes using toggle-switches, and the output was flashing lights. Whee. By 1977 ...
- 339
5
votes
Why did the SWTPC 6800 Computer System not take off?
I strongly suspect CP/M was the key. Plenty of 8080 (and by extension, Z80) machines ran other operating systems, particularly the Radio Shack TRS-80 line. But the basics of Altair, Imsai, Osborne, ...
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