Questions tagged [altair-8800]

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14 votes
1 answer
2k views

How did Altair 8800 interrupts work?

I'm playing around with building an Altair 8800 emulator in my free time in C#. I've read through the Operator's Manual many times in the past, and I'm refreshing my memory of late. I'm struggling to ...
9 votes
2 answers
2k views

Why did the Apple III have more heating problems than the Altair?

The Apple III was famously prone to overheating, to the extent that Apple advised customers to drop the machine a few inches onto the desk in the hope that this would knock chips back into their ...
14 votes
1 answer
2k views

Why is the original Altair BASIC (for the 8080 CPU) source code not available on-line?

As described by The Register in 2001, around 1987 journalists and others started asking Bill Gates for a copy of the source code for the original version of Altair (eventually Micro-Soft) BASIC, ...
8 votes
4 answers
835 views

Could the 6502 have worked with an Altair-style front panel?

I have fond memories of programming the 6502, though I never did any hardware hacking with it. I notice that the Altair, with its iconic front panel, was based on the Intel 8080, and from then on, ...
20 votes
3 answers
2k views

How did the Altair 8800 front panel load the program counter?

My understanding is that when you toggle in an address on the Altair 8800 front panel switches and then press the EXAMINE switch, it loads the program counter with that address, or at any rate does ...
7 votes
3 answers
2k views

Why 18 expansion slots on the Altair 8800?

The Altair 8800 had a backplane with 18 connectors for S-100 cards. Why was the number 18 particularly chosen? It is fairly common for a computer to have the number of expansion cards be a power of 2,...
18 votes
3 answers
6k views

Did anyone ever put half a megabyte of memory in an Altair?

The Altair 8800 typically, at least in the early years after its release in 1975, operated with no more than a few kilobytes of memory, for the excellent and sufficient reasons that memory was ...
22 votes
8 answers
4k views

Why user-assembled kits?

Many early computers were sold as self-assembly kits (you get a box of parts and an instruction leaflet and have to solder them together yourself). For example, the Altair was priced at $439 kit, $621 ...
8 votes
1 answer
516 views

Why was the Altair numbered "8800" even though the processor was an 8080?

The Altair 8800 was a computer using the Intel 8080 processor. Why the difference in numbers?
12 votes
2 answers
2k views

How did the Altair ensure that the −5 V supply was the first connected and last disconnected?

The Wikipedia page for the Intel 8080 processor describes pin 11 as The −5 V power supply. This must be the first power source connected and the last disconnected, otherwise the processor will be ...
13 votes
1 answer
1k views

When did the Altair move ROM to the top of memory?

The 8080 starts running code at location 0 on reset. The natural layout of memory on a computer using that CPU is therefore ROM at the bottom of the memory map and RAM at the top. CP/M demands the ...
3 votes
2 answers
340 views

Why did the SWTPC 6800 Computer System not take off? [closed]

In 1974, a major semiconductor company released its first 8-bit CPU that was good enough to build a serious computer around. In 1975, a smaller company built a computer around it, a horizontal box ...
2 votes
1 answer
348 views

Why was the SWTPC 6800 Computer System cheaper than the Altair?

In 1974, Intel released the 8080, which basically was the first microprocessor good enough to build a serious computer around. That led to the Altair 8800 the following year, which was the beginning ...
8 votes
1 answer
779 views

Why did the Altair use 100-pin edge connectors?

The Altair 8800 was based on what came in later years (much to the displeasure of MITS) to be known as the S-100 bus, because it had 100 lines, because MITS found 100-pin edge connectors were ...
11 votes
2 answers
1k views

Was natural convection ever a consideration in orienting expansion cards?

Many computers have followed the design pattern of a backplane with expansion cards, including arguably the three most influential microcomputers ever built: the Altair 8800, the Apple II and the IBM ...
5 votes
2 answers
1k views

Test emulated 8080 CPU without an OS?

I've found a few 8080 CPU test suites available, but they all assume CP/M or a similar OS is already present and running - they call BDOS for I/O, etc. I'm working towards being able to run CP/M on my ...
12 votes
1 answer
879 views

What additional hardware was required for BASIC on an Altair 8800?

I remember being aware of the Altair 8800 when it made it's mark, but only vaguely. Lately I found myself wondering what hardware was required for the Altair to get BASIC up and running. According ...
11 votes
1 answer
821 views

How many cards could you put on an S-100 bus?

The S-100 bus was something of an industry standard in the 1970s, for 8080 and Z80 computers built on a backplane design. It was invented with the Altair 8800, which apparently provided 16 or 18 ...
4 votes
1 answer
1k views

Source code of front-panel entered Altair 8800 programs

I'm looking for the source code of short programs for the MITS Altair 8800 (let's say < 50 instructions to make the question more specific), so they can be entered by using only the front panel. ...
6 votes
3 answers
756 views

Single-stepping the Altair 8800

I've just been watching a rather interesting series of videos about the MITS Altair 8800. It has a button on the front panel to single-step the CPU one instruction at a time... Except that, on closer ...
4 votes
1 answer
270 views

What was the "biggest" or the "greatest" task ever performed by MITS Altair 8800? [closed]

We know that computer is used for many things, to control many things, to do many jobs, as server, to control airplane traffic, and many things a computer can do. But I am curious about the MITS ...
1 vote
1 answer
1k views

Where can I find and download emulator of Altair 8800 with Intel 8080 processor for Windows?

I would like to look back to the very beginning of personal computer when Paul Allen and Bill Gates started their debut. So I need to find an emulator of the MIT Altair 8800 with Intel 8080 processor ...