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27 votes
Accepted

Anyone up for decompiling some 8080 code for Kaleidoscope?

I had a look at the source and added a few comments (*1). Might not be the expected full high level abstract description, but should be still helpful as a first, tiny step to see its workings. Doing ...
Raffzahn's user avatar
  • 224k
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 ...
Raffzahn's user avatar
  • 224k
25 votes

Anyone up for decompiling some 8080 code for Kaleidoscope?

Thanks to @Raffzahn commented code (in his answer) I was able to port the code into simple C++ code: //--------------------------------------------------------------------------- const int VRAM_xs=64,...
Spektre's user avatar
  • 7,276
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 ...
Raffzahn's user avatar
  • 224k
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 ...
cjs's user avatar
  • 26.6k
15 votes
Accepted

Weird power lines for S-100, why no 5V?

Remember, we're talking about mid 1970s, that's before switching power supplies became common. The Apple II was an exception at that time. And it was almost half a century before tiny sized, dirt ...
Raffzahn's user avatar
  • 224k
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 ...
alephzero's user avatar
  • 6,656
14 votes
Accepted

Intel 8080 and Altair 8800. 256 I/O ports, but only 7 free RST (interrupt subroutines) — how does it work?

I have looked this video - Altair 8800 - Interrupt Acknowledge Cycle and have few questions (I have read wikipedia Intel 8080 article, Altair 8800 Operator's manual, Charles Petzold "Code" ...
Raffzahn's user avatar
  • 224k
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 ...
Martin Maly's user avatar
  • 5,575
12 votes
Accepted

Game cartridges on the S-100 bus?

Short answer: Yes Would it have been possible to plug suitably designed game cartridges into an S-100 slot? Sure. After all, such a cart would be just another ROM/Memory board. Although, some ...
Raffzahn's user avatar
  • 224k
12 votes
Accepted

S-100 bus and device drivers

Like most busses of its time, you had to write your own software to communicate between the cards. The term device driver wasn't widespread at the time, but that is what you were writing. The S-100 ...
Chenmunka's user avatar
  • 8,141
11 votes
Accepted

Is S-100 alive?

Yes, there are still a few communities using and developing S-100 boards. A good place to start is the S100 computers site, which lists a number of new S-100 boards which can be ordered and used to ...
Stephen Kitt's user avatar
10 votes

Intel 8080 and Altair 8800. 256 I/O ports, but only 7 free RST (interrupt subroutines) — how does it work?

1 I/O port <> 1 hardware device 1 RST vector <> 1 interrupt from one device You have read the datasheet under false assumptions. There is no such thing as a 1:1 correlation between these ...
tofro's user avatar
  • 35k
9 votes
Accepted

Differences between 4k, 8k and Extended Altair BASIC?

And I found the answer only moments later when I came across the original manual. The difference is that the 4k version (mainly) did not have strings (!!), lacked a number of math functions (ATN, etc),...
Maury Markowitz's user avatar
8 votes

S-100 bus and device drivers

An important thing is that old-style expansion buses - that includes S100, als well as the PC ISA bus and various proprietary buses, had no enumeration capability - a computer system was not aware of ...
rackandboneman's user avatar
8 votes
Accepted

Can S-100 cards attach to the ZX machines?

Can S-100 cards attach to the ZX machines? That calls for a clear Yes, But :) S-100 closely matches the same signals as the Intel 8080, as does the Z80 which the ZX Spectrum etc., have. Adding a ...
Raffzahn's user avatar
  • 224k
7 votes

Can anyone help provide more information regarding an operating system called I/OS by Infosoft in the early 1980's?

The first page of the article Getting Compatible with CP/M implies it was an alternative name for Infosoft's TSA/OS, and was indeed a CP/M variant.
alephzero's user avatar
  • 6,656
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 ...
paxdiablo's user avatar
  • 4,877
7 votes
Accepted

Which S-100 systems supported both hard- and soft-sectored 8-inch floppies?

On a "standard" soft-sectored 8" disk, the drive generates one (index) pulse per rotation. On a hard-sectored floppy, the same drive will generate 33 (or 17) pulses (32 sector pulses ...
tofro's user avatar
  • 35k
6 votes
Accepted

How was the 8 to 16 bit transition of data lines managed for S-100

[Preface: It might be more appropriate to read the S100 standard documents instead] The S-100 bus had 8 data lines, logically enough since it was originally used with the 8080 and then Z80 CPUs. ...
Raffzahn's user avatar
  • 224k
5 votes

Intel 8080 and Altair 8800. 256 I/O ports, but only 7 free RST (interrupt subroutines) — how does it work?

Manassehkatz is correct about the bus. All components can see all bus activity. So each picks for itself which bus cycles to respond to; ordinarily IO accesses to a particular address or range of ...
Tommy's user avatar
  • 37.3k
4 votes

Can anyone help provide more information regarding an operating system called I/OS by Infosoft in the early 1980's?

AFAIK Mostek M/OS-80 was a licensed derivative of an Infosoft CP/M-compatible operating system. There is an M/OS-80 manual on bitsavers in this directory: http://bitsavers.trailing-edge.com/...
Eric Smith's user avatar
4 votes
Accepted

Why were the data lines of the original S-100 bus unidirectional?

It's rather simple concerning the hardware. To operate the bus without the CPU (while plugged in), the databus needs to be separable from the CPU. That's why buffers are needed. While the processors ...
Raffzahn's user avatar
  • 224k
4 votes

Game cartridges on the S-100 bus?

The S-100 bus was introduced in 1975 and the first processor cards available used the Intel 8080. A large number of cards became available over time, including a variety of video interfaces, both ...
Chenmunka's user avatar
  • 8,141
4 votes

Weird power lines for S-100, why no 5V?

One issue was voltage drop. Another is fault isolation. Voltage Drop: For 7400-series TTL logic (and similar), the Vcc range is 5.00V +/- 5%, or 4.75V..5.25V. Consider that precision, fast-response ...
Technophile's user avatar
4 votes

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

We put a half-meg of memory into an STD bus Z-80 on CP/M 2.0 in the early eighties. It was (IIRC) a hardware + software solution from a company in Ottawa, Canada. The core of the program fit into ...
Flydog57's user avatar
  • 621
3 votes
Accepted

Did 68000 on S-100 have any problem with being big endian?

How does this work from the endian-ness perspective? Endianness is for most parts a software issue. Hardware, especially memory is either agnostic to the way a word ist stored, or doesn't have any ...
Raffzahn's user avatar
  • 224k
2 votes

Intel 8080 and Altair 8800. 256 I/O ports, but only 7 free RST (interrupt subroutines) — how does it work?

The chip has 256 I/O ports, rather than some smaller number, because it was just as easy to provide 256 ports as it would be to provide eight. The part supports eight restart vectors because the ...
supercat's user avatar
  • 36.6k
2 votes

Can S-100 cards attach to the ZX machines?

not quite an answer to the question: In our post-90ies and beginning-of-2000ies ZX practice, we were connecting ISA modems to ZX Spectrums here, used BBSes and FIDO via them (there is software for ...
lvd's user avatar
  • 10.5k
2 votes

Did 68000 on S-100 have any problem with being big endian?

A long time ago I worked on an Alpha Microsystems computer which was S-100 based little-endian, and while I was there we upgraded to a 68000-based system that had been wired (I don't know the details) ...
Eugene Styer's user avatar
  • 1,111

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