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5
votes
2answers
2k views

Why the “jmp” instruction is not working?

I have written the following program in debug.exe: 1165:0100 mov ah, 09 1165:0102 mov dx, 107 1165:0105 int 21 1165:0107 db 'Hello World', 0A, 0D, '$' 1165:0115 jmp 1165:0100 However, when I ...
61
votes
1answer
9k views

What's the story behind the name “X11”?

To this day on Linux configs and startup scripts for the GUI system are stored in /etc/X11. I remember this name appearing alone, or alongside others - XFree86, X.org, X - for as long as I had contact ...
15
votes
1answer
3k views

How to write directly to video memory in MS-DOS?

The base address for the video memory in MS-DOS is 0xB8000. I am trying to write to this address using debug.exe, but I am getting an error: 1165:0103 mov [b8000],ax ^ Error
-6
votes
4answers
1k views

What is the starting address pointed by Stack Pointer in PDP 11?

To which memory location does the stack pointer point at the beginning of the program in PDP 11? And what can be the end address the SP can point to before overflow occurs?
34
votes
6answers
4k views

What was the purpose and history of the C64's special keys?

I never had a Commodore 64 but I've always been curious what the purpose and history of some of the special keys were. In particular: C= Run/Stop Clr/Home Restore I'm mostly used to the standard ...
21
votes
9answers
3k views

Why did CP/M and MS-DOS use the BIOS instead of their own drivers to access hardware?

Modern versions of Windows (and other modern operating systems I suppose) have their own drivers to access hardware. But as I have read, in the old days, if CP/M or MS-DOS wanted to access hardware, ...
16
votes
2answers
1k views

How old-computer emulators work?

I'm wondering how old-computer emulators work. I can think of two possible approaches: "hardware" approach - like a set of components that exactly act as low-level hardware elements. I mean a bus ...
11
votes
3answers
2k views

What do the “byte-select signals” in the 68000 do?

Got a question about how the 68000 addresses memory. Wikipedia says: The 68000 has a 24-bit external address bus and two byte-select signals "replaced" A0. Here is an image of the chip's pins: ...
16
votes
4answers
3k views

Why is the serial port driver named “/dev/ttyS#”?

Based on my understanding, a tty means a computer terminal/teletype, and that /dev/ttyS1 is the driver for serial port 1/COM1 (or more accurately, a driver for UART chip 1 I suppose). But I don't ...
22
votes
2answers
3k views

Blue and yellow stripes on the screen when loading from tape on ZX Spectrum

When loading a program from tape on ZX Spectrum you could see those blue and yellow stripes around the splash screen. I might be mistaken but I believe those were even sometimes used for quite ...
15
votes
1answer
4k views

Why BGR color order

Blue Green Red (BGR) byte ordering exists in a few image processing libraries "for historical reasons", mostly because it seems to have been a Microsoft standard. Does anyone know the historical ...
52
votes
5answers
12k views

Why did base64 win against uuencode?

From the the two methods of encoding 8-bit data as human-readable ASCII, for a time, uuencode format was more popular. USENET 'binaries' groups were filled with uuencoded posts with whatever goodies ...
15
votes
4answers
723 views

Is there software that will run across multiple Commodore 8-bit machines without modification?

I noticed in some of the answers in this question that the Commodore 8-bit line apparently used a jump table at $03xx for entry into the kernel ("kernal" for the pedantic) routines. Figuring that the ...
17
votes
3answers
769 views

Which (micro) computers were dominant in Australia and New Zealand in the 1980s?

Australia and New Zealand are somewhat unique among large, developed, economies because they bridge the culture of (mostly) the West with the geography of the East. I am curious how this may have ...
5
votes
1answer
303 views

Strange visual behaviour on SGI IRIX

I've installed IRIX on SGI Octane and have screen looking like this: (I mean the stripes on all elements of the screen, which doesn't seem as a result of CRT monitor - the screen looks normally on ...
9
votes
2answers
425 views

How many gates does each chip in OCS have?

According to Wikipedia, the original Agnus has 21000 transistors. How many gates would this be? (assuming there's a straightforward way to convert between gates and transistors). What about Denise, ...
23
votes
8answers
2k views

What implementations of BASIC had a robust flood fill operator?

When I learned BASIC on Elektronika BK, I got fascinated with the flood fill (PAINT) operator: how does it know to get to all nooks and crannies of the shape to fill? I've devised an algorithm, tried ...
10
votes
3answers
1k views

Can artifact color mode create 262,144 colors on Amiga OCS?

This is as a follow-up to my previous question on artifact colors and the excellent answers provided there. The images below show a simple example of artifact colors generated using a single bit-...
13
votes
5answers
615 views

When did energy saving start to become important?

There was a time where computers often just stayed on all the time. Computer monitors did not have power save functions... they were either on or off. Processors such as the 6502, 68000, 8086, 286, ...
13
votes
3answers
762 views

Why was OCS low resolution limited to 6 bitplanes?

I'm looking for information whether there has ever been an official statement by Commodore back in the days on why the Original Chipset was limited to doing 6 bitplanes only when running in low ...
9
votes
2answers
846 views

ZiLOG Z80 fan-out (CMOS version, Z84C0006PEC)

I am building a z80 based 8 bit computer, and I really don't want to fry my chip. I was looking at this datasheet, but I couldn't find the fan-out specified. There are some electrical characteristics ...
13
votes
2answers
1k views

What is the “standard” way to implement KERNAL hooks on the C64?

The C64 kernel (or KERNAL as it’s known in the C64 community) routines work via a jump vector table stored in page $03xx. A common programming paradigm to create something like a "device driver" would ...
7
votes
3answers
956 views

How were terminals connected to a PDP-11 computer?

This is how I think terminals were connected to a PDP-11 computer: A PDP-11 computer had only one port that you can connect the console terminal (/dev/console) to, and if you want to connect more ...
8
votes
1answer
728 views

Can anyone help name this game?

This is certainly a long shot... this game has evaded my searching for years and I would love to have this mysterious game named once and for all. It came out prior to 1997 (possibly earlier this is ...
16
votes
1answer
656 views

Does anyone know the specific differences between the NES-001 (NTSC) motherboard revisions?

On each Motherboard of an NES-001 (NTSC) there is a code: NES-CPU-xx These range from 04 to 11 (I think) I would like to know if these are all of the revisions of the NES and what major differences ...
16
votes
3answers
2k views

How did the IBM PC handle multiple physical devices serving memory at the same physical address?

I'm trying to figure out how the IBM 5150 PC handled the case where multiple physical devices (memory chips) were mapped to the same address within the 8088's physical address space. The closest I've ...
7
votes
2answers
741 views

Creating Null Modem Connection between two C64s?

Trying to establish a null modem connection between 2 C64s using 1 Commodore 1660 300 Baud modem and 1 Commodore 1670 1200 Baud modem. Does anybody have detailed instructions on how to configure the ...
20
votes
1answer
885 views

What is the difference between the “Return” an “Enter” key in the VT100 terminal?

What is the difference between the "Return" an "Enter" keys in the VT100 terminal:
16
votes
6answers
4k views

What PC “Clone” technology standards were introduced by clone manufacturers?

IBM famously created the PC standard with the introduction of the first IBM PC in 1981. IBM also extended the standard with the introduction of the PC/AT (1984) and the PS/2 line (1987). However, by ...
16
votes
6answers
2k views

What monitor did Atari recommend for its 8 bit product line?

I am curious what Atari recommended to users as an appropriate monitor for their 8 bit computers (400/800/800xl/etc). For example, my Commodore 64 pairs nicely with a Commodore manufactured 1702 or ...
9
votes
1answer
696 views

What was the difference between “Video Low” and “Video High” on the VIC-20?

I was reading about the Audio/Video port pinouts of the VIC-20 and I noticed that pin 4 is VID L and pin 5 is VID H meaning Video Low and Video High, respectively. I'm familiar with luma, chroma, etc....
8
votes
1answer
321 views

How many bits are stored in a memory location in a PDP-11?

PDP-11 is said to be word addressable, which means every data access returns 16-bit data. Suppose I give a read request for address 100 in memory. Will it return 8 bits (LSB) from address 100 and ...
20
votes
2answers
3k views

Is there a better way to the 6 disks install of Windows 3.1

I want to install Windows 3.1 on my MS-DOS 6.22 Machine. I have the 6 disk images. But I only have 1 or 2 spare Floppy disk that I can write the disk images onto. One way I can think of is to write ...
10
votes
2answers
957 views

Did the VIC-20 support raster scanline tricks like the Commodore 64?

I've been programming the C64 on/off for over 30 years (wow). However, I have a few VIC-20's I want to program. I never had a VIC-20 as a kid so I haven't had much exposure to them. Am I correct in ...
6
votes
1answer
424 views

Can you get the file descriptors of a process in UNIX V7?

In Linux, if I want to get the file descriptors of a process, I would go to the following directory: /proc/<pid>/fd But in UNIX V7, the /proc directory does not exist.
10
votes
2answers
330 views

Where to find thermal paper for Aquarius or Commodore printer?

The thermal printer that was sold for use with the Mattel Aquarius or VIC-20 / Commodore 64 is an Alphacom VP42. This uses thermal paper, 4 3/8" wide. Original paper for these printers is very ...
14
votes
3answers
3k views

Is it possible to expand Amiga 500 rev 8 to 1.5 MB with a 1MB trapdoor expansion?

Is it possible to expand an Amiga 500 rev 8 (not an Amiga 500 plus) to 1.5 MB of Chip RAM using an A501+ expansion? It is plug and play or are modifications required? This is the board: Source: ...
6
votes
1answer
226 views

Was job control supported in UNIX V7 or earlier?

Linux supports job control, i.e. you can start a process in the background, or make a foreground process run in the background, or make a background process run in the foreground, etc. Did any V7 or ...
11
votes
1answer
2k views

Why do many JiffyDOS users install a toggle switch to disable it?

For those that don't know, JiffyDOS is a ROM replacement for a Commodore 64 (and 128, I believe) and its 1541 disk drive. This ROM replacement provides OS shortcuts, faster load times, etc. I've ...
6
votes
2answers
520 views

First flat-panel display technology capable of 640x480

What was the first display technology capable of creating a flat-panel display with 640x480 resolution? (And reasonable size, say 12" to 14".) As far as I can see, three flat-panel display ...
14
votes
4answers
2k views

Did the Intel 8086/8088 not guarantee the value of SS:SP immediately after RESET?

I'm poking at the Intel 8086/8088 (iAPX 86/88) User's Manual, which states on page 2-29 (PDF page 48), table 2-4, CPU State Following RESET, that the state of the CPU after the RESET pin rising ...
10
votes
1answer
419 views

Grid Compass - why such a small display?

The Grid Compass, released in 1982, was arguably the world's first full-fledged laptop, whose only glaring deficiency to modern eyes is the small display, 320x240 with physical size to match, ...
7
votes
2answers
1k views

How early could plasma screens be used in laptops?

Back in the eighties, batteries weren't yet at the point where they could run a laptop with similar computing power to a desktop. If you wanted that much computing power, you just accepted that your ...
28
votes
2answers
3k views

How did MS-DOS assign drive letters in the case of more than two floppy disk drives?

The IBM PC BIOS had provisions for up to four floppy disk drives, by virtue of returning the number of floppy disk drives in a two-bit field plus a none/some flag (allowing for reporting values of 0, ...
18
votes
1answer
1k views

Are the effects of “Retro-Brighting” permanent or temporary?

As many of you know, plastics used in our beloved computers from the 70's, 80's and 90's contained a fire retardant called Bromine. This chemical (along with exposure to the Sun's ultraviolet rays) ...
21
votes
3answers
3k views

When you type on a computer terminal, how are the characters displayed on the screen?

Assume that the following computer terminal is connected to a large computer: When I type something on the keyboard (for example: pwd), is it the computer terminal the one that receives the ...
9
votes
1answer
447 views

Price of early color monitor versus TV

Some computers in the seventies and eighties had the option of output to either a TV or a dedicated monitor. Suppose repurposing an existing TV isn't an option and you are going to be buying a screen ...
8
votes
2answers
411 views

First computers to support Japanese script?

What was the first computer to support Japanese script, not just as a toy demo, but at a level where you could actually use it to get a day's work done with Japanese documents? And how did it do it? I ...
29
votes
4answers
4k views

Why did so many early microcomputers use the MOS 6502 and variants?

Quite a few successful early microcomputers used the MOS 6502 CPU. This included, but was not limited to, systems like the Apple I, Apple II, Commodore PET, and Ataris. A followup known as the MOS ...
23
votes
3answers
2k views

What's the TUBE interface of the BBC micro all about?

I keep reading of the BBC micro's tube interface that was apparently designed as a co-processor interface to the 6502. I would be interested in what were actual applications of this interface and ...

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