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15
votes
3answers
2k views

Why are branches relative in many 8-bit CPUs?

I was looking over an old article on the 6809 and was perusing the opcodes and noticed that the branch instructions came in two flavors, long and short. That sparked a memory about one of the 6502-...
6
votes
1answer
790 views

What was the first programming language to have 'printf'?

I'm curious as to which language was the first to literally have a formatted text output procedure called 'printf'. A trivial question, sure, but I was prompted to ask by a recent question on ZSPL. ...
2
votes
1answer
37 views

Has there ever been a instruction set architecture that did not require instruction decoding at all?

I am studying basic principles of instruction set architectures and am considering what it would take to not have any instruction decoding at all. I.e., all the control lines of the computer would be ...
57
votes
10answers
6k views

Why is the processor instruction called “move”, not “copy”?

Many processors have an instruction called "move" (sometimes spelled MOV) which copies data from one location (the "source") to another (the "destination") in registers and/or memory. It does not do ...
18
votes
5answers
3k views

Why does UNIX ed not have a prompt by default

The line editor ed in UNIX/Linux has a "command mode" and an "insert mode" and there is no visual way to tell which mode you are in. However, there is a -p option that causes it to display a prompt ...
20
votes
3answers
4k views

Wiring a Zilog Z80

I've recently got hold of an old Zilog Z80 microprocessor and I know how to clock and test it. I do not however know how to connect RAM, I/O ports, control switches (for programming instructions into ...
65
votes
8answers
17k views

How were the first ZX Spectrum games written?

Being a child of the 80s I loved my ZX Spectrum, did my best to learn BASIC but I felt like the games I was playing (Jetpac, Dizzy, Renegade etc) were perhaps not written using BASIC. I wondered: how ...
40
votes
2answers
2k views

What precautions to take when powering on old computer for the first time in years

I have a Commodore 128D that hasn't been powered in about 15 years. I want to begin using it again. It has been stored in cool dry places like attached garages, in a cardboard box. I hope this ...
18
votes
8answers
4k views

Intel 8080-based home computers

I'd like to build an FPGA replica of a home computer based on the Intel 8080. I am not looking to design my own computer, since I would like to tap into an existing software base. Were there any ...
6
votes
1answer
199 views

Why were index register contents on IBM 7090 subtracted in forming the effective address?

On IBM 709/7090/7094 mainframes, the effective address of an instruction could be modified by the contents of an index register specified in the instruction encoding. That much is a fairly standard ...
31
votes
5answers
6k views

Did any computers use the Z80B?

The Z80 was one of the most popular CPUs of the seventies and eighties. In almost all cases that I know of, the version used was the Z80A, rated for 4 MHz, sometimes clocked a little slower in order ...
9
votes
1answer
341 views

Why didn't Wozniak's interrupts work on the Apple I monitor program?

In his autobiography, Steve Wozniak recounts[1] his difficulty getting interrupts working on the 6502 microprocessor: The next step was to debug the 256-byte monitor program on the PROMs. I spent ...
3
votes
3answers
410 views

What was stored in memory that was “unavailable to BASIC”?

On home / personal computers (such as before 1984), a machine might be described as having 24k RAM, but only 18k of that available to BASIC. If the machine had BASIC and the OS (or BIOS) stored in ROM,...
9
votes
2answers
707 views

What is the best way to connect an old Tandberg QIC tape drive using today's computers?

I currently have a ton of QIC-250MB tapes that I would like to read from (its been 30 years). I have a Tandberg TDC 3600 SCSI interfaced tape drive but I am lost how to connect it. In the past, with ...
26
votes
1answer
9k views

Did the Windows 95 screensavers use hardware acceleration APIs?

The windows 95 is known for introducing a couple of classic screensavers including: Maze, Pipes and starfield among others. It looks like DirectX is a collection of multimedia APIs but for this ...
32
votes
7answers
10k views

Did the computer mouse always output relative x/y and not absolute?

I am experimenting with a graphics pen and tablet and it got me thinking about the difference between it and my mouse. One huge difference is that the tablet's working area covers the whole screen, ...
7
votes
4answers
618 views

Self-modifying code in commercial games for the (S)NES, Gameboy, Genesis/MD, PC Engine, Atari, etc

I'm curious if there are any extant examples of commercial games for classic consoles (let's say, pre-32-bit era here) which make uses of self-modifying code. As far as I know, all the systems I've ...
29
votes
2answers
20k views

GameBoy Color games do not save any more

I have a Nintendo GameBoy Color with some games that support saving your game status and also have a real-time clock, like Pokémon Red and Pokémon Silver. But recently the game does not save any more,...
11
votes
4answers
2k views

Amiga 500 OCS/ECS vs Mega Drive VDP

Superficially the Amiga 500 and Mega Drive are similar. Both run a Motorola 68000 CPU at similar clocks and both have dedicated hardware for sprite and other graphics operations. Comparing the arcade ...
6
votes
1answer
93 views

Does the TELCOM program on the Tandy Model 100 support any Unix terminal–like control codes?

I've been connecting my Tandy Model 100 to a serial port on a Linux box via the TELCOM program with some success. The main downside is that in whatever the default terminfo/$TERM setting it gets, a ...
27
votes
2answers
2k views

Can the two CPUs in a commodore 128 run at the same time?

The Commodore 128 has two CPUs. One is some variant of the 6502, and the other is a Z80. One CPU is there for compatibility with the Commodore 64, and the other is there presumably to give basic ...
5
votes
1answer
99 views

Using MAI DT4315A as a terminal for RaspberryPI or other linux system

I have an old MAI DT4315A that my company was going to throw out. I'd love to get it setup as a terminal for a linux based system or raspberry pi, just for fun. However, I've never completed anything ...
28
votes
5answers
8k views

Are MS-DOS and Windows 9x vulnerable to Meltdown?

In an interesting crossover between current events and Retrocomputing, the vulnerability known as "Meltdown" was publicly disclosed on January 3rd 2018. The retro-computing tie-in is that this ...
20
votes
8answers
3k views
+50

Do the holes in Jacquard loom punched cards represent input data or program code?

I think they represent data because I feel it is a mechanical machine which is fully configured and the holes decide only that the thread related to each hole must be moved or not. Thus the holes ...
6
votes
2answers
1k views

Using the swap space of Windows 3.1 as a MS-DOS 6.22 temporary directory

I currently have a working installation of MS-DOS 6.22 with Windows 3.1. I can only use Windows or DOS individually so I don't see the point of having a swap-file for Windows taking up space that can'...
12
votes
2answers
538 views

How to connect an Apple IIe to an external Sider hard disk drive

I am a sucker for 8 bit junk components, and recently picked up a Sider hard disk for my Apple //e. I was able to talk myself into the purchase by fondly remembering how I lusted after this piece of ...
0
votes
1answer
146 views

Spider and snake in a square

In the game you were a spider which could run from one wall to the other. The snake could either destroy your net or you. If you reached another wall the room where snake could move got smaller. If ...
10
votes
2answers
2k views

Running DOS, Windows 3, and Windows 98 from one FAT32 partition?

I'd like to setup a Windows 98 SE system that boots into the included MS-DOS 7.1 command line, and which can also run Windows 3.11. I've seen various disjointed posts online that suggest this is ...
25
votes
5answers
4k views

What type of interpreter were most 8-bit BASIC implementations?

I’m a big fan of early/mid 1980s personal computers like the Amstrad CPC, Commodore 64 and the Sinclair Spectrum. One thing these computers all had was a version of BASIC. Well known ones being MS-...
87
votes
6answers
8k views

Were there 8086 coprocessors other than the 8087?

The 8087 math coprocessor for the 8086 (and descendants) nominally added floating point and transcendental (trigonometric and logarithmic) instructions to the 8086. Contrary to naive expectations, the ...
11
votes
2answers
706 views

Limitations for Color Usage in NTSC

In a well known letter to Philip Timmermann, Robert Yannes describes C64 color generation hardware as capable of producing any color (the palette was fixed, of course, but chosen semi-arbitrarily and ...
14
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
3
votes
1answer
293 views

Is there a git build for Windows 9x

Obviously, given age, doesn't have to be as secure and fancy and the modern builds, but is there there a git build for Windows 9x, just like there is for Windows XP? Also wondering whether there is a ...
8
votes
2answers
729 views

Has any major corporation ever successfully sued Microsoft for intellectual property theft?

It is generally agreed that Microsoft stole parts if not entire blocks of intellectual property from Digital Research, Xerox, Apple, and several other major corporations. To keep it simple, lets ...
13
votes
2answers
647 views

Are there any public tools for the TMS34010?

I am interested to learn about the Texas Instruments TMS34010, a 32-bit fully functional CPU with built-in graphics manipulation capabilities, which appeared in Atari's Hard Drivin' arcade boards ...
23
votes
1answer
6k views

What was the first operating system called DOS?

MS-DOS a.k.a. PC-DOS nee QDOS, was commonly just referred to as DOS. But 'disk operating system' is a very obvious acronym; there must have been previous operating systems so called. What was the ...
14
votes
4answers
1k views

How to use BASIC after “LOAD ”$",8 on the C64

After loading a file list from a floppy disk it is hard to program in BASIC because the file list is interpreted as BASIC lines. For example there can be 20 lines with the number 1, because 20 files ...
10
votes
3answers
285 views

Commodore 64 with partly working keyboard (part 2)

I have a C64 that has recently stopped responding to two 'columns' of keys, namely '9,0' 'i,o' 'j,k' and 'n,m' - I've swapped the CIA chips (U1 and U2) to no effect, so I pulled a keyboard from a ...
1
vote
3answers
183 views

How can I clean the RF-Out jack of the SNES

I have got a Snes which is in pretty good shape. My problem is that the RF jack is very dirty and corroted. I haven't tried cleaning it because I think I could accidentally break it. (The jack is ...
-4
votes
1answer
158 views

Why did Western Digital name their drives “Caviar”? [closed]

I'm asking in Retrocomputing because the Caviar line of HDDs was released in the most recent era of retrocomputing. Does anyone know why they named the line "Caviar"? Why do they associate Sturgeons ...
5
votes
0answers
134 views

PET LOAD command and the < key

I remember reading (probably in some issue of the newsletter of the PET Benelux Exchange (PBE)) about a strange effect during tape loading of a PET program. Back in the day, I tried it and it worked. ...
21
votes
7answers
7k views

Why is the Intel 8086 CPU called a 16-bit CPU?

Based on my understanding, the bitness of a CPU specifies how much memory it can address (which is determined by the size of the CPU's address bus I guess). For example: a 32-bit CPU can address 232 ...
7
votes
4answers
479 views

How is PETSCII used by assembly-language programs?

First, a bit of context. I wrote an interactive disassembler for 6502 code that, among other things, attempts to identify ASCII strings automatically. Appropriate source code for different assemblers ...
7
votes
1answer
250 views

Origin of VIC-II (PAL) chip labelled 8656R2?

Wondering why a C64 VIC chip (fully functional) that I got off eBay had an 8565R2 label fitted on top of it: I peeled it off to find this: I haven't ever heard of a VIC-II (PAL) labelled MOS 8656R2. ...
8
votes
4answers
2k views

Writting DSK images onto a 3'' floppy for Amstrad/Sinclair computers

For a project I'm working on, I need to write some disks to test on my Amstrad CPC 6128. I've got some 3'' inch blank disks, and all my Amstrad computers (CPC and PCW) have 3'' inch disks, as well as ...
32
votes
3answers
2k views

Why does the C64's LIST command choke on REM statements with a Shift+L?

On the Commodore 64 and VIC-20, the LIST command will abort with a ?SYNTAX ERROR on any line that contains a REM statement with a Shift+L character. A minimal program triggering the error would look ...
9
votes
4answers
1k views

How did DOS know where to load itself in upper memory?

If I remember correctly, you could ask DOS to load in upper memory by writing something like... DOS=UMB ...somewhere in the CONFIG.SYS file. But the question is, how did DOS know what portions of ...
21
votes
2answers
844 views

What are these tiny TSRs doing?

I've been puzzled by this for a while now. The (very old) game Phantasie comes with three small TSRs that are run prior to running the main game executable. This is the content of the file PH.BAT, ...
2
votes
3answers
155 views

Semis and spaces in MS-alike BASIC PRINT commands

With the exception of DEF FN and the handful of direct-mode commands (CONT, LIST, etc), my interpreter is running most programs, but layout remains an issue. Here are three lines from the BASIC ...
16
votes
4answers
5k views

Why are old computers so vulnerable to temperature changes and moisture?

Interesting discussion by someone thinking of procuring a PDP-11/34, though having difficulty finding suitable space for it: https://www.reddit.com/r/retrobattlestations/comments/dztvci/...

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