All Questions

3
votes
5answers
201 views

What use are the data direction registers in the MOS 6526 CIA?

As described in the MOS 6526 CIA data sheet (at the bottom of page 5) and this answer, the PA0-7 and PB0-7 pins: always act as inputs, even when the data direction register (DDR) is set to 1 ("output"...
20
votes
1answer
2k views

Why was it possible to cause an Apple //e to shut down with SHIFT and paddle button 2?

Looking at the MAME driver for the Apple //e, I noticed an interesting comment: NOTE: On real IIe and IIe enhanced h/w, pressing SHIFT and paddle button 2 will short out the power supply and cause ...
3
votes
1answer
181 views

Apple I and II video output to a contemporary TV set?

Is it possible to connect the unmodified video output from an Apple 1 and Apple II (with their non-standard/our-of-spec NTSC sync pulse levels and/or timings) to a (currently in-production and ...
9
votes
3answers
909 views

What is the best option to connect old computer to modern TV

I was exploring different options of connecting both my Atari ST and C64 to a modern TV. I opted for a composite signal passed through a cheap AV to VGA converter, and although the display works, ...
2
votes
1answer
111 views

can i build a colecovision ac adapter

Can I use multiple small AC adaptors to make a working Colecovision AC adaptor? For example, two 5V, one 12V and the ground. Colecovision AC adaptors are too expensive.
5
votes
1answer
273 views

Where are the pullups for the Commodore 64 keyboard matrix lines?

I'm looking at the schematic and the Service Manual for the Commodore 64. I can't seem to find a schematic for the keyboard itself. It seems clear that the control port 1 joystick has normally open ...
4
votes
1answer
154 views

Atari 1040ST AV video output - blurred and jagged vertical edges

I have an AV cable that connects Atari 1040STE with a AV to VGA converter. For some reason the vertical edges are not sharp, rather jagged or pixelated. I red that old atari would have an issue with ...
9
votes
1answer
246 views

How did the Zip Chip and RocketChip accelerators work for the Apple II?

Though there is already a similar question on the site, this one is more specific to these chips and their technical implementation. There were two accelerators for the Apple II series that were drop-...
5
votes
1answer
156 views

Monitor for an SGI Octane?

I just found myself being the sudden and proud owner of two wonderful Silicon Graphics machines, an Octane and an Octane 2, both in quite good condition (in particular with very few scratches to the ...
15
votes
1answer
286 views

In the original Z80 layout, where are the “traps” located? And what are their effects?

According to Zilog Oral History, Zilog only had a tight schedule to design the Z80. Facing the potential competition, Federico Faggin and Masatoshi Shima were worrying about Japanese semiconductor ...
15
votes
2answers
2k views

Looking for an old image of designing a CPU with plan laid out / being edited on a literal floor

There is an image that I remember seeing, but that I have never been able to find. It shows 2-3 people on their hands and knees, crawling around a blueprint of a chip that had been rolled out over the ...
2
votes
0answers
138 views

Would anyone have made a mechanical, or electronic camera for their computer or robot? [duplicate]

Would anyone have made a mechanical, or electronic camera for their computer or robot ? Parameters Of The Question As a home-project [ Although, any example of a mechanical-tv-camera or mechanical-...
4
votes
0answers
192 views

Does the Commodore 64 power switch have a history of failing?

My original (1983?) Commodore 64 (brown breadbox with grey function keys) has trouble powering on. Specifically, when I flip the power switch the power LED will glow dimly and the machine fails to ...
46
votes
3answers
7k views

Strange math syntax in old basic listing

I'm browsing through an old book "Basic Computer Simulation" from 1983. It contains a line of BASIC code that reads: LET Z1 = M * D1 * (PQ / A) [ 3 I understand all of the code except the "[ 3" I ...
21
votes
2answers
5k views

What is a subpixel in Super Mario Bros, and how does it relate to wall clipping?

What are "subpixels" in Super Mario Bros on the NES? How does it relate to wall clipping? At 4:42 in the following video, the notion is mentioned in the context of how it relates to "wall clipping": ...
5
votes
2answers
1k views

What is this side-scrolling fighting game for the Amiga?

I remember playing this game on an Amiga. I have no idea what it was called.
29
votes
9answers
9k views

How did early x86 BIOS programmers manage to program full blown TUIs given very few bytes of ROM/EPROM?

I've always wondered how so much functionality and relative luxuries(CMOS Configuration Utilities. See: https://geekprank.com/bios/ for an example) included with most popular x86 BIOSes could be ...
31
votes
5answers
4k views

Why does the 6502 have the BIT instruction?

The 6502 has a bit instruction which copies two of the bits into the N and V flags, pretends to and the byte with the accumulator, but discards the result and only affects Z. I'm having a hard time ...
20
votes
3answers
2k views

When and what was the first 3D acceleration device ever released?

Plain and simple, we know that consumer level 3D acceleration devices roughly appeared in the middle of the 90s, with brands like Matrox, 3DFX, Nvidia and so on. However, such technology for sure ...
33
votes
3answers
3k views

Why are C64 games inconsistent with which joystick port they use?

The Commodore 64 has two DB-9 joystick ports. If I'm the only person that ever plays games on it, you would assume that you could just leave a joystick plugged into Port 1 and be done with it. However,...
7
votes
2answers
266 views

Texas Instruments SN502

My father is an engineer that worked at TI directly under Jack Kilby in the early 60’s. This chip was given to him by Kilby as a “thank you” for all his hard work. We also have the accompanying build ...
8
votes
4answers
1k views

Compaq Portable vs IBM 5155 Portable PC

In 1983, Compaq introduced its first product, a portable computer weighing 28 pounds; 128-640K RAM, two 5.25" floppy drives, 9" monochrome CRT for $3590. It was extremely successful in the market, and ...
13
votes
2answers
376 views

What is known about the internal workings of the Z80?

There is a wonderful project called Visual6502, and I've used it from time to time to figure things out, like exactly the difference between rti and rts. It is good to see which control lines were ...
23
votes
4answers
4k views

Can my floppy disk still work without a shutter spring?

One of my floppy disks' shutter spring got lost. Now the shutter can't slide normally. Can I still use the floppy disk?
7
votes
2answers
386 views

What was the Macintosh's BOM cost?

Andy Hertzfeld revealed that the CPU for the original $2495 Macintosh cost just $9.00. How much did the rest of the computer cost? Was the markup really greater than Pepsi's markup on sugar? How much ...
6
votes
4answers
398 views

Set screen resolution in DOS-only PC

I replaced a failed CRT display with a LCD panel with a VGA controller board. There is no problem with the display when the PC boots up. However, if I switch the display off then I get an 'Out of ...
12
votes
2answers
2k views

What is the purpose of the yellow wired panels on the IBM 360 Model 20?

I just finished reading a story about an IBM 360 Model 20 rescue, and some of the pictures caught my eye. Specifically this one: Searching online, led me to several more pictures, all with ...
43
votes
5answers
15k views

What did the 'turbo' button actually do?

I remember the computer I played Commander Keen on as a child had a turbo button that I was forbidden to touch, what did this button actually do?
14
votes
4answers
3k views

Why do the i8080 I/O instructions take a byte-sized operand to determine the port?

I thought the i8080 had 8 16-bit IN ports and 8 16-bit OUT ports. Doesn't that mean the instructions IN d8 ; only index 0-7? OUT d8 can only take 8 possible values? What would it be indexing ...
3
votes
3answers
290 views

Creative uses for serial port? [closed]

I know it's still used for many industrial microcontrollers but that's not what I am asking; I also know that it's quite slow. It's just that I hate seeing an unused port on my desktop pc, while all ...
6
votes
1answer
159 views

Why does the Apple IIgs FPI chip buffer the A14 address signal to the ROM?

In the Apple IIgs computer, the address and data buses of the 65C816 CPU connect directly to the onboard ROM, except for A14, which, according to the schematic, is routed through the FPI ASIC. There's ...
8
votes
1answer
117 views

Patch BBC Master ROM using Sideways RAM?

I have a BBC Master 128 with the standard ROM installed. This includes ADFS v1.50 in slot "D". I want to replace this ADFS in ROM with a patched version, loaded from disk, into Sideways RAM. It is a ...
3
votes
0answers
168 views

Early 1982 PCW article about pseudo random dungeon mapping

I am looking for an article from an issue of Personal Computer World (PCW) from 19821 which related to generating mazes/dungeons using pseudo random seeds, what I think are (now) called procedural ...
9
votes
1answer
313 views

Purpose of using REM when running TR-DOS commands in BASIC

When running TR-DOS commands from within BASIC, it's necessary to prefix the command with RANDOMIZE USR 15619: REM: first. I understand the former command, but not the latter. For example, to load a ...
4
votes
1answer
105 views

How to determine PCB revision of a Sinclair ZX-81

I have a ZX-81 in my collection, but do not know what revision it is. The board text just says "Sinclair ZX81". As far as I know, there were 3 revisions of the ZX-81. What are the landmarks I can ...
8
votes
4answers
1k views

Largest memory peripheral for Sinclair ZX81?

Back in the early to mid 1980s, I vaguely recall seeing an advert in a (I think) UK based computer periodical monthly (Your Computer, or Computer and Video Games), for a memory peripheral that offered ...
48
votes
2answers
7k views

How was the blinking terminal cursor invented?

I was just staring at my blinking terminal cursor: And was wondering where it comes from. Does anybody have some piece of history about the blinking cursor? I couldn't find much online. E.g.: when/...
11
votes
4answers
271 views

Preventing socketed chip corrosion?

I spent a couple hours repairing an Amiga A3000 that wouldn't boot yesterday. The fix was to remove Kickstart ROMs, clean the DIP leads and sockets with contact cleaner, and re-insert. Apparently a ...
8
votes
1answer
351 views

How to use TOSEC?

This is probably a stupid question, but I am struggling to understand how to 'use' TOSEC. For those that are unfamiliar with TOSEC (and assuming I understand it correctly) the project aims to catalog ...
7
votes
1answer
239 views

What are the best file formats for backup & emulation of retro game CDs? And why?

In other words, what are some factual, non-subjective reasons why you might choose (or avoid) a certain file format ? (For example, disk usage, audio accuracy, emulator compatibility, etc). I'm ...
3
votes
1answer
179 views

BASIC09 questions

I only learned of BASIC09 today, and I'm trying to wrap my head around it. The manual talks about it being a compiler, but I'm not sure I see significant differences between its I-code and tokenized ...
11
votes
3answers
4k views

When did game consoles begin including FPUs?

Floating-point coprocessors (FPUs) were an expensive, niche, add-on product for early desktop and home computers. but became commonplace by the mid-1990s, as they began to be included within the most ...
6
votes
1answer
324 views

How to use ISA card in modern PC

(Posted this on HW Rec but got no responses.) Would like to use an ISA expansion card in a modern PC. There are Expensive PCI - ISA adapters (but I cannot find any actually for sale now) USB-ISA ...
32
votes
3answers
6k views

Were any of the books mentioned in this scene from the movie Hackers real?

In this scene from the 1995 movie Hackers, Cereal pulls out several books referred to by different colors of the "technicolor rainbow", including a "green one", "luscious orange", the "Pink Shirt book"...
7
votes
2answers
778 views

Motorola 6845 and bitwise graphics

I'm curious about how graphics were drawn on systems using the Motorola 6845. I understand this was used in the CGA? If so, did the 6845 really work bitwise, was the bitwise graphics entirely separate,...
2
votes
0answers
113 views

Can the quality of a programming language be objectively determined? [closed]

Can there really be an objective way to determine the quality of a programming language or is it all just up to the subjectivity of the programmers when the quality of languages are discussed? Is ...
4
votes
0answers
136 views

Looking for ATARI-ST Graphics Image

I am hoping that someone here collects computer images from days gone by. Many years ago when I used my ATARI-ST I made two drawing I believe I used the art program NEOCHROME, or possibly DEGAS. The ...
5
votes
1answer
247 views

XT IDE causes BASIC not to load properly on IBM 5155

I recently picked up an XT IDE. It works fine for the most part, but when I tried to load BASIC samples from the original IBM DOS 1.1 floppy(I was booting from it), the system hung up, only showing a ...
5
votes
1answer
195 views

Where to find a ROM dump for the Atari ST cartridge 'ACTION'

Back in the day I owned a couple Atari ST, I used a cartridge based program for writing video games. It was called "ACTION" Does anyone remember this program or even better, know where I can get a ROM ...
16
votes
2answers
2k views

Was there ever any real use for a 6800-based Apple 1?

This is kind of a difficult question to phrase since the Apple 1 wasn't really that well adopted of a platform - under 200 of them made and mostly abandoned by the company within 2 years. That being ...

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