PeterI
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How did the Apple II forward binary instructions to the Z80 software card with CPM?
39 votes

They both shared the same memory so it didn't really forward instructions. The Z80 card stopped the 6502 running using the DMA signals and the system swapped between the two by writing to $CN00 where ...

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Why would older video games include fragments of source code?
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27 votes

I'd guess a lot of the systems used for development didn't clean the memory down in between usages. It's also likely that for games "gaps" got left between binary chunks. So if for a hypothetical ...

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Does 10BASE-T need more sophisticated electronics than 10BASE5/10BASE2?
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25 votes

I designed a 10BASET ethernet chip (codename ENZO used in Sage MainLAN https://archive.org/details/byte-magazine-1991-01-rescan/page/n67/mode/2up?q=sage+mainlan) and produced a proposed design for a ...

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How were bugs reported for compilers that were shipped on floppy disks?
23 votes

I worked for Borland in the UK doing support for Turbo C 1 to 1.5. Most contact was via mail or telephone in those days. Bugs were sent over to the US after we did some triage to check if they could ...

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Understanding INKEY$ in ZX BASIC
23 votes

I suspect your confusion is because INKEY$ returns the current state of the keyboard, not a buffered stream of up / down key presses (On serial terminal based systems such as CP/M you'd get the ...

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Was photographic film ever used for digital data storage?
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22 votes

Yes, the IBM 1360 used it. The wikipedia page suggests that it could store 0.5 terabits (64 GiB) of information. https://en.wikipedia.org/wiki/IBM_1360 Fascinating design.

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How was a demo mode implemented in arcade machines
17 votes

For space invaders what happens is the game has short list of movements (11 in ROM but only 10 are used) left and right or stay still. If there is no bullet in flight the player fires, each time the ...

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What are the rules for Applesoft BASIC formatting for code?
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17 votes

This is an AppleSoft issue where it puts spaces either side of a token. PET/CBM BASIC (based off the same code base) doesn't do this. Tokenising ignores spaces, this means it can be difficult on the ...

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Was it feasible to create Win16 software using pre-existing DOS development tools?
15 votes

After doing a bit of research (on Raymond Chen's blog) one of the better examples of things Windows compilers did on 16 bit Windows was to increment BP before pushing it on the stack in a far called ...

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640x480 color display in 1980
15 votes

Well Cromenco have something on page 2 of this issue of byte. https://archive.org/stream/byte-magazine-1980-11/1980_11_BYTE_05-11_High-Resolution_Graphics#page/n1/mode/2up 756x482 in 16 colors, and on ...

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Radio Shack computer trainer kit?
14 votes

I think you're thinking of the Science fair microcomputer trainer: http://www.radioshackcatalogs.com/html/1985/h155.html which had a TMS1100 as the processor (if not there is the digital computer ...

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Calculating the time for a CPU cycle
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13 votes

It's one divided by the clock. So for 0.895 MHz divide 1 by 895000 and the answer is 1.117318 micro seconds. for 1.79 Mhz it's 558.6592 nano seconds. I suspect however that the clock will be some ...

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Transfer files to DOS over serial cable from Linux?
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11 votes

Some sort of comms program that supports Zmodem on the 286 end and use "sz" to send from the unix end. Zmodem has some advantages in that usually the receiving computer will auto start reception of a ...

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Is there a simple way to display ANSI art and animation files in a modern terminal window?
11 votes

I got bored over the weekend and created Ansi-Cat for a Windows command prompt. https://github.com/peteri/Ansi-Cat Does code page 437 -> Unicode conversion, tested it on Windows 8.1 & 10 but you ...

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Why are the PPU registers on the NES mirrored?
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11 votes

Just to expand a bit, a cheap address decoder might not take all the address bits and decode them. For a 8 bit processor a simple address decoding scheme might use a 74LS138 to decode the high address ...

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What was the first mainstream advanced debugger?
10 votes

Microsoft Codeview shipped in 1985 and has most of the features you're asking about (its been a while so I can't be certain it has everything e.g. call stack walking), when I was doing Turbo C support ...

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Retrocomputing software development process/methodologies
9 votes

In my early days on the Apple II (82-83) I used the mini-assembler in the Integer BASIC ROMs to write an assembler of my own using AppleWriter 1 as the text editor. Source code backup was just ...

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Why are my VGA vram to vram copies so slow?
9 votes

Your problem is mostly going to be rep movsb changing that to use rep movsw should help. If the VGA card is on a 8MHz (or 6MHz) original AT bus then the timings work like this: 3 cycles to read or ...

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What do the "byte-select signals" in the 68000 do?
9 votes

The signals are there so in byte addressing mode the 68000 can read and write individual bytes. From memory UDS means that valid data is on bits 8..15 of the data bus and LDS means that valid data is ...

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Why separate cursor keys?
8 votes

I originally thought this keyboard style was introduced by the IBM RT PC in 1986 (I'm ignoring other non PC class machines and workstations) For a PC the first use I saw was on a Compaq Deskpro 386 ...

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Were people building FPGAs out of TTL logic prior to the first sales in 1984?
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8 votes

Yes at one level we did do designs in TTL but usually not the whole structure of an FPGA. From memory I'm pretty sure that the QL ULA was wire wrapped first (I worked with David Karlin the QL designer)...

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Simplest system to create an emulator for
7 votes

PET or TRS80 might work well. Simple hardware with text on screen so they could be emulated with straight text ouput initially adding code for their odd character sets later and unlikely to contain ...

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Was the Apple II ever sold in kit form?
7 votes

The "Red"[1] reference manual says this on the "unpacking" page If you bought an Apple II board only, see the hardware section in this manual on how to get started. Pages 107 & 108 then go into ...

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How did Apple IIe software handle 64K bank switching?
6 votes

You can set which bank you're reading and writing to separately So if you don't want to use the built in routines (AUXMOVE / XFER) your code would typically copy it's self into the aux memory by ...

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Looking for a BASIC decruncher: inserting spaces between keywords
6 votes

If you're happy with a .net core solution you could take my MS Basic clone, load the code and then save it again. https://github.com/peteri/ClassicBasic You would need to remove the EditLine ...

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8086 stack segment and avoiding overflow in interrupts
6 votes

Unless your IRQ routine was large you'd expect enough space to be left on the stack. You could swap to your own dedicated stack before carrying on. Most of the time you would usually just be copying ...

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Where are the authoritative specs for legacy PC/AT devices still in use in today's PCs?
6 votes

ISA bus documentation is very vague and is mostly defined by a mix of the original PC/XT/AT schematics and 8288 / 82288 bus controller provided by Intel. There was never an "official" timing diagram ...

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Why did the Atari 8-bit computers make beeping noises while accessing the disk and cassette drives?
6 votes

For the tape it's mostly leakage from the other stereo track. Data is recorded on one track (in blocks) and the other track is output to the TV audio. This was intended to allow software to have an ...

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Why are Windows 95 installation disks not uniquely bound to a single product key?
6 votes

MSDN always uses the key 335-XXXXXX6 for legacy software which works for old visual studio & windows 95/98 editions. I just checked and VB6 still has the same key. I don't think I ever remember ...

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Use of E,S,D and X for cursor movement
5 votes

For wordstar the original diamond was chosen probably because the ctrl key position on a lot of older keyboards made it a natural extension and it can be used by the left hand solo. It also avoid the ...

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