All Questions

4
votes
2answers
319 views

6502 CMP instruction doesn't compare as expected

I am trying to code in 6502 assembly and for some reason the CMP instruction doesn't work. For example: CLD LDY #$03 LDA #$00 LDX #$05 CMP Y BEQ Equal STX $0200 Equal: BRK ...
3
votes
0answers
39 views

Method for adding firmware to a Commodore 64 expansion card?

The C64 expansion port can and does support multiple IO devices without conflicts. There is 0.5 KiB that is decoded for $DE00-$DFFF, using /IO1 and /IO2 on the expansion port. As long as the devices ...
11
votes
1answer
1k views

How did the ZX80 store both a useful program and screen memory?

I have a vague recollection from my earliest days that the ZX80 only shipped with 1K of RAM. If this RAM was used to store both the program and the contents of the 32x24 screen, wouldn't that mean ...
7
votes
1answer
928 views

How did the 1802 call and return instructions work?

The RCA 1802 processor was used in a number of systems such as the ELF and COMX-35, and also apparently in the US space program (with its hardened variant). From memory, it had a rather unusual set ...
6
votes
2answers
226 views

When did Intel undergo the SEX change?

I am reading the book "The 8086 / 8088 Primer Second Edition" by Stephen P Morse. In it on page 54, it says The 8086 provides instructions to facilitate the task of sign extension. These ...
1
vote
0answers
85 views

Are Unisys ClearPath Libra mainframes still in use in Australia?

By use, I mean are they still actively being developed for. I know this is the case in New Zealand and USA. In particular, is ALGOL code still being written on them?
1
vote
3answers
121 views

Was parsing or operating systems the first user of dollar sign as end of string/input?

According to the question Why did DOS use dollar-terminated strings? DOS uses dollar-terminated strings, inherited from CP/M which used them because DEC also used dollar as the string terminator. ...
14
votes
2answers
1k views

First language with C-like memory management

This is a nerd question but I can’t find anything in google. So, in which programming language did the classical memory management system first be implemented? I mean the division into value types (...
8
votes
2answers
777 views

What is an “unused” memory address?

Reading this page on Commodore 64 memory structure and usage I stumbled across a cell where the table claims that this memory is unused. What exactly does this entail? Does this mean that if you ...
29
votes
7answers
9k views

Last computer not to use octets / 8-bit bytes

I am old enough to remember computers that were not octet oriented. E.g. the first that I used was an ICL 4120. It had 24 bit words which were, when necessary, divided into four 6-bit characters. ...
11
votes
1answer
214 views

C-64 Exchange News Service

I am trying to recall the name of a peripheral I use to have for my C64 in the 1980s. I believe it was called Exchange or X-Change. You hooked it up to your cable TV service and it would decode a ...
9
votes
3answers
656 views

What is the instruction set of the Z4?

I am able to find a few instructions, such as: Fin (presumably "Fine", as in the end of a musical score, ends a program), Fin', (a conditional Fin), St (possibly "Start" -- the need for this is ...
5
votes
3answers
372 views

What to check before powering on TRS80 Model III in unknown condition [duplicate]

Having managed to source a TRS-80 Model III that I'm told hasn't been powered on for quite some time (and I suspect this is a massive understatement), I'm worried that the first thing that might ...
8
votes
2answers
506 views

Instruction set support for multiplication with a constant

Before integer multipliers in silicon, several cpus had some support for multiplication. For instance SPARCv7 has the MULScc multiply-step instruction (several other cpus also have this). As far as ...
0
votes
2answers
177 views

Acorn System 1 - is it a collectable? [closed]

I have one of these things gathering dust at home: Acorn System 1 I have the original manual (when I find it?) too. It did work, the last time I powered it up, 35 years ago. Should I throw it in ...
3
votes
0answers
108 views

Commodore C128 MOS 6526A interchangeability?

I have a working C128 desktop that I'm using to troubleshoot a non-working C128D-CR. I suspected a problem with CIA 2 on the C128D, so I swapped its chip labelled "6526A" with a 1988 year stamp with ...
8
votes
1answer
368 views

Why green phosphor instead of amber?

According to this answer to Why were early personal computer monitors not green? they had a severe disadvantage in that you had to choose between 'too dim' and 'rapid burn-in' whereas amber could ...
2
votes
3answers
302 views

How does memory addressing/mapping work in 8-bit systems?

If I attach a 16 KIB EEPROM to a 6502 or similar, and put some kind of operating system on it, it will run fine, but won't have access to any other chips. So, when a Commodore VIC20 had 5k of ram and ...
-1
votes
0answers
99 views

How do I compile C, C++, or Java code in IRIX? Where can I find compilers for IRIX?

I have asked several questions about IRIX compilers. I have gone from GCC to searching the web for Java Development Kit for IRIX (which I wasted 6 hours trying to find). Is there any website that has ...
2
votes
2answers
100 views

How can I use ImageDisk (.IMD) images with VirtualBox, WinImage, etc.?

I've got ImageDisk installed on my old 486, and I've been ripping some disks for archival purposes (some 3.5", some 5.25"). It spits out .IMD files, which contain some amount of header and metadata, ...
6
votes
1answer
193 views

Trying to identify an Apple II space trading game

I'm trying to identify a game I remember from my first exposure to computers (the Apple II at secondary school back in the late '70s). I remember two games I really enjoyed, the first a Star-Trek-...
57
votes
13answers
12k views

Were later MS-DOS versions still implemented in x86 assembly?

Recently, Microsoft published the source code of old MS-DOS versions on GitHub. What is odd in my opinion is the use of x86 assembly language for everything. The assembly language would not be my ...
2
votes
1answer
147 views

Does IRIX 6.5 on an Indy support other web browsers other than Netscape? If so, where can I find them?

I have an Indy running on IRIX 6.5. The main web browser cannot run very many websites. Are there any other more modern browsers that I can use to run websites such as wayback machine? When I try to ...
6
votes
3answers
973 views

Was cost the only reason why demo cartridge games weren't produced?

I was reading on this page about the Final Fantasy demo cartridge, and I wondered why more cartridge games didn't have demos. From this wiki page: The availability of demos varies between formats....
14
votes
1answer
2k views

Why do old computers perform a long memory test on every boot?

Basically any computers from the mid 90s and earlier perform a slow memory check on every single boot. The more memory there is present, the slower that process becomes, for example: https://www....
3
votes
2answers
69 views

FDD data dropouts after changing disks

I'm building a FDD controller out of a $10 microcontroller. It's mostly working pretty well, and I can read both 720kB and 1440kB PC MFM disks (the only ones I have to test with). However... if I ...
5
votes
2answers
253 views

Was there any indication that video game companies tried to circumvent Game Shark?

Have video game developers blocked the ability of GameShark to find unused content in games (that they either didn't have time to remove unused, or plan to use in an updated version or sequel) I ...
9
votes
3answers
2k views

What happened to ZIP RAM?

I have several retro machines and add-on cards for the Amiga that use ZIP RAM. This vertically mounted chip design enjoyed a brief popularity in the early 1990s, in between the original DIP DRAM and ...
6
votes
1answer
201 views

Weak bits on floppy for copy protection

How did the vendors using copy protection create weak bits on the floppies? This always fascinated me as a kid. I ended up finding a weak bit emulator that would intercept the floppy disk interrupt ...
10
votes
3answers
554 views

Finding byte boundaries in floppy disk MFM bitstreams

I'm building myself a floppy disk interface based on a microcontroller. I'm successfully reading the bitstream off the disk and (probably) decoding the MFM bitstream into actual bits, based on the ...
9
votes
4answers
2k views

Is there a cycle-exact 8086 emulator?

I'm trying to emulate programs from the 80s, but with an accurate clock-speed¹ (pretending its an 8086). Meaning that if a 8086 would take X ms/opcode, the emulator should take X ms (+- a bit of ...
40
votes
2answers
6k views

Why did line printers have 132 columns?

From what I read, most line printers have 132 columns. Also, the VT-220 and presumably other terminals may be switched between 80 columns (that's a usual width) and 132 columns. As I recall, 80 ...
13
votes
1answer
299 views

SYSENTER/SYSEXIT broken on Pentium Pro and Pentium II?

I was just What is linux-gate.so.1?, and it says this Intel recognized this problem early on and introduced a more efficient system call interface in the form of sysenter and sysexit instructions. ...
1
vote
1answer
149 views

What information exists about WD-xsl?

Whilst working on a personal project, I discovered the existence of an old version of the XSLT specification, identified by the namespace http://www.w3.org/TR/WD-xsl instead of the modern https://www....
37
votes
2answers
9k views

Who set the 640K limit?

We all know that "640K should be enough for everyone". But who actually set this limit? The quote is often attributed to Bill Gates, but it doesn't seem like a decision for an Operating System vendor ...
44
votes
11answers
16k views

Why not use fractions instead of floating point?

Considering all those early home computers, the ZX Spectrum, the Galaksija, the VIC-20, the Apple I/II/III, and all of those, they all have some 8-bit CPU which does integer arithmetic and no floating ...
16
votes
2answers
1k views

History of the demise of Matrox from the world of 3D graphics cards

In the last century, a brand of video cards that rhymed with quality, Matrox, was very popular and the choice for professional applications and to some extent for 3D gaming. The benefits of upgrading ...
1
vote
1answer
141 views

How popular was the Canon X-07?

I have this beast, the Canon X-07: The product by itself was of high quality, Z80 and RS-232 compatible and with a lot of peripherals available such as: thermal printer 4 colors tracer infrared ...
4
votes
1answer
184 views

What instructions for the 8086 and subsequent x86 CPUs are not available in Long Mode?

I know from this answer that, Modern x86 CPUs are binary compatible with 8086. You can literally run 8086 binaries on a modern PC, in real mode. (The species analogy is a stretch here, but works ...
3
votes
1answer
172 views

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

The title pretty much says it all. I'm looking for information about an operating system called I/OS by a company called Infosoft in the early 1980's. I think it might have been a CP/M variant and ...
25
votes
10answers
7k views

Did anyone ever use the extra set of registers on the Z80?

The Z80 has the surprising feature of a second set of registers. I suppose these were intended to be used for rapid task switching or interrupt handling, though I think if I were programming a Z80 ...
8
votes
2answers
308 views

6510 I/O port initialisation

TL;DR: With what values are the I/O port registers (locations $00 and $01) on the 6510 initialised when it is powered on? I'm writing a Commodore 64 emulation. The Commodore 64 uses a 6510 ...
3
votes
2answers
144 views

What 286 chipsets support UMBs?

I read in some forums that some 286 boards support UMBs and thus can load drivers and TSRs into the upper 384 KiB of conventional memory. What chipsets support this and do I need special drivers?
7
votes
1answer
152 views

Connecting Panasonic “Penwriter” RK-P400C to modern PC using USB to serial cable

I have a Panasonic "Penwriter" model RK-P400C electronic typewriter/plotter from circa 1985 I'd like to be able to connect to a modern PC. And hopefully even use to draw graphics! Bought in almost new ...
3
votes
3answers
459 views

Z80 16-bit I/O port addresses

The Z80 indirect I/O instructions are a little quirky: the instructions with the standard mnemonic in r, (c) (where r is a stand-in for any of the normal registers) actually puts the register pair bc ...
4
votes
1answer
438 views

Microsoft Flight Simulator 1.0 “DIVIDE BY ZERO” command

I was reading an Wikipedia article named "History Of Microsoft Flight Simulator" and I noticed something weird about Microsoft Flight Simulator 1.0: November 1982 sometime during 1981-82 ...
-2
votes
2answers
199 views

gcc: installation problem, cannot exec 'as': No such file or directory

How do I compile my code that I have typed on my SGI Indy computer? I have already tried to install the GCC/G++ compilers, but when I run my application, I get the error that says: gcc: ...
5
votes
1answer
150 views

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

The bi-directional 8-bit data bus of the Intel 8080 was split into two unidirectional 8-bit data buses. Later these two 8-bit busses would be combined to support a 16-bit data width for more advanced ...
3
votes
2answers
221 views

Can S-100 cards attach to the ZX machines?

S-100 was, as I understand, a very popular way to connect various computer equipment together in the past. Also, from what I understand, S-100 closely matches the same signals as the Intel 8080, as ...
-2
votes
1answer
113 views

Best IRIX Integrated Development Environment for C++ Programming

I tried to install GCC on Irix, but it did not work. I tried to install Code::Blocks on Irix, and it did not work. The GCC gave me parse errors in iostream.h and streambuf.h, and NetScape does not ...

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