dirkt
  • Member for 5 years, 9 months
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Why not use fractions instead of floating point?
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102 votes

When adding or subtracting fractions, you need to find the least common multiple of the two denominators. That's an expensive operation, much more expensive than adding or subtracting floating points, ...

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Why is EEPROM called ROM if it can be written to?
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97 votes

Look at the development: ROM = read-only memory = can only be read when on the board, programmed in the chip factory. PROM = programmable read-only memory = can be programmed with a special programmer,...

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Why did 1950s-60s computers have such wide words?
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75 votes

And if you go back further, e.g. to the ENIAC, you'll see a word size of 40 bits. And if you go back even further, to mechanical calculators, you'll see word sizes determined by the number of decimal ...

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Why did the PDP-11 include a JMP instruction?
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48 votes

Besides the flags, and differences in cycle count, the more important difference is that JMP x uses the effective address of x, while MOV x,R7 uses the value at x. In other words, there's one level ...

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What did the "programs" that "human computers" executed look like?
38 votes

Partial answer: This article describes one flavour in more detail: While the specific tasks a computer did varied according to need and her department, the majority of computing work involved three ...

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Is there still no "digital version of PCBs and ICs" software that all future emulators can use?
33 votes

It is feasible, but not in software, because software is not fast enough. But indeed, it would basically let "anyone" build machines by picking out digital versions of components which ...

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What "unusual" syntax assembly languages are/were there?
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28 votes

Example 1 The PDP-8 had only 8 kinds of instructions, but one of them was "microcoded" operate command: Different bits in this command would turn on different operations, which could be combined. ...

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68000 and memory access speed
28 votes

If you look at the datasheet of a typical DRAM chip of this era, say the Mostek 4116, it indeed has a cycle time of 375ns, so you can't access it at more than 2.6 MHz. But don't confuse the clock ...

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Could you manually eject a floppy quick enough to prevent data loss?
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26 votes

I did that all the time on the Apple II. The reason it worked was that some time was needed for the motor to spin up to the correct speed, and that the Disk II didn't really have an "eject" mechanism, ...

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Purpose of two disk drives on the Osborne 1
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26 votes

Remember that these systems (not only the Osborne 1) didn't have harddisks. Everything ran from floppies. So usually you had one floppy where the program was on, together with OS related files. And ...

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Executable ASCII files before x86?
25 votes

If you go back a lot before the x86, this technique wasn't unusual at all. In fact, writing programs using printable letters and symbols was pretty much the norm for early computers, except that there ...

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

On early IBM PCs, all devices were conntected to the ISA Bus. You can read about how the bus worked in detail here, including timing diagrams. Basically, all devices were just wired together. Some ...

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Size of the PDP-8
22 votes

There were different models of the PDP-8, but most models (say, PDP-8/E) consisted of a number of rackmounted boxes, one of which you could call the CPU (or, compared to a modern PC, maybe the ...

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How did Apple II BASIC programs protect against listing?
21 votes

If I recall correctly, there were lots of variations to implement this scheme. Besides embedding characters in the listing that would reboot, or clear the screen every so often, a particular one I ...

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6510 clock rate of C64: Why was it considerably slower than the 6502 of the Atari 800?
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20 votes

Somewhat of a guess:  The C64 always interleaved CPU and graphics RAM access (with additional graphics cycles if necessary), effectively accessing RAM at 2 MHz. Judging from the ANTIC Timing ...

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How were files transferred between different systems in the late 1980s?
17 votes

No, there were no adapters for different floppies. Data was typically copied by serial port, if it was copied at all: Programs on some 8-bit computer (e.g. Apple II, Commodore 64) wouldn't run on an ...

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Did personal computers ever support 8" floppies?
16 votes

The Olivetti P6060 had 8" floppy drives (two of them). About the size of a typewriter, and ran BASIC, so IMHO it qualifies as "Personal Computer". The Wikipedia page even describes it ...

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Did the transmeta processor architecture work by binary translation?
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16 votes

In the Wikipedia article on Transmeta there's a good example for the Code Morphing process, taken from a PDF document (Wayback archived) with even more details: The operation of Transmeta's code ...

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6502 branch offset calculation
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16 votes

Quick shot, without looking it up in Visual 6502 (which would be the authorative option): Sign extend the branch offset (replicate MSB of offset), that will tell you the ALU input for the PC high ...

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Why were the SC/MP pointers 12-bit (kinda)?
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16 votes

The SC/MP seems to have been designed right from the start with a 12 bit address bus and 4 additional "page" bits. To quote from p. 1-4 of the SC/MP Technical Description: The SC/MP chip has a 16-...

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What makes slot 7 of the Apple ][ unique from 1-6 and how was this used?
16 votes

Yes, slot 7 is unique electrically. Pin 19 (SYNC) and pin 35 (COLOR REF) are only connected for slot 7. These signals where needed by the PAL encoder card, which is why this card only worked in slot 7....

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How does the Commodore 64 address more than 64 kilobytes of memory?
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16 votes

The 6510 CPU used in the Commodore 64 has an additional built-in general purpose I/O port compared to the original 6502 CPU. Address $0000 controls the direction for each of the bits of this I/O port, ...

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Hardware assisted Graphical User Interface?
15 votes

Silicon Graphics started to provide dedicated graphics terminals and workstations in the 80s. So the technology was definitely there, even for 3D. In 1991, they put this technology on a PC expansion ...

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How did the Commodore PET 80 column display work?
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15 votes

As Tommy wrote in the comment: There are two different RAM chips, one for even columns and one for odd columns. Both are read and latched in one cycle (ESD and OSD bus), and the latched output of each ...

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Conditional skip instructions of the PDP-8
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15 votes

If you compare the octal opcodes for the skip instructions, a bcd | ||| 7500 SMA = 111 101 000 000 7440 SZA = 111 100 100 000 7420 SNL = 111 100 010 000 ...

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Is this a bug or an allowed Pascal behavior?
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14 votes

The ISO 7185 Pascal standard, section 6.4.3.5 "File-types", says (my emphasis): There shall be a file-type that is denoted by the required structured-type-identifier text. The structure of ...

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How did the Nova 1200 divide so quickly?
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14 votes

Not a complete answer, but a bit of information from the manual (for several Novas including the 1200): The hardware multiply-divide option for the Nova is actually a peripheral device connected to ...

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Was Apple DOS 3.3 created because of the Apple III?
14 votes

No, conversion to 16-sector format (and the necessary change from DOS 3.2 to DOS 3.3) was a consequence of Steven Wozniak realizing that he could get more capacity by tweaking the Apple II floppy ...

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How are 6502 and 65C02 JMP(abs) processed internally
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14 votes

I can't answer the question "why doesn't the 6502/65C02 use the PC to do the indirection to execute JMP (abs)", but I can answer some of the other points. Visual6502 is the best site to find out ...

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Bootable floppies lock up with floppy drive connected via USB adapter
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14 votes

In the first phase of the boot process, the BIOS loads the first sector of the disk into memory and executes it. The code in this sector then uses the BIOS to load the code for the second phase, which ...

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