Hot answers tagged

38

The reason was cost, since neither the original PET nor the TRS-80 required the extra high resolution and finer dot pitch found in more expensive computer monitors. Virtually all of the computer terminals of the time paired a CRTC with a high-resolution green or amber screen to generate an 80x24 text display, as that was the early standard. This required a ...


31

CRT TVs are analog devices, there is no "pixel", but the size of the spot limits the resolution of the image, as the size of silver nitrate crystals limits the resolution of photo films. Several arrangements of the colour stripes on the CRT tubes have been designed, they are a compromise between resolution, luminosity and the precise alignment of the ...


27

I understand that either nonelectromechanical computing devices (analog) or electromechanical computing devices (digital) were ever developed by humans. That distinction is a bit off, mixing unrelated categorisation. Analogue computers can be as well mechanical, as electromechanical as well as electronic (or pneumatic or hydoponic) - similar digital ...


25

The answer, as always, was cost. 'White' CRTs were cheaper because they were used in B/W TV sets. The color itself has no impact on resolution, but TV tubes didn't need to be as sharp so they could be made cheaper. So why were 'high resolution' monitors green or amber? Because these phosphors have a longer persistence so the image doesn't flicker as much, ...


17

Switches and lights. Here's the panel for an IBM 650: The top row of dials are used to configure in decimal values (the IBM 650 being a decimal machine). The repeated columns of 5 lights with 2 on top indicate 1 of 10 values for each digit of the 10 digit word the IBM 650 used. The lights below that row indicate operation and address. The other dials ...


14

One simple answer is to copy the screen to a buffer elsewhere in memory and save it from there. 10 CLEAR 58455 ... generate the screen image here ... 900 FOR n=0 TO 6911 910 POKE 58456+n, PEEK (16384+n) 920 NEXT n 930 SAVE "image" CODE 58456,6912 It's also possible to disable the prompt immediately before the SAVE, by changing the input / output functions ...


11

According to this answer to a question about the early use of green monitors they had a severe disadvantage in that you had to choose between 'too dim' and 'rapid burn-in' whereas amber could display decent brightness without burn-in. It's be rather careful in accepting the conclusions made there. I can show you several green screens that have been used ...


11

With all these 'or' in between and jumping between various points, requirements and conclusions, it's a bit unclear what your're looking for. If this is about most colour with least memory, then the (unofficial) modes Mode 8 and Mode 13 are your thing. Or was it a limitation of bandwidth with the 6845 chip that couldn't handle both 320 horizontal pixels ...


10

From the point-of-view of someone at the time, you interacted with early computers in the usual way. From the 1930's onwards, business and some science used IBM and Remmington-Rand mechanical punched-card processing machines. You set up the specialized gear-based machines for your job (payroll, overdue accounts, super-hard math equation), punched data onto ...


10

The very short answer is no, because no “green screen” standard is compatible with VGA (which is where 640×480 was introduced). The slightly longer answer is yes, but only in a very small number of situations. The important aspect here is the signal sent from whatever system is driving the display, to the display. Early display adapters (apart from those ...


6

A few points to expand on previous answers: In those days, resolution wasn't limited by phosphor, but by video bandwidth (and video memory). A standard TV had a bandwidth around 2-3 MHz, enough to support a PET or APPLE ][ - style 40x24 text display, or about 320x240 dots. The TRS-80 Model I monitor had slight modifications to the video circuitry to ...


5

Besides TEMLIB's excellent answer relating to the physical characteristics of the TV, it's also worth pointing out the effects of the video input itself as well. For analogue video input, the picture is encoded as a continuously varying value, in the form of a wave. The higher the horizontal resolution you want, the more detailed the variations in this ...


5

There have been many different kinds of I/O devices since the early years: Indicator lights (often coloquially referred to as "blinkenlights") Front panel toggle switches and pushbuttons Punched tape Punched cards Teleprinter There is some more history available at the Computer terminal Wikipedia page.


4

The Harwell Dekatron is an excellent example of this type of machine, not least because it was designed for simplicity and reliability rather than speed, and this in turn makes it easy to understand. This is a machine that operated entirely on decimal numbers, not on text. It has a few buttons on its control panel, which are essentially used to start, stop ...


4

When your memory device is literally "a screen", you can just look and see what is held in memory. (I think, but can't find a reference right now, that actually the display tube was a mirror of the actual storage tube - since the storage tube would have had a metal plate in front of it). The video in the second link is worth watching to get a glimpse of ...


3

The first computer I built was a COSMAC ELF. It didn't have a keyboard or a monitor, no CLIUI/TUI/GUI. It was a full-fledged digital electronic computer. It had 8 toggle switches and a pushbutton for input and a dual 7-segment LED display for output.


3

As has been noted in comments, you have probably damaged your ZX Spectrum+'s hardware by reversing the polarity of the power supply. In mcleod_ideafix's answer to the relevant question this is explained in more detail: You have damaged your Spectrum for sure. [...] [The 7805 regulator] is designed to survive overvoltage and short circuit conditions, but ...


3

According to the Service Manual, first check if you're not using any power saving mode, as they limit brightness. Next check all cables, and if that won't work, replace the display (where the lighting tubes are included). Chances are good that the CCFL-tubes are just worn out. So unless you intend to do some real low level work, you need to live with what's ...


3

They could be interchanged if you define "some effort" as "a lot of effort". The problem isn't so much the CRT tubes themselves, or the choice of 'color' or 'monochrome', but rather the circuitry that drives the electron beam deflection electromagnets, and the power supplies needed to drive those circuits. These circuits are built to sweep the electron gun ...


3

The biggest single problem with long-persistence green monitors is that they were extremely vulnerable to burn-in unless you kept the intensity relatively dim. Amber monitors were usually a lot brighter. Computers like the TRS-80 Model I and Commodore PET didn't use long-persistence grayscale... they used picture tubes literally manufactured for use in ...


2

Early research found that green or amber was easiest on the eyes of people looking at CRT monitors all day. Actually, I preferred amber, myself.


2

Probably an issue with aging capacitors on the display driver board. These become defective over time and need to be replaced. Here's a repair video.


2

It can be done, but in addition to connectors, there are three signal issues. First, the refresh rate can be inflexible (and if it's different, there may be inadequate adjustment capability). Second, the horizontal and vertical synchronization signals may be of different types (polarity, duty cycle). Third, the video voltage levels and drive impedance ...


2

Before terminals, the most common method of interacting with large electronic tabulators, calculators, and computers (IBM mainframe, et.al.) was via punched cards for input, and line printer output for output. Some minicomputers used punched paper tape instead of punched cards. The first terminals were mechanical teletypes (ASR-33, et.al.), with a keyboard ...


2

According to the CPC schematic, the Armstrad uses a gate array to generate video, so we'd need to know how this gate array is programmed for an exact explanation. But expanding on the comment of supercat, we can do an educated guess: Assume we have an 8 bit shift register in the gate array, with a tap for bit C0 at the end, a tap for bit C1 in the middle, ...


1

I am not an expert in Amstrad CPC at all, however I can see some regularities, for example: Not grouping pixel bits in halves (like pixel 0 takes bits 7..4 and pixel 1 takes bits 3..0) allows one to use single shift register, that always shifts by 1 bit. In mode 2, it shifts 8 times for 8 pixels, in mode 1 it shifts 4 times for 4 pixels, where one pixel is ...


Only top voted, non community-wiki answers of a minimum length are eligible