Graphics capability in the original IBM-PC

[tezza]

The ongoing discussion on use of EGA in an XT got me thinking.

The original IBM-PC came out with a crisp text-only MGA card or owners could adopt to use a CGA card. I never used a CGA card at the time, but instead went from MGA to Hercules, then EGA to VGA as I went up through machines.

I now own a CGA card and it’s…well…terrible. Especially text, which is low-res and the flicker (snow?) that occasionally appears.

I would have thought very sharp text AND visual representation of data (graphs, charts etc) was important in business communication even back then, so I’m surprised IBM didn’t release a better text/graphics card when they released the PC, something similar to the Hercules card for example. Why didn’t they make a mono but graphics capable card the default rather than the MGA. The technology was there at the time, wasn’t it?

Or was it that the competition was mainly text-only CP/M machines so no graphics was regarded as “standard” for business?

At the time (1981) Pet’s, Apples, most TRS-80s and several other Japanese machines came standard with some graphics capability. Maybe these were considered to be more hobbyist than serious business machines though, and even monochrome graphics were considered a frill?

Any comments?

Tez

 

[Anonymous Coward]

Yes, CGA is truly a terrible standard. I guess another valid question would be why IBM didn't put more effort into the design of the CGA card. Adding, or in the very least providing some kind of provision to upgrade to 32kb of display memory would have at least made the card somewhat usable (320x200x16 graphics). As it is, the CGA fails in both departments; producing legible text, and displaying "colour" graphics. Four colour graphics?! It's not even worth having colour with those kinds of limitations. I'd take Hercules over CGA any day.

 

[offensive_Jerk]

Is hercules a completely different graphics standard?

 

[Fallo]

Yes, CGA is truly a terrible standard. I guess another valid question would be why IBM didn't put more effort into the design of the CGA card. Adding, or in the very least providing some kind of provision to upgrade to 32kb of display memory would have at least made the card somewhat usable (320x200x16 graphics). As it is, the CGA fails in both departments; producing legible text, and displaying "colour" graphics. Four colour graphics?! It's not even worth having colour with those kinds of limitations. I'd take Hercules over CGA any day.

The PCjr/Tandy graphics represent what CGA should have been from the beginning, but IBM only had a year of development time. At the very least, they should have included palette registers so that you could select your four colors freely rather than have two fixed palettes.

But then again, how attractive was Hercules? Depending on your monitor, graphics were either Sassy Grass Green or Twister Orange (actually the names of Plymouth Duster color schemes from the early '70s, but a close enough description of most monochrome monitors).

CGA's low resolution isn't really anything to complain about, as high-resolution color was very expensive in 1981 and because it also had to be compatible with TVs. Basically, CGA was designed to be like a typical home-computer display of that era, and MDA was intended to be like the displays found on most CP/M boxes.

Is hercules a completely different graphics standard?

Hercules is just MDA with a graphics mode added. The resolution is the same.

 

[Chuck(G)]

If you've got the original 5150 Tech Ref manual, take a look at the MDA schematic (or better yet, the card). There's a lot of stuff there that goes nowhere. My guess is that IBM originally planned to add graphics to the MDA, but ran out of time--the design is unnecessarily complicated otherwise and there are a couple of traces that just dead-end.

I really liked the Herc Plus card, with downloadable fonts and 12-bit character codes. You could do some pretty cool things with it.

 

[tezza]

Hercules is just MDA with a graphics mode added. The resolution is the same.

Indeed, but my question is given that even mono graphics are useful in a business setting (as opposed to no graphics) why not incorporate mono graphics into the MDA standard in the first place? Sharp text AND graphics.

There certainly was a market need. I'm not sure about other countries, but the Hercules graphics card was enormously popular here in NZ, for PCs, XTs and clones until EGA came along. It filled a glaring gap and I'd like to bet most mono machines sold had a herc card as soon as the latter became available. Many business users who wanted graphics couldn't afforded to pay for a colour screen and even if they could, they then would have to suffer with lousy text resolution.

As I say, I'm surprised mono graphics wasn't put into MDA in the first instance. This omission was a boon to the company that manufactured the hercules card though.

Tez

 

[mbbrutman]

I think you need to put things into context.

The original PC 5150 had 16K of memory, with up to 64K on the motherboard. 640K would be a maximum, if the first BIOS didn't have a bug that limit it to 544KB. Competing machines at the time had 16 to 48K. Even a 128KB PC would be luxurious.

The monochrome card requires exact 4KB of RAM. (4000 to be exact.) The character bitmaps come from an onboard ROM. It has no pixel addressability.

The CGA card requires 4x more RAM and far more circuitry. Even though the text is attrocious by other standards, at the time a CGA card driving a high quality RGB monitor was beautiful compared to other machines, which were usually driving some sort of screwed over television arrangement. The monitor was more expensive, and I'm sure the card was too. These were the kind of choices one had to make.

If you really needed both, you could have both ..

I had a compromise on my PCjr. It was a CGA only machine - the monochrome adapter was not an option. And the color monitors were far more expensive. I wound up with a composite monochrome monitor (Amdek 300A) that was sharp enough to use with text because there was only one gun, but could still give me shades of amber for color. This was a reasonable middle choice that people could also make.


Mike

 

[Chuck(G)]

Mike consider that the Apple II had graphics--and I suspect that IBM considered that one of the prime competitors.

The funny thing about the MDA is that IBM didn't even try to put any sort of graphics capability on it--not even "character graphics(i.e. 6-block/char)" as one might find on many earlier terminals and personal computers.

It's a real puzzle.

 

[Great Hierophant]

Mike consider that the Apple II had graphics--and I suspect that IBM considered that one of the prime competitors.

The funny thing about the MDA is that IBM didn't even try to put any sort of graphics capability on it--not even "character graphics(i.e. 6-block/char)" as one might find on many earlier terminals and personal computers.

It's a real puzzle.

I would suggest that IBM had some concerns that prevented this:

The MDA was a full-length board that also had to contain the logic for the printer adapter; the Hercules used some custom logic to get APA capability.
The CGA could give character graphics in color (or black and white with a monochrome composite monitor) and can work in tandem with the MDA card.
IBM used the same character ROM chip on the MDA and CGA.
Businesses which needed both would have found the $$ in their budgets to pay for it.

 

[Chuck(G)]

I don't know. CGA characters are pretty awful, even on a monochrome monitor (IBM never offered one for the CGA).

The printer port on the MDA is what, 4 ICs? And the MDA was far from a "tight" implementation; I was stunned to see how many chips were on it. Clones certainly did the same thing with less. My impression of the MDA was that either a lot of thought hadn't gone into it or it was an incomplete design.

When I bought my 64K 5150, I bought it with MDA because I couldn't stand the look of the CGA text. I couldn't imagine working 8-10 hours a day staring at that.

Of course, early on, if IBM had envisioned the 5150 as some sort of family/educational system like the Apple II (or at least the marketing types did), it might be that more work wasn't done on the MDA because the sales people couldn't imagine anyone wanting to use text-only monochrome graphics.

 

[Fallo]

There certainly was a market need. I'm not sure about other countries, but the Hercules graphics card was enormously popular here in NZ, for PCs, XTs and clones until EGA came along. It filled a glaring gap and I'd like to bet most mono machines sold had a herc card as soon as the latter became available. Many business users who wanted graphics couldn't afforded to pay for a colour screen and even if they could, they then would have to suffer with lousy text resolution.

Hercules was plenty popular in the US, in part because of Lotus 123. Most all monochrome cards made were clones of the Hercules and not the MDA.

Even though the text is attrocious by other standards, at the time a CGA card driving a high quality RGB monitor was beautiful compared to other machines, which were usually driving some sort of screwed over television arrangement. The monitor was more expensive, and I'm sure the card was too. These were the kind of choices one had to make.

Color 80-column text and RGB output were certainly rare and exotic features in 1981, as most computers either just connected to a TV or used MDA-style monochrome text.

Mike consider that the Apple II had graphics--and I suspect that IBM considered that one of the prime competitors.

Note also that CGA graphics, at least with the composite output, are not unlike those of the Apple II.

The funny thing about the MDA is that IBM didn't even try to put any sort of graphics capability on it--not even "character graphics(i.e. 6-block/char)" as one might find on many earlier terminals and personal computers.

As I said, IBM had only a year of development time. Monochrome text and a printer port can't possibly need a huge full-length card, which gives support to the idea that they originally planned a combo color/monochrome card.

CGA also looks strangely incomplete. At the very least, it should have had a 160x200x16 mode (composite mode doesn't count) or palette registers.

When I bought my 64K 5150, I bought it with MDA because I couldn't stand the look of the CGA text. I couldn't imagine working 8-10 hours a day staring at that.

That's nothing. Try CGA 80-column text on a TV and I guarantee you'll go blind in about five minutes.

 

[modem7]

The original PC 5150 had 16K of memory, with up to 64K on the motherboard. 640K would be a maximum, if the first BIOS didn't have a bug that limit it to 544KB. Competing machines at the time had 16 to 48K. Even a 128KB PC would be luxurious.

"if the first BIOS didn't have a bug that limit it to 544KB" should be "if the first BIOS didn't purposely limit it to 544KB".

The limitation is because, by design, the first and second BIOS only reads the first 4 switches of switch bank 2. But that 'by design' decision of IBM's reinforces Mike's point. And to further reinforce Mike's point, a look at the first 5150 Technical Reference reveals that IBM considered at the time that 256KB was maximum: the switch setting page shows settings only up to 256KB and the memory map list RAM past the 256KB point as 'future expansion'.

 

[Marrr]

But then again, how attractive was Hercules?

I would say it was very attractive, with extremely good price/performance ratio. It had good text mode, high-res graphics, printer port, and connected to a cheap mono monitor. All that in the era when color monitors were for many just too expensive, also, who needed color in typical office applications before color printers became popular?
So, no wonder that...

I'm not sure about other countries, but the Hercules graphics card was enormously popular here in NZ, for PCs, XTs and clones until EGA came along.

...here in Poland HGC cards (well, usually clones, eg. based on some Winbond chip) were popular even longer - they definitely outlived EGA.
I remember various price lists from 1993, which listed five video options: Hercules, VGA mono, VGA color, SVGA mono, SVGA color.

So yes, lack of mono graphics option back in 1981 was IBM's mistake.
Oh well, that's the best thing about the open architecture of PC: what IBM screwed up, others corrected...

 

[Andrettigto]

I found back then that CGA text on a good quality RGB monitor was beautiful to work with. And you could change the text color too! The average systems out there were still using composite monitors.

Sure, MDA characters looked better formed on the L-O-N-G persistence monochrome monitor. At the time there was no Hercules option and APA graphics was a powerful lure for most buyers. With 640 x 200 resolution you could finally generate some decent graphics. Not many went for two display cards and monitors!

I recently got a Compaq portable 1 with the monochrome amber display and after getting it working, I notice the CGA characters are much smoother. I thinks it's because of the monitors persistence but it really streaks badly.

I wonder if that's why so many unlucky souls cooked there MGA monitors plugging them into CGA cards?

 

[Chuck(G)]

Sure, MDA characters looked better formed on the L-O-N-G persistence monochrome monitor.

The persistence had nothing to do with it, though IBM did use a long-decay phosphor on the 5151. I used various monitors, from a short-decay white, a medium amber to a l-o-o-o-n-g-tailed green. Given that the monochrome characters were formed as 7x9 characters in a 9x14 box, as compared to the CGA's 5x7 in an 8x8 box, they were better-formed, had clear descenders and much easier on the eyes.

Using a CGA on a really good monitor was worse than using a mediocre one. On a Sony CPD1302 0.26mm resolution monitor, I could easily make out the dots in CGA characters.

 

[Unknown_K]

The persistence had nothing to do with it, though IBM did use a long-decay phosphor on the 5151. I used various monitors, from a short-decay white, a medium amber to a l-o-o-o-n-g-tailed green. Given that the monochrome characters were formed as 7x9 characters in a 9x14 box, as compared to the CGA's 5x7 in an 8x8 box, they were better-formed, had clear descenders and much easier on the eyes.

Using a CGA on a really good monitor was worse than using a mediocre one. On a Sony CPD1302 0.26mm resolution monitor, I could easily make out the dots in CGA characters.

You should be able to make out the dots better on the cheaper units because they had worse dot pitch (maybe a little fuzzier). One thing I hated about the VGA monitor I had with my Packard Bell 286 was the .49 or.5x (forget which) dot pitch. I also visited a friend in the 90's at his work and he had a huge 21" monitor on his DOS CAD machine running at 640x480 and you could play connect the dots on that setup.

 

[mbbrutman]

The persistence had nothing to do with it, though IBM did use a long-decay phosphor on the 5151.

The persistence of the phosphor does matter - it reduces the perceived flicker. Not only are the character boxes more detailed, but the painted characters are less prone to flickering because of the phosphor. (The attribute 'stable' has nothing to do with the size of the character boxes.)



Mike

 

[Chuck(G)]

The persistence of the phosphor does matter - it reduces the perceived flicker. Not only are the character boxes more detailed, but the painted characters are less prone to flickering because of the phosphor. (The attribute 'stable' has nothing to do with the size of the character boxes.)

Yes Mike, but the field rate is the same for both MDA and CGA, so I don't see the line of reasoning that says that it was the long persistence phosphor that was the monochrome display's key advantage. 60Hz is pretty much well inside the human persistence of vision, anyway.

One could, of course, run the MDA (and the CGA) in interlaced mode and the long-persistence phosphor would come in handy, but interlaced displays have their own problems (e.g. "fuzzy" appearance).

 

[Anonymous Coward]

http://en.wikipedia.org/wiki/Flicker_(screen)

"if a CRT computer monitor's vertical refresh rate is set to 60 Hz, most monitors will produce a visible "flickering" effect, unless they use phosphor with long afterglow. Most people find that refresh rates of 70-90 Hz and above enable flicker-free viewing on CRTs. Use of refresh rates above 120 Hz is uncommon, as they provide little noticeable flicker reduction and limit available resolution."

 

[Chuck(G)]

"if a CRT computer monitor's vertical refresh rate is set to 60 Hz, most monitors will produce a visible "flickering" effect, unless they use phosphor with long afterglow. Most people find that refresh rates of 70-90 Hz and above enable flicker-free viewing on CRTs. Use of refresh rates above 120 Hz is uncommon, as they provide little noticeable flicker reduction and limit available resolution."

Isn't that rather subjective? What's the persistence of a monochrome TV display? ISTR that it's pretty short; certainly nothing like the 5151 long green display. Yet the field rate on an NTSC TV is 60Hz; isn't PAL something like 50Hz?