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Comment by distcs | Hacker News Reader

Didn't grow up with Apple 2, sadly! So I have to ask. The text in the OP is hard-wrapped to 40 characters. So did Apple 2 support 40 character width screen?

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Yes, Apple 2 supported only 40 characters natively. You could add an "80 column card" to expand this to 80. This card became standard on the Apple 2e and 2c. Think it was in slot 3 by default. (Feels strange not to write "Apple ][" and "Apple //c" as they were written then!)

Yes, by default the screen width is 40 characters.

Many had an "80 column card" and later versions included it. However, TV screens of the time could not readably display 80 character wide screens.

This is a limitation of the NTSC composite signal. Eighty columns of text will never be readable through a composite connection, no matter how good the monitor is.

Well, that is true for a color signal.

Monochrome monitors take composite and can deliver 600 lines or so,

I think 25 lines of it. The memory layout was not linear but garbled as far as I remember this Woz hack was to do the DRAM refresh as a side effect.

24 lines, for a total of 960 bytes occupying $400 to $7FF. The missing 64 bytes were called "screen holes", peppered throughout that memory range, and were used as scratchpad locations for peripherals. One of those peripherals is the disk drive controller card, and the position of the current track is stored in one of those holes. So if you try to clearing the screen the easy way, by zeroing $400 to $7FF, the disk drive forgets what track it's on and it needs to recalibrate, resulting in an awful noise as the read-write head bangs on a stopper.

I remember modifying that routine into banging the head at different frequencies. You could get into musical note range and turn it into a little organ.

Good point. I forgot about these scratchpad locations. One of my first assembly programs was a reverse scroll functions. Depending on the paddle controller it shifted also one char left/right. Two char spaced apart on each line served boundaries for a street and the car was two stationary char in the middle (depending on the paddle controller pointing left, ahead or right). Due to lack of assembler the whole was hand coded. Due to limited access to the computer it was all written out on paper first.

Also, no lower case. ¹

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