1541 mode versus 1571 mode, 40 column versus 80 column

[videohobbieperson]

Various Commodore subjects 1541 mode versus 1571 mode, 40 column versus 80, etcetera

I have a Commodore 1571 disk drive which has both 1541 mode and 1571 mode. Is 1541 mode compatible only with Commodore 64 software?
'
Is 1571 mode compatible only with Commodore 128 software not designed for usw in 64 mode?

Please explain the differences between 1541 mode and 1571 mode, okay?

I read that 64 software will only work in the 40 column mode
however what meant by 40 and 80 column modes on the Commodore model C128 computer?

Do the column refer to how an image is displayed on the screen and if yes please give more detail, okay?

Do the column have to do with resolution quality?

 

[videohobbieperson]

Reply about 1541 and 1571 modes to me

Reply about 1541 and 1571 modes to me

I would like to make sure I have information from you correct.
On the Commodore 1571 disk drive in 1571 mode if working correctly it
will read disks recorded in both 1571 and 1541 modes unless perhaps
the disk is copy guarded and was recorded on a 1541 disk drive you may
not be able to read it on a 1571 disk drive, correct?.

Is it correct that If you record onto a disk in 1571 mode it will not
work on a 1541 disk drive?

Will the 1571 drive read 1541 and 1571 modes in both 64 and 128
modes or in which all modes for the C128 computer will it read
except for the above exception of copy guarded disks sometimes?

How does one determine if there 1571 disk drive is in 1541 mode or
1571 mode when used on a Commodore C128 computer and how does one put
the 1571 in 1571 mode on a C128 and hew does one switch back to 1541
mode?

When a properly working and properly used 1571 drive is used in 1571
mode it will automacticly read both 1541 and 1571 disks that are
written on and working correctly though will not automaticly record in
1541 mode, correct?

Disks recorded in 1541 mode are not compatib;le with Commodore 8050 and 8250 model disk drives.

 

[carlsson]

1541: Single sided floppy drive. It means it only has one read/write head. In order to use both sides of a floppy disk, you need to cut another write unprotect hole in the side and flip it over.

1571: Double sided floppy drive, i.e. one head on each side. In 1571 mode it automatically can read both sides. When connected to a C64, I believe it defaults to single sided 1541 mode. By sending a command to the drive, it can be toggled over to 1571 mode even when used with a C64:

Switch to double sided (1571) mode:
OPEN 1,8,15,"U0>M1":CLOSE 1

Switch to single sided (1541) mode:
OPEN 1,8,15,"U0>M0":CLOSE 1

It should be noted that a 1541 floppy disk which has been flipped over will not be readable as a double sided 1571 disk. You still need to flip it over to get the back side in 1541 mode. This is due to several factors, the most important one is that when you manually flip a disk, it will rotate backwards relative to the top side. A floppy drive that accesses both sides at the same time will rotate the disk in the same direction on both sides.

I don't know if there is a way to determine the current mode of operation, probably you can read some byte in the internal RAM of the floppy drive but that is a far too advanced topic unless you have a practical example of when you need to know. By using the commands above, you can set the drive in either mode and will be sure which mode it runs in anyway.

Also, you're perfectly correct that 1541 floppy disks are not compatible with the IEEE drives 8050, 8250 or SFD-1001. However 1541 is mostly read compatible with IEEE drives 2031, 2040, 3040, 4040 as well as 3rd party drives of course, of which there were a ton of makes and models.

 

[carlsson]

what meant by 40 and 80 column modes on the Commodore model C128 computer?

Earlier I described the C128 has two different video chips:

VIC-II produces 40 column colour graphics, same chip as in a C64. It outputs composite and S-Video through the round DIN connector.
VDC produces 80 column colour text/graphics, specific for the C128. It outputs monochrome and RGBI through the DB9 connector.

The 80 column display has a higher resolution and can do some high resolution graphics. However Commodore sacrificed sprites so the chip is best used for graphic adventures and business software. In order to use it, you need a monitor which has a RGBI input. This is what we discussed about your 1902A monitor, that it appears to have a RGBI input so you can use it in 80 column mode.

Technically, a C128 in C64 mode could address the VDC too but as mentioned by someone else, there was little point for programmers to make 80 column software which only could run on a C128 in C64 mode, when it just as well could be made to run on a C128 in C128 mode.

 

[Dave Farquhar]

I don't know of a way to sense whether a 1571 is operating in 1541 or 1571 mode. The easiest way was just to see how it responds to an empty 1571-formatted disk. If the disk shows 1328 blocks free, it's in 1571 mode. If it shows 664 blocks free, it's 1541 mode. And if you're not sure what mode it's in, just change it to the mode you want it in, and then you're sure.

But I really think you're getting hung up on details. Use the machine and enjoy it. You'll learn how it works along the way. You're not going to break anything by the drive being in the wrong mode when you try to use a disk.