allan@kpno.UUCP (04/18/84)
SPEED UP YOUR 1541 A recent query on the net about why the 1541 disk drive is so slow got me experimenting. It seems that the disk drive itself is not the culprit at all, but it is the C64 which is slow. I think that the problem is that the video chip in the C64 is so 'clever' that it steals a good fraction of the processor time to display the screen. The timing is so tight that the screen has to be blanked when reading a tape so that the video chip does not steal too much time from the 6510. The VIC20 has a less sophisticated video chip and can accept disk transfer at a somewhat faster rate, and it is possible to speed up the 1541 when using it with a VIC20. This lead me to try the following. My commands are in capitals, the computer's replies are in lower case. POKE 53285,PEEK(53265)-16 : OPEN 15,8,15 : PRINT#15,"UI-" ready. LOAD"FILENAME",8 searching for filename loading filename ready. POKE 53285,PEEK(53265)+16 : OPEN 15,8,15 : PRINT#15,"UI+" ready. The first line turns off the screen and tells the disk that it is taking to a VIC20, i.e. send the data faster. The file is the loaded as usual. Then turn the screen back on and return the disk to normal. This resulted in a decrease in the load time of 25% (30 sec instead of 40sec). It is definitely necessary to turn the screen off as I tried it without changing the screen, and it hung the computer. If you want to try this, it is easiest to type all three lines on the screen in the correct places as otherwise the last two lines must be typed blind. It is only worth doing this for long loads as it takes more than 10 sec to type the lines that speed up the disk. Peter Allan Kitt Peak National Observatory Tucson Az