╘HE ├OMMODORE 1541 DISK DRIVE CONTAINS A SMALL COMPUTER, DEDICATED TO DO CERTAIN TASKS. ╘HE DISK DRIVE'S ╥EAD-╧NLY-═EMORY (╥╧═) CONTAINS ABOUT 16000 BYTES, WHILE THE ╥ANDOM-┴CCESS ═EMORY (╥┴═) CONTAINS STORAGE FOR ABOUT 2000 BYTES.
─ISKS CAN CONTAIN PROGRAM FILES (╨╥╟), ╙EQUENTIAL FILES (╙┼╤), ╒SER FILES (╒╙╥) AND ╥ELATIVE FILES (╥┼╠). ┴LSO ╥ANDOM FILES ARE AVAILABLE.
┴LL DISKS CONTAIN A DIRECTORY THAT CAN BE LOADED (LOAD "$",8) AND THEN LISTED, SHOWING THE LENGTH OF EACH ITEM, ITS NAME AND ALSO ITS TYPE. ╘HE MOST OFTEN TYPE USED ARE PROGRAM (╨╥╟) FILES. ╘O READ THEIR CONTENTS SIMPLY LOAD THE PROGRAM AND THEN TYPE LIST OR L╔ (LOWER CASE EL AND UPPER CASE ╔) FOLLOWED BY PRESSING THE ╥┼╘╒╥╬ KEY.
8002 GO╙4000:INPUT" ╞╔╠┼╬┴═┼";F$:IF P T╚ P╥7,F$":"
8010 OPEN8,8,8,"0:"+F$+",S,R
8012 :GET#8,H$:S=ST:IFP T╚ P╥7,H$;
8013 ? H$;:IFS=0 T╚8012
8020 ?:CL╧8:IFPT╚ P╥7
8021 END
║JU1
╘HINK OF THE OLD PHONOGRAPH MUSIC DISKS; THEY HAVE A SINGLE TRACK LIKE A SPIRAL AND THE INFORMATION ON THAT TRACK STARTS ON THE OUTSIDE, WITH THE NEEDLE READING THE MUSIC FROM THERE CONTINUOSLY UNTIL THE END OF THE SPIRAL TRACK IS REACHED NEAR THE CENTRE OF THE DISK.
╘HE DISKS USED BY THE 64 AND ├64 COMPUTERS HAVE NO SPIRAL TRACK, BUT INSTEAD THERE ARE 35 SELECTABLE TRACKS ON CONCENTRIC CIRCLES ON THE DISK. ┼ACH OF THESE TRACKS IS SUBDIVIDED INTO SELECTABLE BLOCKS, ALSO CALLED SECTORS, EACH CARRYING 256 BYTES, WITH THE OUTSIDE TRACKS 1 TO 17 HAVING 21 BLOCKS/SECTORS EACH, TRACKS 18 TO 24 HAVE 19 EACH, 25 TO 30 HAVE 18 EACH, AND THE NEAR-CENTRE TRACKS 31 TO 35 HAVE 17 EACH ON THEM.
╘HE BIG ADVANTAGE OF USING DISKS OVER USING TAPES IS THAT ON DISKS ANY BLOCK/SECTOR ON ANY TRACK CAN BE SELECTED, AND EVEN ANY OF THE 256 BYTES ON ANY BLOCK/SECTOR CAN BE POINTED TO, READ, AND WRITTEN INTO BY THE DISK DRIVE.
╨ROGRAMS (╨╥╟) ARE TAKEN FROM THE DISK BY THE LOAD COMMAND, AND ARE WRITTEN ONTO THE DISK BY THE SAVE COMMAND; LOAD "NAME",8 FOR EXAMPLE WILL TAKE THE PROGRAM CALLED NAME FROM THE DISK AND LOAD IT USUALLY INTO MEMORY STARTING AT 2049, WITH A COMPULSORY ZERO IN 2048.
╘HERE IS AN OPTION TO LOAD THE ╨╥╟ ELSEWHERE BY USING LOAD "NAME",8,1 IF THAT PROGRAM, LOCATED ELSEWHERE IN MEMORY, HAS BEEN SAVED PREVIOUSLY BY THE SAVE "NAME",8,1 COMMAND. ╘HE NUMBER 8 INDICATES A SPECIFIC DISK DRIVE; MORE THAN ONE DISK DRIVES CAN BE IN USE, THEIR DEVICE NUMBERS BEING 8 TO 11.
╘O CHANGE, FOR EXAMPLE, THE DEVICE NUMBER OF A DISK DRIVE FROM THE USUAL 8 TO 9 USE THIS, OR A SIMILAR, PROGRAM:
║JU0
10 OPEN 15,8,15:REM" ╘ELLS DRIVE 8 THAT A CHANGE IS COMING
12 P╥15,"M-W"C╚(119)C╚(0)C╚(2)C╚(9+32)C╚(9+64):REM "─ETAILS OF THE REQUIRED CHANGE.
║JU1
╔NSTEAD OF THIS SOFTWARE CHANGE A HARDWARE CHANGE OF THE DEVICE NUMBER CAN BE MADE TO A DISK DRIVE BY REMOVING ONE OR TWO SPECIFIC LINKS ON THE PRINTED CIRCUIT BOARD INSIDE THE DISK DRIVE.
╘O OPEN A ╙┼╤ FILE FOR READING, OFTEN CONTAINING THE DATA USED BY A ╨╥╟ FILE, USE, FOR EXAMPLE,
OPEN 2,8,2,"0:NAME,S,R"
WHERE THE FIRST 2 IS THE OPTIONAL NUMBER SELECTED BY THE USER, THE 8 IS THE DEVICE NUMBER OF THE DISK DRIVE, THE SECOND 2 IS THE NUMBER OF THE SELECTED BUFFER (A PORTION OF THE MEMORY LOCATED INSIDE THE DISK DRIVE), THE 0 INDICATES THAT MORE THAN TWO BUFFERS CAN BE USED, FOLLOWED BY THE NAME OF THE ╙┼╤ FILE. ╘HE S INDICATES THAT IT IS A ╙┼╤ FILE, AND THE R WILL CAUSE READING FROM THAT FILE. ╔NSTEAD OF THE R, W CAN BE USED IF, INSTEAD OF READING FROM, WRITING INTO THAT ╙┼╤ FILE IS TO BE DONE. ╬OTE THAT EACH DISK CAN BE WRITE-PROTECTED BY COVERING THE SLOT ON THE SIDE OF THE DISK, AND IF A FILE NAME EXISTS ALREADY THERE WILL BE A WARNING MESSAGE, FOLLOWED BY A STOP. ╘HESE CAN BE DISABLED BY USING "@0: INSTEAD OF "0: ABOVE.
╔NSTEAD OF THE S, P WILL REFER TO A ╨╥╟ FILE, OR U TO A ╒SER (╒╙╥) FILE, MAINLY USED FOR MACHINE LANGUAGE.
├LOSING THE FILES IS SIMPLE; CLOSE 2 WILL CLOSE FILE 2. ┴FTER COMPLETION OF A SAVING OPERATION, OR OTHERWISE AFTER COMPLETION OF WRITING INTO A DISK, THE FILE ═╒╙╘ BE CLOSED IMMEDIATELY.
╞OR RANDOM FILES, THE OPEN STATEMENT INCLUDES THE OPTIONAL FILE NUMBER, THE DEVICE NUMBER, THE NUMBER OF THE CHANNEL AND "#" INDICATING TO THE DISK DRIVE THAT ANY BUFFER CAN BE USED BY THE DISK DRIVE. ╞OR EXAMPLE:
OPEN 2,8,2,"#"
╙EVERAL COMMANDS ARE AVAILABLE FOR RANDOM FILES:
╘O READ A BLOCK OF BYTES USE B-R.
╘O WRITE INTO A BLOCK OF BYTES USE B-W.
╘O FIND (ALLOCATE) A STILL FREE BLOCK AND THEN RESERVE IT USE B-A.
╘O FREE (MAKE AVAILABLE) A RESERVED BLOCK FOR A POSSIBLE NEW USE, USE B-F.
╘O GET THE POINTER TO MOVE TO A SPECIFIC BYTE INSIDE A BUFFER USE B-P, SO THAT THIS SPECIFIC BYTE CAN THEN BE EITHER READ FROM, OR WRITTEN INTO.
╘HE USER1 ("U1:"OR"UA:") COMMAND WILL ENABLE THE READING, USING INPUT# OR GET# TO FOLLOW, OF A WHOLE BLOCK, NOT ONLY JUST ONE BYTE AS PER POINTER POSITION.
╘O READ A WHOLE BLOCK FROM A DISK USE:
PRINT#FILE#,"U1:",CHANNEL;DRIVE;TRACK;BLOCK.
╞OR WRITING INTO A WHOLE BLOCK, USING PRINT# TO FOLLOW, USE USER2 ("U2:"OR"UB:") INSTEAD.
