Most computers have an operating system. An operating system is a piece of software that manages hardware, software resources and provides services for programs.
You may have wondered if it is possible to have an operating system with this 8-bit computer! The answer is yes.
Commodore used an operating system (OS) called Kernal. Kernal is a low-level OS, containing a set of low-level hardware interfaces. KERNAL consists of 39 functions. These functions form the basis for higher-level routines in BASIC (such as LOAD, SAVE, INPUT and PRINT). The KERNAL functions are accessible via a jump-table, at the end of addressable memory ($FF81 – $FFF3). KERNAL occupied the last 8KB of address space ($E000 – $FFFF).
| ACPTR | $FFA5 | 65445 | Input byte from serial port |
| CHKIN | $FFC6 | 65478 | Open channel for input |
| CHKOUT | $FFC9 | 65481 | Open a channel for output |
| CHRIN | $FFCF | 65487 | Get a character from the input channel |
| CHROUT | $FFD2 | 65490 | Output a character |
| CIOUT | $FFA8 | 65448 | Transmit a byte over the serial bus |
| CINT | $FF81 | 65409 | Initialize the screen editor and VIC-II Chip |
| CLALL | $FFE7 | 65511 | Close all open files |
| CLOSE | $FFC3 | 65475 | Close a logical file |
| CLRCHN | $FFCC | 65484 | Clear all I/O channels |
| GETIN | $FFE4 | 65508 | Get a character |
| IOBASE | $FFF3 | 65523 | Define I/O memory page |
| IOINIT | $FF84 | 65412 | Initialize I/O devices |
| LISTEN | $FFB1 | 65457 | Command a device on the serial bus to listen |
| LOAD | $FFD5 | 65493 | Load RAM from device |
| MEMBOT | $FF9C | 65436 | Set bottom of memory |
| MEMTOP | $FF99 | 65433 | Set the top of RAM |
| OPEN | $FFC0 | 65472 | Open a logical file |
| PLOT | $FFF0 | 65520 | Set or retrieve cursor location |
| RAMTAS | $FF87 | 65415 | Perform RAM test |
| RDTIM | $FFDE | 65502 | Read system clock |
| READST | $FFB7 | 65463 | Read status word |
| RESTOR | $FF8A | 65418 | Set the top of RAM |
| SAVE | $FFD8 | 65496 | Save memory to a device |
| SCNKEY | $FF9F | 65439 | Scan the keyboard |
| SCREEN | $FFED | 65517 | Return screen format |
| SECOND | $FF93 | 65427 | Send secondary address for LISTEN |
| SETLFS | $FFBA | 65466 | Set up a logical file |
| SETMSG | $FF90 | 65424 | Set system message output |
| SETNAM | $FFBD | 65469 | Set up file name |
| SETTIM | $FFDB | 65499 | Set the system clock |
| SETTMO | $FFA2 | 65442 | Set IEEE bus card timeout flag |
| STOP | $FFE1 | 65505 | Check if STOP key is pressed |
| TALK | $FFB4 | 65460 | Command a device on the serial bus to talk |
| TKSA | $FF96 | 65430 | Send a secondary address to a device commanded to talk |
| UDTIM | $FFEA | 65514 | Update the system clock |
| UNLSN | $FFAE | 65454 | Send an UNLISTEN command |
| UNTLK | $FFAB | 65451 | Send an UNTALK command |
| VECTOR | $FF8D | 65421 | Manage RAM vectors |
The operating system provided a screen editor, flashing cursor and a prompt that says READY.
Commodores had an OS but it was different to today’s in some of the ways that it handled tasks. It did provide a method of interacting with the user and handling I/O. I/O such as disk drives were not handled by the operating system like today’s would – this is because the disk drives were like a computer themselves. This meant that the drive could carry out the required task while the main computer did something else.