Address in hex. Contents / Function 
0000
-001F
 16 registers for interrupt level 0 (normal execution) 
0020
-003F
 16 registers for interrupt level 1 (Async. comm.) 
0040
-005F
 16 registers for interrupt level 2 (Tape/Disk/Printer/Serial I/O) 
0060
-007F
 16 registers for interrupt level 3 (Keyboard) 
0055
 Printer Status Byte A
    Bit 0: Print emitter latch 3
    Bit 1: Print emitter latch 2
    Bit 2: Print emitter latch 1
    Bit 3: Wire check or not ready
    Bit 4: Forms emitter B
    Bit 5: Forms emitter A
    Bit 6: Not end of forms
    Bit 7: Left margin signal
0057
 Printer Status Byte B
    Bit 0: Print motor latch B (0 = not B)
    Bit 1: Print motor latch A (0 = not A)
    Bit 2: Print emitter interrupt
    Bit 3: Not ready interrupt
    Bit 4: Forms motor latch B (0 = not B)
    Bit 5: Forms motor latch A (0 = not A)
    Bit 6: Forms control interrupt
    Bit 7: Timer interrupt
0082
-008A
 Temporary storage for Diskette I/O Supervisor
(save of return address in R2 for internal subroutines)		 
008F
 Tape Status Byte
    Bit 0: End Of Tape (EOT)
    Bit 1: No device address E response
    Bit 2: Tape running
    Bit 3: Cartridge in place
    Bit 4: Erase on
    Bit 5: LED and erase OK
    Bit 6: File protected
    Bit 7: No beginning of tape (BOT)
0090
 Internal variable for I/O Supervisor
Diskette:
    Bit 0:
    Bit 1:
    Bit 2: ?
    Bit 3: 1=MFM
    Bit 4: ?
    Bit 5:
    Bit 6:
    Bit 7: ? 
009A
 Internal variable for I/O Supervisor
Diskette: Cylinder number for I/O		 
009C
 Internal variable for I/O Supervisor
Diskette: Side for I/O (0=Side 0, other=Side 1)		 
009E
 Internal variable for I/O Supervisor
Diskette: Sector number for I/O		 
00A0
 Constant $0000 
00A2
 System flags
    Bit 0: 1=No retries after CRC errors during Diskette I/O
    Bit 1:
    Bit 2:
    Bit 3:
    Bit 4:
    Bit 5:
    Bit 6:
    Bit 7:

    Bit 8:
    Bit 9:
    Bit 10:
    Bit 11:
    Bit 12:
    Bit 13:
    Bit 14: 1=Withing hexdump routine
    Bit 15: 
00A4
 System flags
    Bit 0: 1=ATTN pressed
    Bit 1:
    Bit 2:
    Bit 3: 1=Keyboard interrupt without Key Pending Flag
    Bit 4:
    Bit 5: 1=APL, 0=BASIC
    Bit 6: 1=I/O active
    Bit 7: 1=CRT on, 0=CRT off

    Bit 8: Level 0 Mode - 1=RWS, 0=ROS
    Bit 9: Level 1 Mode - 1=RWS, 0=ROS
    Bit 10: Level 2 Mode - 1=RWS, 0=ROS
    Bit 11: Level 3 Mode - 1=RWS, 0=ROS
    Bit 12: Printer status - 1=Printer busy, 0=Printer ready
    Bit 13: Printer status - ???
    Bit 14: Printer status - ???
    Bit 15: (1=Translate scancode?)
00A6
 Address to the routine for device test
Tests if a given device (given in IOCB) is present and ready.
R2 = return address, R3 = address of IOCB
If the device is ready the routine jumps back to R2+2 else "ERROR 0xx yyy" in line 16 is printed and a jump to R2 is done.		 
00A8
 Highest available RWS address
After restart it is the same value as in $00AA; after loading some IMFs or Customer Support Routine this value decreases.		 
00AA
 Last available address in R/W Storage (RAM).
This is the location of the last main memory address. A 32kB system will have a value of $7FFF.		 
00AC
 Address of routine to jump into Executable ROS
R2 = return address, R8 = destination address in ROS, eventually with additional parameters depending on the function called		 
00AE
 Address of the I/O Supervisor Routine in Executable ROS that executes all I/O operations controlled by an IOCB. 
00B0
 Scan- or keycode of last pressed key 
00B6
 
00BE
 Address of the first usable memory location, usually $0700.
At ($BE)-$20 the system code 'IBM5100 ' (13 chars.) can be found, like the one needed for the directory entry on a diskette.
Attention: Several ROS routines use that area as temporary storage and for internal variables! For example the vector table for the supervisor routines is located at $07C0. 
00C0
 Address of the Screen Dump Routine in Executable ROS
This routine is called e.g. by pressing the keys CMD-Print.		 
00D2
 Temporary storage for Diskette I/O Supervisor
Return address to caller of I/O Supervisor		 
00D6
 (IMF flags)
    Bit 14: 1=Translated Sort Message installed
 
00D8
 Address of the vector table containing the entry points to the I/O Supervisor, for device addresses 0 to F. Each table entry consists of two words, the first word is the address of the builtin (ROS) I/O Routine, the second word, if not zero, the address of a user defined routine in RWS. 
00E6
 $0F40 
00E8
 Diskette Status Byte A
    Bit 0: Write mode
    Bit 1: Read mode
    Bit 2: Diagnostic mode
    Bit 3: Index
    Bit 4: Erase gate
    Bit 5: Diskette 2
    Bit 6: CRC error
    Bit 7: Read/write overrun
00E9
 Diskette Status Byte B
    Bit 0: New media
    Bit 1: MFM mode
    Bit 2: Filter control
    Bit 3: Current select
    Bit 4: Head engaged
    Bit 5: Head selected (0 = head 0)
    Bit 6: Access line
    Bit 7: Access line
00F8
 $1000 
00FA
 $100A
Address of the error message routine in ROS that prints 
ERROR 0xx yyzz
in the last line.
Parameters: R3=Address of IOCB, return address in R2 
00FC
 Address of HOLD routine 
00FE
 $0D00
Address of hexdump routine 
01C0
 $0501 
01C2
 $0202 
01C4
 $0503 
01C6
 $0204 
01F0
 $1DFA
ROS routine that clears the screen to the end.
Parameters: R14=Start address, return address in R2 
01F2
 $1D4A
ROS routine that converts hex digits into integer
Parameters: R14=Address of the hex digits, result in R15 
01F4
 $1C7C 
01F8
 $1CF6 
0200
-05FF
 Display buffer, 1kB in total. 
0600
-0700
 Help routines in machine language
$0600 has a jump routine into the Executable-ROS (and back again), $0630 (at least on a 5110) contains the device test routine.		 
0B00
 Load and start address for machine language programs 
0B42
-0B55
 Addresses of the IOCBs for file numbers FL0 to FL9 in BASIC mode 
120E
 Start of a BASIC program in token form