System information

per block is given by BLS/128. Physical sectors on the disk media are also numbered
consecutively. If the physical sector size is also 128 bytes, a one-to-one relationship exists
between logical and physical sectors. The logical-to-physical translation table (XLT) maps this
relationship, and a skew factor is typically used in generating the table entries. For instance, if the
skew factor is 6, XLT will be:
Logical: 0 1 2 3 4 5 6 ...... 25
Physical: 1 7 13 19 25 5 11 ...... 22
The skew factor allows time for program processing without missing the next sector. Otherwise,
the system must wait for an entire disk revolution before reading the next logical sector. The
skew factor can be varied, depending on hardware speed and application processing overhead.
Note that no sector translation is done when the physical sectors are larger than 128 bytes, as
sector deblocking is done in this case. See also sector, SKF, and XLT.
SKF: A diskdef macro library parameter specifying the skew factor to be used in building XLT.
If SKF is zero, no translation table is generated and the XLT byte in the DPH will be 0000H.
software: Programs that contain machine-readable instructions, as opposed to hard-ware, which
is the actual physical components of a computer.
source file: ASCII text file usually created with an editor that is an input file to a system
program, such as a language translator or text formatter.
SP: Stack pointer. See stack.
spooling: Process of accumulating printer output in a file while the printer is busy. The file is
printed when the printer becomes free; a program does not have to wait for the slow printing
process.
SPT: See sectors per track.
stack: Reserved area of memory where the processor saves the return address when a call
instruction is received. When a return instruction is encountered, the processor restores the
current address on the stack to the program counter. Data such as the contents of the registers can
also be saved on the stack. The push instruction places data on the stack and the pop instruction
removes it. An item is pushed onto the stack by decrementing the stack pointer (SP) by 2 and
writing the item at the SP address. In other words, the stack grows downward in memory.
syntax: Format for entering a given command.
SYS: See system attribute.
Appendix H : Glossary CP/M Operating System Manual
H-17