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+## Memory Layout
+
+On a 8080, there are no segments, the addresses are as displayed.
+
+On on the 8086, a single segment with a value of 0x0100 is assumed.
+This implies that the first 4k of memory are not used.
+
+The BDOS may be recompiled for starting at a lower address, in this case,
+the minimum memory requirement may be less than 64k.
+
+|Start|Size|Function|
++-+-+-+
+|F000|4k|BDOS and hw drivers|
+||var|BDOS data|
+|SP|var|Stack, growing down|
+|||Free memory|
+|0100|up to stack|Transient Program Area|
+|0080|128 bytes|Command line and disk buffer|
+|0000|128 bytes|System data area|
+
+## Application program interface
+
+It is using the `call 5` convention with CP/M compatible syscall numbers.
+
+File I/O is done via FCB blocks.