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Write down some ideas in README

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Nero 2019-10-08 10:22:31 +00:00
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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.