diff --git a/README.md b/README.md
index 0235527..81db91d 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,15 @@
+## Components
+
+The BIOS is in the uppermost 2K of the memory area - it provides basic character and disk I/O functions.
+It it expected to stay static and not be unloaded by the user program.
+The BIOS may hook into interrupts if necessary to provide its functionality.
+Depending on your hardware, a different BIOS binary may be used.
+
+The BDOS is in the 2K below the BIOS, it provides a filesystem driver to work atop of the BIOS.
+It is agnostic to the underlaying hardware configuration.
+A user program might overwrite memory up to the end of the BDOS.
+Upon program exit, the BIOS will reload the BDOS from disk.
+
 ## Memory Layout
 
 On a 8080, there are no segments, the addresses are as displayed.
@@ -5,18 +17,21 @@ 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 BIOS and FDOS may be recompiled for starting at a lower address, in this case,
 the minimum memory requirement may be less than 64k.
 
 |Start|Size|Function|
 |--|--|--|
-|0xF000|4k|BDOS and hw drivers|
-||var|BDOS data|
+|0xF800|2k|BIOS / hw drivers|
+|0xF000|2k|BDOS|
+|...|...|BDOS data area, disk deblocking buffers|
 |SP|var|Stack, growing down|
-|||Free memory|
-|0x0100|up to stack|Transient Program Area|
+|...|...|Free memory|
+|...|var|Heap, growing up|
+|0x0100|var|Transient Program Area|
 |0x0080|128 bytes|Command line and disk buffer|
-|0x0000|128 bytes|System data area|
+|0x0008|120 bytes|BIOS data area|
+|0x0000|8 bytes|BDOS data area|
 
 ## Application program interface
 
@@ -28,17 +43,10 @@ File I/O is done via FCB blocks.
 
 |Offset|Size|Usage|
 |--|--|--|
-|0x00|3 bytes|warm reboot jump instruction|
+|0x00|3 bytes|warm reboot/program exit jump instruction|
 |0x03|byte|unused (would be iobyte)|
 |0x04|byte|default drive|
 |0x05|3 bytes|syscall jump instruction|
-|0x08|8 bytes|8080 RST 1 interrupt code|
-|0x10|8 bytes|8080 RST 2 interrupt code|
-|0x18|8 bytes|8080 RST 3 interrupt code|
-|0x20|8 bytes|8080 RST 4 interrupt code|
-|0x28|8 bytes|8080 RST 5 interrupt code|
-|0x30|8 bytes|8080 RST 6 interrupt code|
-|0x38|8 bytes|8080 RST 7 interrupt code / debugger|
-|0x40|varies|area reserved for usage by RDOS|
+|0x08|120 bytes|interrupts and work area for BIOS|
 |0x80|byte|length of command line|
 |0x81|127 bytes|command line with $length bytes plus a trailing 0x0D|