DOS Memory Management
Because it was based on the Intel 8080 processor, MS-DOS has a maximum segment s
It has 4 segment registers (each 16 bits):
Extra segment (ES) - application specific
Addressibility up to 1 Mbyte is achieved by extending (in 8088 and 8086 and later processors) registers to 20 bits. Segment register is shifted 4 bits left and logical address added in.