[PDF] Memory Layout and Access Chapter Four - utclujro

What are the four registers of a 8086 processor?

The 8086 through 80286 processors have four segment registers: cs, ds, ss and es. The80386 and later processors have these segment registers plus fs and gs. The cs (code seg-ment) register points at the segment containing the currently executing code. The CPUalways fetches instructions from the address given by cs:ip.

How many kilobytes can an 8086 address?

Now, this might seem rather limiting. After all, with only four segment registers onthe 8086 you can address a maximum of 256 Kilobytes (64K per segment), not the fullmegabyte promised. However, you can change the segment registers under program con-trol, so it is possible to address any byte by changing the value in a segment register.

Should you use segment registers as data registers?

You should never use the segment registers as data registers to hold arbitrary values.They should only contain segment addresses. But more on that, later. Throughout this textyou’ll see the abbreviated operand sreg used wherever segment register operands areallowed (or required).

Does the 80x86 family use segmented addressing?

Of course, despite the fact that the 80x86 family uses segmented addressing, the actual(physical) memory connected to the CPU is still a linear array of bytes. There is a functionthat converts the segment value to a physical memory address.