1. Simulation of computer system

2. Simulation tools
VHDL (VHSIC Hardware Description Language) is a hardware description language used in electronic design automation to describe digital and mixed-signal systems such as field-programmable gate arrays and integrated circuits. VHDL can also be used as a general purpose parallel programming language.
Drawback of VHDL
Big language
Require high end compiler
Commercial market
The language is not for expression of computer systems modelling at lower levels.

3. Process orientation
User level threading:- A scheduling mechanism selects a thread known to be ready for execution and execution control is handled to that thread.
 Thread of execution is the smallest sequence of programmed instructions that can be managed independently by an operating system scheduler. The scheduler itself is a light-weight process. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process. Multiple threads can exist within the same process and share resources such as memory, while different processes do not share these resources.
Hold Statement
Wait Statement

4. Memory Hierarchy Magnetic tapes disks I/O processor CPU Main memory
Cache
Register
Main Memory
Magnetic Disk
Magnetic Tape

5. Virtual Memory Referencing
Give the programmer the illusion that the system has a very large memory, even though the computer actually has a relatively small main memory
Address Space(Logical) and Memory Space(Physical)
virtual address
(logical address)
physical address
address space
memory space
address generated by programs actual main memory address
Mapping

6. Page Fault
Hit ratio

7. High level computer –system simulation

8. CPU Simulation

9. Pipelines