Operating System Lecture 2 PDF

Operating System Top Level View of Computer Functions and Structure Lecture 2 Computer Functions There are four basic functions that a computer can perform: 1. Data Processing: The computer must be able to process data. 2. Data Storage: Computer can store data...

Operating System Top Level View of Computer Functions and Structure Lecture 2 Computer Functions There are four basic functions that a computer can perform: 1. Data Processing: The computer must be able to process data. 2. Data Storage: Computer can store data either short-term or long-term data storage. 3. Data Movement: The movement of data from/to IO devices. 4. Control: The control unit controls these three functions. 2 Computer Structure The internal structure of the computer has four main structural components: —Central Processing Unit (CPU): Controls the operation of the computer and performs its data processing functions; often simply referred to as processor. —Main Memory: Stores data. —I/O: Moves data between the computer and its external environment. —System Interconnection: Some mechanism that provides for communication among CPU, main memory, and I/O (e.g., a system bus is consisting of a number of conducting wires to which all the other components attach). 3 Computer Structure 4 Computer Structure The most complex component is the CPU. Its major structural components are as follows: —Control Unit: Controls the operation of the CPU and hence the computer —Arithmetic and Logic Unit (ALU): Performs the computer’s data processing functions —Registers: Provides storage internal to the CPU —CPU Interconnection: Some mechanism that provides for communication among the control unit, ALU, and registers 5 Program Concept Hardwired systems are inflexible General purpose hardware can do different tasks, given correct control signals Instead of re-wiring, supply a new set of control signals What is a program? A sequence of steps For each step, an arithmetic or logical operation is done For each operation, a different set of control signals is needed Function of Control Unit For each operation a unique code is provided —e.g. ADD, MOVE A hardware segment (instruction interpreter) accepts the code and issues the control signals We have a computer! Components The Control Unit and the Arithmetic and Logic Unit constitute the Central Processing Unit Data and instructions need to get into the system and results out —Input/output Temporary storage of code and results is needed —Main memory Computer Components: Top Level View AC AC = Accumulator Instruction Cycle Two steps: —Fetch —Execute Fetch Cycle Program Counter (PC) holds address of next instruction to fetch Processor fetches instruction from memory location pointed to by PC Increment PC —Unless told otherwise Instruction loaded into Instruction Register (IR) Processor interprets instruction and performs required actions Execute Cycle Processor-memory —data transfer between CPU and main memory Processor-I/O —Data transfer between CPU and I/O module Data processing —Some arithmetic or logical operation on data Control —Alteration of sequence of operations – e.g. jump Combination of above Example The processor contains a single data register, called an accumulator (AC). Both instructions and data are 16 bits long. Thus, it is convenient to organize memory using 16-bit words. The instruction format provides 4 bits for the opcode, so that there can be as many as 24 = 16 different opcodes, and up to 212 = 4096 (4K) words of memory can be directly addressed. Example Question Given a hypothetical machine that has five memory and I/O instructions: 0001 = Load AC from memory 0010 = Store AC to memory 0011 = Load AC from I/O 0111 = Store AC to I/O 0101 = Add to AC from memory In these cases, the 12-bit address identifies a particular I/O device. Show the content of IR for the following: 1. Load AC from I/O device 5. 𝟑𝟎𝟎𝟓 → 𝑰𝑹 2. Add contents of memory location 940. 𝟓𝟗𝟒𝟎 → 𝑰𝑹 3. Store AC to I/O device 6. 𝟕𝟎𝟎𝟔 → 𝑰𝑹 Example of Program Execution Example of a program fragment that adds the contents of the memory word at address 940 to the contents of the memory word at address 941 and stores the result in the latter location. Question Expand the previous example to show content of MAR and MBR? Instruction Cycle State Diagram Question For example, the PDP-11 instruction ADD A,B results in the following sequence of states: iac, if, iod, oac, of, oac, of, do, oac, os. Question Consider a hypothetical 32-bit microprocessor having 32-bit instructions composed of two fields: the first byte contains the opcode and the remainder the immediate operand or an operand address. —What is the maximum directly addressable memory capacity (in bytes)? —Discuss the impact on the system speed if the microprocessor bus has – a 32-bit local address bus and a 16-bit local data bus, or – a 16-bit local address bus and a 16-bit local data bus. —How many bits are needed for the program counter (PC) and the instruction register (32)? Thank You 22