Basic Elems of a Computer System: Processor(defn):
Controls the operation of the computer and performs its data processing functions. When there is only one processor it is often referred to as the Central Processing Unit.
Basic Elems of a Computer System: Main memory (defn):
Stores data and programs this memory is typically volatile. That is to say, when the computer is shut down, the contents of the memory are lost. In contrast , the contents of disk memory are retained even when the computer system is shutdown. Main memory is also referred to as real memory or primary memory.
Basic Elems of a Computer System: I/O Modules(defn):
Moves data between the computerand its external environment.
The external environment consists of a variety of devices, including secondarymemory devices (e.g. disks), communications equipment and terminals.
Basic Elements of a Computer System: System Bus (defn):
Provides for communication among processors, main memory and I/O modules.
A program to be executed by a processor consists of a set of instructions stored in memory. In its simplest form...
Instruction processing consists of twosteps:
(1) The processor Reads OR FETCHES instructions from memory one at a time...
(2) The processor EXECUTES each instruction.
Instruction Execution typesofactions of execution:
Four action categories for processor execution/actions:
Processor-memory: Data may be transferred from processor to memory or memory to processor.
Four action categories for processor execution/actions: Processor-I/O (defn):
Data may be transferred to or from a peripheral device by transferring between the processor and an I/O module.
Four action categories for processor execution/actions: Data processing (defn):
The processor may perform some arithmetic or logical operation on data.
Four action categories for processor execution/actions: Control (defn):
An instruction may specify that the sequence of execution be altered.
Program Counter:Holds address of the instruction to be fetched next.
PC is incremented after each fetch.
Instruction Register: Fetched instruction is loaded into the Instruction Register.Instruction being executed.
CPU Registers: MAR(defn):
Memory address register: Specifies the address in memory for the next read or write.
CPU Registers: MBR:(defn):
Memory buffer register: contains data to be written into memory or which receives the data read from memory.
CPU Registers: I/O AR(def'n):
Input/output Address register Specifies a particular I/O Device.
Cpu Registers: I/O BR(def'n):
Input/output Buffer register:Used for the exchange of data between an I/O module and the processor.
Interrupts fill in the blanks:
a) Device controller or other system hardware issues an interrupt
b) Processor finishes execution of current instruction.
c) Processor signals acknowledgment of interrupt.
d) Processor pushes Processor Status Word (PSW) and Program Counter (PC) onto control stack
e) Processor loads new PC value based on interrupt
a) Save remainder of process state information.
b) Process interrupt.
c) Restore process state information.
d) Restore old PSW and PC.
Interrupts: Program Status Word (defn in Stallings book):
The PSW contains statusinformationabout the currently running process, including memory usage information, condition codes, and other status information, such as an interruptenable/disable bit and a kernel/user mode bit.