04 - Lecture 04 Ex - ITEC 255 Computer Organization &...

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ITEC 255 – Computer Organization & Architecture / TUTORIAL / Lecture 4 Q1: What is the von &eumann architecture based on? A1: It’s based on three concepts which are: i. Data and instructions are stored in a single read-write memory. ii. Memory contents are addressable by location, irrespective of what data they contain. iii. Sequential execution occurs from one instruction to the next. Q2: What is a hardwired program? A2: A particular computation can be performed by configuring the basic logic components which are design exclusively for the same computation. The outcome can be seen in a form of a program only in hardware which can be called as hardwired program . Q3: Draw up the basic Instruction Cycle of a program’s process. Briefly, explain your drawing. A3: A program execution consists of continuous process of fetching and executing instructions until some specific situation or condition needs the instruction cycle to stop. A fetch cycle must precede an execute cycle. At the beginning of each instruction cycle, the processor gets an instruction from memory, and places it in one of the registers (IR) in order to perform (execute) the instruction. Q4: At the fetch cycle, the fetched instruction is interpreted by the processor to perform the necessary actions. List the categories of actions/functions that these may fall into. A4: These are: 1. CPU-to-Memory. 2. CPU-to-I/O. 3. Data processing. 4. Control. Q5: What are interrupts and how are they useful? A5: Normally called Interrupt Requests (IRQ), it’s a signal informing a program that an event has occurred. When a program receives an interrupt signal, it takes a specified action (which can be to ignore the signal). Interrupt signals can cause a program to suspend itself temporarily to service the interrupt. Interrupt signals can come from a variety of sources. For example, every keystroke generates an interrupt signal. Interrupts can also be generated by other devices, such as a printer, to indicate that some event has occurred. These are called hardware interrupts. Interrupt signals initiated by programs are called software interrupts . A software interrupt is also called a trap or an exception.
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PCs support 256 types of software interrupts and 15 hardware interrupts. Each type of software interrupt is associated with an interrupt handler -- a routine that takes control when the interrupt occurs. For example, when you press a key on your keyboard, this triggers a specific interrupt handler. The complete list of interrupts and associated interrupt handlers is stored in a table called the interrupt vector table , which resides in the first 1 K of addressable memory. This table contains pointer to routines representing an interrupt type, and each interrupt number is reserved for a specific purpose. An interrupt vector table is also called a dispatch table. Interrupts improves processing efficiency. Interrupts are used to ensure adequate service
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04 - Lecture 04 Ex - ITEC 255 Computer Organization &...

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