Go on. Explore!

lvl 0 • 0 xp

lvl 1

Home Market Decks Interests

OS Chapter 1

memorize.ai (lvl 286)

(0)

14 cards

()

Section 1

Preview this deck

A typical instruction-execution cycle, as executed on a system with a von Neumann architecture

Front

1 / 14

iOS Dev Swift

0.0

0 reviews

5			0
4			0
3			0
2			0
1			0

Active users

All-time users

Favorites

Last updated

6 years ago

Date created

Mar 1, 2020

Cards (14)

Section 1

(14 cards)

A typical instruction-execution cycle, as executed on a system with a von Neumann architecture

Front

First fetches an instruction from memory and stores that instruction in the instruction register. The instruction is then decoded and may cause operands to be fetched from memory and stored in some internal register. After the instruction on the operands has been executed, the result may be stored back in memory.

Back

mode bit

Front

A bit, called the mode bit, is added to the hardware of the computer to indicate the current mode: kernel (0) or user (1). With the mode bit, we can distinguish between a task that is executed on behalf of the operating system and one that is executed on behalf of the user.

Back

Variable Timer

Front

A variable timer is generally implemented by a ﬁxed-rate clock and a counter. The operating system sets the counter. Every time the clock ticks, the counter is decremented. When the counter reaches 0, an interrupt occurs. For instance, a 10-bit counter with a 1-millisecond clock allows interrupts at intervals from 1 millisecond to 1,024 milliseconds, in steps of 1 millisecond.

Back

Interrupt

Front

The occurrence of an event is usually signaled by an interrupt from either the hardware or the software. Hardware may trigger an interrupt at any time by sending a signal to the CPU, usually by way of the system bus.

Back

Privileged Instructions

Front

The dual mode of operation provides us with the means for protecting the operating system from errant users—and errant users from one another. We accomplish this protection by designating some of the machine instructions that may cause harm as privileged instructions. The hardware allows privileged instructions to be executed only in kernel mode.

Back

At the very least, we need two separate modes of operation

Front

user mode and kernel mode

Back

System Call/Monitor Call

Front

Software may trigger an interrupt by executing a special operation called a system call (also called a monitor call).

Back

Job Pool

Front

Since, in general, main memory is too small to accommodate all jobs, the jobs are kept initially on the disk in the job pool. This pool consists of all processes residing on disk awaiting allocation of main memory.

Back

Timer

Front

To accomplish this goal, we can use a timer. A timer can be set to interrupt the computer after a speciﬁed period. The period may be ﬁxed (for example, 1/60 second) or variable (for example, from 1 millisecond to 1 second).

Back

RAM and DRAM

Front

General-purpose computers run most of their programs from rewritable memory, called main memory(also called random-access memory, or RAM). Main memory commonly is implemented in a semiconductor technology called dynamic random-access memory (DRAM).

Back

Ideally, we want the programs and data to reside in main memory permanently. This arrangement usually is not possible for the following two reasons:

Front

1. Main memory is usually too small to store all needed programs and data permanently. 2. Main memory is a volatile storage device that loses its contents when power is turned off or otherwise lost.

Back

System Process or System Daemons

Front

Once the kernel is loaded and executing, it can start providing services to the system and its users. Some services are provided outside of the kernel, by system programs that are loaded into memory at boot time to become system processes, or system daemons that run the entire time the kernel is running.

Back

Multiprogramming

Front

Multi programming increases CPU utilization by organizing jobs (code and data) so that the CPU always has one to execute.

Back

Interrupt Vector

Front

Generally, the table of pointers is stored in low memory(the ﬁrst hundred or so locations).These locations hold the addresses of the interrupt service routines for the various devices. This array, or interrupt vector, of addresses is then indexed by a unique device number, given with the interrupt request, to provide the address of the interrupt service routine for the interrupting device. Operating systems as different as Windows and UNIX dispatch interrupts in this manner.

Back