OPERATING SYSTEMS in Java

Encoder Code 128 Code Set C in Java OPERATING SYSTEMS

OPERATING SYSTEMS
Recognizing Code128 In Java
Using Barcode Control SDK for Java Control to generate, create, read, scan barcode image in Java applications.
Code 128B Maker In Java
Using Barcode drawer for Java Control to generate, create Code 128 Code Set C image in Java applications.
[CHAP. 6
Decode Code 128B In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
Barcode Encoder In Java
Using Barcode printer for Java Control to generate, create bar code image in Java applications.
Programmed I/O Simple character-at-a-time (byte-at-a-time) I/O is sometimes called programmed I/O to distinguish it from interrupt-driven I/O or direct memory access (DMA), which we will discuss shortly. With programmed I/O, the driver checks to see if the device is available (not busy). If so, the driver will write a character to the buffer on the controller, and command the transfer to begin with a set control; clear flag (different computers may name these status bits differently). Set control tells the device to start, and clear flag makes the device appear busy. The driver then loops, testing for the flag to be set. When the byte is transferred, the controller will clear the control bit and set the flag bit. The driver will find the flag bit is set, and that will indicate that the transfer is complete and the device is again available to accept another character. The unfortunate characteristic of programmed I/O is that the computer can spend a great deal of time waiting for a slow device. In the time it takes to process a character out to a 56K baud modem, for example, the computer could easily perform 200 to 1000 other instructions. Interrupt-driven I/O To avoid the waste of computing power using programmed I/O, virtually all operating systems today use interrupt-driven I/O. With interrupt-driven I/O, the program requesting the transfer is blocked (suspended) while the bytes are being transferred. The operating system copies the bytes to be transferred into system memory space so that the suspended program can be temporarily removed from memory, if necessary. Then the OS calls the initiator section of the device driver. The initiator moves the first byte into the controller s buffer, commands the controller to begin, and then returns to the OS. The OS then decides which process to execute while waiting for the I/O to complete. When the character has been transferred, the controller generates a hardware interrupt. An interrupt causes the OS to take control. The OS saves the state (register contents, program counter value, etc.) of the currently executing program, and calls the continuator section of the driver for the interrupting device. If there are additional bytes to transfer, the continuator puts the next byte into the controller s buffer, commands the controller to begin again, and returns to the OS. The OS then restores the state and resumes execution of the other process. When the last character has been transferred, the continuator will return to the OS, signaling that the suspended process can be restarted. Now the OS can choose among the available processes, and restart whichever one is of highest priority. The key advantage of interrupt-driven I/O is that the CPU works on other processes while the controller transfers the data to the device. This is a very substantial improvement in the efficient use of computing resources, but it is still true that processing interrupts imposes overhead which can be substantial, especially when interrupts are frequent. Direct Memory Access A further improvement in efficiency is possible when the I/O device is relatively fast, like a disk drive or a tape drive. The computer design may include one or more direct memory access (DMA) controllers (or channels). A DMA controller is a computer within the computer that specializes in I/O, and its purpose is to drastically reduce the number of interrupts that the OS must service. When DMA is used, the driver sets up the DMA transfer once, passing the address of the buffer to be transferred to the DMA controller and telling the DMA controller which device to transfer to/from. The driver then returns to the OS, and the OS begins executing another process. The DMA controller takes care of moving the information directly from/to memory and to/from the device. The only interrupt the OS sees is the one from the DMA controller when the entire transfer is complete. Strictly speaking, DMA can be used with any device, but usually DMA is used only by drivers of fast devices that would otherwise generate many frequent interrupts. DMA channels are usually few in number, so their use is usually reserved for devices for which the DMA channels make the most difference.
Bar Code Scanner In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
Painting Code128 In Visual C#
Using Barcode creator for Visual Studio .NET Control to generate, create Code 128C image in .NET framework applications.
CHAP. 6]
Encoding Code 128C In Visual Studio .NET
Using Barcode printer for ASP.NET Control to generate, create ANSI/AIM Code 128 image in ASP.NET applications.
Code 128 Creation In Visual Studio .NET
Using Barcode generator for Visual Studio .NET Control to generate, create Code-128 image in .NET applications.
Creating Code-128 In VB.NET
Using Barcode maker for .NET Control to generate, create USS Code 128 image in VS .NET applications.
EAN13 Drawer In Java
Using Barcode generator for Java Control to generate, create EAN-13 image in Java applications.
Create GS1 - 12 In Java
Using Barcode printer for Java Control to generate, create UPC-A Supplement 5 image in Java applications.
DataBar Drawer In Java
Using Barcode printer for Java Control to generate, create GS1 DataBar Limited image in Java applications.
Print ISBN - 10 In Java
Using Barcode creator for Java Control to generate, create ISBN - 13 image in Java applications.
UPC - 13 Maker In Java
Using Barcode maker for Android Control to generate, create European Article Number 13 image in Android applications.
Reading Barcode In Visual C#.NET
Using Barcode Control SDK for .NET framework Control to generate, create, read, scan barcode image in Visual Studio .NET applications.
Bar Code Recognizer In Visual C#
Using Barcode scanner for .NET Control to read, scan read, scan image in VS .NET applications.
Barcode Encoder In Objective-C
Using Barcode printer for iPhone Control to generate, create barcode image in iPhone applications.
GTIN - 128 Creation In Objective-C
Using Barcode generation for iPad Control to generate, create UCC.EAN - 128 image in iPad applications.
Barcode Reader In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
UPCA Reader In None
Using Barcode scanner for Software Control to read, scan read, scan image in Software applications.
Copyright © OnBarcode.com . All rights reserved.