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The great exception is network devices, which do not turn up in the file system but are handled separately. Device files are used to apply access rights to the devices and to direct operations on the files to the appropriate device drivers. Unix makes a distinction between character devices and block devices. The distinction is roughly as follows:
An instruction set architecture (ISA) is an abstract model of a computer, also referred to as computer architecture.A realization of an ISA is called an implementation.An ISA permits multiple implementations that may vary in performance, physical size, and monetary cost (among other things); because the ISA serves as the interface between software and hardware.
In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. [1] A device or program that executes instructions described by that ISA, such as a central processing unit (CPU), is called an implementation of that ISA.
In character (STR and BSC) modes, the device relied on particular characters to define frame boundaries; in bit (HDLC and SDLC) modes earlier devices relied on physical-layer signals, while later devices took over the physical-layer recognition of bit patterns. A synchronous line is never silent; when the modem is transmitting, data is flowing.
Additionally, if the same hardware exposes both character and block devices, there is a risk of data corruption due to clients using the character device being unaware of changes made in the buffers of the block device. Most systems create both block and character devices to represent hardware like hard disks.
The term fixed-block architecture was created by IBM in 1979 [3] to distinguish this format from its variable-length record format. Each track is divided into fixed-length blocks, consisting of an ID field and a data field. Application programs refer to blocks by relative block number, and cannot address them by cylinder, head and record.
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A hardware architecture, then, is an abstract representation of an electronic or an electromechanical device capable of running a fixed or changeable program. [ 7 ] [ 8 ] A hardware architecture generally includes some form of analog, digital, or hybrid electronic computer , along with electronic and mechanical sensors and actuators.