Q. 13 Explain the file system related to Information Management with file operations only.
Q.14 Explain the following terms in case of magnetic disk
Q. 15 Explain internal and external fragmentation.
Q. 16 What are device drivers?
Q.17 What is VDU ? Explain the following terms
Q. 18 Explain the use of video RAM. Explain data bytes and attribute bytes.
Q.19 Why keyboard is referred as memory map terminal? Explain the multiple memory location involved in the input-output operations between the keyboard and screen.
Ans : 1) The file system related to IM allows the user to define files and directories and allocate/deallocate the disk space to each file.
2) A file is a collection of related information. It can be program or data.
3) File operations : The file concept is implemented by the operating system. System calls
are provided to create, read, write, rewind and delete files.
(a) Create a file : For Creating a file, first whether sufficient space is available for that file is checked. If it is available, entry for new file must be made in directory.
(b) Write to a file : For whiting to a file, there is command in which name of the file is given. Then Operating system search for that file in directory entry and write to it
(c) Reading a file : For reading a file, there is a system call in which file is specified. Then operating system searches for that file in directory entry and read it.
(d) Rewind a file : The directory is searched for appropriate entry and file is reset to the beginning of file.
(e) Delete a file: To delete a file, directory entry is searched and if file is found, it releases the memory space and that directory entry now become invalid.
Q.14 Explain the following terms in case of magnetic disk :
(i) Tracks and Sectors
(ii) Seek time
(iii) Transmission time
(ii) Latency time/ Rotational delay
Ans : i) Tracks and Sectors : Magnetic disk surface is made up of concentric circles called tracks. The number of tracks varies depending on the disk type. A track is further divided into smaller areas called sectors.
A sector is a smallest unit of information which can be read from or written to the disk.
Sector varies from 32 bytes to 4096 bytes and track contains 4 to 32 sectors per track and
from 75 to 500 tracks per disk surface.
ii) Seek time: The time required for read/write heads to move to the correct track is called as seek time.
iii) Transmission time : The time required for activate Read/Write head for appropriate surface and read data is called as transmission time.
iv) Latency time/Rotational delay : The time required for requested sector on track to rotate below the head is called as latency time or rotational delay.
Q. 15 Explain internal and external fragmentation.
Ans : Internal fragmentation :
Wastage of memory space within partition is called as internal fragmentation. A file consists of number of blocks. Consider the block size of a O.S is 1024 bytes and a file is of 3499 bytes. Then, when it is loaded in memory for execution it would have allocated 4 blocks. Thus last 597 bytes would be wasted. This is called as internal fragmentation.
Larger block size causes more internal fragmentation.
External fragmentation :
Variable partition suffers from external fragmentation,
Suppose a job of 512 bytes is terminated and new job is of 256 bytes is loaded in the partition then 256 bytes of memory is wasted. T his is called as external fragmentation.
Q. 16 What are device drivers?
Ans : 1) Device drivers are software programs required for each device
2) Each device will require different drivers as per functionality.
3) A device driver knows how the buffers flags, register contro! and status bits should be used for a particular device
4) Some device drivers are useful for data conversion
5) For simply reading a character from a device involves complex sequence of device specification operations
6) Rather than writing the code every time, the device driver was simply used from library.
Q.17 What is VDU ? Explain the following terms :
(a) Dumb terminal
(b) Intelligent terminal
Ans : 1) A visual display unit (VDU) or terminal is nothing but a common I/O medium.
2) There are generally two parts of terminal I/O hardware :
i) Input unit e.g. keyboard
ii) Output unit e.g. screen
3) There are two types of terminals :
i) Dumb terminal
ii) Intelligent terminal.
i) Dumb terminal :
(a) A dumb terminal consists of a microprocessor on which small programs can run and limited amount of memory.
(b) It is responsible for basic I/O operations.
(¢) A dumb terminal does no processing on input characters.
ii) Intelligent terminal :
(a) An intelligent terminal has powerful hardware and software than a dumb terminal.
(b) It also has more amount of memory.
(c) It can carry out some process on input characters also it can process programs
idependently.
Q. 18) Explain the use of video RAM. Explain data bytes and attribute bytes.
Ans: i) The video RAM is basically the memory that the terminal hardware itself has.
i) Anytime all characters stored in the video RAM are displayed on the screen by the video
controller using display electronics.
iii) All particular informations (attributes) are stored in video RAM.
iv) Video RAM consists of 2000 databytes (0 to 1999) preceded by 2000 corresponding attribute bytes (0 to 1999) as shown in figure.
v) A typical alphanumeric screen can display 25 lines each consisting of 80 characters i.e. 25 X 80 = 2000 characters.
vi) Data Byte : All 2000 characters are stored in video RAM. To display any specific character on the screen at a specific position all ASCII or EBCDIC code for that character is to move in video RAM.
vii) Attribute Byte : There is one attribute byte for each data byte. This byte tells the video controller how the character is to be displayed. It signifies whether the corresponding data character which is stored next to it in the video RAM is to be displayed bold, underlined, blinking or in reverse video et
Q.19 Why keyboard is referred as memory map terminal? Explain the multiple memory location involved in the input-output operations between the keyboard and screen.
Ans: (a) Terminals have a video RAM generally with 2000 data bytes preceded by 2000 corresponding attribute bytes.
(b) Anytime, all the 2000 characters (25 lines X 80 columns on screen) stored in video RAM are displayed on the screen by the video controller.
(c) The video RAM is treated as part of the main memory only.
(d) Therefore, for moving any data in or out of the video RAM, ordinary load or store instructions are sufficient.
(e) So, keyboard is referred as memory terminal.
The following multiple memory locations are involved in the input-output operations between the keyboard and screen:
(a) Small memory within the keyboard itself : When a character is keyed in, the 8-bit ASCII
EBCDIC code is generated which is stored temporarily in the memory of the terminal itself.
(b) The video-RAM (data and attribute byte) : The ASCII or EBCDIC code for the character is
to move the video RAM at the corresponding position with appropriate co-ordinates.
(c) The operating system buffers : The operating system has one buffer for each terminal and two separate buffers for input and output operations.
(d) The I/O area of the application program : When the user finishes keying in the data, the data stored in operating system buffer for that terminal is flushed out to the I/O area of the application program which wants that data.
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