Shared devices

Printers
Projectors
Webcams
External hard drives
VIRTUAL DEVICES

In this report, we will discuss three types of storage media: shared devices, virtual devices, and
sequential access storage media.

Shared devices are assigned to several processes and can be shared by several processes at the same
time by interleaving their requests. Interleaving must be carefully controlled by the Device Manager. All
conflicts must be resolved based on pre-determined policies.

Shared devices are devices that can be used by multiple users or systems simultaneously. Here are some
examples of shared devices:

Printers: Printers are commonly shared devices in offices or schools, where multiple users need to print
documents.

Scanners: Scanners can also be shared devices, allowing multiple users to scan documents and save
them to a shared network location.

Projectors: Projectors are often shared devices in conference rooms or classrooms, where multiple users
may need to display presentations or videos.

External hard drives: External hard drives can be shared devices, allowing multiple users to access and
store files on a shared drive.

Webcams: Webcams are shared devices commonly used for video conferencing, allowing multiple users
to participate in a virtual meeting.

Smartboards: Smartboards are shared devices used in classrooms or meeting rooms, allowing multiple
users to interact with a digital whiteboard.

Network-attached storage (NAS) devices: NAS devices are shared devices that provide centralized
storage and file sharing capabilities for multiple users on a network.
Multi-function devices: Multi-function devices, such as all-in-one printers, scanners, and fax machines,
can be shared by multiple users for different purposes.

Virtual devices are dedicated devices that have been transformed into shared devices. For example,
printers (dedicated devices) can be converted into sharable devices through a spooling program.
Spooling is used to speed up slow dedicated I/O devices. Another example is the USB controller, a virtual
device that acts as an interface between OS, device drivers, and applications and the devices that are
attached via the USB host.

---
Sequential access storage media store records sequentially. Direct access storage devices (DASD) store
either sequential or direct access files. There are vast differences in their speed and sharability.

Paper was the first storage medium: printouts and punch cards were used. Magnetic tape was used for
secondary storage on early computer systems; now it is used for routine archiving and storing back-up
data. Records on magnetic tapes are stored serially and record length is determined by the application
program. Each record is identified by its position on the tape. Tape is mounted and fast-forwarded to
access a single record which can be a time-consuming process.

Data is recorded on 8 parallel tracks that run the length of tape. The ninth track holds parity bit for
routine error checking. Density of tape determines number of characters that can be recorded per inch.
Records can be stored individually or in blocks which provides an efficient way of storing records.

Interrecord gap (IRG) is the gap between records about 1/2 inch long regardless of the sizes of the
records it.

--
// In a direct access storage device, data can be accessed directly, while in a sequential access storage
device, data is accessed sequentially². Direct access takes less time since each block has a unique
address of its physical location, but in a sequential access storage device, everything is in a linear
sequence². All previous addresses in a sequential access storage device must be read before the current
address can be accessed². Originally, direct access storage devices included only HDDs and systems such
as magnetic drums and data cells, but DASDs now include SSDs, optical discs, PC storage devices and
redundant array of independent disks (RAID) storage systems¹.
I hope that helps! Let me know if you have any other questions//

//chatgpt
Shared devices are those that are assigned to multiple processes at the same time, and their requests
are interleaved to ensure efficient use of the device. However, it is essential to
carefully control the interleaving process using a device manager to avoid conflicts and resolve them
based on predetermined policies.

Virtual devices, which are dedicated devices transformed into shared

devices using a spooling program. Spooling is used to speed up slow dedicated I/O devices such
as printers. For instance, a USB controller is a virtual device that acts as an interface between
the operating system, device drivers, applications, and the devices attached via the USB host.

Moreover, the report delves into sequential access storage media and direct access storage devices
(DASD).
Sequential access media store records sequentially, while DASD store either sequential or direct access
files. The report highlights the vast differences in speed and sharability between the two types of
storage media.

The report also provides an overview of magnetic tapes, which were one of the earliest storage media
used for secondary storage on computer systems. Magnetic tapes store data serially, and each record
is identified by its position on the tape. To access a single record, the tape is mounted and fast-
forwarded,
which is a time-consuming process. However, data is recorded on eight parallel tracks that run the
length of
the tape, and the ninth track holds parity bit for routine error checking. The density of the tape
determines
the number of characters that can be recorded per inch, and records can be stored individually or in
blocks.

Blocking is an efficient way of storing records, as it requires fewer I/O operations and less tape is
wasted.
However, it also has some disadvantages, such as overhead and software routines needed for blocking,
deblocking,
and record-keeping, and buffer space wasted if only one logical record is needed.

The report concludes with the advantages and disadvantages of magnetic tapes. Magnetic tapes are
low-cost
and offer compact storage capabilities, making them a good medium for backing up magnetic disks and
long-term
archival file storage. However, they have access time variability and are not suitable for routine
secondary
storage or interactive applications.

//p1
In advanced operating systems, devices such as disk packs or other Direct Access Storage Devices
(DASDs) can be shared by multiple processes at the same time. This is done by interleaving their
requests, which is carefully controlled by the Device Manager. Conflicts between requests from different
processes must be resolved based on pre-determined policies.

Virtual devices are dedicated devices that have been transformed into shared devices. For example,
printers (which are typically dedicated devices) can be converted into sharable devices through a
spooling program. Spooling is used to speed up slow dedicated Input/Output (I/O) devices. Another
example of a virtual device is a USB controller, which acts as an interface between the Operating
System (OS), device drivers, and applications, and the devices that are attached via the USB host.

Simultaneous Peripheral Operation On-Line (SPOOL) is a technique used to allow multiple programs
to share a single physical device, such as a printer or tape drive. This technique is used to improve
the efficiency of I/O operations and reduce the wait time for processes that require access to these
shared devices.

//p2
Sequential Access Storage Media refers to storage devices that store data in a sequential order, one
after the other. They are different from Direct Access Storage Devices (DASD), which allow random
access to any data location. Sequential Access Storage Media include early storage mediums such as
printouts and punch cards, as well as modern mediums such as magnetic tapes.

Records on magnetic tapes are stored in a sequential order, and their length is determined by the
application program. Each record is identified by its position on the tape, and the tape must be fast-
forwarded to access a specific record, which can be a time-consuming process. Magnetic tapes use an
inter-record gap (IRG) and an inter-block gap (IBG) to separate records and blocks of records. The
transfer rate of a magnetic tape is determined by the tape density and transport speed.

Blocking is a technique used to efficiently store records on magnetic tapes. It involves grouping records
into blocks to reduce the number of I/O operations needed and minimize tape wastage. However,
blocking also requires overhead and software routines, which can waste buffer space if only one logical
record is needed.

Magnetic tapes have several advantages, including low cost, compact storage capabilities, and suitability
for long-term archival file storage and backing up magnetic disks. However, they also have
disadvantages, such as access time variability, poor suitability for routine secondary storage, and lack of
suitability for interactive applications.

//
The report is discussing shared devices, virtual devices, and sequential access storage media in advanced
operating systems.

Shared devices are devices that are assigned to multiple processes simultaneously. For example, disk
packs or other Direct Access Storage Devices (DASDs) can be shared by interleaving requests from
different processes, which is carefully controlled by the Device Manager. Conflicts between requests
from different processes must be resolved based on predetermined policies.

Virtual devices are dedicated devices that have been transformed into shared devices using a spooling
program. Spooling is used to speed up slow dedicated Input/Output (I/O) devices. Examples of virtual
devices include printers and USB controllers.

Storage media refers to any physical device or medium that is used to store digital data or information.
These media can be internal or external to a computer or other digital device and can range from hard
drives, solid-state drives, and memory cards to optical disks, magnetic tape, and cloud storage. Storage
media vary in their capacity, speed, cost, and durability, and are selected based on the specific needs
and requirements of the user or organization.

Sequential access storage media are storage media that store records sequentially. Examples of
sequential access storage media include paper, which was the first storage medium, and magnetic
tapes, which were used for secondary storage in early computer systems and are still used for routine
archiving and storing backup data. Data on magnetic tapes is recorded on eight parallel tracks that run
the length of the tape, and the density of the tape determines the number of characters that can be
recorded per inch. Records on magnetic tapes can be stored individually or in blocks. Blocking provides
an efficient way of storing records, but it requires overhead and software routines for blocking,
deblocking, and record-keeping, and buffer space is wasted if only one logical record is needed.

Magnetic tapes have advantages and disadvantages. They are low-cost and offer compact storage
capabilities, making them a good medium for backing up magnetic disks and long-term archival file
storage. However, they have access time variability and are not suitable for routine secondary storage or
interactive applications.

//

Shared Devices
 Assigned to several processes
 All conflicts must be resolved based on pre-determined policies

Virtual Devices
 Dedicated devices that have been transformed into shared devices
 Spooling is used to speed up slow dedicated I/O devices
 SIMULTANEOUS PERIPHERAL ORERATION ON-LINE

Sequential Access Storage Media

Storage media
1. Sequential access media - Store records sequentially
 2. Direct access storage devices (DASD) - Store either sequential or direct access files

There are vast differences in their speed and sharability

Paper - First storage medium: printouts, punch cards
Magnetic tape - Used for secondary storage on early computer systems; now used for routine archiving
& storing back-up data

Blocking- is a technique used to efficiently store records on magnetic tapes

 Advantages of blocking:
 Disadvantages of blocking:

 Advantages of magnetic tapes:

 Disadvantages of magnetic tapes: