5.

Examines PC memory system to identify different type of memories

and their main characteristics.
Computer memory is any physical devices that used to store data, instructions and information
temporarily or permanently in Computer system.

There are two types of memory devices. They are;

1. Volatile memory
2. Non-volatile memory

Volatile Memory

Volatile memory is computer memory that requires an active power connection to function. When the
power to a volatile memory source is shut off, volatile memory loses its contents, and the information
is deleted.

The advantages of volatile memory are: it functions fast, and it is well-suited to protecting sensitive
information. This needs power to preserve stored data that means this type of memory totally depend
on electrical power.

Reason for this memory has semi-conductors. In side semi-conductor is having capacitors. The
capacitor can be either charged or discharged; these two states are taken to represent the two values of
a bit, conventionally called 0 and 1. Since even "non-conducting" transistors always leak a small
amount, the capacitors will slowly discharge, and the information eventually fades unless the
capacitor charge is refreshed periodically.

Below are volatile memories

1. Random Access Memory

2. Register Memory
3. Cache Memory

1. Random Access Memory

Alternatively referred to as main memory, primary memory, or system memory, Random Access
Memory (RAM) is a hardware device that allows information to be stored and retrieved on a
computer.

As the computer boots, parts of the operating system and drivers are loaded into memory, which allows
the CPU to process the instructions faster and speeds up the boot process. After the operating system has
loaded, system software and application software that the user works, such as the browser you're using to view
this page, is loaded into memory while it is running. If too many programs are open the computer will swap the
data in the memory between the RAM and the hard disk drive.

Special feature of RAM can access straight away main memory. For this memory addresses are used from each
storing locations. CPU can take data from anywhere in the RAM there’s no special procedure. So this memory
call Random Access Memory.

RAM is fast and different types of capacities they have. Example 512kB, 1GB, 2 GB, 4GB, 8GB, 16GB,etc.

1
There are two types of RAMs. They are;

1. DRAM – Dynamic RAM

2. SRAM – Static RAM

Dynamic Random Access Memory

Dynamic random access memory (DRAM) is a type of memory that is typically used for data or
program code that a computer processor needs to function. DRAM is a common type of random
access memory (RAM) used in personal computers (PCs), workstations and servers. Random access
allows the PC processor to access any part of the memory directly rather than having to proceed
sequentially from a starting place. RAM is located close to a computer’s processor and enables faster
access to data than storage media such as hard disk drives and solid-state drives.

DRAM stores each bit of data or program code in a storage cell consisting of a capacitor and a
transistor, and is typically organized in a rectangular configuration of storage cells. A DRAM storage
cell is dynamic in that it needs to be refreshed or given a new electronic charge every
few milliseconds to compensate for charge leaks from the capacitor.

DRAM is one option of semiconductor memory that a system designer can use when building a
computer. Alternative memory choices include static RAM (SRAM), electrically erasable
programmable read-only memory (EEPROM), NOR flash and NAND flash. Many systems use more
than one type of memory.

The main advantages of DRAM are its simple design, speed and low cost in comparison to alternative
types of memory. The main disadvantages of DRAM are volatility and high power consumption
relative to other options.

Static Random Access Memory

Static Random Access Memory (Static RAM or SRAM) is a type of RAM that holds data in a static
form, that is, as long as the memory has power. Unlike dynamic RAM, it does not need to be
refreshed. SRAM stores a bit of data on four transistors using two cross-coupled inverters. The two
stable states characterize 0 and 1. During read and write operations another two access transistors are
used to manage the availability to a memory cell. To store one memory bit it requires six metal-oxide-
semiconductor field-effect transistors (MOFSET). MOFSET is one of the two types of SRAM chips;
the other is the bipolar junction transistor. The bipolar junction transistor is very fast but consumes a
lot of energy. MOFSET is a popular SRAM type. The term is pronounced "S-RAM", not "sram."

Static RAM provides faster access to data and is more expensive than DRAM. SRAM is used for a
computer's cache memory and as part of the random access memory digital-to-analog converter on a
video card. SRAM is more expensive and holds less data per unit volume. Therefore, it is more
commonly used in cache and video card memory only.

2
 2. Memory Registers

Memory register is a high-speed storage area of the CPU. All data must
be represented in a register before it can be processed. For example, if
two numbers are to be multiplied, both numbers must be in registers, and
the result is also placed in a register. (The register can contain
the address of a memory location where data is stored rather than the
actual data itself.)

A register is a discrete memory location within the CPU designed to hold temporary data and
instructions.

A modern CPU will hold a number of registers. There are a number of general purpose registers that
the programmer can use to hold intermediate results whilst working through a calculation or
algorithm.

The number of registers that a CPU has and the size of each (number of bits) help determine the
power and speed of a CPU. For example a 32-bit CPU is one in which each register is 32 bits wide.
Therefore, each CPU instruction can manipulate 32 bits of data.

Then there are special-purpose registers designed to carry out a specific role. Each of these registers
are given a name so that the programmer can write their software code to access them. Different
manufacturers of CPU chips call them by different names (which makes life interesting for a
professional programmer!)

3. Cache Memory

Caches are designed to alleviate this bottleneck by making the data used most often by the CPU
instantly available. This is accomplished by building a small amount of memory, known
as primary orlevel 1 cache, right into the CPU. Level 1 cache is very small, normally ranging
between 2 kilobytes (KB) and 64 KB.

The secondary or level 2 cache typically resides on a memory card located near the CPU. The level 2
cache has a direct connection to the CPU. A dedicated integrated circuit on the motherboard, the L2
controller, regulates the use of the level 2 cache by the CPU. Depending on the CPU, the size of the
level 2 cache ranges from 256 KB to 2 megabytes (MB). In most systems, data needed by the CPU is
accessed from the cache approximately 95 percent of the time, greatly reducing the overhead needed
when the CPU has to wait for data from the main memory.

3
Computers are equipped with different levels of Cache Memory - They are:
1. Primary Cache Memory/Level 1 [L1]
2. Secondary Cache Memory/Level 2 [L2]
3. Tertiary Cache Memory/Level 3 [L3]

Primary Cache Memory/Level 1 [L1]

Primary cache memory (Level 1) is built within the relevant Central Processing Unit and it has a very
small capacity. When data and instructions are needed for the Central Processing Unit, at first it
checks to see whether those are there in the Primary Cache Memory. If not, it looks for the data in the
secondary cache memory. If found, it is brought from L2 cache to L1 cache.

Secondary Cache Memory/Level 2 [L2]

Secondary cache memory (Level 2), which is fixed on the motherboard and located very close to the
Central Processing Unit, possesses more capacity compared to the Primary cache memory. How ever,
the speed of the Secondary cache memory access is less than the Primary cache memory access. If the
required data is not in the secondary cache then it is ckecked in L3 cache memory.

Tertiary Cache Memory Level 3 [L3]

The Tertiary Cache Memory is usually found in modern computers and is fixed on the motherboard. It
possesses even more capasity than the L2 cache. However, the access speed is less than that for the
L2 cache. If the required data/ information is not available in the L3 cache, then it is checked in the
RAM.

4
Non-Volatile Memory (NVM)
Non-volatile memory is memory that does not require a connection to a power source to retain
information. Unlike volatile memory, NVM does not require its memory data to be periodically
refreshed. It is commonly used for secondary storage or long-term consistent storage. In other words,
when the power source to which the memory is connected is shut off, the memory does not lose the
information it has. Common examples of non-volatile memory are computer hard-disk drives, seen in
the picture above, or flash drives. Hard-disk drives hold more long-term data such as files and
documents. The advantage of non-volatile memory is longer-term retention of information

Non-volatile memory is highly popular among digital media; it is widely used in memory chips for
USB memory sticks and digital cameras. Non-volatile memory eradicates the need for relatively slow
types of secondary storage systems, including hard disks.

Non-volatile memory is also known as non-volatile storage.

Non-volatile data storage can be classified into two types:

 Mechanically addressed systems

 Electrically addressed systems

Mechanically addressed systems make use of a contact structure to write and read on a selected
storage medium. The amount of data stored this way is much larger than what's possible in
electrically addressed systems. A few examples of mechanically addressed systems are optical disks,
hard disks, holographic memory and magnetic tapes.

Electrically addressed systems are categorized based on the write mechanism. They are costly but
faster than mechanically addressed systems, which are affordable but slow. A few examples of
electrically addressed systems are flash memory, FRAM and MRAM.

Some examples of NVM include:

 All types of read-only memory

 Flash memory
 Most of the magnetic storage devices, such as hard disks, magnetic tape and floppy disks
 Earlier computer storage solutions, including punched cards and paper tape
 Optical disks

Read Only Memory

Read-only memory (ROM) is a type of storage medium that permanently stores data on personal
computers (PCs) and other electronic devices. It contains the programming needed to start a PC,
which is essential for boot-up; it performs major input/output tasks and holds programs or software
instructions.
Because ROM is read-only, it cannot be changed; it is permanent and non-volatile, meaning it also
holds its memory even when power is removed. By contrast, random access memory (RAM) is
volatile; it is lost when power is removed.

5
There are numerous ROM chips located on the motherboard and a few on expansion boards. The
chips are essential for the basic input/output system (BIOS), boot up, reading and writing to
peripheral devices, basic data management and the software for basic processes for certain utilities.

Other types of non-volatile memory include:

 Programmable Read-Only Memory (PROM)

 Electrically Programmable Read-Only Memory (EPROM)
 Electrically Erasable Programmable Read-Only Memory (EEPROM; also called Flash ROM)
 Electrically Alterable Read-Only Memory (EAROM)

However, these types of non-volatile memory can be altered and are often referred to as
programmable ROM. One of the original forms of non-volatile memory was mask-programmed
ROM. It was designed for specific data such as bootstrap, which contains the startup code. Mask-
programmed ROM can never be changed.
Because ROM cannot be changed and is read-only, it is mainly used for firmware. Firmware is
software programs or sets of instructions that are embedded into a hardware device. It supplies the
needed instructions on how a device communicates with various hardware components. Firmware is
referred to as semi-permanent because it does not change unless it is updated. Firmware includes
BIOS, erasable programmable ROM (EPROM) and the ROM configurations for software.

Some ROM is non-volatile but can be reprogrammed, this includes:

 PROM - Programmable read-only memory (PROM) is read-only memory ( ROM ) that can be
modified once by a user. PROM is a way of allowing a user to tailor a microcode program
using a special machine called a PROM programmer. This machine supplies an electrical
current to specific cells in the ROM that effectively blows a fuse in them. The process is
known as burning the PROM.

 Erasable Programmable Read-Only Memory (EPROM): This is programmed with the use of
very high voltages and exposure to approximately 20 minutes of intense ultraviolet (UV) light.

 Electrically-Erasable Programmable Read-Only Memory (EEPROM): This is used in many

older computer BIOS chips, is non-volatile storage that can be erased and programmed several
times and allows only one location at a time to be written or erased. An updated version of
EEPROM is flash memory; this allows numerous memory locations to be altered
simultaneously.

 Ultraviolet-Erasable Programmable Read-Only Memory (UV-EPROM): This is read-only

memory that can be erased by the use of ultraviolet light and then reprogrammed.

ROM is also often used in optical storage media such as various types of compact discs, including
read-only memory (CD-ROM), compact disc recordable (CD-R) and compact disc rewritable (CD-
RW).

6
 Flash Memory

Flash memory is a type of nonvolatile memory that erases data in units called blocks. A block stored
on a flash memory chip must be erased before data can be written, or programmed, to the microchip.
Flash memory retains data for an extended period of time whether a flash-equipped device is powered
on or off.

Flash memory evolved from erasable programmable read-only memory (EPROM) and electrically
erasable programmable read-only memory (EEPROM). Flash is technically a variant of EEPROM,
but the industry reserves the term EEPROM for byte-level erasable memory and applies the term flash
memory to larger block-level erasable memory. Devices using flash memory erase data at the block
level and rewrite data at the byte level (NOR flash) or multiple-byte page level (NAND flash). Flash
memory is widely used for storage and data transfer in consumer devices, enterprise systems and
industrial applications.

How flash memory works

A basic flash memory cell consists of a storage transistor with a control gate and a floating gate,
which is insulated from the rest of the transistor by a thin dielectric material or oxide layer. The
floating gate stores the electrical charge and controls the flow of the electrical current.

Comparison chart

Volatile memory Non-volatile memory

Does not require a power source to retain

Requires a power source to retain information.
information.

When power source is disconnected, information is lost When power source is disconnected,
or deleted. information is not deleted.

Often used for temporary retention of data, such as with Often used for long-term retention of data,
RAM, or for retention of sensitive data. such as files and folders.

Volatile vs Non-volatile memory

What are the differences between volatile and non-volatile memory? They are:

 Requirement (or lack thereof) of a power source for storage.

 Usage and advantage of each kind of memory.
Where volatile memory requires a power source to retain its information, a non-volatile memory
source does not. If the power source to volatile memory is shut down, the volatile memory will have

7
its information quickly deleted. If the power source to non-volatile memory is shut down, the non-
volatile memory retains its information.

Volatile memory is often used because it is faster, as well as because it is better suited to retaining
sensitive information because shutting off a power source can quickly delete that information.
Random access memory, or RAM, is a form of volatile memory. RAM is used to temporarily hold the
data required to run programs and applications on an electronic device.

Non-volatile memory is used because it is better suited to long-term retention of information. An

example of a non-volatile memory device is a computer hard-disk drive, which is used to hold data
such as files and documents.

Basic Input Output System – BOIS

Bios Chip and Battery

BIOS (basic input/output system) is the program a personal computer's microprocessor uses to get the
computer system started after you turn it on. It also manages data flow between the computer's
operating system and attached devices such as the hard disk, video adapter, keyboard, mouse and
printer.

BIOS is an integral part of your computer and comes with it when you bring it home. (In contrast, the
operating system can either be pre-installed by the manufacturer or vendor or installed by the user.)
BIOS is a program that is made accessible to the microprocessor on an erasable programmable read-
only memory (EPROM) chip. When you turn on your computer, the microprocessor passes control to
the BIOS program, which is always located at the same place on EPROM.

When BIOS boots up (starts up) your computer,

1. First identify all the hardware devices like HDD, Key Board, Mouse and others

2. Then determines whether all of the hardware devices are in place and operational.

3. After loads the operating system (or key parts of it) into your computer's random access
memory (RAM) from your hard disk or diskette drive.

This process is calling as Booting.

8
Complementary Metal Oxide Semi-conductor (CMOS Chip)

The CMOS is also a computer chip on the motherboard, but more specifically, it
is a RAM chip. This is a type of memory chip which stores information about the
computer components, as well as settings for those components. However,
normal RAM chips lose the information stored in them when power is no longer
supplied to them. To retain the information in the CMOS chip, a CMOS battery
on the motherboard supplies constant power to that CMOS chip. If the battery is
removed from the motherboard or runs out of juice (e.g. a dead CMOS battery),
the CMOS would lose the information stored in it. Any settings you made in the
CMOS setup would be lost, and you would need to make those settings changes
again after a new CMOS battery was put on the motherboard. For example, with
a dead CMOS battery the time and date will reset back to the manufactured date
if it has been off for a long period of time.

Secondary Storage

Secondary Memory or the Secondary Storage is the device which stores data and information
permanently. This is also called External Storage. There are internal storage devices as well as
external portable secondary storage devices.

1. Magnetic Media Devices

Data is stored here by using magnetic field.

Example 1 - Hard disk Drive

The Hard Disk Drive (HDD), which is commonly used to store data and information, is located inside
the computer. However, there are external hard disks as well. Today there are hard disks with large
capacity due to the development of the technology. The user can read and write the data stored in
HDD. Therefore, this medium is called Read / Write Memory.
The capacity of a hard disk ranges from 250 GB to 4 TB. The
maximum capasity will increase with technological
development.

Hard Disk is made of several components.

1. Platter – This is a metallic, aluminum or ceramic disk and
data can be stored on both sides using magnetic media. There
can be several platters in a hard disk.

9
2. Spindle – Holds the platter and rotates it.

3. Head – Reads the magnetic data in the platter and

writes on the platter. There are two heads for a
platter; one on top and one on bottom.

4. Actuator arm – Moves the head. This enables

reading and writing data anywhere in the platter.

5. Power connector – Connects the Hard Disk to

power which is needed for its function.

6. IDE connector – Transmits data to the platter

7. Actuator – An electronic device which moves

the arm connected to it. This is operated by a motor.

Example 2 - Magnetic Tape

Used mostly in sever computers for back up due to its larger storage
capasity. But tape is not used in day today life as it is slow in reading
and writing.

Example 3 - Optical media

Since data stored digitally on a disk is read and written by laser beam, it is called optical media.
Optical media is commonly used to carry data and information and there are several types. The
followings are some of them;

10
3. Solid State Devices
Since these devices contain solid parts and does not contain moving parts they are called Solid State
Devices. They are used to read and write data and information.

Example 1 - USB Flash Drive

This has become a very popular secondary storage device due to its
easy portability and the ability to read and write data fast.

Example 2 - Memory Card

This has the same function of USB flash drive. However, the
method of connecting to the computer is different and it is smaller in
physical size. This is used in digital cameras, mobile phones and
computer gaming devices.
E.g. - SD Card (Secure Digital Card)

Memory Devices

Volatile Memory Non-Volatile Memory

Register Cache RAM ROM Secondary

Memory Memory Storage
Density Lowest Higher than Higher than High Density Highest
Density Register Cache Density
Memory Memory
Capacity Lowest Higher than Higher than High Capacity Highest
Capacity Register Cache Capacity
Memory Memory
Access Associative Associative Random Random Sequential
Method Access Access Access Access Access or
Direct Access
Access Time Lowest Time. Higher time Higher Time Higher Time. Lowest seep
Fast than Register than Cache Lower Speed. and Highest
Memory. Memory. Access Time.
Faster than
RAM
Cost Highest Cost Lower cost Lower cost Lower cost Lowest Cost.
than Register than Cache than Volatile
Memory Memory Memory

11
Different Types of Memory Deviation

Comparing memory types

Memory Physical Access Capacity Price Access

Type Size Method Speed
Register Very Small Straight / Small High Cost Very High
Random
Cache Very Small Straight / Small High Cost Very High
Random
RAM Medium Straight / Medium Normal High
Random
ROM Medium Straight / High Small Slow
Random
Main High Straight / Very High Small Slow
Storage Random
(HDD)
Magnetic High Iterative Very High Small Very Slow
Tape
Storage

Associate Memory for Develop the Computer Efficiency.

Affection of Memory to develop the Computer Efficiency.

Memory is a vital part of both machine and human. Without it we as humans would not have any
consciousness and the ability to create. In machines, and especially in computers, memory allows the
machine to function in various ways, for example software to be run and data to be saved and
processed.

In computer system there are two types of memory. They are: Physical Memory and Virtual Memory.
The physical memory of a computer is mainly RAM. It's been proven that adding more memory to a
computer system increases its performance. The computer processor search for instructions that are
stored in the RAM memory of the computer to be executed. If those instructions are not stored in the
RAM memory, they will have to be transferred from the hard disk (or from any other storage system,
such as floppy disks, CD-ROMs and Zip-disks) to the RAM memory - the well-known process of
"loading" a program.

If there isn't enough room in memory for all the information the CPU needs, the computer has to set
up what's known as a virtual memory file. In so doing, the CPU reserves space on the hard disk to
simulate additional RAM. This process, referred to as "swapping", slows the system down. In an
average computer, it takes the CPU approximately 200ns (nanoseconds) to access RAM compared to
12,000,000ns to access the hard drive. To put this into perspective,

So, a greater amount of RAM memory means that more instructions fit into that memory and,
therefore, bigger programs can be loaded at once. All the present operating systems work with the
multitask concept, where we can run more than one program at once. You can, for example, have a
word processor and a spreadsheet open ("loaded") at the same time in the RAM memory. However,
depending on the amount of RAM memory that your computer has, it is possible that those programs
have too many instructions.

12
The problem is that the hard disk is a mechanical system, and not an electronic one. This means that
the data transfer between the hard disk and the RAM memory is much slower than the data transfer
between the processor and the RAM memory.

To have a clearer idea, suppose your computer has 64 MB of RAM memory and all the programs that
are loaded (open) at the same time use 100 MB. This means that the system is using the virtual
memory feature, making changes with the hard disk. However, if that same computer had 128 MB, it
would not be necessary to make any changes with the hard disk (with the same programs loaded),
making the computer faster.

The more peripherals you add to a computer, or the more advanced applications you ask it to perform,
the more RAM it needs to operate smoothly.

The terms 32-bit and 64-bit refer to the way a computer's processor (also called a CPU), handles
information. The 64-bit version of Windows handles large amounts of random access memory (RAM)
more effectively than a 32-bit system. To install a 64-bit version of Windows, you need a CPU that's
capable of running a 64-bit version of Windows. The benefits of using a 64-bit operating system are
most apparent when you have a large amount of random access memory (RAM) installed on your
computer, typically 4 GB of RAM or more. In such cases, because a 64-bit operating system can
handle large amounts of memory more efficiently than a 32-bit operating system, a 64-bit system can
be more responsive when running several programs at the same time and switching between them
frequently.

Types of Memory

Register Memory

According to the memory hierarchy CPU Register memory is high speed access memory and this
memory need to store data and command temporary. The read and write data can be done by clock
cycle.
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Cache Memory

Cache memory is placed in between computer main memory and central processing unit, which is low
capacity memory than main memory but access speed is higher than main memory. This memory can
be placed inside or outside of the processor. Cache memory is essential part for the high efficiency of
the computers. The cache memory inside the processor called Internal Cache Memory and the cache
memory outside the processor called External Cache Memory.

Virtual Memory

Computer main memory (RAM) capacity depends on the installed chips capacity. But this capacity
is not enough for process more programs working together. A computer can address more memory
than the amount physically installed on the system. This extra memory is actually called virtual
memory and it is a section of a hard disk that's set up to emulate the computer's RAM.

The main visible advantage of this scheme is that programs can be larger than physical memory.
Virtual memory serves two purposes. First, it allows us to extend the use of physical memory by
using disk. Second, it allows us to have memory protection, because each virtual address is translated
to a physical address.

Following are the situations, when entire program is not required to be loaded fully in main memory.

 User written error handling routines are used only when an error occurred in the data or
computation.

 Certain options and features of a program may be used rarely.

 Many tables are assigned a fixed amount of address space even though only a small amount of
the table is actually used.

 The ability to execute a program that is only partially in memory would counter many
benefits.

 Less number of I/O would be needed to load or swap each user program into memory.

 A program would no longer be constrained by the amount of physical memory that is

available.

 Each user program could take less physical memory, more programs could be run the same
time, with a corresponding increase in CPU utilization and throughput.

The purpose of virtual memory is to enlarge the address space, the set of addresses a program can
utilize. For example, virtual memory might contain twice as many addresses as main memory. A
program using all of virtual memory, therefore, would not be able to fit in main memory all at once.
Nevertheless, the computer could execute such a program by copying into main memory those
portions of the program needed at any given point during execution.

14
To facilitate copying virtual memory into real memory, the operating system divides virtual memory
into pages, each of which contains a fixed number of addresses. Each page is stored on a diskuntil it is
needed. When the page is needed, the operating system copies it from disk to main memory,
translating the virtual addresses into real addresses.

The process of translating virtual addresses into real addresses is called mapping. The copying of
virtual pages from disk to main memory is known as paging or swapping.
Modern microprocessors intended for general-purpose use, a memory management unit, or MMU, is
built into the hardware. The MMU's job is to translate virtual addresses into physical addresses. A
basic example is given below −

Virtual memory is commonly implemented by demand paging. It can also be implemented in a

segmentation system. Demand segmentation can also be used to provide virtual memory.

Disk Cleanup

Disk Cleanup is a Microsoft software utility first introduced with Windows 98 and included in all
subsequent releases of Windows. It allows users to remove files that are no longer needed or that can
be safely deleted.

Disk Cleanup can delete Temporary Internet Files (associated with Internet Explorer), Downloaded
Program Files, and Offline webpages. Disk Cleanup also allows you to empty the Recycle Bin, delete
Temporary Files, Compress Old Files, and delete Thumbnails.

15
Using Disk Cleanup will almost certainly rid your system of a substantial amount of unneeded files.
You could stop here and not suffer any ill consequences, but there are a lot of gaps and empty spaces
on the hard drive where the files were removed. This would be an excellent time to run
Disk Defragmenter to organize the hard drive into contiguous sections. The hard drive heads will
spend less time seeking all the pieces of a file and you'll see another performance boost.

CHECK DISK (CHKDSK)

CHKDSK is a system tool in DOS,OS/2 and Windows. It verifies the file system integrity of a
volume and fixes logical file system errors. To use CHKDSK, computers must have the Autochk.exe
file already on their system.

Admins have options for what switches to run with CHKDSK. For example, using /f tells CHKDSK
to fix any errors it finds. Using /r tells CHKDSK to look for and recover any readable information in
a disk's bad sectors.

On Windows NT operating systems, CHKDSK can also check the disk surface for bad sectors and
mark them. (In MS-DOS6.x and Windows 9x, this is a task done by Microsoft Scan Disk.)Windows
Server version of CHKDSK is RAID-aware and can fully recover data in bad sectors of a disk in
a RAID-1 or RAID-5 array if other disks in the set are intact.[1]
CHKDSK can be run from DOS prompt, Windows Explorer, Windows Command
Prompt or Recovery Console. It is similar to the fsck command in Unix.

Defragmentation

Defragmentation is the process of locating the noncontiguous fragments of data into which a
computer file may be divided as it is stored on a hard disk, and rearranging the fragments and
restoring them into fewer fragments or into the whole file. Defragmentation reduces data access time
and allows storage to be used more efficiently.

Defragmentation helps user to access the files on a hard disk for faster data access. After the files are
removed operating system tries to fill the vacant space with new files. If a new file is too big to fit, it
stores the excess data at another location. Over time, hundreds of files are scattered all over the disk
in non-contiguous space resulting n higher data access time.

Some operating systems automatically defragment storage periodically; others require that the user
occasionally use a special utility for this purpose. Windows 98 comes with a built-in defragmenter as
a "system tool" that the user can run. Windows NT did not come with a defragmenter because its file
system, NTFS, was designed to minimize fragmentation; however, NT users often find one necessary
and several vendors provide defragmenters. Windows 2000 comes with a "light" version of the
Diskeeper defragmenter; some users (especially corporate users) use Diskeeper or some other full-
function defragmentation program to manage storage efficiency and performance. Windows
XP comes with a utility called "Disk Defragmenter."

16
Device Drivers

More commonly known as a driver, a device driver or hardware driver is a group of files that
enable one or more hardware devices to communicate with the computer's operating system. Without
drivers, the computer would not be able to send and receive data correctly to hardware devices, such
as a printer.
If the appropriate driver is not installed, the device may not function properly, if at all. For Microsoft
Windows users, a driver conflict or an error can be seen in the Device Manager. If problems or
conflicts are encountered with a driver, the computer manufacturer or hardware manufacturer will
release a driver update to fix the problems.

There are device drivers for printers, displays, CD-ROM readers, diskette drives, and so on. When
you buy an operating system, many device drivers are built into the product. However, if you later
buy a new type of device that the operating system didn't anticipate, you'll have to install the new
device driver. A device driver essentially converts the more general input/output instructions of the
operating system to messages that the device type can understand

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