HackTrick

There are plenty of software which locks drives and folder to protect your confidential data. Why waste money on such tools when you can do it with a simple registry tweak? Here’s how:
Caution: Before you attempt these tweaks, please make sure that you have a backup of your registry, just incase something goes wrong in the middle.
Locking Folders:
Consider you want to lock a folder named XXXX in your E:\, whose path is E:\XXXX.
Now open the Notepad and type the following

ren xxxx xxxx.{21EC2020-3AEA-1069-A2DD-08002B30309D}

Where xxxx is your folder name. Save the text file as loc.bat in the same drive.
Open another new notepad text file and type the following

ren xxxx.{21EC2020-3AEA-1069-A2DD-08002B30309D} xxxx

Save the text file as key.bat in the same drive.
Steps to lock the folder:
To lock the xxxx folder, simply click the loc.bat and it will transform into control panel icon which is inaccessible.
To unlock the folder click the key.bat file. Thus the folder will be unlocked and the contents are accessible.
Locking Drives:
We don’t usually prefer to lock our drives, but sometimes it becomes nesscary. Say for instance you might have stored your office documents in D:\ and you don’t want your kids to access it, in such case this technique can be useful for you. Please don’t try this tweak with your root drive (usually C:\ is the root drive) since root drives are not intended to be locked because they are mandatory for the system and application programs.
Start & Run and type Regedit to open Registry editor
Browse HKEY_CURRENT_USER\Software\Microsoft\Windows\Curre ntVersion\Policies\Explorer
Create a new DWORD value NoViewOnDrive and set its value as
2^ (Alpha Number of Drive Letter-1) where Alpha number are simple counting of alphabets from A to Z as 1 - 26
For example: to lock C:\, Alpha number of C is 3 so 2^ (3-1) = 4 (decimal value)
To lock more drives, calculate the value of each drive and then set sum of those numbers as value
To unlock your drive just delete the key from the registry

This tip is very interesting for home and some small office users, who wants to restrict user's ability to shutdown their computer. You can hide the Shutdown button from the Start menu using registry editor and also restrict access to shutdown .

Follow the given steps to hide system shutdown button from start menu:

*

To use this feature, you will need to be logged into your computer with

administrative rights.

*

Click Start button and type regedit in Run option then press Enter for next.
*

Here locate the location to:
*

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion \Policies\Explorer

*

Here in right side panel, right click to create a new DWORD value with name NoClose.
*

Now assign number 1 to its value data box.
*

Now close the registry editor and restart your computer after any changes to go into effect.
*

But next time, if you want to unhide the shutdown button then simply change the value data box to 0 or delete this DWORD item.
*

Again close the registry editor and restart your computer after any changes to go into effect.

*

Many times in schools, colleges & offices surfing some sites like orkut,etc are banned !
To overcome this you can unblock these or block some other websites and play pranks !

Do The Following :
For eg you want to block www.xyz.com !

* Open the folder C:\WINDOWS\system32\drivers\etc
* There you will find a file named HOSTS
* Click on the file and press SHIFT and now right click on it .
* From the right click menu select Open with .
* Now, select Notepad to open the file from the list !
* Now, in the file under the line 127.0.0.1 localhost add another line as 127.0.0.2 www.xyz.com.
* Now, File>>Save !

Now, open your web browser and try openning www.xyz.com , it will not load !

To unblock sites just do the opposite !

1.Minimize Hack

The first hack that I have here is the popular Firefox Minimize Hack that has recently flashed through the internet. The purpose of this hack tries to keep Firefox from eating up your physical RAM and instead puts the burden on your hard drive, or at least that is the general reason behind it. To implement this hack, perform the following steps.
1. With Firefox up and running, type about:config and hit enter.
2. Right click on the new page and select New -> Boolean.
3. In the pop-up window, type in “config.trim_on_minimize” without quotes and hit enter.
4. In the next pop-up window, select True and hit enter.
5. Restart your browser

Result:With that done, open up a bunch of tabs and monitor the memory usage. In my first run without this hack, Firefox was using 137.8 Mb of Ram. With all 30 tabs open again, Firefox was using 118.4 Mb, but when minimized this dropped to an astounding 4 Mb. However, this was too good to be true, I left Firefox minimized and came back 12 minutes later and the memory use had slowly creeped up to 42.4 Mb. While this was 10 times larger than the initial 4.2 Mb, I was still saving about 75 Mb.

This next group of hacks all relate to the network.http group in about:config. Basically these various options open up your network connection to Firefox, permitting it to access information online as quickly as your connection will permit you. Since the majority of readers utilize broadband connections, this will benefit you, but people using dial up modems (56k) this is not going to benefit you much, sorry. To implement these hacks, perform the following steps.

1. With Firefox up and running, type about:config and hit enter.
2a. Find the entry called “network.http.pipelining” and set it to “true”.
2b. Find the entry called “network.http.proxy.pipelining” and set it to “true”.
2c. Find the entry called “network.http.pipelining.maxrequests” and set it to 16-32, but beware, if set too high you may risk banning yourself from various servers by being mistaken for a DoS attack.
3. Restart your browser.
Result:With these options enabled, webpages load faster, pictures in particular. When I went to Flickr.com and started clicking around, all the pictures loaded at one time unlike how it used to load one picture at a time.

This can be an impressive bit of personalization. Use your name or moniker to brand Internet Explorer. Go to HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\ and left-click on Main to change the string "Window Title" to whatever you wish.

here are the steps to perform:-

Logic: the server has a major bug in it, by which it fails to block two simultaneous connections
from the phone and establishes a connection with full internet working,

Supported devices: all phones with multichannel gprs support

For connection on your mobile phone:-

1) Make two connections like bsnlportal and BSNLPORTAL1

(names of profile don’t matter, u can keep one as billgates and shahrukhkhan lol..
the basic purpose of names is to enable the user to differentiate between the two accounts,)

2) Select the application you got to have the full connection working on.
Surpassingly “web” now just select “bsnlportal” profile and select a link like wap.cellone.in the page will get open,
just press the red button such that the “web” application goes in the background.
Make sure that the gprs connection is still established with the web app.
Two parallel lines on the top left of the screen will confirm this

3) Now open any other app that requires web connection like opera.
Select BSNLPORTAL and open any other link like wap.google.com, u will get error –

the aim of using the other app is to perform multi-channel gprs,
this is verified by seeing some dots on the pre-existing connection established by “web”

(step 2)

“Access denied.

Technical description:
403 Forbidden - You are not allowed to communicate with the requested resource.”

4) close opera and open web and open a site like esato.com

5) if everything is done as said here then esato will load and voila! We have the whole internet!

For connection on pc.

1)create a connection and enter the number to be dialed as *99***1#

2) enter the following string as extra initialization command

3)now dial from pc, the connection will be established

4)pick the phone and open “web” open “wap.cellone.in” the phone shows error .

5) close “web” and then from the browser open www.google.com
and voila! The whole intenet is here

settings for profiles

apn: celloneportal
ip: 192.168.51.163
port : 8080

leave other fields blank as they are of the least concern!

the browser settings on pc too go the same as mentioned above!

Requirements:
1. Airtel live (available 4 free)
2. Nokia series60 handset eg 6600,6630,n series,7610,6670 etc
3. Opera wap browser 4 mobile
Procedure:-

1. Go to ur connection settings and make a new internet profile using the default settings of airtel live.
name that new profile as nething(for eg masala); change the home page of that profile to nething u like for
eg www.google.com.

2. Go to ur Opera browser and set the default connection as AIRTEL LIVE. this is the original settings u received
thru airtel.

3. Go to the services(in n6600) and Web(N6630) and change the default profile for connection as masala (newer one).

**Note: always make sure that ur access point is airtelfun.com

Apply:-

1. Open Opera and u will see that homepage of Airtel Live is opened. Minimize the application.

2. Now open web using the duplicate Profile and u will see that two gprs connections will work simultaneously
and at the web or the services page it will show "Unable to connect" or any error. well thats the signal of ur success.

3. Simply go on the Opera with web on and open any site u want for free. No Charges No nothing.

U can also use it through ur computer..........







someone said dis too

The main principle behind this is we hav 2 fool the bsnl techies 2 activate portal and thus get gprs
activated / get "G" signal on ur cell as bsnl portal (wap.cellone.in) needs "gprs signal on ur cel
(whether gprs is formaly activated/registerd or not (by my method )i dont know)

NORMALLY THEY DONT DO THAT INSPITE OF THE FACT THAT THEY SHOULD ACTIVATE GPRS SIGNAL SERVICE FOR PORTAL!!!
AND THEY WILL GIVE U NO OF REASONS----
---THAT portal is message based , so go to cellone icon in menu and use that sms based portal (what the f**k)
---THAT portal service will be activated when u will activate gprs by filling up form and registering at nearest CCN!!
---THAT ur handset has some problems (if u say that "G" signal is not present)
----etc,etc!!

U HAVE 2 ACTIVATE PORTAL FIRST WHICH IS FREE AND U CAN EAT UP CC'S FOR THIS REASON!!
SO WHAT U HAV 2 DO IS--
1) SEND PORTAL to 3733 AND CONFIRMATION SHD COME WITH 5 MIN AT-MAXIMM !!
2) SEND FOR ATLEAST 20-30 TIMES (CAN B ANY MORE THAN THAT)
JUST S**K UP THE NETWORK(3733) WITH THESE MESSAGES !!!
THAT'S FREE NO!! BOTH ON POST AND PRE!!
3) NOW ALONG ALSO SEND 20-40 SMS AS GPRS TO 3733
(NO OF SMS DIRECTLY PROPORTIONAL 2 HATE FOR BSNL AND HOW EARLY U WNAN GET UR GPRS ACTIVATED) this is also
free both on post and pre!!
4) U WILL GET CONFIRMATION IN BOTH CASES AND MSG TELLS U 2 GET SETTINGS FROM 9400024365, THE NO OF CC!!
HERE AT MY PLACE I CAN DIAL 9419024365 ALSO!
BOTH R TOLL FREE AND BOTH R LOCATED IN CHANDIGARH!!!
(((((((AND SOME OF THE CC'S SAY they cant give such sensitive information that where they r located,
as if thay have a 3 rd world of their own! and the other dumbs said that they r in chandigarh!!!!)))))

I WOULD ADVISE ALL FIRST, 2 call them once 2 get the settings!!
(most of the times that is incorect but gives u an idea of settings in ur area))
Try and in ur 1 st call only,
talk roughly and tell them u r calling 10-20th time just for settings and is that their service!!!
5) Now when u get them save them AND plz post them here!!!
6) now GET ATLEAST 2-3 COMPLAINTS REGISTERED( each after 1 day) THAT UR PORTAL HAS NOT ACTIVATED AND GET THEIR SERIAL NO.
and in the end bombard them abt the status of all those complaints !!
b4 registering ur complaint they will hesitate much and always say taht they will b sendin new settings
which r accurate! but dont belive them and just register complaints!!
6)AFTER THAT, u have 2 only wait until "G" signal is there on ur screen!!

LOOK, WHAT I HAVE WRIITEN ABV IS METHOD by which i got activated my "G" service !!! without fillin any form or
such and without any money drain!!
may be since it bypasses the formal way of registeration, that is why this trick is working !!!!!!!!!!!!


U may also Try this

first open ur msg window and type LIVE and send it to 2567 so that after 5 min u get the setting of Airtel
Live or if u have already no need for this procedure.
now then open that setting and copy all the settings from it and create one access point manually
which has all the settings like Airtel Live has.
now only one change will be there and it would be in access point name which is "Airtelmms.com"
instead of originally "Airtelgprs.com".
ok u've done it just active that setting and access free airtel gprs on ur phone.



a recent comment says dat

Guys i tried and its working, I'm using airtel chennai,..the Method TWO worked,
also i request everyone to change the Phone number from *99***2 to *99***1 and its working,..
it'll get connected at 462.8kbps but its the speed between the phone and your computer but actual BAndwidth is 42kbps

these are all the tricks i know so far

~cheers~
You need a PC or a Laptop and the required connectivity tools ,ie.,
Serial/USB cable OR Infrared Device OR Bluetooth dongle

1) Activate Airtel Live! ( It’s FREE so no probs)

2) Create TWO Airtel gprs data accounts (yep TWO) and select the
FIRST as the active profile.

3) Connect your mobile to the PC (or Laptop) and install the driver for
your mobile’s modem.

4) Create a new dial-up connection using the NEW CONNECTION
WIZARD as follows

Connecting Device : Your mobile’s modem
ISP Name : Airtel (or anything you like)
Phone Number : *99***2# / Try 99***1
Username and Password : blank

5) Configure your browser and download manager to use the proxy
100.1.200.99 and port 8080.( My advice is to use Opera since you
can browse both wap and regular websites)

6) Connect to the dial-up account. You will be connected at 115.2
kbps (but remember, that is a bad joke).

7) Pick up your mobile and try to access any site. You will get “Access
Denied…”(except for Airtel Live!). IT DOES NOT MATTER.
Keep the mobile down.

8 ) On the PC ( or Laptop) open your browser, enter any address ,
press ENTER and…….WAIT

9) After a few seconds the page will start to load and you have the
WHOLE internet at your disposal.


************************************************************************************

Under DATA COMM
~~~~~~~~~~~~

APN : airtelfun.com

USERNAME : blank

PASSWORD : blank

PASS REQ : OFF

ALLOW CALLS : AUTOMATIC

IPADDRESS :

DNSADDRESS :

DATA COMP : OFF

HEADER COMP : OFF


Under INTERNET PROFILES
~~~~~~~~~~~~~~~~

INTERNET MODE : HTTP or WAP (both worked for me)

USE PROXY : YES

IP ADDRESS : 100.1.200.99

PORT : 8080

USERNAME :

PASSWORD :

No Risk Here, Try it and Enjoy

*************************************************************************************


1st go to settings menu then to connectivity tab now choose the option Data comm.
then "DATA ACCOUNTS" go to new account now the settings r as follows

ACCOUNT TYPE:GPRS
NEW ACCOUNT NAME:A1
APN:airtelfun.com
usr name: (blank)
password: (blank)

now save it
NOW!
go to Internet Setting in connectivity here choose intrnet profile--go to new profile setting are as below
NAME:A1
CONNECT USING:A1(which was created in data comm.)
save it
now u would be able to see it now selest it and take "more" option
then select setting here in use proxy option it will be selected no if it is no then change it into yes
now go to proxy adress and give the adress as
100.1.200.99 and then the port number as 8080
Usr name:
password:
now save all the settings u made . come back 2 connectivity
choose streaming settings now in connect using option choose a1 that we created leave the use proxy option as no itself
THESE R THE SETTINGS
now access airtellive! from ur activated SE phone goto VIDEO GALLERY OR VIDEO UNLIMITED(varies according to states)
choose live streaming then choose CNBC OR AAJTAK WHILE CONNECTING TO MEDIA SERVER cancel AFTER 9 or 10 sec then
type any web adress if it shows access denied then once again select CNBC and wait for a few more sec than before
if its fully connected also no prob its free then cancel it or if ur connected then stop it and the internet is
ready to take of .GOOD LUCK SE AIRTEL USERS


*************************************************************************************

well theres sort of a way but its not tryed much:

Create an access point for your phone, going bye my 7610 i follow this path,

Settings, Connection, Access points, Options, New access point,default settings

now these are the settings wich i have used

ConnectionName: realy you can use anything here even poopoo if you want as long as you can remember it,

Data bearer: GPRS

Access point name, ok now you need to put the name that you gave to your (BT,NTL,or wot eva)

connection when pairing it up with pc, ok now

Username: just put none

Password: No

Authentication: Normal

Gateway IP Address : 0.0.0.0

ok now go to

settings,,connection,,and select GPRS

set the GPRS connection to when available, and the access point to none

thats it for the settings... ok now;


Create a serial port connection from ur pc to ur phone ,

this serial connection must always be on when you want to use your pc internet connection as a gprs connection for ur phone!!



Install the software u need to surf the web ,,netfronts cool

hope this wrks with you matey.........

Trick Airtel Live GPRS access for PC 115.2 Kbps Internet

u need a PC or a Laptop and the required connectivity tools ,ie.,

Serial/USB cable OR Infrared Device OR Bluetooth dongle



1) Activate Airtel Live! ( It's FREE so no probs)



2) Create one Airtel gprs data accounts and select the

it as the active profile.

CODEUnder DATA COMM

~~~~~~~~~~~~

GATEWAY : 100.1.200.99

APN : airtelfun.com



USERNAME : blank



PASSWORD : blank



PASS REQ : OFF



ALLOW CALLS : AUTOMATIC

IPADDRESS :

DNSADDRESS :

DATA COMP : OFF

HEADER COMP : OFF

Under INTERNET PROFILES

INTERNET MODE : HTTP or WAP (both works)

USE PROXY : YES

IP ADDRESS : 100.1.200.99



PORT : 8080



USERNAME :



PASSWORD :



3) Connect your mobile to the PC (or Laptop) and install the driver for

your mobile's modem.



4) Create a new dial-up connection using the NEW CONNECTION

WIZARD as follows



Connecting Device : Your mobile's modem

ISP Name : Airtel (or anything you like)

Phone Number : *99***1#

Username and Password : blank



5) Configure your browser and download manager to use the proxy

100.1.200.99 and port 8080.( My advice is to use Opera since you

can browse both wap and regular websites)



6) Connect to the dial-up account. You will be connected at 115.2

kbps (NOTE* 115.2 KBPS IS A SPEED BETWEEN UR PC AND PHONE ).



7) Pick up your mobile and try to access any site. You will get "Access

Denied..."(except for Airtel Live!). IT DOES NOT MATTER.

Keep the mobile down.



8 ) On the PC ( or Laptop) open your browser, enter any address ,

press ENTER and.......WAIT



9) After a few seconds the page will start to load and you have the

WHOLE internet at your disposal.





QUOTE

pls Note If u are getting any error wile dialing a dial up connection than go to

Control panel>> Phone and modem>>>select modem and click on its
properties >>advanced

and enter the following initialization commands

CODEAT+CGDCONT=2, "IP","airtelfun.com","",0,0

and click on ok now connect to gprs it will be conn

Activate AIRTEL LIVE on Your GPRS Phone.......Which is free of cost as you all know.
In airtel live ,there is a yahoo zone which gives you Y!Mail n Y! Messenger service for Rs 30/per month.......
but using my method you can run the Y!Messenger for as long as you want for ZERO CHARGE.......

Go to 'Go to Address' option.....

Type in http://in.mm.yahoo.com n as page opens...LOGIN n njoy uninterrupted n free messenger services.........

CONNECTING PEOPLE..........GAUFIRE..............LOlzzzzzzzzzz

Happy Chatting...........

====Memory hierarchy====

[[Image:NEC 128mb ram.JPG|right|thumb|One module of 128MB NEC SD-RAM.]]

Many computer systems have a memory hierarchy consisting of [[CPU register]]s, on-die [[Static random access memory|SRAM]] caches,

external [[cache]]s, [[DRAM]], [[paging]] systems, and [[virtual memory]] or [[swap space]] on a hard drive.

This entire pool of memory may be referred to as "RAM" by many developers, even though the various subsystems can have very different [[access time]]s,

violating the original concept behind the ''random access'' term in RAM. Even within a hierarchy level such as DRAM,

the specific row, column, bank, rank, channel, or [[interleave]] organization of the components make the access time variable,

although not to the extent that rotating [[storage media]] or a tape is variable. (Generally,

the memory hierarchy follows the access time with the fast CPU registers at the top and the slow hard drive at the bottom.)

In most modern personal computers,

the RAM comes in easily upgraded form of modules called '''[[DIMM|memory module]]s''' or '''[[DIMM|DRAM module]]s'''

about the size of a few sticks of chewing gum. These can quickly be replaced should they become damaged or too small for current purposes.

As suggested above, ''smaller'' amounts of RAM (mostly SRAM) are also integrated in the [[CPU]] and other [[IC]]s on the [[motherboard]],

as well as in hard-drives, [[CD-ROM]]s, and several other parts of the computer system.

=====Swapping=====

If a computer becomes low on RAM during intensive application cycles, the computer can resort to [[swapping]]. In this case,

the computer temporarily uses [[hard drive]] space as additional memory.

Constantly relying on this type of backup memory is called [[Thrash (computer science)|thrashing]],

which is generally undesirable because it lowers overall system performance. In order to reduce the dependency on swapping,

more RAM can be installed.

The notion of read-only data can also refer to file system permissions.

Computer memory types

Volatile

* DRAM, e.g. DDR SDRAM

* SRAM

* Upcoming

o Z-RAM

o TTRAM

* Historical

o Williams tube

o Delay line memory

Non-volatile

* ROM

o PROM

o EAROM

o EPROM

o EEPROM

* Flash memory

* Upcoming

o FeRAM

o MRAM

o CBRAM

o PRAM

o SONOS

o RRAM

o Racetrack memory

o NRAM

* Historical

o Drum memory

o Magnetic core memory

o Plated wire memory

o Bubble memory

o Twistor memory

Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices.

Because data stored in ROM cannot be modified (at least not very quickly or easily),

it is mainly used to distribute firmware (software that is very closely tied to specific hardware, and unlikely to require frequent updates).

Modern semiconductor ROM chips are not immediately distinguishable from similar chips like RAM modules, except by the part numbers printed on the package.

In its strictest sense, ROM refers only to mask ROM (the oldest type of solid state ROM),

which is fabricated with the desired data permanently stored in it, and thus can never be modified.

However, more modern types such as EPROM and flash EEPROM can be erased and re-programmed multiple times;

they are still described as "read-only memory" because the reprogramming process is generally infrequent, comparatively slow,

and often does not permit random access writes to individual memory locations, which are possible when reading a ROM.

Despite the simplicity of mask ROM, economies of scale and field-programmability often make reprogrammable technologies more flexible and inexpensive,

so that mask ROM is rarely used in new products as of 2007.

A typical PROM comes with all bits reading as 1. Burning a fuse during programming causes its bit to read as 0.

The memory can be programmed just once after manufacturing by "blowing" the fuses (using a PROM blower), which is an irreversible process.

Blowing a fuse opens a connection while blowing an antifuse closes a connection (hence the name).

Programming is done by applying high-voltage pulses which are not encountered during normal operation (typically 12 to 21 volts).

Read-only means that, unlike the case with conventional memory, the programming cannot be changed (at least not by the end user).

Advantages

* Reliability

* Stores data permanently

* Moderate price

* Built using integrated circuits, rather than discrete components.

* Fast: speed is between 35ns and 60ns.

EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared), which stands for Electrically Erasable Programmable Read-Only Memory,

is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed,

e.g., calibration tables or device configuration.

When larger amounts of static data are to be stored (such as in USB flash drives) a specific type of EEPROM such as flash memory is more economical than

traditional EEPROM devices.

"Cache memory" redirects here. For the general use, see cache.

Diagram of a CPU memory cache

Diagram of a CPU memory cache

A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory.

The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations.

As long as most memory accesses are to cached memory locations,

the average latency of memory accesses will be closer to the cache latency than to the latency of main memory.

When the processor needs to read from or write to a location in main memory,

it first checks whether a copy of that data is in the cache. If so, the processor immediately reads from or writes to the cache,

which is much faster than reading from or writing to main memory.

A hard disk drive (HDD), commonly referred to as a hard drive, hard disk, or fixed disk drive,

[1] is a non-volatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces.

Strictly speaking, "drive" refers to a device distinct from its medium, such as a tape drive and its tape, or a floppy disk drive and its floppy disk.

Early HDDs had removable media; however, an HDD today is typically a sealed unit (except for a filtered vent hole to equalize air pressure) with fixed media.[2]

An HDD is a rigid-disk drive, although it is probably never referred to as such. By way of comparison,

a so-called "floppy" drive (more formally, a diskette drive) has a disc that is flexible. Originally, the term "hard" was temporary slang,

substituting "hard" for "rigid", before these drives had an established and universally-agreed-upon name.

Some time ago, IBM's internal company term for a HDD was "file".[citation needed]

A floppy disk is a data storage medium that is composed of a disk of thin,

flexible ("floppy") magnetic storage medium encased in a square or rectangular plastic shell.

Floppy disks are read and written by a floppy disk drive or FDD, the initials of which should not be confused with "fixed disk drive",

which is another term for a hard disk drive. Invented by IBM, floppy disks in 8-inch (200 mm), 5¼-inch (133⅓ mm),

and the newest and most common 3½-inch (90 mm) formats enjoyed many years as a popular and ubiquitous form of data storage and exchange,

from the mid-1970s to the late 1990s. However, they have now been largely superseded by flash and optical storage devices.

CD-ROM (an abbreviation of "Compact Disc read-only memory") is a Compact Disc that contains data accessible by a computer.

While the Compact Disc format was originally designed for music storage and playback,

the format was later adapted to hold any form of binary data. CD-ROMs are popularly used to distribute computer software,

including games and multimedia applications, though any data can be stored (up to the capacity limit of a disc).

Some CDs hold both computer data and audio with the latter capable of being played on a CD player,

whilst data (such as software or digital video) is only usable on a computer (such as PC CD-ROMs). These are called Enhanced CDs.

Although many people use lowercase letters in this acronym, proper presentation is in all capital letters with a hyphen between CD and ROM.

It was also suggested by some, especially soon after the technology was first released, that CD-ROM was an acronym for "Compact Disc read-only-media",

or that it was a more 'correct' definition. This was not the intention of the original team who developed the CD-ROM,

and common acceptance of the 'memory' definition is now almost universal.

This is probably in no small part due to the widespread use of other 'ROM' acronyms such as Flash-ROMs and EEPROMs where 'memory' is usually the correct term.

Access time is the time delay or latency between a request to an electronic system, and the access being completed or the requested data returned.

* In a telecommunications system, access time is the delay between the start of an access attempt and successful access.

Access time values are measured only on access attempts that result in successful access.

* In a computer, it is the time interval between the instant at which an instruction control unit initiates a call for data or a request to store data,

and the instant at which delivery of the data is completed or the storage is started.

* In disk drives, disk access time is the time required for a computer to process data from the processor and then retrieve the required data from a storage device,

such as a hard drive. For hard drives, disk access time is determined by a sum of the seek time, rotational delay and transfer time.

o Seek time - is the time for the access arm to reach the desired disk track.

o Rotational delay - the delay for the rotation of the disk to bring the required disk sector under the read-write mechanism.

It greatly depends on rotational speed of a disk, measured in revolutions per minute (RPM).

o Transfer time - time during which data is actually read or written to medium, with a certain throughput.

Theoretical averages of the access time or latency are shown in the table below,

based on the empirical relation that the average latency in milliseconds for such a drive is about 30000/RPM:

Seek Time : It is the amount of time between when the CPU requests a file and when the first byte of the file is sent to CPU.

Times between 10 to 20 milliseconds are common.

In computing, memory latency is the time between initiating a request for a byte or word in memory until it is retrieved.

If the data are not in the processor's cache,

it takes longer to obtain them, as the processor will have to communicate with the external memory cells.

Latency is therefore a fundamental measure of the speed of memory: the less the latency, the faster the reading operation.

However, memory latency should not be confused with memory bandwidth, which measures the throughput of memory.

It is possible that an advance in memory technology increases bandwidth (an apparent increase in performance),

and yet latency increases (an apparent decrease in performance). For example, DDR memory has been superseded by DDR2,

and yet DDR2 has significantly greater latency when both DDR and DDR2 have the same clock frequency. DDR2 can be clocked faster,

however, increasing its bandwidth; only when its clock is significantly greater than that of DDR will DDR2 have lower latency than DDR.

Memory latency is also the time between initiating a request for data and the beginning of the actual data transfer. On a disk,

latency is the time it takes for the selected sector to come around and be positioned under the read/write head.

In computer technology, an opcode (operation code) is the portion of a machine language instruction that specifies the operation to be performed.

Their specification and format are laid out in the instruction set architecture of the processor in question

(which may be a general CPU or a more specialized processing unit). Apart from the opcode itself,

an instruction normally also has one or more specifiers for operands (i.e. data) on which the operation should act,

although some operations may have implicit operands, or none at all. There are instruction sets with nearly uniform fields for opcode and operand specifiers,

as well as others (the x86 architecture for instance) with a more complicated, varied length structure. [1]

In computer programming languages, the definitions of operator and operand are almost the same as in mathematics.

Additionally, in assembly language, an operand is a value (an argument) on which the instruction, named by mnemonic,

operates. The operand may be a processor register, a memory address, a literal constant, or a label.

A simple example (in the PC architecture) is

MOV DS, AX

where the value in register operand 'AX' is to be moved into register 'DS'. Depending on the instruction, there may be zero, one, two, or more operands.

execution of instruction

The context in which execution takes place is crucial. Very few programs are executed on a bare machine.

Programs usually contain implicit and explicit assumptions about resources available at the time of execution.

Most programs are executed with the support of an operating system and run-time libraries specific to the source language that provide crucial

services not supplied directly by the computer itself. This supportive environment, for instance,

usually decouples a program from direct manipulation of the computer peripherals, providing more general, abstract services instead.

Pipelining redirects here. For HTTP pipelining, see HTTP pipelining.

Basic five-stage pipeline in a RISC machine (IF = Instruction Fetch, ID = Instruction Decode, EX = Execute, MEM = Memory access, WB = Register write back)

Basic five-stage pipeline in a RISC machine (IF = Instruction Fetch, ID = Instruction Decode, EX = Execute, MEM = Memory access, WB = Register write back)

An instruction pipeline is a technique used in the design of computers and other digital electronic devices to increase their instruction throughput

(the number of instructions that can be executed in a unit of time).

Pipelining assumes that with a single instruction (SISD) concept successive instructions in a program sequence will overlap in execution,

as suggested in the next diagram (vertical 'i' instructions, horizontal 't' time).

Most modern CPUs are driven by a clock. The CPU consists internally of logic and flip flops. When the clock signal arrives,

the flip flops take their new value and the logic then requires a period of time to decode the new values.

Then the next clock pulse arrives and the flip flops again take their new values,

and so on. By breaking the logic into smaller pieces and inserting flip flops between the pieces of logic,

the delay before the logic gives valid outputs is reduced. In this way the clock period can be reduced.

For example, the RISC pipeline is broken into five stages with a set of flip flops between each stage.

1. Instruction fetch

2. Instruction decode and register fetch

3. Execute

4. Memory access

5. Register write back

Hazards: When a programmer (or compiler) writes assembly code,

they make the assumption that each instruction is executed before execution of the subsequent instruction is begun.

This assumption is invalidated by pipelining. When this causes a program to behave incorrectly, the situation is known as a hazard.

Various techniques for resolving hazards such as forwarding and stalling exist.

A non-pipeline architecture is inefficient because some CPU components (modules) are idle while another module is active during the instruction cycle.

Pipelining does not completely cancel out idle time in a CPU but making those modules work in parallel improves program execution significantly.

Processors with pipelining are organized inside into stages which can semi-independently work on separate jobs.

Each stage is organized and linked into a 'chain' so each stage's output is inputted to another stage until the job is done.

This organization of the processor allows overall processing time to be significantly reduced.

Unfortunately, not all instructions are independent. In a simple pipeline, completing an instruction may require 5 stages.

To operate at full performance, this pipeline will need to run 4 subsequent independent instructions while the first is completing.

If 4 instructions that do not depend on the output of the first instruction are not available,

the pipeline control logic must insert a stall or wasted clock cycle into the pipeline until the dependency is resolved.

Fortunately, techniques such as forwarding can significantly reduce the cases where stalling is required.

While pipelining can in theory increase performance over an unpipelined core by a factor of the number of stages

(assuming the clock frequency also scales with the number of stages), in reality, most code does not allow for ideal execution.

Depending on architecture, the operands may be register values, values in the stack, other memory values,

I/O ports, etc, specified and accessed using more or less complex addressing modes. The types of operations include arithmetics, data copying,

logical operations, and program control, as well as special instructions (such as CPUID and others).

An instruction cycle (also called fetch-and-execute cycle,

fetch-decode-execute cycle (FDX) is the time period during which a computer reads and processes a machine language instruction from its memory or

the sequence of actions that the central processing unit (CPU) performs to execute each machine code instruction in a program.

The name fetch-and-execute cycle is commonly used. The instruction must be fetched from main memory,

and then executed by the CPU. This is fundamentally how a computer operates, with its CPU reading and executing a series of instructions

written in its machine language. From this arise all functions of a computer familiar from the user's end.

The fundamental operation of most CPUs, regardless of the physical form they take,

is to execute a sequence of stored instructions called a program.The program is represented by a series of numbers that are kept in

some kind of computer memory. There are four steps that nearly all von Neumann CPUs use in their operation: fetch, decode, execute, and writeback.

Abbreviation for central processing unit, and pronounced as separate letters.

The CPU is the brains of the computer. Sometimes referred to simply as the central processor,but more commonly called processor,

the CPU is where most calculations take place. In terms of computing power, the CPU is the most important element of a computer system.

On large machines, CPUs require one or more printed circuit boards. On personal computers and small workstations,

the CPU is housed in a single chip called a microprocessor.

Since the 1970's the microprocessor class of CPUs has almost completely overtaken all other CPU implementations.

The CPU itself is an internal component of the computer.

Modern CPUs are small and square and contain multiple metallic connectors or pins on the underside.

The CPU is inserted directly into a CPU socket, pin side down, on the motherboard.

Each motherboard will support only a specific type or range of CPU so you must check the motherboard manufacturer's specifications

before attempting to replace or upgrade a CPU. Modern CPUs also have an attached heat sink and small fan that go directly on top of the CPU to help dissipate heat.

Two typical components of a CPU are the following:

* The arithmetic logic unit (ALU), which performs arithmetic and logical operations.

* The control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.

Abbreviation of arithmetic logic unit, the part of a computer that performs all arithmetic computations, such as addition and multiplication, and all comparison operations.

The ALU is one component of the CPU (central processing unit).

Short for control unit, it is a typical component of the CPU that implements the microprocessor instruction set.

It extracts instructions from memory and decodes and executes them, and sends the necessary signals to the ALU to perform the operation needed. Control Units

are either hardwired (instruction register is hardwired to rest of the microprocessor) or micro-programmed.

In computing, "word" is a term for the natural unit of data used by a particular computer design.

A word is simply a fixed-sized group of bits that are handled together by the machine.

The number of bits in a word (the word size or word length) is an important characteristic of a computer architecture.

The size of a word is reflected in many aspects of a computer's structure and operation.

The majority of the registers in the computer are usually word-sized. The typical numeric value manipulated by the computer is probably word sized.

The amount of data transferred between the processing part of the computer and the memory system is most often a word.

An address used to designate a location in memory often fits in a word.

Also called clock rate, the speed at which a microprocessor executes instructions.

Every computer contains an internal clock that regulates the rate at which instructions are executed and synchronizes all the various computer components.

The CPU requires a fixed number of clock ticks (or clock cycles) to execute each instruction. The faster the clock,

the more instructions the CPU can execute per second.

Clock speeds are expressed in megahertz (MHz) or gigahertz ((GHz).

The internal architecture of a CPU has as much to do with a CPU's performance as the clock speed,

so two CPUs with the same clock speed will not necessarily perform equally. Whereas an Intel 80286 microprocessor requires 20 cycles to multiply two numbers,

an Intel 80486 or later processor can perform the same calculation in a single clock tick. (Note that clock tick here refers to the system's clock,

which runs at 66 MHz for all PCs.) These newer processors, therefore, would be 20 times faster than the older processors even if their clock speeds were the same.

In addition, some microprocessors are superscalar, which means that they can execute more than one instruction per clock cycle.

Like CPUs, expansion buses also have clock speeds. Ideally, the CPU clock speed and the bus clock speed should be the same so that neither component

slows down the other. In practice, the bus clock speed is often slower than the CPU clock speed, which creates a bottleneck.

This is why new local buses, such as AGP, have been developed.

(n) A, special, high-speed storage area within 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.)

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.

Usually, the movement of data in and out of registers is completely transparent to users, and even to programmers.

Only assembly language programs can manipulate registers. In high-level languages,

the compiler is responsible for translating high-level operations into low-level operations that access registers.