What is a byte, and what are the other units of measure for digital information?

A byte is a unit of measure for digital information. A single byte contains eight consecutive bits, and is capable of storing a single ASCII character, like "h".

A kilobyte (KB) is 1,024 bytes, not one thousand bytes as might be expected. This odd number results from the fact that computers use binary (base two) math, instead of a decimal (base ten) system.

Computer storage and memory is often measured in megabytes (MB). A medium-sized novel contains about 1MB of information. 1MB is 1,024 kilobytes, or 1,048,576 (1024x1024) bytes, not one million bytes. Again, this number results from the fact that computers use binary math.

Similarly, one gigabyte (GB) is 1,024MB, or 1,073,741,824 (1024x1024x1024) bytes. A terabyte (TB) is 1,024GB; 1TB is about the same amount of information as all of the books in a large library, or roughly 1,610 CDs worth of data. A petabyte (PB) is 1,024TB. Indiana University is now building storage systems capable of holding petabytes of data. An exabyte (EB) is 1,024PB. A zettabyte (ZB) is 1,024EB. And finally, a yottabyte (YB) 1,024ZB.

We count in base 10 by powers of 10:

  10¹ = 10

  10² = 10*10 =  100

  10³ = 10*10*10 = 1,000

  10⁶ = 1,000,000

Computers count by base 2:

  2¹ = 2

  2² = 2*2 = 4

  2³ = 2*2*2 = 8

  2¹⁰ = 1,024

  2²⁰ = 1,048,576

So in computer jargon, the following units are used:

Note: Many hard drive manufacturers use a decimal number system to define amounts of storage space. As a result, 1MB is defined as one million bytes, 1GB is defined as one billion bytes, and so on. Since your computer uses a binary system as mentioned above, you may notice a discrepancy between your hard drive's published capacity and the capacity acknowledged by your computer. For example, a hard drive that is said to contain 10GB of storage space using a decimal system is actually capable of storing 10,000,000,000 bytes. However, in a binary system, 10GB is 10,737,418,240 bytes. As a result, instead of acknowledging 10GB, your computer will acknowledge 9.31GB. This is not a malfunction but a matter of different definitions.

Also see:

·       On a PC, what are the differences between various kinds of memory?

·       What is virtual memory?

·       Where can I find information on units of measurement and how to convert between them?

What is Kerberos?

Developed by MIT, Kerberos is a system that provides authenticated access for users and services on a network. At Indiana University, your Kerberos identity is established through your Network ID. Thus, Kerberos is used to access the dial-in modem pools and Account Management Service, as well as the Mac OS X computers in the Student Technology Centers.

With Kerberos, by exchanging time-sensitive tickets, you can make transactions secure without sending passwords in plaintext over the network. For a program to take advantage of Kerberos, it must be Kerberized, which means that it can obtain tickets from the Kerberos server and negotiate with a Kerberos-aware service. Just about any program can be Kerberized, including web browsers, telnet applications, POP email clients, and print utilities. Similarly, services that can be made Kerberos-aware include web sites, printers, file servers, and POP mail servers. Though it's a fairly complex protocol, following are a few basic characteristics:

·       Every user and every service has a password. Only the owner of the password and the Kerberos server know this password. Passwords must remain confidential, as Kerberos provides no inherent protection against those that are stolen.

·       When you use a program that makes an initial ticket request to the Kerberos server, it will ask you for your Kerberos username and password. The program will then send a ticket request to the Kerberos server. The server will respond by sending you a ticket-granting ticket that it encrypts by plugging your password into an encryption algorithm. Because only you and the Kerberos server know what your password is, only you will be able to decrypt and use the ticket-granting ticket. This ticket-granting ticket normally expires eight hours after it is issued.

·       Once you have a ticket-granting ticket, you may then use Kerberized programs to request services from Kerberos-aware servers. The Kerberized program sends your ticket-granting ticket to a ticket-granting server (usually the Kerberos server itself) with a request to transact with a specific service (e.g., a printer, a POP email server). The server gives you a ticket that lets you conduct a transaction with the service and also insures that both you and the service are who you say you are.

·       Kerberos gives you the option to encrypt data sent over the network. This means that the entire transaction between you and a Kerberos-aware service will be in unreadable ciphertext rather than plaintext.

For more information about Kerberos, consult the newsgroup comp.protocols.kerberos or MIT's Kerberos page:

  http://web.mit.edu/kerberos/www/

Also see:

·       At IU, how do I set up a Unix computer as a Kerberized application server?

What are kernels and microkernels?

A core feature of any operating system, the kernel is responsible for managing memory and I/O, handling device signals, task scheduling, and other essential tasks. It is one of the first components loaded into memory during the boot process, and remains active as long as the computer is operational. Kernels vary widely in function and scope, but always greatly affect their operating system's capabilities. For this reason, particularly in Unix, administrators tweak the kernels to best suit their requirements.

Compared to a typical kernel, a microkernel is compact, performing only the basic functions universal to all computers. Designed to be integrated into different operating systems, a microkernel works with OS-specific servers that provide higher level functions. This component-based structure improves a system's portability, but potentially at the expense of performance. Mach and its derivatives, the most prominent examples of the microkernel architecture, are the foundations of systems such as Tru64 Unix, the GNU Hurd, and Mac OS X.

Also see:

·       About Linux

·       What is Mach?

·       What is BSD?

·       For Mac OS, what is MachTen?

In Mac OS and Mac OS X, what is the Keychain, and how do I use it?

Introduced in Mac OS 9 and continued in Mac OS X, the Keychain consolidates various passwords in one place and makes them accessible through a master password. When an application (including the Finder) needs to access a password stored in the Keychain, the application asks you to unlock the Keychain if it is not already open.

Note: If you are using Mac OS 9 without Multiple Users turned on, you may need to create a Keychain. For more information, see the Knowledge Base document In Mac OS 9, how do I create a Keychain?

Adding items to the Keychain

Many applications store their passwords in the Keychain automatically. You may also add file server passwords and, in Mac OS 9, encrypted file passwords. For specific instructions on adding these passwords, see the following Knowledge Base documents:

·       In Mac OS 9, what is Apple File Security, and how do I use it to encrypt a file?

·       In Mac OS X, how do I store file server passwords in my Keychain?

·       In Mac OS 9, how do I add file servers to the Keychain?

Applications that employ passwords (such as FTP clients and web browsers) must be written specifically to use the Keychain. Currently, neither Internet Explorer nor Netscape directly supports the Keychain for password-protected sites, but other web browsers, as well as many FTP, SFTP, and email clients, do.

Keychain settings

To change the password and other settings for an existing Keychain, use Keychain Access.

In Mac OS X, Keychain Access is located in the Utilities folder, which in turn is in the Applications folder. Then, from the Edit menu, select Change Settings for Keychain "[NAME]" or Change Password for Keychain "[NAME]" as appropriate, where [NAME] is the name of your Keychain.

In Mac OS 9, from the Apple menu, select Control Panel and then Keychain Access. Then, from the Edit menu, choose "[NAME]" settings... , where [NAME] is the name of your Keychain. You may be prompted for your password again, and then in the next dialog box, you may adjust your settings.

For more information about the Keychain, consult the built-in Mac Help, available from the Help menu of Keychain Access or the Finder.

Also see:

·       In Mac OS, how can I password-protect my computer?

·       What books are available for Mac OS and Mac OS X computers, and where can I find them?

·       For Mac OS, what FTP clients are available and how do they compare?

·       In Mac OS 9, how do I add file servers to the Keychain?

·       For Mac OS X, what native FTP and SFTP clients are available, and how do they compare?

·       In Mac OS X, how do I password-protect my computer?

At IUB, what is Kiva Everywhere?

Kiva Everywhere is Kiva Networking's wireless system, which provides access to the Internet at KSpots around Bloomington.

Through a partnership between UITS and Kiva Networking, all Indiana University students, faculty, and staff have access to Kiva Everywhere. Through Kiva Everywhere KSpots, you can make an IU VPN connection to the Internet from a variety of off-campus locations using your IU Network ID. These locations include much of downtown Bloomington, local parks, and several popular restaurants and bars.

Note: IU users have to make a VPN connection to the IU network in order to use the Kiva Everywhere KSpots. For more information, see The basics of VPN at IU.

If you have problems connecting through Kiva Everywhere, see the Kiva Networking support page.

Also see:

·       What IP address will I get when using Kiva Everywhere for my wireless Internet connection?

·       In Windows, how do I connect to a Kiva Everywhere KSpot using my IU username and password?