hard drive v. memory

Hard Drive

A 3.5 inch hard drive with the cover removed. A hard disk drive is a device used for the long-term storage of computer data (e.g., the operating system, programs, documents, music, and pictures). Data is stored magnetically on one or more rotating platters. Hard drives are non-volatile, meaning they retain stored information even when powered down. Modern consumer hard drive capacities range from several hundred gigabytes to a few terabytes. ‘Disk space’ may refer to the amount of unused space available on the hard drive.

Memory

A RAM module for a desktop computer. Random-access memory, or RAM, is used to store open programs and the data those programs use while running. When a computer is turned on, operating system files are loaded into RAM from the hard drive. RAM data is stored electrically in capacitors within integrated circuits. Because it is a type of volatile memory, all data written to RAM is lost when the computer is turned off. Laptop and desktop PC’s typically come with between one and twelve gigabytes of RAM, making the amount of installed RAM a few hundred times smaller than the hard drive size.

Per gigabyte, hard drives are much cheaper than RAM. However, because they contain moving parts, hard drives are orders of magnitude slower than RAM when reading or writing data.

Sharpened.net on memory and hard disk space

raster v. vector graphics

Computer graphics are stored as either raster or vector images.

Raster

In a raster image, also called a bitmap, a picture is represented as a rectangular grid of pixels, each of which is assigned a color value. Photographs and scanned images are saved as bitmaps. If a raster image is enlarged to the point that individual pixels become visible, it will appear grainy, with jagged edges. Higher quality raster images require larger file sizes with higher resolutions.

Examples

Programs: Adobe Photoshop, GIMP, Microsoft Paint

File formats: JPEG, PNG, GIF, BMP

Vector

Magnification as a vector image (top) and a bitmap (bottom). Note the loss of quality when enlarging a bitmap. Who doesn’t enjoy a nice refreshing bottle of ice cream?Vector graphics are represented with basic geometric structures such as points, lines, curves, and polygons. These shapes are stored as mathematical equations. Vector images are used for graphic design, including logos, text, and clipart. Vector graphics can be arbitrarily magnified or reduced with no loss of quality, while retaining their crisp, smooth edges. Vector files are usually smaller than comparable raster files, and a vector image’s file size remains constant regardless of scale. Discrete objects in vector drawings can be individually moved, scaled, rotated, and otherwise manipulated.

Examples

Programs: Adobe Illustrator, CorelDRAW, Inkscape

File formats: PDF, SVG, AI, EPS

Mike’s SketchPad on raster v. vector graphics

sleep mode v. hibernate mode

Image courtesy of PantherKut.com. Sleep and hibernate are power saving states for computers and other electronic devices.

In sleep mode, also known as stand by or suspend, the computer uses much less power than it does when running normally. This is done by saving the state of open programs and documents to RAM (memory), reducing the RAM refresh rate, turning off the monitor, cutting power to the CPU, spinning down the hard drive(s), and placing the power supply in a reduced power mode. Sleep mode can be entered after a defined period of inactivity, when a button is pressed, or on laptops, when the lid is closed. Under the Advanced Configuration and Power Interface (ACPI) standard, sleep mode is state S3.

In hibernate mode, the entire system state (the contents of the RAM) is saved to the hard drive, and the system powers down. Hibernation is most often used in mobile computers, where battery life and complete loss of power are significant concerns. Hibernation is ACPI state S4.

• Sleep consumes perhaps a tenth as much power as running normally; hibernation is equivalent to the computer being turned off, and drains almost no power.
• Waking from sleep can take as little as a few seconds. While waking from hibernation takes less time than a cold boot, it can still take several minutes.
• In the event of power loss, a sleeping computer will lose all of the data in memory, such as unsaved documents. A hibernating computer will be unaffected by loss of power.

Microsoft’s FAQ on turning off computers

Lifsoft.com on sleep mode v. hibernate mode

Internet v. World Wide Web

The Internet is a global network of computer networks. It is the hardware and software infrastructure that enables millions of computers to communicate with one another.

The World Wide Web is one of many services accessed through the Internet. It is a collection of documents (Web pages) that can be viewed on a browser, and which are connected to each other via hyperlinks.

A communications protocol is an agreed upon format for exchanging data between devices. The Internet operates on a set of protocols, collectively referred to as the Internet Protocol Suite, sometimes called TCP/IP after two of the most important protocols on it. The Web uses HTTP (Hypertext Transfer Protocol). In addition to HTTP, the Internet supports protocols for email, instant messaging, file transfers, peer-to-peer networks, and newsgroups.

Webopedia on Internet v. World Wide Web

wiseGEEK on Internet v. World Wide Web

differential v. incremental backup

Backing up all of the files on a computer’s hard drive requires a considerable amount of time and disk space, but most of the data stored on the drive changes slowly or not at all. Therefore, after a full backup has been made, more efficient methods can be used to backup only the files that have changed.

A differential backup backs up the files that have changed since the last full backup. For example, one might schedule a weekly full backup on Sunday, and subsequent daily differential backups. Monday’s backup would include everything that had changed since Sunday. Tuesday’s differential would also include all files that had changed since Sunday, and so on. As time elapses, and changes accumulate, differential backups get successively larger. Monday’s backup could be quite small, but Saturday’s backup could be substantially bigger. To restore data, only the last full backup and the last differential backup are required.

An incremental backup backs up the files that have changed since the last backup of any kind, whether it was full or incremental. Using a schedule like the one above, Monday’s incremental backup would cover changes since Sunday, Tuesday’s would only cover changes since Monday, and so on. To reconstitute data, the last full backup and every incremental backup since then are required.

Compared to incremental backups, differential backups are slower to backup, faster to restore, and create larger backups. Incremental backups are faster to backup, slower to restore, and create smaller backups.

Acronis on differential v. incremental backup

Backup.info on differential v. incremental backup