What are DPI, DIP, DP, PPI, SP and Screen Resolutions in Android?

Understanding Android Screen Densities and Terminology

Portrait v LandscapeThis article provides an overview of Android screen densities and the various acronyms that occur when dealing with a device’s screen. Android’s popularity as a mobile device Operating System has resulted in a proliferation of hardware on the market. This has provided great choice for the consumer and forced continuous innovation from the manufacturers. In a few short years there has been rapid innovation in all areas: CPU capabilities, memory size, form factors, keypads, cameras, sensors, batteries, power consumption and screen technologies. The screens have been getting bigger, thinner, sharper, tougher and more responsive to touch. This has forced the Android SDK to move rapidly with the hardware technology (and the hardware to feed upon Android ideas). Explained here is how the variety of screen sizes are handled by the OS, finishing with a summary table of the acronyms covered.

What makes up an Android Screen

Android Coordinate SystemFor those of you new to technology here’s how a device screen works. The screen is made of thousands of small dots called pixels arranged in a grid. The pixels running from left to right are known as the X pixels or X-axis. The pixels running from top to bottom are known as Y pixels or Y-axis. The resolution of the display is the number of pixels in X-axis multipled by the number of pixels in the Y-axis. A 320 by 480 display will have 320 pixels in the X-axis and 480 pixels in the Y-axis, this will also be stated simply as 320×480 (and in this case x is the multiplication, or times, sign and not the X-axis!).

To show an image on the display the color of the pixels are set by a program running on the device. Look at the article How Computer Screens and Printers Show Images for more details on how dots make up an image. Because the Android coordinate system runs left to right and top to bottom then plotting a line from 0,0 to 100,100 results in a line that slopes down from the top left of the screen, compared to one that slopes up from bottom left on a normal maths chart.

To get a idea of the variety of screens seen on Android devices look at the article Example List of Android Device Screen Resolutions and Sizes (which also shows that the various screen resolutions are given names). Continue reading

Back to the Future for Computers

The return of the “bicycle for our minds”.

Sinclair Research ZX Spectrum 48K

Sinclair Research ZX Spectrum

What happened to the computer? If you are old enough to remember the 1980’s you may recall the explosion of home computers that occured, some of the most popular being:

  • Sinclair Research’s ZX80, ZX81 and Spectrum.
  • Commodore Business Machines VIC-20, Commodore 64 and Amiga.
  • Atari’s 400, 800 and ST.
  • Acorn Computers BBC Micro, Electron and Archimedes
  • Apple IIe
A Simple Basic Program on an Atari Screen

A Simple Basic Program

Unlike the video games consoles (such as the Atari 2600) not only could these systems be used to play games they could also be programmed, usually in Beginner’s All-purpose Symbolic Instruction Code (BASIC). These easy to use computers provided many with the education needed to forge successful careers and build successful businesses in the new Information Technology industry that emerged in the 1990’s as the Internet sprang into life. What was great about these computers was the immediacy, intimacy, responsiveness and quick boot time. It was only seconds from turning the power on to starting to type a computer program. A computer program that could easily access the raw hardware of the computer. Unlike the typical computers purchased on the high street today, which are over engineered, power hungry, bloated and slow booting devices. So despite a quarter of a century of technological advances how did we end up with expensive devices that kids cannot easily program. Continue reading

Move My Documents and Other Personal Folders in Windows 8.1, 8 and 7

A Tutorial on Moving User My Documents and Personal Folders to Another Drive

Default Folders are Created for Windows UsersEach user on a Windows computer (Windows 8.1, Windows 8 and Windows 7 and earlier) is given a private location on the PC into which they can store their work. This work can be pictures, documents, music, emails, videos and anything else that they use or generate. It is private because other users cannot view their files (unless they are logged in as an Administrator). When a user logs on they can work with their private files and any Public files. To let other users see their work it needs be moved or copied into the relevant Public folders, or a directory needs to be marked as shared.

Root Users FolderThe default installation for Windows is to put all the users folders onto the same hard disk drive as the operating system itself, usually the first, and only, hard disk in the system, called the C: drive. This drive will also hold any additional programs that are installed. Each user is located under the Users folder on C:, so a user call John Doe has folders located at C:\Users\John Doe. Under the users main folder is a folder to store different types of files that programs generate or use. For example there is a Contacts folder (at C:\Users\John Doe\Contacts) to store, well, contacts (name, address, phone numbers, etc.). Use Windows Explorer to view the Users folders. Open Windows Explorer via the Start button, All Programs and Accessories, or in Windows 8.1 hold the Windows key and press E. The various folders created by Windows for the user can be seen under the user’s name from the Desktop icon (Windows 7) or under C:\Users\User Name in Windows 8.1.

Some of the folders are also accessible via the various Library icons. In Windows 7 in Explorer some folders begin with My, such as My Documents or My Music. However, the actual folder name on the hard disk does not have My, thus My Documents in Explorer points to C:\Users\John Doe\Documents. This table shows the folder name, the display name in Explorer and whether or not a public version is available, located at C:\Users\Public (this folder itself can be used to make files public).

User Folders
Folder Win 7 Name in Explorer Public Version
Contacts Contacts  N/A
Desktop Desktop  Public Desktop
Documents My Documents  Public Documents
Downloads Downloads  Public Downloads
Favorites Favorites  N/A
Links Links  N/A
Music My Music  Public Music
Pictures My Pictures  Public Pictures
Saved Games Saved Games  N/A
Searches Searches  N/A
Videos My Videos  Public Videos

Locating all the user folders on the one hard disk drive along with Windows and all the programs makes configuration and manufacture of a new computer easier. Unfortunately it has several disadvantages: Continue reading