Wikipedia:Reference desk/Archives/Computing/2012 April 25
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BIOS INT 10H source of pixel data for characters
When a call to INT 10H comes and the ASCII bits describing, say, the character 'A' are in AL, where exactly in the computer are the bits that describe the pixel formation of the glyph 'A' that INT 10H goes to to get them on the screen? If your answer is that 10H's job ends when it tells the graphics card in language it understands to put 'A' on the screen, my question remains, where exists the pixel data for the most basic of characters before anything so fancy as font files are loaded up? 126.96.36.199 (talk) 12:15, 25 April 2012 (UTC)
- In a "real" PC (in times of yore, before layers of emulation abstracted how so many things worked) there was a character ROM which stored 9x14 pixel bitmaps for each character in code page 437. In the original IBM Monochrome Display Adapter this was a discrete ROM device, over which the card would brook no override. Later cards, with more memory, allowed to to copy this ROM in the the card's own RAM (they were all addressable locations in the host PC's address space) and direct the controller to use that instead (allowing you to alter the appearance of characters). I don't off hand know the memory map involved. -- Finlay McWalterჷTalk 13:12, 25 April 2012 (UTC)
- Hmm, on further cogitation I don't think that (in early devices) the graphics adapter's ROM or RAM were mapped into the host device's Memory-mapped I/O (because they'd take up too much room). They were later, but I've lost my giant-book-of-graphics-chips of that era, so I don't know the specifics of when. -- Finlay McWalterჷTalk 13:28, 25 April 2012 (UTC)
- The actual character array (that we might call the screen) was an area of memory in the display adapter's limited RAM. INT 10H calls (which were often implemented by code in the graphics adapter's own expansion ROM) would read and write character codes into this space. Asynchronous to that, the graphics adapter continually generated a stream of pixels as the raster proceeded along and down the screen. As it did so, it would fetch a byte or two from the character map, and would look up the corresponding bitmap data in the character rom, giving actual pixels for it to emit. -- Finlay McWalterჷTalk 13:17, 25 April 2012 (UTC)
- For some diagrams, this page discusses the character generator circuitry for an early Atari computer; the arrangements (for that part) were much the same in an IBM-MDA. -- Finlay McWalterჷTalk 13:36, 25 April 2012 (UTC)
Hi, I'm new to Xcode and can't seem to find out how to add loads of text to the screen, I tried adding it to a label but this seems to have a finite amount of characters it allows to get displayed, I added a scroll bar in the hope that I could view the text which is not displayed, does anyone know how I could add more text to the screen thanks, I am also trying to link to a website with a button but can't seem to do this without leaving the application.188.8.131.52 (talk) 13:43, 25 April 2012 (UTC)
Here i got a question regarding gmail account , My question is this, can i delete the digits in my gmail username. Like my username is <redacted>email@example.com , i want to delete the 55 in my username,is thid possible. Any help will be greatly appreciated. — Preceding unsigned comment added by 184.108.40.206 (talk) 13:52, 25 April 2012 (UTC)
- You have to create a new account, if the name usman is still available. — Preceding unsigned comment added by 220.127.116.11 (talk) 14:22, 25 April 2012 (UTC)
- From Google's help pages: "it's not currently possible to change your Gmail username after you've registered. You can, however, create another Google Account with a different Gmail username." - Cucumber Mike (talk) 14:24, 25 April 2012 (UTC)
- If you do create a new account, it's possible to automatically forward any emails you get from one to the other. So you don't have to check both accounts. And you can change the "from" address of your mail so it reads which ever one you prefer. - Akamad (talk) 23:05, 25 April 2012 (UTC)
Running process and automatic sleep
If Windows 7 is running a process (like doing a backup) and it's set to get to sleep in a time shorter than that needed to the backup, what would happen? Go to sleep anyway? — Preceding unsigned comment added by 18.104.22.168 (talk) 14:05, 25 April 2012 (UTC)
- Windows provides many ways to let a process know that the system is changing: for example, WM_CLOSE tells a desktop-application style program that it "should please stop running." Other messages exist, including special cases for system hibernation and sleep events. An application programmer may choose to handle these messages, or ignore them. The operating system may decide to wait pleasantly for a response, or it may shut down anyway, depending on the type of shutdown (and the permissions of the person or program who initiated it). For example, read this Microsoft tech note on writing good power-aware applications, which links to an explanation of, e.g., the PBT_APMSUSPEND event, a special message sent to the application "about two seconds" before the machine goes to sleep. (If your application's designer couldn't write the code to save your work - or at least to put it in a consistent, recoverable/resumable state - in under two seconds, you need a better application).
- On POSIX-compliant computers, we have two ways to interrupt a process and tell it that it needs to stop running. Loosely speaking, these are SIGTERM, which tells the process "Please terminate, you have a few moments to wrap up." We also have SIGKILL, which doesn't tell the process very much at all: the kernel will kill the process for you.
- Ultimately, remember that the operating system's job is to politely mediate requests between many different programs (and potentially, many users); and to politely balance hardware realities (like turning the power off) against software requests (like a program that needs more time to save your work to disk). Good software-engineers use all the information that the system provides so that the program does the right thing without confusing the user. Nimur (talk) 16:44, 25 April 2012 (UTC)
- WM_CLOSE means that the user clicked the X in the upper right corner of the window or did something equivalent like pressing Alt+F4. The application is free to respond however it wants, just as with any other button click or key press. WM_CLOSE is sometimes sent in other ways—for example, when you try to terminate an application in Task Manager, I think it sends WM_CLOSE first and waits a few seconds before resorting to more drastic measures. I don't think this is relevant to the original question, though, which was about whether a backup application can/will prevent the computer from sleeping.