Опубликован: 06.08.2012 | Доступ: свободный | Студентов: 1180 / 25 | Оценка: 5.00 / 5.00 | Длительность: 53:41:00
Лекция 2:

Before you install

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Making the file systems

Armed with this knowledge, we can now proceed to make some decisions about how to install our systems. First, we need to answer some questions:

  • Do we want to share this disk with any other operating system?
  • If so, do we have data on this disk that we want to keep?

If you already have another system installed on the disk, it is best to use that system's tools for manipulating the partition table. FreeBSD does not normally have difficulty with partition tables created by other systems, so you can be reasonably sure that the other system will understand what it has left. If the other system is Microsoft, and you have a slice that you don't need, use the MS-DOS FDISK program to free up enough space to install FreeBSD. If you don't have a slice to delete, you can use the FIPS program to create onesee "Installing FreeBSD" , Installing FreeBSD, page 52.

If for some reason you can't use MS-DOS FDISK, for example because you're installing FreeBSD by itself, FreeBSD also supplies a program called fdisk that manipulates the partition table. Normally you invoke it indirectly via the sysinstall program—see page 63.

Disk size limitations

Disk storage capacity has grown by several orders of magnitude since FreeBSD was first released. As it did so, a number of limits became apparent:

  • The first was the BIOS 504MB limit on IDE disks, imposed by their similarity with ST-506 disks. We discussed this on page 32. FreeBSD works around this issue by using a loader that understands large disks, so this limit is a thing of the past.
  • The next limit was the 1 GB limit, which affected some older SCSI host adapters. Although SCSI drives always use LBA addressing internally, the BIOS needed to simulate CHS addressing for Microsoft. Early BIOSes were limited to 64 heads, 32 sectors and 1024 tracks (64 x 32 x 1024 x 512 = 1 GB). This wouldn't be such a problem, except that some old Adaptec controllers offer a 1 GB compatibility option. Don't use it: it's only needed for systems that were installed with the old mapping.
  • After that, it's logical that the next limit should come at 2 GB. There are several different problems here. The only one that affects FreeBSD appears to be a bug in some IDE controllers, which don't work beyond this limit. All of them are old, and IDE controllers don't cost anything, so if you are sure you have this problem, you can solve it by replacing the controller. Make sure you get one that supports DMA

    Other systems, including many versions of UNIX System V, have problems with this limit because 2^{31} is the largest number that can be represented in a 32 bit signed integer. FreeBSD does not have this limitation, as file sizes are represented in 64 bit quantities.

  • At 4 GB, some IDE controllers have problems because they convert this to a CHS mapping with 256 heads, which doesn't work: the largest number is 255. Again, if you're sure this is the cause of problems you may be having, a new controller can help.
  • At 8 GB the CHS system runs out of steam. It can't describe more than 1024 cylinders, 255 heads or 63 sectors. Beyond this size, you must use LBA addressing if your BIOS supports it.
  • You'd expect more problems at 16 GB, but in fact the next limitation doesn't come until 128 GB. It's due to the limitations in the original LBA scheme, which had only 28 bits of sector address. The new standard extends this to 48 bits, which should be sufficient for the next few years. FreeBSD already uses the new standard, so this limitation has never been an issue.

None of these problems affect FreeBSD directly. The FreeBSD bootstrap no longer uses the system BIOS, so it is not bound by the restrictions of the BIOS and the controller. If you use another operating system's loader, however, you could have problems. If you have the choice, use LBA addressing. Unfortunately, you can't do so if the disk already contains software that uses CHS addressing.

Other things to consider are:

  • If you have other software already installed on the disk, and you want to keep it, do not change the drive geometry. If you do so, you will no longer be able to run the other software.
  • Use LBA addressing if your hardware supports it.
  • If you have to use CHS, and you don't have any other software on the drive, use the drive geometry specified on the disk itself or in the manual, if you're lucky enough to get a manual with the disk. Many BIOSes remap the drive geometry in order to get Microsoft to agree to work with the disk, but this can break FreeBSD disk mapping. Check that the partition editor has these values, and change them if necessary.
  • If all else fails, install Microsoft in a small slice at the start of the disk. This creates a valid partition table for the drive, and the installation software understands it. Once you have started the installation process, the Microsoft partition has fulfilled its purpose, and you can delete it again.

Display hardware

For years, UNIX users have worked with a single 80x25 character mode display. Many people consider this extremely old-fashioned, but in fact the flexibility of the UNIX system made this quite a good way to work. Still, there's no doubt of the advantage of a system that offers the possibility of performing multiple operations at once, and this is one of the particular advantages of UNIX. But you normally need a terminal to interact with each task. The best way to do this is with the X Window System. You might also want to use a desktop, a set of programs that offer commonly used functionality.

In many other environments, the GUI and the graphical display are the same thing, and in some systems, notably Microsoft, there is no clear distinction between the operating system and the GUI. In UNIX, there are at least four levels of abstraction:

  • The kernel runs the computer.
  • X interfaces with the kernel and runs the display. It doesn't display anything itself except possibly a display background, by default a grey cross-hatch pattern.
  • The window manager gives you control over the windows, such as moving, resizing and iconification (often called minimizing in other systems). It provides the windows with decorations like frames, buttons and menus.
  • The desktop provides commonly used applications and ways of starting them. Many people get by without a desktop by using window manager functionality.

Why do it this way? Because it gives you more choice. There are dozens of window managers available, and also several desktops. You're not locked in to a single product. This has its down side, though: you must make the choice, and so setting up X requires a little more thought than installing Microsoft.

The hardware

X runs on almost any hardware. That doesn't mean that all hardware is equal, of course. Here are some considerations:

The keyboard

X uses the keyboard a lot more than Microsoft. Make sure you get a good one.

The mouse

X prefers a three-button mouse, though it has provisions for up to five buttons. It can support newer mice with rollers and side buttons, but most software does not use them. Some mice, such as the Logitech wireless mouse, require undocumented sequences to enable some buttons (the thumb button in the case of Logitech). X does not support this button.

Get the best mouse you can. Prefer a short, light switch. It must have at least three buttons. Accept no substitutes. Look for one with an easy-to-use middle button. Frequently mice with both a middle button and a roller make it difficult to use the middle button: it's either misplaced, too heavy in action, or requires pressing on the roller (and thus possibly turning it). All of these prove to be a nuisance over time.

Older mice connected via the serial port or a special card (&bus mouse&). Nowadays most mice are so-called PS/2 mice, and USB mice are becoming more popular.

The display board and monitor

X enables you to do a lot more in parallel than other windowing environments. As a result, screen real estate is at a premium. Use as big a monitor as you can afford, and as high a resolution as your monitor can handle. You should be able to display a resolution of 1600x1200 on a 21" monitor, 1280x1024 on a 17" monitor, and 1024x768 on a 14" monitor. Premium quality 21" monitors can display 2048x1536. If that’s not enough, we'll look at multiple monitor configurations on page 523.

Laptop hardware

If you have a laptop, you don't get any choice. The display has a native resolution which you can't change. Most laptops display lower resolutions by interpolation, but the result looks much worse than the native resolution. LCD screens look crisper than CRT monitors, so you can choose higher resolutions modern laptops have display resolutions of up to 1600x1200.

If you're going to use your laptop for presentations with overhead projectors, make sure you find one that can display both on the internal screen and also on the external output at the same time, while maintaining a display resolution of 1024x768: not many over head projectors can display at a higher resolution.

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Владимир Шишкин
Владимир Шишкин
Россия, Киров
Олег Страхов
Олег Страхов
Россия