Successful completion of the Hardware & Architecture section of the LPI exam requires familiarity with Personal Computer (PC) expansion cards and peripherals and how those devices interact with the system BIOS and the Linux Kernel. This includes understanding the difference between Industry Standard Architecture (ISA) and Peripheral Component Interconnect PCI as well as what interrupts (IRQs), Input/Output (I/O) ports and Direct Memory Access (DMA) channels are used for. If you are the type of person whose PC spends as much time with the cover off as it does with the cover on you probably have a good head start on the preceding items. You will also need to know about Small Computer Systems Interface (SCSI) and Universal Serial Bus (USB) architectures, which are perhaps more difficult subjects. SCSI is more commonly used in high-end servers and may not be familiar to PC users. USB although more common in PC's is relatively new feature in the Linux kernel.

Expansion cards communicate with the PC using three basic methods, i/o ports, interrupts and DMA. The Linux kernel must keep track of these communication resources in order to properly interact with the expansion cards. The system administrator can see the kernel's view of i/o ports, interrupts and DMA channels by looking in the proc filesystem. There are three files in particular to note.

All of these files can be viewed using the cat command. For example, cat /proc/ioports will show the the i/o ports used by the system. Take a moment to become familiar with the contents of these files. See if you can identify the various devices in your PC. Below are some excepts from the three files from a typical PC:

bash$ head -5 /proc/ioports
0000-001f : dma1
0020-003f : pic1
0040-005f : timer
0060-006f : keyboard
0070-007f : rtc

bash$ head -5 /proc/interrupts
           CPU0
  0:     204783          XT-PIC  timer
  1:       2410          XT-PIC  keyboard
  2:          0          XT-PIC  cascade
  5:       4004          XT-PIC  aic7xxx

bash$ cat /proc/dma
 4: cascade

Most modern expansion cards have their resources assigned automatically using plug-and-play (PnP) technology and it is rare to find a card that requires manual configuration. The way resources are assigned to a card depends upon which bus technology it uses. All PCI cards are designed to be plug-and-play and are assigned resources by the PC's BIOS during boot-up. The results of the configuration can be viewed using the lspci command. Older ISA cards may need to have their resources assigned by the operating system rather than the BIOS. Linux systems use the isapnp command and the corresponding /etc/isapnp.conf file to set up ISA plug-and-play cards. The pnpdump command queries ISA plug-and-play cards to find their desired resource configuration and its output can be used to construct the /etc/pnp.conf file.

Exploration of the /proc/ide directory reveals information about IDE devices present in the system. Of particular interest is the /proc/ide/hda directory since it contains information about the first, bootable IDE hard disk in the system. Two files in the /proc/ide/hda directory, capacity and geometry, are used to describe the size of the hard disk. The example below shows the contents of the files for an 80G hard disk.

bash# cat /proc/ide/hda/geometry
physical     38322/16/255
logical      9732/255/63

bash# cat /proc/ide/hda/capacity
156355584

The output of geometry shows the size in a cylinder/head/sector (CHS) format while capacity shows the size in logical block addressing (LBA) format. The older CHS format is limited to 1024 cylinders and can only describe disks up to 8G in size. Because of this limitation modern hard disks are almost always described using LBA. The Linux kernel uses LBA exclusively and provides the CHS parameters in geometry for informational purposes only. Because the operating system uses LBA it is important that the PC BIOS also be configured to use LBA.

In addition to IDE many high-performance systems use SCSI. Typical SCSI devices attached to a Linux system include hard drives, cd-roms and tape drives, but there can be others as well. All SCSI devices must be attached to a SCSI Host Adapter in order to interact with the system. The SCSI adapter is responsible for handling communication between the SCSI devices and the Linux kernel. Information about the host adapter and the devices attached to it will appear in the proc filesystem under the /proc/scsi directory. The following example shows a typical /proc/scsi directory.

bash# ls -F /proc/scsi
aic7xxx/  scsi

The directory aic7xxx contains information about the configuration of the host adapter (an Adaptec 2940 in this case.) There are many manufacturers of SCSI host adapters so the name and contents of the directory will vary depending on the partcular setup.

There is also a file named /proc/scsi/scsi that shows all SCSI devices as seen by the Linux kernel. An example is shown below.

bash# cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
  Vendor: IBM      Model: DNES-309170W     Rev: SA30
  Type:   Direct-Access                    ANSI SCSI revision: 03
Host: scsi0 Channel: 00 Id: 04 Lun: 00
  Vendor: PHILIPS  Model: CDD2600          Rev: 1.07
  Type:   CD-ROM                           ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 05 Lun: 00
  Vendor: IOMEGA   Model: ZIP 100          Rev: E.03
  Type:   Direct-Access                    ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 06 Lun: 00
  Vendor: HP       Model: HP35480A         Rev: 1009
  Type:   Sequential-Access                ANSI SCSI revision: 02

Take a moment to look at the information contained in the file. Notice how each device on the SCSI bus has its own unique SCSI ID number. Hard disks are generally given lower SCSI ID's than CD-ROM's and tape drives and ID 0 is reserved for the bootable hard disk.

When accessing SCSI devices in Linux it is done using nodes in the /dev directory just like any other piece of hardware. Refering to the example above the IBM hard disk would be accessed as /dev/sda while the Iomega Zip disk is /dev/sdb. The Philips CD-ROM is /dev/sr0 and the HP tape drive is /dev/st0.

Support for USB first appeared in Linux kernel version 2.2 and became much more robust in kernel version 2.4. USB is very similar to SCSI in many respects. The system has a USB host controller which functions much like a SCSI host adapter and USB storage devices appear as SCSI disks in the /dev directory.

In order for USB devices to be recognized there must be USB support in the kernel either compiled in or loaded as a module. In the case of a modular kernel the files required for basic USB support are as follows.

The kernel will also need to have modules loaded for the particular USB device being used. For example acm for USB modems and usb-storage for storage devices like USB hard drives and USB CD-ROMs.

Many times it is also necessary to include hotplug support in the kernel because most USB devices are designed to be added and removed from the system without requiring a reboot. There is also a userspace program /sbin/hotplug that helps the kernel deal with dynamically adding and removing USB devices. /sbin/hotplug does this by looking for a shell script (also called an agent) in the /etc/hotplug directory with the same name as the USB device being added or removed. The agent is responsible for handling the particulars of adding and removing the device.

Modems and sound cards are given special attention on the LPI exam since they can be slightly more complicated than other types of hardware.

Modems have extra requirements to work properly with Linux and these are listed below.

In addition to setting up modem hardware the LPI exam also covers setting up a Point-to-Point Protocol (PPP) connection to an Internet provider. DSL and Cable modem users may want to refresh their memories by skimming the pppd and chat man pages or the PPP-HOWTO.

Sound cards are typically difficult to configure because they use many different resources (i/o ports, interrupts & DMA channels) making it more likely that some sort of resource conflict will occur.

You can gauge your familiarity with the subject of Hardware & Architecture by answering the practice questions below.

Listed below are some documents that may be helpful when preparing for the Hardware & Architecture portion of the LPI 101 exam.