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Booting or bootstrapping:
. The reprogramming of hardware to do tasks by turning power on.
. This happens when BIOS loads itself into RAM, performs POST & calls the OS kernel and drivers into RAM.
. BIOS resides in the form of ROM or EEPROM chips on the motherboard.
. BIOS version and date can be seen in the BIOS menus. If it is very old, it is good to upgrade the BIOS. This can be done using a BIOS disk/flash drive etc.
Bus:
. communication channels over which peripherals communicate with the cpu.
. bus exist on the mother board.
. current bus architecture is called PCI. PCI replaced ISA that came with PC-AT in 1984. Hence ISA was also called AT Bus.
. PCI supports 32 bit devices. ISA supported upto 16 bit devices.
-To see PCI devices:
# cat /proc/pci
or # lspci
Try and compare the above cmds.
-Ports:
. When cpu needs to communicate to peripheral devices, it does so by writing to IO ports or simply ports.
. each device has its own separate port that is not shared with other devices.
-To see the IO ports on the system:
# cat /proc/ioports
-Note: ports are denoted in hexadecimal eg. 37A
-Interrupts:
. interrupts or IRQs are signals generated by peripherals for the cpu to know.
. when the cpu receives an interrupt signal, it temporarily suspends all its activities and attends to the interrupt (thats why called 'interrupt').
. interrupts may be shared between peripheral devices (unlike ports)
-To see interrupts:
# cat /proc/interrupts - current interrupts
# dmesg | grep -i share - to see shared interrupts besides other things.
-Dma:
. direct memory access
. for faster peripheral devices, generating interrupts to talk to cpu and then gain access to RAM could slow things down.
. dma solves this problem by granting the peripheral direct access to memory areas; basically bypassing the cpu.
# cat /proc/dma
# dmesg | grep -i dma - to see dma info besides other things.
-Plug n Play (pnp)
. with the advent of newer and multitude of peripherals, ports and interrupts became scarce. for instance two devices could not share ports or irqs.
. thats when plug n play (pnp) concept came into being.
. pnp devices report a set of interrupts/ports they need for working at boot time to bios and the system then doles those ports/irqs on need basis.
. These days, pnp is a standard feature of most computers.
-Disk types:
. ide - low cost, smaller
. scsi - bigger, better perf (usually in servers)
. sata - improvement over ide
-To see disk info:
# cat /dev/hdx - ide
or # cat /dev/sdx - scsi
-Note: /dev is a virtual fs like /proc.
. was designed for connecting streaming devices like tapes and block devices like disks, cds, dvds etc. but now extended to printers/scanners.
. was designed to allow multiple devices on one bus--the bus-controller controlling the data traffic.
. scsi standard defined by ANSI.
-useful:
. cat /proc/scsi/scsi, scsi_info, sginfo.
-Usb
. Universal Serial Bus
. USB version 2.0 supports speeds upto 480 Mbps.
. usb cable has 4 wires - two for signals and one each for power and ground.
-To see usb info:
# cat /proc/bus/usb
# cat /proc/bus/usb/devices
Extras:
-Linux filesystem is a single fs with the / as the top root dir. -To view the different devices like floppy, cdrom etc, on the same fs, you mount them on their mount points.
-in this regard, different mount points are treated as different devices.
-This is different from Windows where every drive letter (A, B, C..) has its own fs.
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