Linux Hardware and Software Architecture

What is Linux?

Unlike other Operating System, Linux, an extraordinary OS, has an interesting background which dates back to the 60's. It is a Unix - like operating system. Linux was started by Linus Benedict Torvalds who was a student at Finnish University student in 1992. Linus was looking for a free robust (v.s. stink) OS on an Intel box. He became interested in Andrew Tanenbaum's Minix and wrote the software. Linus made it freely available on the Internet. It adopts Unix's open source code architecture. It has been ported to many computers ranging from mainframes to personal computers.

Hardware and Software Architecture

Hardware (HW) Architecture (Intel Compatible PC)

Motherboards (Intel Compatible Chips x86)
Intel - [3-6]86 (Pentium Pro, II, and III)
AMD (Advanced Micro Devices) - K5, and K6
Cyrix - 6x86
Controllers: a device controlling data transfers between computer and peripheral device).
EIDE (Enhanced Integrated Device Electronics) Systems Interface Controllers): it may come with to 2 IDE interfaces on the mother board or expansion card. Each interface supports 2 hard drives. (i.e. master and slave).
SCSI (Small Computer Systems Interface): it can handle up to 7 daisy chained SCSI devices (such as tape drives, and hard drives) per card.
System Bus: a collection of wires through which data is transmitted from one part of a computer to another.
ISA (Industry Standard Architecture)
PCI (Peripheral Component Interconnect)

Expansion cards
Video card (display adaptor): Matrox, ATI, and 3dfx,
Modem
Sound card
Ethnet Adaptor
PC card (PCMCIA) - Ethernet and modem for laptop
RAM:
DRAM - Dynamic Random Access
EDO - Extended Data Output DRAM
SDRAM - Synchronous DRAM which is two times faster than EDO

SIMMS (single in-line memory module): 30-pin (8 or 9 bit wide), 72-pin (32 or 36 bit). Dual in-line memory module (DIMM), provides a 64-bit bus. Pin: thin metal feet.
Mice: serial and PS/2
Tape Drives: SCSI one works better
Serial and Parallel Port
Joystick: Amiga, Gamepads, Logitech and etc.

Miscellaneous CPU

Sparc, Alpha, PA-RISC, and Motorola and IBM PowerPC.

Software (SW) Architecture

System Kernel: People call it kernel for short;
I.e. Operating System
Kernel is the mediator between the application programs and hardware. To communicate with kernel, the application programs need to invoke system calls. The major subsystems in kernel are:

Processes: a program in execution.
state: running, stopped, waiting and zombie.
creation and termination: spawn and kill.
signal: causes the process to temporarily suspended.
messages: passing messages between processes. E.g.: client and server environment.

Memory: Primary and secondary memory (swap device) allocation and management.

File System: a logical way to manage files on the hard drive. When opening files via a system call which is open, the kernel returns file descriptors (integer) for manipulating.

standard input: 0
standard output: 1
standard error: 2

Linux supports many different file systems. E.g. ex2, NTFS, AFS, FAT, VFAT and etc. A file's information (owner, permissions, and type) is kept in an "inode".

I/O: Input and output. The kernel interrupts the CPU upon receiving interrupts (IRQ) to control different devices such as disk and tape drives for I/O.
pipe: E.g. ls | wc
redirection:
ls > output
mail friend < letter
Commands: sh and editors (ed, emacs, and vi)
Applications: Doom, Netscape, and IE

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