3. FUNCTIONS OF AN OPERATING SYSTEM
Oversee operation of computer
Store and retrieve files
Schedule programs for execution
Coordinate the execution of programs
12. THE BOOT PROCESS: BIOS
Custom settings are read from CMOS
Complementary Metal-Oxide Semiconductor
Memory used to store configurable system
settings
System setup utility
Power-on self-test (POST) is run to check
system function
13. THE BOOT PROCESS: POST
POST
BIOS instructs CPU to read code stored at various
locations and compares it to known values
BIOS loads low-level drivers and interrupt handlers
for basic hardware
Checks video card
Initializes video BIOS
Tests video card and video memory
BIOS information (version, date, manufacturer)
is displayed
14. THE BOOT PROCESS: WARM VS COLD BOOT
BIOS checks memory location 0x0472
Value of 0x1234 indicates a reboot and rest of
post is skipped
Any other value indicates a cold boot and the
following steps are performed
RAM is tested
Values are written then read from each memory
cell
BIOS tests for existence of floppy disks, hard
drive, and optical drives
15. THE BOOT PROCESS: HANDOFF
After POST BIOS hands off control to operating
system
BIOS instructs CPU to begin executing the
operating system boot loader
Code found in sector zero of primary HDD
Operating system replaces many of the device
drivers and interrupt vectors that BIOS loaded
16. THE BOOT PROCESS: PLUG AND PLAY
ENUMERATION
The operating system adds special device
drivers called enumerators
ISA bus enumerator
SCSI bus enumerator
PCI bus enumerator
PCIe bus enumerator
Port enumerator
Operating system asks each enumerator to
identify which devices it has and what
resources they require
17. THE BOOT PROCESS: RESOURCE ARBITRATION
Operating system assigns resources to each
enumerated device
IRQ
DMA
Memory addresses
If no new devices are discovered, stored PnP
information is used
Operating system loads appropriate high-level
device drivers for each PnP device
Drivers initialize each device
18. THE BOOT PROCESS: FINISHING UP
Operating system mounts disk drives for use
Video drivers are installed to allow for use of
video hardware
Operating system services are initialized
User logon screen displayed
20. PROCESSES
Program: a set of instructions given to a
computer
Process: a program in execution
Process state: the current status of a process
including the contents of the relevant CPU
registers
22. PROCESS ADMINISTRATION
Processes compete for operating system
attention and computer resources
Operating system coordinates execution of
processes
Scheduler
Dispatcher
23. SCHEDULER
Scheduler manages a
pool of processes
which are currently
being executed
Adds new processes
Removes completed
processes
This pool is a
collection of process
control blocks (PCBs)
24. DISPATCHER
Responsible to ensuring processes get
scheduled for CPU time
The act of changing from one process to
another is called a context switch
PCBs are packed/unpacked
Cooperative multitasking
Processes remove themselves from running state
Preemptive multitasking
Dispatcher evicts process when time slice expires
Occurs on interrupt
