Architecture Flashcards
Multi-Tasking
Multi-Tasking: A system can perform more than one Process at a time
• Pre-emptive multi-tasking mode: The operating system manages use of system resources.
• Cooperative mode: An application manages use of system resources.
Multi-Processing
Multi-Processing: is the use of two or more central processing units (CPUs) within a single computer system
Multi-Threading
Multi-Threading: A system can manage use by more than one user at a time or multiple requests within
a single process
Multi-Programming
Multi-Programming: A system that can have two or more programs running on one CPU
The Ring Model
The Ring Model- Processes communicate between layers via system calls o Ring 0- Kernel o Ring 1- Other OS Components not in 0 o Ring 2- Device Drivers o Ring 3- User apps
Hypervisor mode
Hypervisor mode (aka Ring -1) allows virtual guests to operate in Ring 0
o Type 1 (aka bare metal) runs directly on host HW (VMWare ESX)
o Type 2 runs as an app on normal OS (eg VMware Workstation, VirtualBox)
Computer bus
Computer bus- communication channel between CPU, memory, & I/O devices. Some computers use 2 buses:
o Northbridge- (aka MCH- Memory Control Hub) between CPU, RAM, video memory
o Southbridge- (aka ICH- I/O controller Hub) connects I/O devices (slower than Northbridge)
components of a CPU
The three components of a CPU:
• Control Unit: Manages CPU access
• Registers: Keeps track of memory location of next set of instructions and manages state
• Arithmetic Logic Unit (ALU): Performs calculations, fed by the control unit
FDX
Fetch & Execute- CPUs fetch machine instructions and execute them in 4 steps (FDX- fetch, decode, execute):
- Fetch
- Decode
- Execute
- Write result
Pipelining
Pipelining- combines multiple FDXs into one combined process
Interrupt
Interrupt: A special input into the CPU. An interrupt table tells the CPU where to go to address the interrupt condition (where to find the interrupt handler).
Task
Task- a heavyweight process
Thread
Thread- child processes (LWP- lightweight process) spawned by a process; share memory for lower overhead
Watchdog timer
Watchdog timer- recovers/reboots a system after a critical process hangs or crashes
CISC
CISC (Complex Instruction Set Computer)- larger set of machine instruction (x86)
RISC
RISC (Reduced Instruction Set Computer)- used in Sparc, PDAs, Cell phones
RAM
RAM- hold instructions and data
Cache
Cache- fastest; used by CPU registers; uses SRAM
SRAM
SRAM (Static)- flip-flops store bits; maintains integrity as long as power is supplied
DRAM
DRAM (Dynamic)- stores bits in capacitors; slower & cheaper; leak charge and must be refreshed
ROM
ROM- stores firmware, BIOS; types are EPROM & EEPROM (e.g. flash)
Virtual Memory
Virtual Memory: Using secondary storage to simulate RAM. This process is also referred to as paging or swapping.
o A security risk with virtual memory is that files may not be deleted after use.
o Page fault- occurs when kernel attempts to access a page stored in swaps space
o Thrashing- sys spends large amounts of time copying data to/from swap space
WORM
WORM- Write once read only storage can be used for records retention (CD-R, DVD-R)
Absolute Address
Absolute Address: (Direct) The actual physical address of the memory segment