Configuring the Operating System Configure Performance Options Processor scheduling and memory usage Virtual memory Memory for network performance Configure Environment Variables Configure Startup and Recovery Configure Power Options

Configure Processor Scheduling Start/Control Panel/System/Advanced System settings/Advanced Performance Settings/Advanced Allows the user to configure how processor resources are allocated Background services setting –All programs running will receive equal amount of processor time Program setting –All programs running at the server console will receive most processor’s resources

Configure Data Execution Prevention(DEP) Start/Control Panel/System/Advanced System settings/Data Execution Prevention While programs are running, DEP monitors how they use memory Computer viruses, Trojan horses and worms try to access memory spaces allocated to system functions

Protection on x86 Both Linux and Win32, only 0 and 3 are used Access to segments done by evaluating: –CPL: internal register stores current privilege level –DPL: descriptor privilege level –RPL: requestor’s privilege level Level

Configure Virtual memory Virtual memory expands the limitation of physical RAM by using disk memory When the current running program exceeds the RAM, it uses the disk space as the actual memory, except it is slower. The mapping of physical memory to virtual memory is know as paging Good article on setting virtual memory: – ualMemoryPageFileEtc.htm

Virtual Memory Useful when the combined size of the program, stack, data exceeds the available physical memory Memory Management Unit(MMU) maps virtual addresses to physical addresses Page table

Paging Pages –virtual address space divided into pages –typical 4K byte size (e.g. 64K program in 16 pages) –program extends over 1 page will take the entire additional page Page Frames –physical address space divided into page frames –same size as pages (e.g. 32K memory in 8 page frames) Page Tables –tells which page frame is assigned to each page of the virtual address(VA)

Virtual and Physical Addresses The relation between virtual addresses and physical memory addresses given by page table

Internal Operations of MMU Specify 16-bit address and a 4-KB page size using 4 bits for virtual pages and 12 bits for offset present bit also called valid bit(v bit) in x86

Multilevel Page Tables 32-bit address space has 1 million 4KB pages Get around having to store huge page tables in memory all the time

Multilevel Paging Example 0x corresponds to PT1 =0x01, PT2=0x03, offset =0x04 MMU uses PT1 to index into the top level table and PT1=1 corresponds to addresses 4M-8M MMU uses PT2 to index into the second level table and PT2=3 points to 3x4096 to 4x within the 4M chunk If page is not in memory, Present/absent bit =0 and accessing the page causes a page fault If page is in memory, present/absent bit =1 and the second page memory and offset forms the physical address 4M chunk 4K chunk

Paging Overhead 4 MB page tables are kept in memory To access VA 0x , we need to do 3 memory references. A large burden! –look up entry 0x48 in page directory –look up entry 0x345 in page table –look up address (page frame number| 678) Use hardware Translation Lookaside Buffers (TLB) to speed up the VA to PA mapping

Backing Store (a) Paging to static swap area - problem with process that increases in size after starting (b) Backing up pages dynamically - allocate disk space when the page is swapped out and deallocate it when it is swapped back in Proc size Proc size