OS Exam 2
RAID 0+1
A RAID 0 configuration created by combining two RAID 1s. Provides both speed and redundancy, but requires at least four disks.
thrashing
A condition of excessive paging in which the operating system becomes sluggish. memory access time = disk access time - low CPU utilization which results in the CPU thinking it needs more processes which leads to more pages requested
Mean time to failure (MTTF)
The average amount of time until the next hardware failure. If there are more disks, chance of failure increases
What is the backing store?
The backing store is an area where a process is stored, usually a fast disk, when swapped out of main memory.
What does each entry in the page table contain?
The base address of each page in physical memory.
password vulnerabilities
guessing with dictionary attack, shoulder surfing, keyboard logger, sharing/writing down, storing/packet sniffing
hashed page table
hash value is virtual page number, linked list of elements
What is an alternative to hierarchical paging for large (>32 bits) address sizes?
hashed page table
steganography
hide secret in plain site in an image. Must know the key to find the message
directory linear list
holds <name, metadata> pairs pro: simple cons: slow if there are gaps after deletion
advisory lock
software must enforce lock
malware
software that is intended to damage or disable computers and computer systems. - extorsion, DDoS, keylogger, click fraud, spambot, steal software, ransomware
CD-ROM
compact disc-read-only memory
What disk scheduling algorithm is typically used with SSDs?
FCFS
CIAAA
confidentiality, integrity, authentication, availability, authorization
mandatory lock
OS enforces lock
page size tradeoff
- internal fragmentation when page size is small - low TLB hit ratio and increased page count if page size is small
cons of single process allocation
- process may not need all the space - one process at a time - process can destroy the OS and we want to share memory
goals of multi programming
- sharing - transparency - protection - efficiency
working set implementation
- use bits: clock algorithm - idle time for each page: amount of CPU received by a process since last access to page - if use bit, clear idle time - if use bit not set, set idle time - if idle time < T, proc in working set
If a mount point is '/home' and the device 'jane/programs' is mounted on the mount point, what is the complete path name to access the 'programs' directory?
/home/jane/programs
speedup formula
1 / ((1-f) + (f/speedupf))
Provide at least two different approaches for allocating disk blocks to files.
1. Contiguous Allocation - each file occupies a set of contiguous blocks 2. Linked Allocation - each file is a linked list of disk blocks, which may be scattered anywhere on the disk. 3. Indexed Allocation - provides an index block that consolidates all of the file pointers together into one location, the index block.
List the three general disk scheduling algorithms
1. FCFS (first come first serve) 2. SSTF (shortest seek time first) 3. SCAN (starts at one end and moves to the other, reversing back when it gets to each end)
What two forms of I/O are stored in a unified buffer cache?
1. File data 2. Process pages
What are the three strategies for selecting a free hole from the set of available holes?
1. First fit 2. Best fit 3. Worst fit
What are the two ways a computer can access disk storage?
1. I/O ports (host-attached storage) 2. Distributed File Systems (network-attached storage)
What are the two conflicting trends of I/O devices?
1. Increased standardization of software and hardware interfaces. 2. An increasingly broad variety of I/O devices.
What are the two general approaches for implementing a directory?
1. Linear List - list of file names with pointers to the data blocks. 2. Hash Table - Linear list stores directory entries, but a hash data structure is used; greatly reducing directory search time.
What are the two protocols associated with NFS?
1. Mount Protocol 2. NFS Protocol
What is one benefit of using slab allocation?
1. No memory is wasted due to fragmentation. 2. Memory requests can be satisfied quickly.
What are the four levels where security measures must be taken?
1. Physical 2. Human 3. Operating System 4. Network
Provide examples of at least two system and network threats.
1. Port Scanning 2. DDOS
List at least three different services provided by the kernel I/O subsystem.
1. Scheduling 2. Buffering 3. Caching
What are the two fundamental ways of accessing a file?
1. Sequential Access 2. Direct Access
What are the three possible outcomes when writing to disk?
1. Successful completion 2. Partial failure - failure after successfully writing some of the sectors 3. Total failure - failure before disk write occurs
Provide examples of at least three program threats.
1. Trojan Horse 2. Trap Door 3. Logic Bomb 4. Stack and Buffer Overflow 5. Viruses
What are the two forms of fragmentation?
1. external fragmentation 2. internal fragmentation
page replacement algorithm
1. identify page to replace 2. write victim page to disk (could use dirty bit to detect if page has been altered and if it needs to be copied) 3. read selected page into vacated frame
requirements for asymmetric encryption
1. must be difficult to compute private key 2. must be difficult to compute plaintext even when given plaintext-cuphertext pairs
Using the buddy system, if a request for 200KB of kernel memory is made, how much is actually allocated?
256KB
If a page offset is 13 bits, how large (in bytes) is the page?
2^13 bytes
advanced encryption standard (AES)
A block cipher created in the late 1990s that uses a 128-bit block size and a 128-, 192-, or 256-bit key size. Practically uncrackable.
translation lookaside buffer
A cache that keeps track of recently used address mappings to try to avoid an access to the page table. - spacial and temporal locality
What is a controller?
A collection of electronics that can operate a port, a bus, or a device.
hard link
A file joined to other files on the same filesystem that shares the same inode.
journaling file system
A file system that keeps track of changes not yet committed to the file system's main part by recording the intentions of such changes in a data structure known as a "journal".
paging
A memory management scheme where a computer stores and retrieves data from secondary storage for use in main memory - divide memory into fixed-size chunks - 2^n sized chunks - physical = frame, logical = page pros: - no external fragmentation - easy to set up and take down page table - enables page sharing by having multiple pages pointed to the same frame cons: - internal fragmentation - page table memory reference (complex, less efficient, mmu only stores base address of page tables)
When does a page fault occur?
A page fault occurs when a process tries to access a page that has not been brought into memory.
What are the two parts of an address generated by the CPU?
A page number An offset
reference string
A particular string of memory references used to compute the number of page faults on that string to evaluate page replacement algorithms
amdahl's law
A rule stating that the performance enhancement possible with a given improvement is limited by the amount that the improved feature is used. It is a quantitative version of the law of diminishing returns.
master boot record
A small program that runs whenever a computer boots up.
page fault frequency
A too high frequency causes trashing bc process needs more frames, a too low frequency is caused by too many allocated frames. Upper and lower bound need to be set.
defragmentation
A utility that reduces the amount of fragmentation by physically organizing the contents of the disk to store the pieces of each file contiguously.
single level directory
All files are contained in the same directory and have unique names.
first fit
Allocate the first hole that is big enough; N/2 blocks may be wasted - leaves average sized holes - O(n) or Omega(1)
worst fit
Allocate the largest hole - O(n) or Omega(n)
best fit
Allocate the smallest hole that is big enough - leaves some large and some small holes - O(n) or Omega(n)
What is a volume?
An entity containing a file system. Can be a subset of a device (partition), a whole device, or multiple devices linked together into a RAID set.
demand paging
An extension to paged memory management in which pages are brought into memory only when referenced - less memory, less I/O, faster response - OS requires policy for swapping pages and locating each page in memory or on disk - every first access requires page fault
privilege escalation attack
An unauthorized attempt to increase permission levels.
LRU-K
Combining recency and frequency. Keep time of last K references for each page. Remove page with oldest Kth reference time. If only one page has fewer than K references, remove it. If mutiple pages have fewer than K references, use LRU. cons: expensive
List the three different times at which address binding may occur:
Compile Time Load Time Execution Time
fixed size partitions
Divide memory into fixed-size chunks. Too big, wastes space for smaller processes; too small, limits size of the process. Can result in internal fragmentation.
What is the name of the encryption algorithm where the same key is used to encrypt and decrypt?
Symmetric Encryption Algorithm
prepaging
Bringing in all the initial pages, to prevent the high amount of page faults in the beginning. - cons: may force out needed pages for no reason
8.4 What is the only reasonable condition that can be used to prevent deadlocks from occurring?
Circular wait - Impose a total ordering of all resource types, and require that each process requests resources in an increasing order of enumeration.
What is an alternative to a nonblocking system call?
Asynchronous System Call
8.6 What is the name of the classic deadlock avoidance algorithm?
Banker's Algorithm
L2 Cache
Cache that is slightly slower than L1 cache but has a much larger capacity.
L1 Cache
Cache used by a CPU for short-term storage of data and instructions. It is the fastest and closest to the CPU.
file operations
Create, Read/Write, Get/Set Attribute, Rename, Delete, Truncate
List at least three operations that may be performed on a file.
Creating, Writing, Reading, Repositioning within, Deleting, Truncating
RAID-6
Disk striping with extra parity. Like RAID 5, but with more parity data. Requires five or more drives, but you can lose up to two drives at once and your data is still protected.
RAID-5
Distributed Parity Requires N + 1 Disks Survives single disk failure
Name one type of distributed information system.
Domain Name Service (DNS), Network Information Service (NIS), Common Internet File System (CIFS), Lightweight Directory-Access Protocol (LDAP)
indexed allocation
Each file has its own index block(s) of pointers to its data blocks pros: no external fragmentation, random access cons: wast of space because there's an additional block for the index
True or False? A physical address space is at least as large as a virtual address space.
False
True or False? I/O operations do not have a significant impact on performance.
False
True or False? Shared memory is typically not implemented using memory mapping.
False
True or False? The lifecycle of an I/O request does not require many CPU cycles.
False
True or False? An address generated by the CPU is also referred to as a physical address
False, an address generated by the CPU is a logical address. An address seen by the memory unit is a physical address
True or False? Most modern systems swap entire processes to swap space.
False; Most modern systems swap pages to swap space, not entire processes.
contiguous file allocation
Files stored in sequential block/cluster addresses pros: little overhead for metadata, good performance for sequential access, simple to calc random addresses cons: external and internal fragmentation, can't grow without moving whole file
What is the fundamental difference between global and local page replacement?
Global page replacement allows a process to select frames of memory from all available memory, where local page replacement only allows the process to select frames of memory from those frames specifically allocated to that process.
tree-structured directory
Had a root directory, with each file having their unique path name. Directories contain files and subdirectories, but can't share them. Relatively easy to traverse + no garbage collection.
What is the term when a system diverts an intruders to a location where the system can monitor the intruder's activity?
Honeypot
juiced page table
Includes additional page information such as valid-invalid bit and permission information.
buffer overflow attack
Inputting so much data that the input buffer overflows. The overflow contains code that takes control of the computer.
What page replacement algorithm is used by Windows?
LRU (least recently used)
What page replacement algorithm could be implemented using a stack or counters?
LRU (least recently used) algorithm
clock algorithm
LRU is expensive so we approximate. Keep reference bit for each page in frame. When page is referenced, set the bit. Start search at the next victim frame. If reference bit is set, clear it and continue. Stop at page with already cleared bit and replace it. Also referred to as Second-Chance Algorithm.
Tertiary Storage
Large data storage, inexpensive, Removable, Large seek time (CD, DVD)
file abstraction
Logical storage unit mapped by OS to device. - user: names collection of bytes - OS: map bytes as a collection of blocks on physical nonvolatile storage device
free frame list
Maintained to keep track of which frames can be allocated.
Name one type of remote file system.
Manually transferring files i.e. FTP, Distributed File System (DFS), World Wide Web, Cloud computing.
memory overload
Many processes loaded, few executing. Swap idle processes to backing store! cons: swapping a process in the waiting state means you have to swap the process back in before it's needed
What is the most common technique for security attacks?
Masquerading - one participant in a communication pretends to be someone else (another host or person)
RAID-1
Mirroring File blocks are duplicated between physical drives. Survives single disk failure. pros: high disk space utilization cons: high redundancy, requires 2N disks and 2X the writes, minimum of 2 drives
extent-based allocation
Multiple contiguous extents per file. Improves contiguous allocation as file can grow over time. Also helps with external fragmentation. Advantages: - Limited overhead for meta-data -Very good performance for sequential accesses - Simple to calculate random addresses Disadvantages: - External/Internal fragmentation can still be a problem - Not able to grow file when run out extents
paging address translation
N = Size of page M = Size of address space offset = n bits page # = m bits high order bits = page number low order bits = offset within page
List at least three attributes of a file.
Name, Identifier, Type, Location, Size, Protection
What is the name of the page replacement algorithm that operates by replacing the page that will not be used for the longest period of time?
OPT (Optimal Page Replacement) algorithm
software perfect LRU
OS maintains an ordered list of physical pages by reference time. When page is referenced, move page to front of list. When a victim is needed, pick the page at the bottom of the list. cons: slow on memory reference and fast on replacement
internal file structure
OS writes sequence of bytes, application can encode complex structure. - extension, magic number, and OS metadata
What are the three components of a 32-bit ARM address?
Outer page Inner page Offset
What are the three general classifications of users in connection with each file?
Owner, Group, Universe
points of compromise
Physical - Inappropriate site access Human - Compromise credential holder (phishing, pretexting, etc) Operating System - Compromise protector Network - Compromise transport
symbolic links
Pointers to other files; they can point to items on other drives or other parts of the network and don't affect the link count
file locking
Precaution which allows only one user at a time to edit a data file, such as a spreadsheet.
variable size partitions
Process requests memory size it needs. Placement depends on availability. Exiting processes create holes, system coalesces adjacent holes into new spaces. Can result in external fragmentation.
dynamic relocation
Protect processes from one another; requires hardware support (MMU).
which RAID would be best for swap space?
RAID 0
which RAID would be best for a database?
RAID 5 or 6
What two registers can be used to provide a simple form of memory protection?
Relocation register Limit register
FIFO page replacement
Replace the oldest page; simple to implement and fair, but many page faults if some pages are needed often
LRU Page Replacement
Replace the page that has not been used for the longest period of time pros: gets close to optimal cons: harder to implement bc have to track accessed pages, dislodges warm pages, doesn't handle all workloads well, doesn't deal with frequency of access
bit vector
Represents the list of free blocks with either 1 or 0 Advantages: -Simple -Fast -Easy to find sets of contiguous blocks con: large vector
access matrix
Rows represent Domains. Columns represent Objects.
What is the first step of implementing a security defense?
Security Policy
boot block
Simple code that knows the location and length of the remainder of the bootstrap program.
trap door
Special code that when triggered circumvents normal security
RAID-0
Striping File blocks are split between physical drives pros: high performance, no redundancy, better throughput, high data transfer capacity cons: minimum of 2 drives
balance set
Sum of working sets of all active processes. Process should not be scheduled unless working set is resident in main memory. - if too large, move some working sets back into inactive set
file metadata
System information associated with each file (name, type, location, size, permission, protection, access, special, usage data), stored on disk.
What is the term that describes when a page number is not present in the TLB?
TLB miss. A memory reference to the page table is made, and the page and frame number are added to the Translation Look-aside Buffer (TLB)
Where does the Windows system place its boot code?
The MBR (master boot record), the first sector of a disk.
spatial locality
The locality principle stating that if a data location is referenced, data locations with nearby addresses will tend to be referenced soon. - programs spend 90% of the time in 10% of the code
two-level paging
The page table is also paged, limiting the size of the page table.
temporal locality
The principle stating that if a data location is referenced then it will tend to be referenced again soon. - programs spend 90% of the time in 10% of the code
code signing
The process of assigning a certificate to code. The certificate includes a digital signature and validates the code.
soft link
This link can be a reference to a file or directory that can span multiple file systems. If the original file or directory is deleted, then the original content is lost.
symmetric key
This type of encryption uses the same key to encrypt and decrypt
What is the fundamental reason RAID is used?
To address performance and reliability issues.
What is the most common way of structuring directories?
Tree-structured
social engineering
Tricking a user into revealing their password or other sensitive data. phishing, pretexting, spoofing
True or False? 4KB is a typical page size.
True
True or False? A given device may require different drivers for different operating systems.
True
True or False? A program does not need to be stored in memory in its entirety.
True
True or False? Approximation algorithms are almost always used when implementing LRU.
True
True or False? Disk blocks are made up of one or more sectors.
True
True or False? IA-32 address translation involves both paging and segmentation.
True
True or False? If a system crashes, all transactions in the log file were not completed to the file system.
True
True or False? In a pure demand paged system a page is never brought into memory until it is needed
True
True or False? Magnetic disks provide the bulk of secondary storage for modern computer systems.
True
True or False? Most CPUs allow some interrupts to be ignored so that a critical instruction cannot be interrupted.
True
True or False? Solid state disks have the same characteristics as traditional hard disks.
True
True or False? The vfork() system call does not use copy on write.
True
True or False? With pure demand paging, the page fault rate is initially very high.
True
True or False? Fragmentation can still occur in paging systems.
True, Internal fragmentation can still occur. External fragmentation cannot
user authentication
Use something the user knows, something the user has, or something the user is
request paging
User specifies which pages are needed for process. cons: memory management by hand, users don't always know what they need, users are not impartial
memory-mapped files
Using virtual memory techniques to treat a sequentially accessed file as routine memory access.
what happens when a set of processes frequently reference many different pages?
Virtual memory illusion breaks because constant page faulting
working set
a collection of pages to be kept in main memory for each active process in a virtual memory environment to avoid thrashing
RAID 1+0
a combination of RAID 1 and RAID 0 that requires at least four disks to work as an array of drives and provides the best redundancy and performance.
partition
a subdivision of a hard drive's surface that is defined & used as a separate drive
SSTF
a form of SJF but may cause starvation of some requests.
pretexting
a form of social engineering in which one individual lies to obtain confidential data about another individual
one way hash function
a function that is easy to compute on every input, but hard to invert given the image of a random input. fast, small, and unique
Storage Area Network (SAN)
a high-speed network with the sole purpose of providing storage to other attached servers
access control list
a list attached or linked to a specific resource that describes users or user groups and the nature of permitted access File 1: {(Domain 1: R), Domain 2: W)} Password: {(Bob: R)} - good for users bc they associate permissions at creation time - finding access rights is expensive
buddy algorithm
a memory allocation technique that divides memory into halves to try to give a best-fit and to fill memory requests as suitably as possible. to allocate: 1. find smallest free block B that is larger than R 2. While R > B/2: a. divide B into B1 and B2 b. B = B1 and B2 remains free 3. allocate B (B = 2^n and R < 2^n) to free: 1. mark block as free 2. coalesce buddy blocks back together
Network Attached Storage (NAS)
a network-connected computer dedicated to providing file-based data storage services to other network devices.
read-ahead
a requested page and several subsequent pages are read and cached
C-SCAN
a scheduling strategy for direct access storage devices that's used to optimize seek time. It moves only in the forward direction. At the end, it moves back to 0 and sweeps up again.
format string attack
a type of input validation attacks in which certain print functions within a programming language can be used to manipulate or view the internal memory of an application
copy-on-write
allows both parent and child processes to initially share the same pages in memory
external fragmentation
as processes are loaded and removed from memory, the free memory space is broken into little pieces exists when there isn't enough total memory space to satisfy a request
hardware perfect LRU
associate register with each page. When page is references, store system clock in register, so when a victim is needed, scan all registers to find oldest one. cons: fast memory access, slow on replacement
nonrepudiation
being able to prove who encrypted a message
one-time password
block that holds a password list chain that hold a secret s, n passwords where P_i+1 = f(Pi) and Pn = f(s).
virus
code that can replicate itself by attaching to another program
logic bomb
code that when activated causes damage
disk controller
determines the logical interaction between the device and the computer
combine paging and segmentation
divide segments into pages pros: sparse address space, no external fragmentation, segments can grow, processes can run with a page swapped to disk, increased flexibility of sharing cons: overhead of accessing memory, must allocate page tables contiguously, large page tables
ACL's and Groups
domain can be (user, group) pairs. password: {(Bob, sysadmin: RW)} "Bob in group sysadmin can RW to password"
linked allocation
each file is a linked list of disk blocks pros: no external fragmentation cons: bad random access, bad sequential bandwidth, pointer overhead, not as reliable bc of pointer accuracy
contiguous memory allocation
each process is contained in a single section of memory that is contiguous to the section containing the next process - static, dynamic, fixed, and variable pros: - protection, dynamic relocation, simple and inexpensive, fast and parallel cons: - fixed size (weird sizing), variable (fragmentation), no partial sharing
confidentiality and authentication with asymmetric encryption
encrypt message with receiver's public key. Then encrypt encryption with senders private key.
volume
entity which contains a file system
cache
faster memory to temporarily store recently-accessed data.
UNIX directory structure
file with names an i-node numbers
Belady's Anomaly
for some page replacement algorithms, the page-fault rate may increase as the number of allocated frames increases
What system call initiates copy on write?
fork()
What must be done to a disk before it can be used for storage?
formatting - dividing into sectors for reading and writing
linked list free-space implementation
free blocks point at each other. - store in groups - store count of number of free blocks in next block because blocks are typically freed in contiguous chunks pro: cons:
per-process replacement
free pool of pages. Equal, fixed allocation. Proportional allocation. pros: page fault in one proc doesn't affect other procs, relieves interference from other processes. cons: Potentially inefficient allocation of resources
full vs incremental backup
full: large and time-consuming incremental: only changed data, but complex for recovery
Capabilities
implement matrix row as a list of (resource, rights) pairs associated with the domain Domain 1: {(File 1: R), (File 2: RW)} Bob: {(Password: R)} - revoking access is difficult - hard to tell when there are no more references to an object
key distribution problem
in symmetric encryption, where encryption key can be intercepted which puts the security of the encrypted message at risk
page table valid bit
indicates if the page is in memory valid: normal paging invalid: fetch page from disk and update page table
code injection attack
input includes code that is then executed by the attacked system
LFU page replacement
instead of tracking the recency of use, track how many times a page is used. cons: never forgets old pages
memory management unit
maps virtual address space to physical address space - process generate a logical address - OS uses base register + logical address to get physical address
linked block sizes
larger: internal fragmentation smaller: more pointer overhead and less efficient random access
SCAN disk scheduling
like an elevator; sweep up and sweep down, repeat
main memory problems
limited capacity, cost, persistence, portability
principal of least privilege
limited to the lowest level necessary to perform the required tasks.
file allocation table
linked list information for all files on disk. - metadata is first block of file - pros: improved random access - cons: read from 2 disks for each data read
multi-level index
linked list of index blocks - index block points to a set of index blocks pros: smaller blocks and support for larger files cons: multiple reads to find address, indirect blocks cached in main memory
inverted page table
lists every memory frame with its associated process and page. Any frame without an associated page entry is available for allocation. pro: one page table with size = # real frames con: long lookup time
static address binding
locations determined at compile time, load time, or execution time
segmentation
logical address space divided into logical segments. Physical memory doesn't need to be contiguous. - logical address is broken into segment # and offset pros: flexible, allows growing and shrinking, independent segment growth, provides protection for segments, allows shared segments and dynamically allocated segments cons: each segment has to be contiguously allocated
What is the term for the smallest unit of transfer between a disk?
logical block
TLB miss
lookup that fails because the table does not contain a valid translation for that virtual address
static relocation
memory is split into blocks and each block can hold a process (fixed size process) - each process is placed anywhere in memory - modify addresses statically when loading processes pros: - allows multiple processes to run - requires no hardware support cons: - no protection of privacy - have to allocate contiguously - wasteful space usage and cannot grow
block
minimum unit to read or write
graph directory
more general than a tree structure. Allows both acyclic and generl with general structures allowing loops.
FCFS disk scheduling
most inefficient disk scheduling algorithm.
Single Large Expensive Disk (SLED)
old way of mass storage?
page fault policy
page selection and page replacement
salted hashed password
password is concatenated with n-bit random string before being hashed and stored
physical vs logical backup
physical: block-by-block perfect restoration logical: recursively dump files and directories
directory hash table
pro: faster cons: hash table implementation
global replacement
process selects a replacement frame from the set of all frames; pros: flexibility of allocation, minimize number of page faults cons: one process can take a frame from another, one process can hog memory, processes depend on each other
per-user replacement
pros: Users running more processes cannot hog memory cons: Inefficient allocation
links
reference to file or directory must keep a reference count on a file - cons: loops degrade performance
Memory Heirarchy
registers -> cache -> main memory -> electronic disk -> magnetic disk -> optical disk -> magnetic tapes (fast -> slow and expensive -> cheap)
domain
set of (object, right) pairs - processes run in one at a time but may switch
logical address space
set of all logical addresses generated by a program. Starts at 0
Redundancy Array of Independent Disks (RAID)
spreads data across several smaller disks and reads in parallel.
Helical Bits
tape where bits are written at an angle across the tape. Decreases inter-symbol interference allowing higher bit density. pro: greater data rate and good for backups cons: slow seek rate
jailing
temporarily running code in a controlled environment and look for problems
seek time
the time it takes for a read/write head to move to a specific data track
What term is used to describe the situation where a process spends more time paging than executing?
thrashing
latency
time it takes for the spin sector to move under the head
network file structure
transparent use of remote file systems -mounting involved attaching a remote file system problems: permissions and cascading mounts (cycles)
8.7 True or False? The wait-for graph can only be used for deadlock detection when there is a single instance of each type.
true
certificate authority
trusted third party whose public key is distributed
internal fragmentation
unused memory that is internal to a partition breaks the physical memory into fixed-size blocks (usually of base 2) and allocate memory in units based on block size. The memory allocated to a process may be slightly larger than the requested memory
asynchronous cache write
update cache, flush later. better performance but vulnerable to loss is there's a crash.
asymmetric encryption
used in public key encryption, it is scheme in which the key to encrypt data is different from the key to decrypt. - RSA cons: slow (1000 times slower than symmetric)
certificate
user identity and public key signed by trusted third party
block consistency
verifying blocks are not allocated multiple times and are in one of the free block list or in a file 1 time.
VFS
virtual file system
file consistency
when deleting a file, deallocate each block, add blocks to free list, add i-node to free list, remove file from directory - recursively search directory to verify all reference counts (high means last reference delete doesn't remove a file, low means premature deletion)
What term is used to describe the set of pages a process is currently referencing?
working set
kevin mitnick
worlds most celebrated computer hacker
What does the acronym WAFL stand for?
write-anywhere file layout
synchronous cache write
writes go all the way to the disk