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+### Distributed Shared Memory
+
+#### DHT/Chord
+
+Files are stored on distributed systems.
+
+$Hash(IP)$ is node's id.
+
+Suppose $suc_i$ is the next available node from $i$.
+
+Finger Table: maintain $suc_{u+2^i}$ for every node $u$. Time complexity lowered to $O(\log n)$.
+
+File is hashed to a number $x$, and is stored in several successors after $x$. Any machine can quickly get $suc_x$ and ask the machine for the file.
+
+Some machines may go offline. Every machine's finger table is self-maintained.
+
+When a machine enter the system, notify other machines to update finger table.
+
+#### Distributed Systems
+Chip: SoC (System on Chip)
+
+Board: SMP (Symmetric Pultiprocessing)
+
+LAN: Cluster
+
+Internet: Grid $\to$ Cloud
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+### Memory Management
+
+Reallocation, Swapping, Overlay, Replacement
+
+#### Swapping
+Memory <- exchange processes -> disk storage
+
+#### Virtual Memory & Paging
+
+Consider a part of disk as extension of memory
+
+#### Page replacement algorithms
+
+Optimal algorithm is based on the future
+
+- NRU (not recently used) algorithm
+
+Referenced bit and Modified bit
+
+- FIFO algorithm
+- Second-chance algorithm
+- Clock algorithm
+- LRU (least recently used) algorithm
+- Working set algorithm
+
+#### Physical Memory Management
+Buddy System (UNIX)
+
+Maintain lists of blocks of $2^i$ size.
+
+Breaks large blocks into 2 smaller blocks when allocating.
+
+Merge requirements:
+- same size
+- next to each other
+- after merging into a $2^{i+1}$ size block, the beginning of block should be a multple of $2^{i+1}$
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+### Security
+
+#### Buffer Overflow Attacks
+
+The attack is able to bypass the canary and modify the return address directly.
+
+![](p1.png)
+
+#### Code Reuse Attacks
+
+![](p2.png)
+
+#### Format String Attacks
+
+If not enough args provided, compiler will reserve space for these args. These can be used to either leak information or modify registers.
+
+![](p3.png)
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