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+# W3D2&W8D1&W11D2
+
+# W3D2
+
+## Process & threads
+
+#### 1. synchronize
+
+- lock, mutex, semaphore
+  - mutex means: mutual exclusion.
+  - method 1: lock variable. 
+  - method 2: Peterson. 
+
+- CLI/busywaiting/sleepwakeup
+
+#### 2. Process/Thread Scheduling
+
+#### 3. Memory consistency
+
+**memory barriers:** to protect the code sequences, which might be edit by compiler, tomasulo,  etc..
+
+> A barrier is: Cannot change two code if one is before-barrier and the other is after-barrier.
+
+#### 4. CPU scheduling
+
+- Q: who's next?!
+  - according to priority.
+- Avoiding locks
+  - Read-copy-update
+
+**Scheduling methods:** 
+
+Run Queue(round robin). time-slice as a unit. 
+
+**Tradeoff:** context switch
+
+# W8D1
+
+### 1. Security
+
+**Exp: ** login, password, DoS
+
+**Definition: ** TCB
+
+### 2. Authentication
+
+Methods of authenticating users when they attempt to log in based on one of three general principles:
+
+- Something the user knows.
+- Something the user has.
+- Something the user is.
+
+### 3. Buffer Overflow Attacks
+
+### 4. Multilevel SecurityBell-LaPadula Model
+
+Bell-LaPadula Model rules for information flow:
+
+- The simple security property
+  Process running at security level k can read only objects at its level or lower
+- The property
+  Process running at security level k can write only objects at its level or higher
+
+# W11D2
+
+### 1. Multi-core/Processor/computer
+
+SMC/SMP/cluster/Grid/Cloud...
+
+multi: shared memory, multi-CPU
+
+UMA-NUMA
+
+multiple spinlock, bus
+
+- Avoid cache thrashing!
+- Time sharing, the art of scheduling
+
+"Gang scheduling" : A gang of related threads are scheduled as a unit, a "gang"
+
+"Computational Graph": ->"A platform for ML"
+
+"Distributed Shared Memory": Like page table, with indices
+
+### 2. Graph computing
+
+relations between Nodes, allocation of resources,...
+
+GraphChi
+
+Speed up executing, space less, locality is good.
+
+And we have algorithms.
+
+Object-based middleware "**CORBA**"
+
+Based on CORBA. Distributed systems.
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