Vault sync: 2022-01-26 13:34:31

School/Analyse/Periode 2/Week 1.md

@@ -4,4 +4,35 @@ Handles devices that allow the computer system to:
 * Communicate and interact with the outside world
 	- Screen, keyboard, printer
 
-* Store information
+* Store information
+
+![[io-subsystem.png]]
+
+# The Control unit
+Program stored in memory. (machine language in binary)
+
+Task of control unit is to execute programs by:
+* Fetch: from memory the next instruction
+* Decode: instruction to determine what to do
+* Execute: issuing signals to ALU, memory and IO systems.
+
+Repeats until HALT instruction.
+
+# Typical Machine Instructions
+MOV: move data from a to b
+ADD: add numbers
+SUB: subtract numbers
+JMP: transfers program control flow to the indicated instruction
+
+![[example-machine-lang.png]]
+
+# CPU Time vs IO Time
+Total time required to run program is: CPU Time + IO Time
+
+Typical time to read from IO: 20ms
+Typical time to run instruction: 20ns
+CPU can execute up to 200 million instructions while a block is read from a hard disk.
+
+Conclusion: While I/O is executed, CPU is idling.
+
+![[cpu-vs-io.png]]