3/29 The Components of the System Unit

System unit
--> Case that contains electronic components of the computer used to process data

Chips
-->Small piece of semi-conducting material on which integrated circuits are etched
-->Chips are packaged so they can be attached to a circuit board

Motherboard
-->Main circuit board in system unit
-->Contains adapter card,processor chip, and memory chips
-->Also called system board

Machine cycle
-->Four operations of the CPU comprise a machine cycle

FOUR STEPS
1.FETCH 擷取
2.DECODE 解碼
3.EXECUTE 執行
4.STORE 寫回

Pipelining 管線作業
-->CPU begins fetching second instruction 
before completing machine cycle for first instruction
-->Results in faster processing

Register 暫存器
-->Temporary high-speed storage area that holds data and instructions

Memory
--> Electronic components that store instructions, data ,and results
--> Consists of one of more chips on motherboard or other circuit board
--> Each byte stored in unique location called address, similar to seats on a passenger train

Random access memory(RAM) 隨時存取記憶體(又稱揮發性記憶體)
-->Memory chips that can be read from and written to by processor
-->Also called main memory or primary storage
-->Most RAM is volatile (揮發性), it is lost when computer's power is turned off
--> SRAM DRAM

Read-only memory (ROM) 唯讀記憶體
-->Memory chips that store permanent data and instructions
-->Nonvolatile memory, it is not lost when computer's power is turn off

Access time 存取時間
-->Amount of time it takes processor to read data from memory
-->Measured in nanosecond (ns)

記憶體 奈秒
硬碟     毫秒
記憶體速度快