Computer Revision

Computer Revision

1. Embedded system

   • Due to limited functions, the computer in an embedded system is easier to design, cheaper, efficient.
   • Embedded systems are computers inside a larger dedicated system.
   • Not embedded system: kettle, iron, hoover, toaster, oven.

2. Structure and function

   • The control unit has overall control to execute instructions by following the FDE cycle
   • The CPU contains, control unit, ALU, registers and cache.
   • The arithmetic Logic unit is used for arithmetic operations +-*/ an dfor logic operations using AND, OR, and NOT
   • The cPU usdes registers to temporarily holds tiny bits of data needed.
   • The CPU fetches an instruction from memory decode and excute it (FDE Cycle) repeatedly
   • The cache is very fast memory in the cpu used to store regulary used data to speed up processing.

3. Fetch-Decode-Execute cycle

   • the number of instructions carried out per second is the clock speed. Bigger number= faster CPU
   • The CPU carries out instructions one after another, billion of times a second.
   • The instructions are carried out during the Fetch-Decode-Execute (FDE) cycle.
   • DECODE - The Cpu works out what instructions in MDR wants it to do
     • DECODE: Control unit works out what to do.
   • FETCH - 1. Copy memory address from PC to MAR. 2. Copy instructions stored in memory to MDR. 3. Add 1 to PC
     • FETCH: PC is copied to MAR. The address is sent to RAM using address bus. RAM sends data stored in that memory location on data bus. This data is stored in MDR.
   • EXECUTE - The instruction is carried.

4. Multiple Cores and Cache and Virtual Memory

   • Modern processors have multiple cores. Each core is a separate CPU. More cores mean the processor can do more things at once. Which makes the computer system faster
   • cache is very fast memory in the processor. Small in size and expensive compared to RAM. Used to store frequently used data. Speeds up processing because CPU does not need to ask memory for the data.
   • Virtual memory is Secondary storage used as extra RAM. RAM is a finite resources VM makes it appear as though there is infinite amount of RAM. When RAM is full, some less used data is copied to secondary store.

5. Secondary storage media. advantages and disadvantages

   • hard disk drive, magnetic tape. Used Magnetised metal particles to store data. metal particles arranged a certain way to indicate 1 or 0. Cheap. large capacity. Slower than SSD. Longer life than SSD. Some noise.
   • Compact Disc, Blu ray. data is etched on reflective surface into pits. data is read using laser that is reflected on the reflective surface. Very Cheap to copy. Portable. Lightweight. Low capacity
   • SSD, Pen drives, Sd card. uses a type of flash memory. Expensive, Lower capacity, faster than HDD. Shock proof. Silent. Limited lifespan.

6. Hardware

   • A General purpose computer system such as PC and smartphones can be used for multiple purposes.
   • A computer system is either general purpose or dedicated.
   • A dedicated system has specific functions such as the dishwasher or the heating control system.

7. Hexadecimal/ and those things

   • Binary - the system use by computers using only digits 1 and 0
   • Bit- short for binary digit.
   • Denary- base 10, our regular numbering system, using digits 0-9
   • Transistors- Computers are mad out of million of transistor is a tiny switch that can be on or off. Binary 1 or 0 is used to represent the state of these switches.
   • Hexadecimal. - number system using base 16. -Each digit is one of 0-9,A,B,C.D,E,F. - Because each 4 bits can be easily written using a single hexadecimal. -easier for human to read/write as shorter.
     • How to work it out: Make a table Look at each set of 4 bits in isolation. This four bits make 10. 10 is A. This four bits make 13. 13 is D. AD
   • Hex-Denary. Make a table. 5*16. A is 10. 5*16+10= 90 .
     • Denary-Hex. Make a table How many 16 goes into 228?14. 14 = E What is the remainder? 14*16= 224. Remainder is 4. E4
   • Binary to decimal
     • 4 bit
     • 8 bit
   • Binary addition

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