Understand Computer Storage and Data Types

Transcription

1 Understand Computer Storage and Data Types

2 Lesson Overview Students will understand computer storage and data types. In this lesson, you will learn: How a computer stores programs and instructions in computer memory Memory stacks and heaps Memory size requirements for the various data storage types Numeric data and textual data

3 Guiding Questions 1. How are program instructions stored in a computer? 2. Identify the different data types that can be used and the values they can hold.

4 Activator Name the components of a computer. What components are involved in storing program instructions?

5 Review Terms Data type a definition of a set of data that specifies the possible range of values of the set, the operations that can be performed on the values, and the way in which the values are stored in memory. Garbage collection a process for automatic recovery of heap memory. Heap a portion of memory reserved for a program to use for the temporary storage of data structures whose existence or size cannot be determined until the program is running. Memory a device where information can be stored and retrieved. Stack a region of reserved memory in which programs store status data such as procedure and function call addresses, passed parameters, and sometimes local variables.

6 How a computer stores programs in memory A computer keeps data and programs in storage as follows: Primary storage Otherwise known as random access memory (RAM), it is made of memory chips. In common usage, it refers only to a computer s main memory, the fast semiconductor storage (RAM) directly connected to the processor. Secondary storage Otherwise known as a hard drive, it consists of a read/write head that floats above rotating platters coated with a magnetic material.

7 Memory Stacks and Heaps Variables are stored in either a stack or heap based on their type: Value types (e.g.: int, double, float) go on the stack. Reference types (String, Object) go on the heap. * Value types in classes are stored with the instance of the class on the heap. The stack Values in the stack are managed without garbage collection because items are added and removed from the stack as last in, first out (LIFO) every time you enter or exit a scope, like a method or statement A StackOverFlowException occurs because you have used up all the available space in the stack.

8 Memory Stacks and Heaps (continued) The heap A heap-based memory allocation occurs when we create a new object, at which point the compiler figures out how much memory is needed and allocates an appropriate amount of memory space and returns a reference representing the memory address. A heap is used for dynamic allocation of memory. The Microsoft.NET Framework uses garbage collection to free up space during run time. Garbage collection is an automatic process for recovery of heap memory. Blocks of memory that had been allocated but are no longer in use are freed, and blocks of memory still in use may be moved to consolidate the free memory into larger blocks.

9 Data Types Numeric data types Integral types (e.g.: byte, char, int) Floating-point types (float, double) Decimal Boolean Example: bool done = false;

10 Data Types Numeric data types Integral types (e.g.: byte, char, int) Floating-point types (float, double) Decimal Boolean bool done = false;

11 Integral Types Type Range Size sbyte -128 to 127 Signed 8-bit integer byte 0 to 255 Unsigned 8-bit integer char U+0000 to U+ffff Unicode 16-bit character short -32,768 to 32,767 Signed 16-bit integer ushort 0 to 65,535 Unsigned 16-bit integer int -2,147,483,648 to 2,147,483,647 Signed 32-bit integer uint 0 to 4,294,967,295 Unsigned 32-bit integer long -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 Signed 64-bit integer ulong 0 to 18,446,744,073,709,551,615 Unsigned 64-bit integer

12 Floating-Point Types Type Approximate Range Precision float ±1.5e 45 to ±3.4e38 7 digits double ±5.0e 324 to ±1.7e digits

13 Decimal Type Type Approximate Range Precision decimal ± to ± significant digits

14 Using the Numeric Data Types byte numkids = 15; char letter = p ; int worldpopulation = ; float money = f; double lotsamoney = 2.4E+12; decimal testgrade = 89.5m;

15 Lesson Review Describe how the program statement below is stored in memory: int tennispoints = 30; Identify the appropriate data types for each of the following values true