Cirrus Logic CS485 Bedienungsanleitung PDF herunterladen (Seite 7)

CS485G Spring 2015 7

6. The operating system allocates physical space, which also looks like

an array ranging from address 0 to a limit determined by how much

physical memory the machine has.

7. Within a process, the program uses memory for various purposes.

The compiler decides where in memory to put various items, includ-

ing the instructions, initialized data, uninitialized data, stack, and

heap.

8. A 32-bit architecture generally means that integers are contained in

32 bits, and that virtual addresses use 32 bits (unsigned). The max-

imum address is therefore 4G-1. That memory size is too small for

some applications.

9. A 64-bit architecture generally means that integers are contained in

64 bits, and that virtual addresses use 64 bits (unsigned). The max-

imum address is therefore about 1.8 × 10

. The x86 64 architecture

supports only 48-bit addresses, which gives 256TB.

10. Architectures generally support multiple data formats. So a 64-bit

architecture might be able to manipulate 8-bit, 16-bit, 32-bit, 64-bit,

and 128-bit integers.

9 Strings and Buffers

1. A C string is an array of bytes, each representing a single character,

terminated by a null (zero) byte.

2. Declaration

(a) char

myString;

(b) char myString[];

3. The representation is typically 7-bit ASCII.

4. Some representations, such as UTF-8, might use several bytes for a

single Unicode character. So the length of the array is not necessarily

the number of characters.

5. There is no need to worry about byte ordering; the start of the string

always has the lowest address in memory.

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Cirrus Logic CS485 Bedienungsanleitung Seite 7