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╔════════════════════════════════════════════════════╗
║ Lesson 2 Part 020 F-PC 3.5 Tutorial by Jack Brown ║
╚════════════════════════════════════════════════════╝
┌───────────────────┐
│ What is a BYTE? │
└───────────────────┘
- The smallest piece of data that can be accessed by most
microcomputers.
- Consists of a memory unit of 8 binary bits. A binary bit is a 0 or 1)
|0|1|1|1|0|1|0|1| <--- bit pattern in memory cell or byte.
7 6 5 4 3 2 1 0 <--- bit number
- Bit 0 is called the low order bit, bit 7 is called the high order bit.
- The bit pattern in a cell may represent:
i) any decimal number from 0 through 255.
ii) any hexadecimal number from $00 through $FF.
iii) any binary number from 00000000 through 11111111
- Often the byte is often used as the data structure to represent an
ASCII character.
┌───────────────────┐
│ What is a WORD? │
└───────────────────┘
- Consists of two bytes or 16 binary bits.
- The bit pattern in a word can represent:
i) any unsigned decimal number from 0 through 65,535
ii) any unsigned hexadecimal number from $0000 through $FFFF
iii) any binary number from 0000000000000000 through 1111111111111111
- Often the word is used as the data structure to represent short
integers in computer languages such as C, Pascal and Forth.
- ** The numbers we place on Forth's parameter stack are words **
** and hence are short integers from 0 through 65,535 decimal **
- 8 bit micro processors such as the 6502, 8080 use the word as a memory
pointer into their 64K address space. Micro processors such as the
80x86 and 680x0 often use the word as a pointer into a 64K segment or
array of 64K bytes.
┌───────────────────────────┐
│ Forth's parameter stack. │
└───────────────────────────┘
All computers represent numbers internally as bit patterns of zeros and
ones. The numbers on Forth's parameter stack are 16 bits wide and can
be used to represent either 16-bit signed integers or 16-bit unsigned
integers.
┌────────────────────────────────────┐
│ Please move to Lesson 2 Part 025 │
└────────────────────────────────────┘