Computer Architecture and Programming Languages

• CPU - Central Processing Unit - The "brains" that performs the computations.
• Main Memory - Where everything must be for the CPU to use it.
• Input and Output - Devices used to enter or display information.
  • Storage - A disk (or similar device) for saving programs and data.
• IFSM 310 is an entire course about computer architecture.

Main Memory / RAM

• Main memory is also known as RAM (Random Access Memory)
• To run any program, it must be loaded from the disk into RAM.
• RAM is volatile - All memory is lost when the power is off.
• For something to be permanent, it must be written to a disk (storage).
• RAM is composed of bits.

Bits - Binary Digits

• A bit has two possible values: 0 or 1.
• Hardware representation: voltage, current, magnetic field, reflectivity, ...
• Everything is represented as bits. (numbers, characters, sound, images, program instructions, ...)
• Groups of 8 bits are called called bytes.
• A common size for RAM is 256 MB (megabytes).
• Each byte has an identifying address.

CPU - Central Processing Unit

• CPU is typically implemented as one chip.
• The CPU gets machine instructions from memory, and does them one at a time.
• An machine instruction contains an opcode that tells what to do and generally one or more operand addresses that specify what to do it to.
• Machine instructions are very small steps: eg, add the byte at location 253398 to the byte a location 84992 and store the result in byte 234344.
• The CPU is able to do these instructions very rapidly. A common speed might be 1 GHz, which means that it does something (part or all of an instruction) in a billionth of a second.
• Different types of CPUs use different instructions (Intel x86, Power PC, Sparc, ...).
• Unfortunately, humans cannot easily work with binary machine instructions (hence the use of programming languages).

Input / Output

• Input / Output devices transfer bits into or out of memory or CPU.
• The hard disk is like other devices, but is sometimes grouped separately because of its use to store programs and data (storage).
• Relatively slow compared to CPU and RAM.

Machine-Human Mismatch - Programming languages

• Machine instructions are difficult for humans to use (eg, 0000011011000101)
• Human language can not be understood by machines, at least directly.
• The compromise is to choose a "programming language" that humans can read and write, and that can be translated by a program into machine instructions.

Hierarchy of Programming Languages

1. Machine instructions - Too difficult for humans.
2. Assembly language
   • Each machine instruction represented symbolically. Eg "AR R12, R5".
   • Easy to understand and translate, but tediously detailed.
   • Not portable - specific to one type of CPU.
   • Is not commonly used for mainstream programming.
3. High-level language - Mainstream programming.
   • Human "readable" language

     if (age > 21)
        canDrink = true;

   • Usually portable - can be translated for different CPUs.
   • Examples: Pascal, Cobol, Perl, Visual Basic, C, C++, Java, C#, ...
   • Human writes "source program". It's translated into an "object program" by a compiler.
4. Natural languages (English, Deutsch, ...)
   • Impractical to translate into machine instructions.
   • Surprisingly ambiguous. "He saw a bottle of wine on the table and drank a glass of it."