LEC 1 Flashcards
Memory Machine
- Input/Output communicates information between memory and outside world
- CPU manipulates information from memory
- CPU interprets information from memory as data or instructions
How many can 8 bits represent?
255
What is 16 bytes in bits in SIMD mode?
128
How is byte sequence interpreted as?
data in continuous bit sequences
Instructions with distinct fields
What is operation field?
what is to be done
What is operand fields?
what is to be manipulated
- absolute value
- register number
- address of value in memorry
Where does the CPU fetch instructions from?
The memory
What type of sequences does the memory have?
Byte sequence
What does the program counter do?
- Register
- Holds memory address for next instruction-
- Automatically increment after each instruction
- Branch instruction changes instruction sequence
What are the examples of instructions to manipulate registers?
• E.g. load register with value from memory
address
• E.g. add value to register
• E.g. store value from register at memory address
Instructions can also change program
counter with an example?
To change order of execution
E.g. branch to new address
E.g. branch to new address depending on values in
other registers
What can instructions do ?
- manipulate registers
- Change program counter
Machine code is very hard to?
- write
- read
- debug
- not portable between different CPUS
- very rarely constructed by hand
- as fast as it gets
What is the characteristics of assembly language?
One to one correspondence with machine code
• No loss of efficiency
Assembly language is CPU specific
• No universal assembly language
• Not portable between CPUs
Translated to machine code by assembler program
• How to write very first assembler…?
Improvement from machine code but very limited
abstractions
Hard to read/write/debug
Specialist skill
E.g. device drivers, BIOS, small embedded systems,
(part of) computer OS
What is the textual memory description of assembly language?
- Address -> Label
* Bit sequence ->Constant
What is the textual instruction fields of assembly language?
• Operations ->mnemonics • Operands Value -> Constants Address->Label Register ->Mnemonic
What is C’s overview?
Strict, strongly typed, imperative system
programming language
Combines high-level constructs with low
level access to type representations and
memory
What does stack in memory organisation contain?
• Allocated automatically • Global declarations • Local declarations • Function parameters
what does heap do in memory organisation?
- Allocated by program
- C.f. Java “new”
- No garbage collection
what does type var_name do?
• Allocates space for new variable of type
called name on stack
what does var_name do?
• Can contain letters, digits and “_” • Must start with a letter • C convention lower case = variable name UPPER CASE = symbolic constant
Can group declarations for same type?
yes
What does the amount of space for type depend on?
type
platform
compiler
How to measure type sizes in bytes?
int sizeof(type)
returns the number of bytes for type
Declaration: type name
Associates name with enough memory for
type
&name
Address of 1st byte allocated to variable
name
What is constant? as expression
value of constant
What is name? as expression
value from memory
