Chapter 4
Logical vs Physical Address and Relocation
Learn base/limit based relocation and why logical addressing enables flexible loading.
CPU creates logical addresses; MMU converts them to real RAM addresses.
Address translation is the bridge between process view and actual memory hardware.
Address Spaces
From notesClear explanation
Each process uses logical address space; MMU maps it to physical locations while enforcing bounds.
What it really means
Users see apartment number, building admin maps it to actual room location.
Key takeaway
Translation gives both flexibility and protection.
Relocation Strategies
From notesClear explanation
Static relocation adjusts addresses at load time; dynamic relocation adjusts during execution using base/limit hardware.
What it really means
Dynamic relocation lets a process move without rewriting its code.
Key takeaway
Runtime relocation supports safer multiprogramming.
Base-Limit Working Example
Added clarityClear explanation
MMU first checks logical address against limit; if valid, it adds base value to generate physical address.
What it really means
Logical address is seat number within your own row; base tells where your row begins in physical hall.
Example
Base=12000, Limit=4000, Logical=350 => valid and Physical=12350. Logical=4200 => trap (out of range).
Key takeaway
Always mention both bounds check and base addition in answers.
- - Saying logical address is already physical
- - Forgetting limit check before memory access
- - Confusing static relocation with dynamic relocation
- - Logical address generated by CPU
- - Physical address used by RAM hardware
- - Dynamic relocation = base add + limit check at runtime
Physical Address = Base Register + Logical Address
Exam lens for this topic
What evaluators usually expect in structured exam answers.
Must-use keywords
- - logical address
- - physical address
- - base and limit
- - relocation
- - dynamic relocation
Answer flow
- - Write exact definition in first line
- - Explain mechanism in ordered bullets
- - Add one short example or scenario
- - Close with key takeaway and one exam keyword
Practice Questions
Describe fixed and variable memory allocation in short.
Source: Winter 2023 Q4(B) OR
Answer focus: Link allocation style to address handling and relocation needs.
Explain paging mechanism in MMU with suitable example.
Source: IMP Questions
Answer focus: Address split and mapping logic.
Extra clarity files
These are clearly marked additions, separate from source notes.