Slides: Paging

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# Paging
## CSC 213 – September 18, 2026

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# Agenda for Today
1. Department Events
2. Upcoming Work
3. Hexadecimal Review
4. Paging
5. Wrap Up

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# Department Events

## CS Table: Digital Sovereignty
.indent[
  Tuesday, September 22nd at noon in JRC 224C
]

## CS Picnic (RSVP Required)
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  Friday, September 25th at 5pm in Merrill Park East  
  RSVP by Monday (link in email)
]

*To receive a token, send an email to let me know you attended no more than 48 hours after the event.*

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# Upcoming Work

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# Assignment 3: Archive Printer

**Due:** Monday, September 21st by 11:59pm  
**Late Deadline:** Wednesday, September 23rd at 10:00am

## Questions
**Should the archive printer just display the contents of one archive?**  
Yes.
When you reach the end of the archive data, just return from `print_contents` and the program will exit.

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# Virtual Memory Lab

**Due:** Wednesday, September 23rd by 11:59pm  
**Late Deadline:** Monday, September 28th by 11:59pm

## Questions
*No new questions yet.*

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# Hexadecimal Review

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# Whiteboard: Hex Digits

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# Hexadecimal Math
Consider two pointer values:
- `p = 0x7FF25310`
- `q = 0x7FF2430C`

1. Which pointer has a lower address?

2. If these pointers are the start and end of an array, how large is the array in bytes? *(Hint: the end of an array is a pointer just past the last byte.)*

3. How many bytes do you think an element of the array takes up?

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# Pointer Alignment
Which of these pointers are aligned to multiples of 8 bytes?
What about 16 or 32 byte alignment?

1. `0x55500410`
2. `0xCA7F00D5`
3. `0x00400008`
4. `0x7FFD1040`
5. `0x64430CC0`
6. `0x1D2C3B4A`

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# Paging

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# Whiteboard: Basic Paging Example

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# Real Parameters for 32-bit x86
Let's consider how the basic paging scheme we just discussed would work on a 32-bit x86 machine.
The design of x86 gives us two important parameters:

**Pointer Size:** 32 bits (four bytes)  
**Page Size:** 4096 bytes (4KB)

From those parameters, we can determine more information about the address space:

1. How large is an address space?
   In other words, how many bytes can we address with a 32-bit pointer?
   
2. How many pages make up an address space?

3. Let's assume a single entry in a page table takes up 4 bytes (32 bits).
   How large will one page table be?

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# Whiteboard: Multi-Level Page Tables

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# Reminders

## Upcoming Deadlines
- **Archive Printer:** due next Monday, or Wednesday morning with a token
- **Virtual Memory Lab:** due next Wednesday, or the following Monday with a token

## Need help? Use your resources!
- Book an appointment during office hours
- Attend mentor office hours
- Review slides, readings, and other course resources
- Use tools like `gdb` and AddressSanitizer to catch and diagnose issues

## Reading

- **Beyond Physical Memory: Mechanisms** (OSTEP, Chapter 21)
            
- **Beyond Physical Memory: Policies** (OSTEP, Chapter 22)