Working with the Unix OS

Processes I
The u area contains
- pointer to process table identifiers
- real and effective user ids
- timer fields
- how to react to signals
- control terminal "login terminal"
- error field
- return value
- amount of data to transfer
- user buffer address
- file offset
- current directory
- user file descriptors
- limits to restrict size of process
- permission modes mask
Layout of System Memory
A process has three logical sections:
- text
- data
- stack
The compiler generates addresses for a virtual address space and machine’s memory management translates this to
physical memory.
Regions
A Region is a contiguous area of virtual
address space of a process that can be
treated as a distinct object.
Several processes can share a region. e.g.
processes can execute the same program,
share one copy of text region; processes
can share a common shared memory area.
Each process contains a private per
process region table called a pregion.
Figure 7. Processes and Regions
Pages and Page Tables
In a memory management architecture based on pages, the hardware divides physical memory into a set of
equalized blocks called pages.
If a machines has 2^32 bytes of physical memory and a page size of 1k, it has 2^22 pages of physical memory,
every 32-bit address can be treated as a pair consisting of a 22-bit page number and a 10-bit offset into the page.
Logical Page Number | Physical Page Number
0 177
1 54
2 209
3 17
Assuming a page is lK bytes, want to access virtual memory address 68, 432. Therefore it is in the stack region,
byte offset 2986 in the region, counting from 0, with byte offset 848 of page 2, physical address 986k.
Memory management register triples
- address of the page table in phys
- first virtual address mapped
- number of pages in the page table
100