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- Memory management
Static relocation with protection keys (IBM S/360
approach):
- Protection Key = a small integer stored with each chunk of memory.
The chunks are likely to be 1k-4k bytes.
- Keep an extra hardware register to identify the current process.
This is called the process id, or PID. 0 is reserved for the operating system'sprocess id.
- On every memory reference, check the PID of the current process
against the key of the memory chunk being accessed. PID 0 is allowed to touchanything, but any other mismatch results in an error trap.
- Additional control: who is allowed to set the PID? How does OS
regain control once it has given it up?
- This is the scheme used for the IBM S/360 family. It is safe but
inconvenient:
- Programs have to be
relocated before loading. In some systems (e.g. MPS) this requires completerelinking. Expensive.
- Cannot share information between two
processes very easily
- Cannot swap a process out to secondary
storage and bring it back to a different location
Dynamic memory relocation: instead of changing the
addresses of a program before it is loaded, we change the address dynamicallyduring every reference.
- Under dynamic relocation, each program-generated address (called a
logical or virtual address) is translated in hardware to a physical, or realaddress. This happens as part of each memory reference.
- Show how dynamic relocation leads to two views of memory, called
address spaces. With static relocation we force the views to coincide so thatthere can be several levels of mapping.
Base and bounds, segmentation
Base&bounds relocation:
- Two hardware registers: base address for process, bounds register
that indicates the last valid address the process may generate.
Each process must be allocated contiguously in real
memory.
- On each memory reference, the virtual address is compared to the
bounds register, then added to the base register. A bounds violation results inan error trap.
- Each process appears to have a completely private memory of size
equal to the bounds register plus 1. Processes are protected from each other. Noaddress relocation is necessary when a process is loaded.
- Typically, the OS runs with relocation turned off, and there are
special instructions to branch to and from the OS while at the same time turningrelocation on and off. Modification of the base and bounds registers must also
be controlled.
- Base&bounds is cheap -- only 2 registers -- and fast -- the
add and compare can be done in parallel.
- Explain how swapping can work.
- Examples: CRAY-1.
Problem with base&bound relocation:
- Only one segment. How can two processes share code while keeping
private data areas (e.g. shared editor)? Draw a picture to show that it cannotbe done safely with a single-segment scheme.
Multiple segments.
- Permit process to be split between several areas of memory. Each
area is called a segment and contains a collection of logically-relatedinformation, e.g. code or data for a module.
- Use a separate base and bound for each segment, and also add a
protection bit (read/write).
- Each memory reference indicates a segment and offset in one or
more of three ways:
- Top bits of
address select segment, low bits the offset. This is the most common, and thebest.
- Or, segment is selected implicitly by the operation being
performed (e.g. code vs. data, stack vs. data).
- Or, segment is
selected by fields in the instruction (as in Intel x86 prefixes).
Questions & Answers
how does Neisseria cause meningitis
is the branch of biology that deals with the study of microorganisms.
studies of microbes
Louisiaste
when we takee the specimen which lumbar,spin,
How bacteria create energy to survive?
Bacteria doesn't produce energy they are dependent upon their substrate in case of lack of nutrients they are able to make spores which helps them to sustain in harsh environments
_Adnan
But not all bacteria make spores, l mean Eukaryotic cells have Mitochondria which acts as powerhouse for them, since bacteria don't have it, what is the substitution for it?
Muhamad
they make spores
Louisiaste
what is sporadic nd endemic, epidemic
the significance of food webs for disease transmission
Abreham
food webs brings about an infection as an individual depends on number of diseased foods or carriers dully.
Mark
explain assimilatory nitrate reduction
Assimilatory nitrate reduction is a process that occurs in some microorganisms, such as bacteria and archaea, in which nitrate (NO3-) is reduced to nitrite (NO2-), and then further reduced to ammonia (NH3).
Elkana
This process is called assimilatory nitrate reduction because the nitrogen that is produced is incorporated in the cells of microorganisms where it can be used in the synthesis of amino acids and other nitrogen products
Elkana
Examples of thermophilic organisms
Give Examples of thermophilic organisms
Shu
advantages of normal Flora to the host
Prevent foreign microbes to the host
Abubakar
they provide healthier benefits to their hosts
ayesha
They are friends to host only when Host immune system is strong and become enemies when the host immune system is weakened . very bad relationship!
Mark
cell is the smallest unit of life
Fauziya
cell is the smallest unit of life
Akanni
cell is the structural and functional unit of life
Hasan
is the fundamental units of Life
Musa
what are emergency diseases
There are nothing like emergency disease but there are some common medical emergency which can occur simultaneously like Bleeding,heart attack,Breathing difficulties,severe pain heart stock.Hope you will get my point .Have a nice day ❣️
_Adnan
define infection ,prevention and control
Innocent
I think infection prevention and control is the avoidance of all things we do that gives out break of infections and promotion of health practices that promote life
Lubega
Heyy Lubega hussein where are u from?
_Adnan
which site have a normal flora
Many sites of the body have it
Skin
Nasal cavity
Oral cavity
Gastro intestinal tract
Safaa
skin,Oral,Nasal,GIt
Sadik
How can Commensal can Bacteria change into pathogen?
Sadik
How can Commensal Bacteria change into pathogen?
Sadik
what are the advantages of normal Flora to the host
Micheal
what are the ways of control and prevention of nosocomial infection in the hospital
Micheal
part of a tissue or an organ being wounded or bruised.
Wilfred
what term is used to name and classify microorganisms?
Binomial nomenclature
adeolu
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Source:
OpenStax, Operating systems. OpenStax CNX. Aug 13, 2009 Download for free at http://cnx.org/content/col10785/1.2
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