COT 4600 Operating Systems Spring 2011

Dan C. MarinescuOffice: HEC 304Office hours: Tu-Th 5:00 – 6:00 PM

Last time: Complexity of Computer Systems Iteration Names and The Basic Abstractions

Today: Discussion of “Hints for Computer Systems Design” by Butler Lampson. Basic Abstractions

Memory. Interpreters. Communication links.

Next time Naming;

Use by: value/name; Binding and indirection Generic naming model Practical design of naming scheme; Contexts, Name overloading

Lecture 6 – Tuesday, February 1, 2011

2Lecture 6

Lecture 6 3

Names and the three basic abstractions Memory stores named objects

write(name, value) value READ(name) file system: /dcm/classes/Fall09/Lectures/Lecture5.ppt

Interpreters manipulates named objects machine instructions ADD R1,R2 modules Variables call sort(table)

Communication Links connect named objects HTTP protocol used by the Web and file systems Host: boticelli.cs.ucf.edu put /dcm/classes/Spring11/Lectures/Lecture6.ppt get /dcm/classes/Spring11/Lectures/Lecture6.ppt

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Lecture 6 4

Communication latency- time it takes the first bit sent to reach the receiver

Latency

Bandwidth

Bandwidth- number of bits/bytes transmitted per unit of time

t1

t2

t3

t4t5

t6

Time Time

Sender Receiver

Program Storagedevice

t2t3

t1

Operation latency- time it takes the command to read the device

Latency

Bandwidth- number of bits/bytes transmitted per unit of time

Bandwidth

t4

t5

t6

4

Lecture 6 5

Memory Hardware memory:

Devices RAM (Random Access Memory) chip Flash memory non-volatile memory that can be erased and

reprogrammed Magnetic tape Magnetic Disk CD and DVD

Systems RAID File systems DBMS (Data Base management Systems)

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Lecture 6 6

time

WRITE item A in cell M

AM

READ from cell M

AM

A A

Read/Write Coherence è the result of a READ of a memory cell should be the same as the most recent WRITE to that cell.

Before-or-after atomicity è the result of every READ or WRITE is as if that READ or WRITE occurred either completely before or completely after any other READ or WRITE

Current READ/WRITE

Previous READ/WRITE

Next READ/WRITE

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Lecture 6 77

Lecture 6 8

RAID 3 and 4

Raid 3 Striped set with dedicated parity or bit interleaved parity or byte level parity.

Raid 4 improves reliability, it adds error correction

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Lecture 6 9

RAID 5 and 6 Raid 5 striped disks with parity combines three or more

disks to protect data against loss of any one disk. The storage capacity of the array is reduced by one disk

Raid 6 striped disks with dual parity combines four or more disks to protect against loss of any two disks.  Makes larger RAID groups more practical. Large-capacity drives lengthen the time needed to recover from

the failure of a single drive. Single parity RAID levels are vulnerable to data loss until the failed drive is rebuilt: the larger the drive, the longer the rebuild will take. Dual parity gives time to rebuild the array without the data being at risk if a (single) additional drive fails before the rebuild is complete.

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Lecture 6 1010

Figure 2.3 from textbook

Lecture 6 11

Interpreters The active elements of a computer system Diverse

Hardware Processor, Disk Controller, Display controller Software

script language: Javascropt, Pearl, Python text processing systems: Latex, Tex, Word browser : Safari, Google Chrome,Thunderbird

All share three major abstractions/components: Instruction reference tells the system where to find the next

instruction Repertoire the set of actions (instructions) the interpreter is

able to perform Environment reference tells the interpreter where to find the its

environment, the state in which it should be to execute the next instruction

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Lecture 6 12

An abstract interpreter

The three elements allow us to describe the functioning of an interpreter regardless of its physical realization.

Interrupt mechanism allowing an interpreter to deal with the transfer of control. Once an instruction is executed the control is passed to an interrupt handler which may change the environment for the next instruction.

More than a single interpreter may be present.

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Lecture 6 1313

Figure 2.5 from the textbook

Lecture 6 1414

Figure 2.6 from the textbook

Lecture 6 1515

Figure 2.7 from the textbook