COT 4600 Operating Systems Spring 2011 Dan C. Marinescu Office: HEC 304 Office 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, 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 3

Lecture 6 4 4

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) 5

Lecture 6 6 6

7 7

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 8

Lecture 69 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. 9

Lecture 610 Figure 2.3 from textbook

Lecture 611 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 11

Lecture 612 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. 12

Lecture 613 Figure 2.5 from the textbook

Lecture 614 Figure 2.6 from the textbook

Lecture 615 Figure 2.7 from the textbook