'Uncategorized' Category

  • Modern Datastores: Three Case Studies

    December 22, 2016

    The storage of persistent data requires data structures that use the capabilities of a block store to organize and index information for efficient and complete retrieval. Traditionally file systems were the data structures organizing block stores. The traditional alternative to a file system as a database, which constituted an entirely different field of computing than [...]

  • The FAT Filesystem

    November 14, 2016

    File systems are a collection of data structures that use block stores for data persistence. File systems add features to the data, including ways of labeling the data for retrieval, protection and ownership mechanisms, and mechanisms for recovery of data from unfortunate loss or misuse. One of the most popular file system is the FAT [...]

  • Classical ACID Persistence

    November 13, 2016

    Persistent data is a key resource provided by the operating system. The classical persistent store is files, and filesystems are often topics found in classic operating system textbooks. Other forms of persistence are archives, on-disk swap storage, source code control systems such as Subversion and Git, databases, and configuration systems such as the Microsoft Registry [...]

  • The Process Lifecycle

    September 24, 2016

    Processes are created by other processes using system calls. At least one thread is created, and that thread can create other threads in that process. When all threads have completed their tasks, the process begins a process of dissolution. The process is first placed in a dead state, where the process context still exists, but [...]

  • Virtual Threads and the Context Switch

    September 24, 2016

    The process abstraction models the requirements for running programs. It is a container for the context, and collected resources that will be used by a running program. A thread is the ability or the actuality of executing the program. The Thread Abstraction is the conception of a thread. Physical threads, which are what carry out [...]

  • The Thread Abstraction

    September 23, 2016

    A process is a data context and one or more threads that run in that context. A thread is the ability or the actuality of executing a sequence of instructions. The computer instructions are loaded into memory is a part of the context. A thread is the running or potential running of that code. A [...]

  • Virtual Machines and Hypervisors

    September 4, 2016

    Virtual Machines and Hypervisors For reasons of efficiency or convenience, it is desirable that an entire operating system be run as a guest of another operating system. The host operating system creates a software entity that models the hardware of a physical machine, called the virtual machine (VM), and presents this to the guest operating [...]

  • Proxy SSH

    June 13, 2015

    There was a post on this in February, however I’d like to reiterate. Proxy SSH was described in this helpful article. It consists of running “nc” (netcat) on one machine to pass all of the ssh connection onto another machine. It depends on the .ssh/config file to disguise this, so it works completely has if [...]

  • Socks

    May 29, 2010

    Ssh has a thing called DynamicForward. It is actually SOCKSv5. Since Firefox is socks enabled, you can use your mcclellan account as a proxy for web browsing. This is useful, for instance, to get to web pages that are only available from inside UM, such as CCS, or some of our internal-only sites. In .ssh/config [...]

  • Square roots mod p

    April 12, 2010

    The structure of Z/pZ (a.k.a. integers mod p) is simple when p-1 is not divisible by 4, that is, p=3 (4). In this case -1 is a quadratic non-residue, else there would be a subgroup of the four 4-th roots of 1, and the order of a subgroup divides the order of the group. Therefore [...]

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