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In most UNIX systems, virtual file systems (VFS) are applied to support multiple concrete underlying file systems. Beneath Mac OS X there is a UNIX-based foundation, where a file system component of Darwin is based on extensions to BSD and an enhanced VFS. To join a VFS, a concrete file system must supply a set of functions, which is the interface between the VFS and the concrete file system. For the Darwin VFS, it is able to support hierarchical file system (HFS), HFS+, Universal Disk Format (UDF) for hard disk drives and CDs and DVDs, ISSO 9660 for CD-ROM volumes, Windows NT File systems (Mac OS X can read NTFS-formatted volumes but cannot write to them), Unix File System (supported but use dis-encouraged in Max OS X), and MS-DOS FAT file systems.

In traditional operating systems (OS), such as UNIX, system calls are interface between user processes and an OS kernel. A system call function could be fork(), which creates a new process, a running program. A user process could invoke fork() to request the kernel to create a new process that is a duplicate of itself on its behalf. A system call may involve data exchange. For example, a waitpid() invocation waits for child process to change state. The calling process/thread will suspend its execution until status of information for one of its terminated child processes is available, or until delivery of a signal whose action is either to execute a signal-catching function or to terminate the process. Some system calls could be handled at user space. But most system calls are handled in the OS kernel. At first edition UNIX, the OS has fewer than 35 documented system calls. If you are able to access a UNIX system, you can check system call numbers in system header file sys/sysc

Carmine Gallo authored "The Presentation Secrets of Steve Jobs." Here is the summary of the video clip. 1) Maintain eye contact Why Steve Jobs can? Secrets: few words in his presentation file; no reading slides; and rehearsing as many times as possible. 2) Open posture Nothing or prevent barriers between him and his audience. 3) Effective hand gestures He uses hand gestures virtually every sentence. At the end of this video, there is a comparison between Steve Jobs with a speaker who needed to improve his presentation skills. We learn from masters.

I am learning Operating Systems. Today my reading is focus on Android, the mobile operating system. In Android, when a program is running, a virtual machine called Dalvik is created. The Dalvik virtual machine is a Java interpreter machine optimized for Android platforms. It is said that Dalvik is capable of running along an application compilation enhancing the execution performance of the applications. David's running code is not Java's byte code, which has a benefit to conserve more battery-power during long-run of applications. The trade off is that Dalvik is not compatible with Java's SE library, and Java ME class libraries, etc. Fortunately, it has its own vast amount of resources that can be applied to do the make up.