When they say map, they mean that each kernel thread is assigned to a certain number of user mode threads. Kernel threads are used to provide privileged services to applications (such as system calls ). They are also used by the kernel to keep track of what all is running on the system, how much … Read more
We used Andrew Tannenbaum’s Modern Operating Systems at the university I attended. I highly recommend it for it’s clear explanations of the tradeoffs inherent in many of the design decisions that you’ll run up against. This book is a little bit more “fair and balanced” than the Minix book. I also recommend this book because, … Read more
Linux x86 ring usage overview Understanding how rings are used in Linux will give you a good idea of what they are designed for. In x86 protected mode, the CPU is always in one of 4 rings. The Linux kernel only uses 0 and 3: 0 for kernel 3 for users This is the most … Read more
First, let me introduce some terminology. A critical section (CS) is a sequence of instructions that can be executed by at most one process at the same time. When using critical sections, the code can be broken down into the following sections: // Some arbitrary code (such as initialization). EnterCriticalSection(cs); // The code that constitutes … Read more
Paravirtualization is virtualization in which the guest operating system (the one being virtualized) is aware that it is a guest and accordingly has drivers that, instead of issuing hardware commands, simply issue commands directly to the host operating system. This also includes memory and thread management as well, which usually require unavailable privileged instructions in … Read more
Imagine three (3) tasks of different priority: tLow, tMed and tHigh. tLow and tHigh access the same critical resource at different times; tMed does its own thing. tLow is running, tMed and tHigh are presently blocked (but not in critical section). tLow comes along and enters the critical section. tHigh unblocks and since it is … Read more
Stack overflow refers specifically to the case when the execution stack grows beyond the memory that is reserved for it. For example, if you call a function which recursively calls itself without termination, you will cause a stack overflow as each function call creates a new stack frame and the stack will eventually consume more … Read more
While the answer is fairly complex, and requires understanding the basics of electrical systems & circuits (KVL, KCL), binary numbers, and boolean logic, we can describe the process at a high level: code (represented by plain text words) is compiled, assembled and ultimately translated into a combination of Zeroes and Ones, which represent low and … Read more
There’s an excellent explantation of virtual memory over on superuser. Simply put, virtual memory is a combination of RAM and disk space that running processes can use. Swap space is the portion of virtual memory that is on the hard disk, used when RAM is full. As for why 32bit CPU is limited to 4gb … Read more
Detection at compile time If you’re doing this to have different implementations depending on the OS, it is more useful to have separate files with the implementation of that feature and add build tags to each of the files. This is used in many places in the standard library, for example in the os package. … Read more