SPCBL Assistant Maintenance Engineer Exam: 20.11.2021প্রশ্ন ও সমাধান

Kernel: The kernel is the core program of an operating system that has direct control over the hardware — CPU, memory, and devices. Every system call (file I/O, process scheduling, memory allocation) is ultimately serviced by the kernel, making it the most privileged and critical part of the OS.

Cache Memory: A small, very high-speed memory placed between the CPU and RAM to hold frequently accessed data/instructions. It is faster than RAM but more expensive; using it reduces the average memory access time by exploiting locality of reference (temporal and spatial).

Virtual Memory: A memory-management technique that gives a process the illusion of a large, contiguous main memory by using part of the disk (swap space) as an extension of RAM. This lets programs larger than physical RAM run, using techniques like paging and page replacement.

RAID (Redundant Array of Independent Disks): Combines multiple physical disks into one logical unit to improve performance, provide redundancy, or both.

RAID Level	Technique	Benefit
RAID 0	Striping	Speed, no redundancy
RAID 1	Mirroring	Full redundancy, no speed loss on writes
RAID 5	Striping + distributed parity	Balance of speed, redundancy, and cost

Exam takeaway: Memory hierarchy speed order is Registers > Cache > RAM > Virtual Memory (disk); RAID improves availability/performance but is not a substitute for backups since it doesn't protect against accidental deletion or corruption.