Chapters 4-5 Part I – Computer Organisation and Architecture in [B2] Flashcards
Characteristics of memory system.
Location
- Internal (e.g., processor registers, cache, main
- memory)
- External (e.g., optical disks, magnetic disks, tapes)
Capacity
- Number of words
- Number of bytes
Unit of Transfer
- Word
- Block
Access Method
- Sequential
- Direct
- Random
- Associative
Performance
- Access time
- Cycle time
- Transfer rate
Physical Type
- Semiconductor
- Magnetic
- Optical
- Magneto-optical
Physical Characteristics
- Volatile/nonvolatile
- Erasable/nonerasable
Organization
-Memory modules
Memory hierarchy of computer
What is cache memory?
– Structure and relationship with main memory?
What are the elements of cache design?
What is MMU and how does it affect cache addresses?
We need to map from virtual to physical addresses, using
memory-management unit (MMU): a hardware component that
translates each virtual address into a physical address in main memory.
When virtual addresses are used, the system designer may choose to place the cache between the processor and the MMU or between the MMU and main memory. A logical cache, also known as a virtual cache, stores data using virtual addresses. The processor accesses the cache directly, without going through the MMU. A physical cache stores data using main memory physical addresses.
One obvious advantage of the logical cache is that cache access speed is faster than for a physical cache, because the cache can respond before the MMU performs an address translation. The disadvantage has to do with the fact that most virtual
memory systems supply each application with the same virtual memory address space. That is, each application sees a virtual memory that starts at address 0. Thus,
the same virtual address in two different applications refers to two different physical addresses. The cache memory must therefore be completely flushed with each application context switch, or extra bits must be added to each line of the cache to
identify which virtual address space this address refers to.
What are cache misses/hits?
When a cache hit occurs, the data and address buffers are disabled and communication is only between processor and cache, with no system bus traffic.
When a cache miss occurs, the desired address is loaded onto the system bus and the data are returned through the data buffer to both the cache and the processor
How do CPU write to and read from caches?
The CPU reads from and writes to caches by performing cache lookups, handling cache hits or misses, and adhering to specific cache policies and coherency mechanisms. The design of these mechanisms is crucial for optimizing the overall performance of the system
What are replacement algorithms? Can you name some?
Replacement algorithms are used in cache management to decide which cache line or block should be evicted (replaced) when new data needs to be brought into the cache and there is no available space. The goal is to maximize the use of cache space and minimize the impact on performance.
Replacement Algorithms:
- Least recently used (LRU)
- First in first out (FIFO)
- Least frequently used (LFU)
- Random Replacement
Brief idea about types of semiconductor memory.
Semiconductor memory is a type of digital data storage that uses semiconductor technology to store and retrieve data. There are several types of semiconductor memory, each with its own characteristics, advantages, and applications. Here’s a brief overview of the main types:
RAM, ROM, Flash Memory, Cache Memory etc….
The basic element of a semiconductor memory is the memory cell. Although a variety of electronic technologies are used, all semiconductor memory cells share certain
properties:
■ They exhibit two stable (or semistable) states, which can be used to represent binary 1 and 0.
■ They are capable of being written into (at least once), to set the state.
■ They are capable of being read to sense the state.
