Memory
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This document summarizes different types of memory and memory performance parameters. It discusses RAM as volatile primary memory that stores information for the operating system and software. It also describes secondary memory, cache memory, and virtual memory. The document defines memory performance parameters like access time, cycle time, latency, block access time, block size, and bandwidth. Finally, it compares memory segmentation and paging, noting that segmentation allows programs and data to be broken into independent address spaces while paging is used to get a large linear address space without needing additional physical memory.
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Memory
- 2. Memory • What is memory? • Memory Types • Memory Performance Parameters • Memory Segmentation and Paging
- 3. What is memory? Memory is any physical device capable of storing information temporarily or permanently. For example, Random Access Memory (RAM), is a volatile memory that stores information on an integrated circuit used by the operating system, software, and hardware.
- 4. Memory Types There are several types of Memory some are below RAM(Primary memory) Secondary Memory Cache Memory Virtual Memory
- 5. Memory Performance Parameters Symbol Definition Units Meaning 𝒕 𝒂 Access time time Time to access a memory word 𝑡 𝑐 Cycle time time Time from start of access to start of next access 𝑡𝑙 Latency time Time to access first word of a sequence of words 𝒕 𝒃𝒍=𝑡𝑙+ k/ω Block access time time Time to access an entire block of words k Block size words Number of words per block ω Bandwidth words/time Word transmission rate
- 6. Memory Segmentation and Paging Memory Segmentation Paging Allows programs and data to be broken up into logically independent address spaces. Paging is used to get a large linear address space without having to buy more physical memory Segmentation can be performed only in the case when a programmer provides inputs to the system. Paging is a process that is performed by the computer itself. Memory segment facilitate sharing of procedures. Paging does not facilitate sharing of procedures.
Editor's Notes
- RAM (Random Access Memory) : Its a volatile memory, its used as a temporary storage for data, because data on it can be accessed randomly & at a greater speed. It has high reading & writing speed as compared to the Hard-Disk. It's used by the processor to read & write (i.e. process) data, because it can do that with a good speed without slowing down the processing. It can't retain data after its power supply is cut. It has a capacity limit. Hard-Disk : Its your 'the storage thing'. You can read or write data into it whenever you want. But it has got less speed as compared to RAM in case of reading & writing. It can retain data after its power supply is cut. It has its limit depending on your wallet size (expand it till you get tired). ROM (Read Only Memory) : It's a no-volatile storage place with only reading access. Data can be written to it only using 'not-so-similar' techniques. It retains data even after the power supply to it is cut. Its has a capacity limit less than that of a RAM. Data is written to it at a normal speed. Its used primarily in the startup process of a computer. eg. In any old Nokia s60 phones (using a file manager) you can see a drive in which you can see the data, play the tunes but can't delete them. That's because that's the ROM. Cache memory Cache memory is the memory which is used to speed up the memory retrieval process Virtual memory U.S. currency ("cash"),
- ta= h*Tc +(1-h)*M where h = hit rate (1-h) = miss rate Tc = time to access information from cache M = miss penalty (time to access main memory) Cycle time consists of latency and transfer time
- paging The 6-bit page value is used to select a proper entry in process page table. the 6-bit process entry occupying the six most significant bit and the 10-bit offset occupying the 10 least significant bit forms a 16-bit physical address. Segment The 4-bit segment of a logical address selects the proper entry in the process segment table. The base value is added to the 12 bit offset value to get the 16 bit physical address.