Analytical View of Garbage Collection in Solid State Media File Systems
1.0 Overview
Solid State media's such as flash memory are non-volatile computer memory that can be electrically erased and reprogrammed. These are specific types of EEPROM's that are erased and programmed in large blocks.
Flash memory is non-volatile, which means that it does not need power to maintain the information stored in the chip. In addition, flash memory offers fast read access times and better kinetic shock resistance than hard disks (Table 1).
Though flash memory has many advantages, its special hardware characteristics impose design challenges on storage systems.
Media Access Time
Read (512B) Write (512B) Erase
DRAM 2.56µs 2.56µs -
NOR Flash 14.4µs 3.53ms 1.2s (128kB)
NAND Flash 135.9µs 226µs 2-3ms (16kB)
Disk 12.4ms 12.4ms -
Table 1. Characteristics of different storage media. (NOR Flash: Intel 28F128JF3A-150, NAND Flash: K9F5608U0M)
1.1 Architecture
1.1.1 Partitions
Flash memory is divided into one or many sections of memory called partitions. A multi-partition architecture allows system processor to multi-task the I/O operations with the flash memory. While the processor can read from one partition, it can write/erase in another.
Figure 1. Partitions, Blocks and Pages
1.1.2 Blocks
In addition to partitions, flash memory is further divided into sections of memory called blocks (Figure 1). Flash memory devices in which all blocks are of the same size are symmetrically-blocked, while devices which are asymmetrically-blocked generally have several blocks that are significantly smaller than main array of flash blocks. Small blocks are typically used for storing small data or boot code. Block sizes vary 64kB to 256kB.
1.1.3 Pages
Each block in flash memory comprises of fixed number of pages (Figure 1). A page is typically of size 512B to 2kB. While erase operations can be done only on blocks, I/O operations can be done on every page.
1.2 Programming Data
Flash devices allow programming values from logical "1" to "0", but not from "0" to "1" (Figure 2). To program values back to "1"s requires erasing a full block. In most cases when data is data edited, it can either be re-written to the same block by caching the original, erasing the block and re-writing over it, or by writing the edited file to a new location in flash and the old one invalidated. Eventually, invalid data needs to be reclaimed which is usually done as a background process.
1 1 1 1 1 1 1 1 1 1
1 0 1 0 0 1 1 0 1 0
1 1 1 1 1 1 1 1 1 1
Figure 2. Flash Programming Limitations
2.0 Flash File System Functions
While flash file systems have many functions in common with file systems for other media, there are many that are unique to file systems for flash devices.
2.1 Wear Leveling
Each block in a flash memory device has a finite number of erase-write cycles (~ 10,000 to 100,000).
The EEPROM chip can store up to one kilobytes of data and is divided into 64 words with 16 bits each. Some memory is inaccessible or reserved for later us...
...y without booting up, enabling a user to simply push a button and the computer will turn exactly as it was when it was turned off. Mobile devices will benefit from MRAM as it has less power demands, allowing for much longer uses on a single charge. Further, MRAM’s durability and low power needs make it ideal for defense and aerospace technologies as well as for the primary data storage technology for satellites.
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Main memory size is 256 bytes. Each byte has a unique 8-bit address consisting of an integer in the range 00 (hexadecimal) to FF (hexadecimal).
SOCs integrate capabilities to connect the SOC to external memory devices and nonvolatile storage devices using glue-less interfaces. Glue-less is a term used to indicate that there is no additional logic needed to connect the two devices, for example, connect the SOC to DDR DRAM. In addition to attaching to memory devices, an SOC provides segment- or application-specific interfaces. Examples of integrated devices are general purpose input/output pins, interfaces such as Ethernet, USB, PCIe, serial ports, I2C, expansion parallel buses, and integrated display controllers. Many of these devices interface to nonvolatile storage such as NOR Flash via Serial Peripheral Interconnect (SPI), and native bus interface types. As a general rule, these integrated items are predominantly digital logic elements. Because we need to add analog capabilities, features such as flash memory and digital/analog converters are common, but these capabilities require special features of the silicon manufacturing process.
USB flash disk is small but that goes the same to the disk space as well.
One of the types of storage includes short-term memory. According to an article written by Saul McLeod in 2009 there are three key aspects of short-term memory. this comprised of limited capacity, limited duration, and encoding. Limited capacity in short-term memory and we allow seven (plus or minus two) items to be stored at a time (Miller 1956). The limits of your durations of storage is very delicate and can be lost forgotten with distraction or time passing.
There are two types of memory in a PLC. It is usually in the main PLC module and mostly non-expandable using other modules though modern PLCs have slots for additional memory cards. This is to prevent any unauthorized change in the PLC program and its functioning. The Executive Memory or program memory is the one that receives and holds program instructions (usually ROM). The data memory or scratch pad is the work area used to temporarily store information produced by the processor during the scan operation. These are volatile memory
In recent years, optical disk drive has become one of major data storage devices in auxiliary memory devices and AV systems. The reasons for this popularity are its short access time compared with that of magnetic tape drive, exchangeability of disks, and almost unlimited lifetime [New Fine Seek Control for Optical Disk Drives]
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Page Tables allow pages to be stored non-contiguously in memory, each page has an associated page table with a logical ...
Encoding is the process of placing information into memory. Storage is the process of retaining information in memory. Getting information out of memory is called retrieval. Out of the three, the most important is Encoding, because you must pay attention to the information that you want to place into your memory. It is the starting point, although there are three levels known within this beginning step.
According to the dictionary, Memory is defined as a device that is used to store data or programs (sequences of instructions) on a temporary or permanent basis for use in an electronic digital computer. Computers represent information in binary code, written as sequences of 0s and 1s. Each binary digit (or "bit") may be stored by any physical system that can be in either of two stable states, to represent 0 and 1. Such a system is called bistable. This could be an on-off switch, an electrical capacitor that can store or lose a charge, a magnet with its polarity up or down, or a surface that can have a pit or not. Today capacitors and transistors, functioning as tiny electrical switches, are used for temporary storage, and either disks or tape with a magnetic coating, or plastic discs with patterns of pits are used for long-term storage.(Dictionary.com 20014)
We put all of the data onto the platters. They are inside of the hard
There are four types of memory. These are the RAM, ROM, EEPROM and the Bootstrap loader. The RAM, also known as Random Access Memory, is the temporary space where the processor places the data while it is being used. This allows the computer to find the information that is being requested quickly without having to search the hard drive space. Once the information has been processed, and stored onto a permanent storage device, it is cleared out of the RAM. The RAM also houses the operating system while in