FAT -File System Guide

FAT -File System GuideDescribes the FAT (File Allocation Table) file system that was -originally devised for MS-DOS. -

Introduction

FAT -file system was originally used by IBM PCs and is an industrial standard for -file systems, supported by all operating systems that execute on PCs. Symbian -OS FAT file system implementation supports FAT12, FAT16 and FAT32. FAT file -system is used for storing user data on NAND Flash, internal RAM drives and -removable media such as SD cards and MMC cards.

Background information

On a FAT file system , the -smallest size of data storage that can be allocated to a file called a cluster. -The FAT structure is used to track how clusters are allocated to each file. -The FAT table stores the address of the clusters. The cluster size is different -on different media.

Over the years this file system has been enhanced -to keep track of increasing drive sizes. The number after the FAT relates -to the size of the entry in the FAT data structure, for example FAT12 uses -12 bit entries.

FAT features

FAT provides the following features:

The industrial standard -for filing systems on PCs.
Used for user storage.
There is a rugged FAT -system that can cope with the loss of power during a write operation.
Used on a wide variety -of media such as NAND Flash, internal RAM drives and removable media like -SD cards and MMC cards.
There is a maximum upper -limit for the size of a drive, which has been increased in FAT32

When files are written or deleted from the media, the files can be -scattered over the media known as fragmentation. The fragmentation results -in slower access times of the files.

Leaf Directory -Name Cache

Leaf directory name refers to the parent directory path -of a file or a folder. For example the leaf directory of a file somefile.txt in -the path C:\1\2\3\4\5\6\somefile.txt is C:\1\2\3\4\5\6\. -Each leaf directory name cache entry contains the following information:

Full path of the leaf -directory
Starting cluster number
Most recently used entry -position

To perform any file operations such as read, write or update the -file must be first located. The leaf directory name cache improves the performance -of locating a file in deeply nested directories. The number of entries that -can be cached is configured in the estart.txt file. See Leaf Directory Name Cache -Configuration Tutorial, for more details.

Directory -Cache

A directory is a file that contains a list of files and directory -names. The list items are called directory entries. Each directory entry contains -the filename, size of the file, starting cluster of the file and other metadata -information. The maximum size of a directory entry is 32 bytes. Directory -cache is used to store the directory entries. In the older versions of Symbian platform, -the directory cache was implemented as a fixed array. The new directory cache -is variable and allows the device creators to customise with a dynamic range.

The -configuration of directory cache specifies the size of the directory cache -dynamically. The size of a directory cache depends on the available system -memory. The dynamic range can be configured in the estart.txt file. -See Dynamic Directory -Cache Configuration Tutorial, for more information. The global cache -memory manager allocates the memory to the different cache on each drive.

Global Cache -Memory Manager

The global cache memory manager is introduced to -dynamically manage the cache memory on different drives. The global cache -memory is configured to reserve the address space required by different cache -memories. The estart.txt file is used to configure the -global cache memory manager. There are two parameters:

GlobalCacheMemorySize parameter -specifies the overall memory available to various cache. The parameter is -specified in kilobytes and the recommended value is 32768. The maximum value -depends on the sum of maximum size required by cache on each drive.
LowMemoryThreshold specifies -the percentage of RAM that should be reserved for the system. When the memory -on RAM reaches the threshold value, the dynamic memory growth is stopped. -The default value is 10% of RAM.

The text below is the sample estart.txt entry -for the global cache memory manager.

-… - -[CacheMemory] -GlobalCacheMemorySize 32768 -LowMemoryThreshold 10 -

The maximum or the global cache memory reserves address space -but the actual memory allocation depends on the available system memory.

-Using - ECom - -File Server + + + + + +FAT +File System GuideDescribes the FAT (File Allocation Table) file system that was +originally devised for MS-DOS. +

Introduction

FAT +file system was originally used by IBM PCs and is an industrial standard for +file systems, supported by all operating systems that execute on PCs. Symbian +OS FAT file system implementation supports FAT12, FAT16 and FAT32. FAT file +system is used for storing user data on NAND Flash, internal RAM drives and +removable media such as SD cards and MMC cards.

Background information

On a FAT file system , the +smallest size of data storage that can be allocated to a file called a cluster. +The FAT structure is used to track how clusters are allocated to each file. +The FAT table stores the address of the clusters. The cluster size is different +on different media.

Over the years this file system has been enhanced +to keep track of increasing drive sizes. The number after the FAT relates +to the size of the entry in the FAT data structure, for example FAT12 uses +12 bit entries.

FAT features

FAT provides the following features:

The industrial standard +for filing systems on PCs.
Used for user storage.
There is a rugged FAT +system that can cope with the loss of power during a write operation.
Used on a wide variety +of media such as NAND Flash, internal RAM drives and removable media like +SD cards and MMC cards.
There is a maximum upper +limit for the size of a drive, which has been increased in FAT32

When files are written or deleted from the media, the files can be +scattered over the media known as fragmentation. The fragmentation results +in slower access times of the files.

Leaf Directory +Name Cache

Leaf directory name refers to the parent directory path +of a file or a folder. For example the leaf directory of a file somefile.txt in +the path C:\1\2\3\4\5\6\somefile.txt is C:\1\2\3\4\5\6\. +Each leaf directory name cache entry contains the following information:

Full path of the leaf +directory
Starting cluster number
Most recently used entry +position

To perform any file operations such as read, write or update the +file must be first located. The leaf directory name cache improves the performance +of locating a file in deeply nested directories. The number of entries that +can be cached is configured in the estart.txt file. See Leaf Directory Name Cache +Configuration Tutorial, for more details.

Directory +Cache

A directory is a file that contains a list of files and directory +names. The list items are called directory entries. Each directory entry contains +the filename, size of the file, starting cluster of the file and other metadata +information. The maximum size of a directory entry is 32 bytes. Directory +cache is used to store the directory entries. In the older versions of Symbian platform, +the directory cache was implemented as a fixed array. The new directory cache +is variable and allows the device creators to customise with a dynamic range.

The +configuration of directory cache specifies the size of the directory cache +dynamically. The size of a directory cache depends on the available system +memory. The dynamic range can be configured in the estart.txt file. +See Dynamic Directory +Cache Configuration Tutorial, for more information. The global cache +memory manager allocates the memory to the different cache on each drive.

Global Cache +Memory Manager

The global cache memory manager is introduced to +dynamically manage the cache memory on different drives. The global cache +memory is configured to reserve the address space required by different cache +memories. The estart.txt file is used to configure the +global cache memory manager. There are two parameters:

GlobalCacheMemorySize parameter +specifies the overall memory available to various cache. The parameter is +specified in kilobytes and the recommended value is 32768. The maximum value +depends on the sum of maximum size required by cache on each drive.
LowMemoryThreshold specifies +the percentage of RAM that should be reserved for the system. When the memory +on RAM reaches the threshold value, the dynamic memory growth is stopped. +The default value is 10% of RAM.

The text below is the sample estart.txt entry +for the global cache memory manager.

+… + +[CacheMemory] +GlobalCacheMemorySize 32768 +LowMemoryThreshold 10 +

The maximum or the global cache memory reserves address space +but the actual memory allocation depends on the available system memory.

+Using + ECom + +File Server

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