Editing Memory Card

The PS2 memory card file system has a fairly simple design, with some allowances made for the limitations of flash memory. It's overall structure is similar to the well known MS-DOS FAT file system. It uses a file allocation table (FAT) to keep track of allocated space and a hierarchical directory system where all of a file's metadata is stored in its directory entry. Like the FAT file system, which groups disk sectors into clusters, the PS2 memory card file system groups flash memory pages in to clusters. On standard PS2 memory cards, the cluster size 1024 bytes, or 2 pages long.

*The Superblock
The key to the PS2 memory card file system is the superblock. Located in the first page of the memory, this is the only part of the file system with a fixed location. While some things like the do end up in fixed locations on standard 8M memory cards, you shouldn't rely on this. 

{| class="wikitable" style="font-size:small;"
|-
! Block Nº !! Cluster Nº !! Page Nº !! Offset !! Length !! Name !! Example !! Description
|-
| rowspan="21" style="background-color:#DDDDDD;" | 0 <br /> '''superblock''' || rowspan="20" style="background-color:#DDDDDD;" | 0 || rowspan="19" style="background-color:#DDDDDD;" | 0 || 0x000000 || 0x01C (28 bytes) || '''magic''' || Sony PS2 Memory Card Format || Memory Card identifyer
|-
| 0x00001C || 0x00C (12 bytes) || '''version''' || 1.2.0.0 || Memory Card format version. '''(1.2.0.0 = full support for bad_block_table map)'''
|-
| 0x000028 || 0x002 (2 bytes) || '''page_len''' || 512 || Page size in bytes (without ECC)
|-
| 0x00002A || 0x002 (2 bytes) || '''pages_per_cluster''' || 2 || Number of pages in a cluster
|-
| 0x00002C || 0x002 (2 bytes) || '''pages_per_block''' || 16 || Number of pages in an block
|-
| 0x00002E || 0x002 (2 bytes) || ''not used'' || FF00 ||
|-
| 0x000030 || 0x004 (4 bytes) || '''clusters_total''' || 8192 || Total number of clusters
|-
| 0x000034 || 0x004 (4 bytes) || '''alloc_start''' || 41 || First allocatable cluster number. Cluster values in the FAT and directory entries are relative to this
|-
| 0x000038 || 0x004 (4 bytes) || '''alloc_end''' || 8135 || Cluster offset number after the highest allocatable cluster. Relative to '''alloc_start'''. Not used.
|-
| 0x00003C || 0x004 (4 bytes) || '''cluster_rootdir''' || 0 || Cluster offset of the first cluster of the root directory. Relative to '''alloc_start'''. Must be zero.
|-
| 0x000040 || 0x004 (4 bytes) || '''bblock1''' || 1023 || Backup1 block number
|-
| 0x000044 || 0x004 (4 bytes) || '''bblock2''' || 1022 || Backup2 block number
|-
| 0x000050 || 0x080 (128 bytes) || '''ind_fat_table''' || 8 || '''Indirect FAT Table''' cluster number
|-
| 0x0000D0 || 0x080 (128 bytes) || '''bad_block_table''' || -1 || Bad blocks table (damaged blocks index)
|-
| 0x000150 || 0x001 (1 byte) || '''card_type''' || 2 || Memory card type '''(2 = PS2 memory card)'''
|-
| 000x0151 || 0x001 (1 byte) || '''card_flags''' || 0x52 || Memory Card features '''(0x01 = ECC support, 0x08 = Bad Block support, 0x10 = Erased state zeroed)'''
|-
| 0x000152 || 0x002 (2 byte) || ''not used'' || FF ||
|-
| 0x000154 || 0x0BC (188 bytes) || ''unknown'' || ||
|-
| 0x000200 || 0x010 (16 bytes) || '''ECC''' || || Error Correction Code. The last 16 bytes of all the pages are reserved for this code. See explain below
|-
| style="background-color:#DDDDDD;" | 1 || || || ''not used'' || ||
|-
| style="background-color:#DDDDDD;" | Up to 7 || style="background-color:#DDDDDD;" | Up to 15 || || || ''not used'' || ||
|-{{cellcolors|black}}
| colspan="8" |
|-
| rowspan="5" style="background-color:#DDDDDD;" | 1 || rowspan="2" style="background-color:#DDDDDD;" | 8 <br /> '''ind_fat_table''' || style="background-color:#DDDDDD;" | 16 || 0x002100 || 0x210 (528 bytes) || '''Indirect FAT Table''' || || rowspan="18" style="background-color:#DDDDDD;" | '''FAT File System'''
|-
| style="background-color:#DDDDDD;" | 17 || || || ||
|-
| rowspan="2" style="background-color:#DDDDDD;" | 9 || style="background-color:#DDDDDD;" | 18 || 0x002520 || 0x210 (528 bytes) || '''FAT Table''' ||
|-
| style="background-color:#DDDDDD;" | 19 || || || ||
|-
| style="background-color:#DDDDDD;" | Up to 15 || style="background-color:#DDDDDD;" | Up to 31 || || || ||
|-
| style="background-color:#DDDDDD;" | Up to 4 || || || || || ||
|-
| rowspan="5" style="background-color:#DDDDDD;" | 5 || rowspan="2" style="background-color:#DDDDDD;" | 40 || style="background-color:#DDDDDD;" | 80 || || || ||
|-
| style="background-color:#DDDDDD;" | 81 || || || ||
|-
| rowspan="2" style="background-color:#DDDDDD;" | 41 <br /> '''alloc_start''' <br /> '''cluster_rootdir''' || style="background-color:#DDDDDD;" | 82 || 0x00A920 || 0x210 (528 bytes) || '''Allocatable Clusters''' ||
|-
| style="background-color:#DDDDDD;" | 83 || || || ||
|-
| style="background-color:#DDDDDD;" | Up to 47 || style="background-color:#DDDDDD;" | Up to 95 || || || ||
|-
| style="background-color:#DDDDDD;" | Up to 1004 || || || || || ||
|-
| rowspan="5" style="background-color:#DDDDDD;" | 1005 || rowspan="2" style="background-color:#DDDDDD;" | 8040 || style="background-color:#DDDDDD;" | 16080 || || || ||
|-
| style="background-color:#DDDDDD;" | 16081 || || || ||
|-
| rowspan="2" style="background-color:#DDDDDD;" | 8041 || style="background-color:#DDDDDD;" | 16082 || 0x819120 || 0x210 (528 bytes) || '''Reserved Clusters''' ||
|-
| style="background-color:#DDDDDD;" | 16083 || || || ||
|-
| style="background-color:#DDDDDD;" | Up to 8047 || style="background-color:#DDDDDD;" | Up to 16095 || || || ||
|-
| style="background-color:#DDDDDD;" | Up to 1021 || || || || || ||
|-{{cellcolors|black}}
| colspan="8" |
|-
| rowspan="3" style="background-color:#DDDDDD;" | 1022 <br /> '''bblock2''' || rowspan="2" style="background-color:#DDDDDD;" | 8176 <br /> '''alloc_end''' || style="background-color:#DDDDDD;" | 16352 || 0x83BE00 || 0x210 (528 bytes) || '''Temporal Data''' || || rowspan="3" style="background-color:#DDDDDD;" | '''Backup Block 2''' <br />  Used to store the number of the block that is going to be programmed
|-
| style="background-color:#DDDDDD;" | 16353 || || || ||
|-
| style="background-color:#DDDDDD;" | Up to 8183 || style="background-color:#DDDDDD;" | Up to 16367 || || || ||
|-{{cellcolors|black}}
| colspan="8" |
|-
| rowspan="3" style="background-color:#DDDDDD;" | 1023 <br /> '''bblock1''' || rowspan="2" style="background-color:#DDDDDD;" | 8184 || style="background-color:#DDDDDD;" | 16368 || 0x83DF00 || 0x210 (528 bytes) || '''Temporal Data''' || || rowspan="3" style="background-color:#DDDDDD;" | '''Backup Block 1''' <br /> Used to store a copy of the data that is going to be programmed to a block
|-
| style="background-color:#DDDDDD;" | 16369 || || || ||
|-
| style="background-color:#DDDDDD;" | Up to 8191 <br /> '''clusters_total''' || style="background-color:#DDDDDD;" | Up to 16383 || || || ||
|}

A standard Ps2 Memory Card is composed by 1024 blocks, each block contains 16 pages of 528 bytes, for a total of 528*16*1024=8.650.752 bytes (0x840000)

Total ECC data is 16*16*1024=262.144 bytes

This gives an available space to store data of: Total-ECC = 8650752-262144 = 8388608 bytes = 8mb

*Backup Blocks
Two complete blocks are reserved to deal with the possibility of the memory card being removed by the user when data is being saved. Writing data to card requires erasing and reprogramming an entire block

Before writing a block, both '''bblock1''' and '''bblock2''' are erased. Then a copy of the new data that is going to be written is stored in '''bblock1''', and the number of the block that is going to be written is stored in '''bblock2'''. The block being programmed is then erased and writed. Finally, '''bblock2 is erased'''

Recovery caused by removal of the memory card is implemented whenever a memory card is inserted into the PS2 by checking '''bblock2''', if it's not erased, then programming is assumed to have not been completed. The contents of '''bblock1''' are then copied to the block given in '''bblock2'''. Then '''bblock2''' is erased

*Error Correction Code (ECC)
The data area of each page (512 bytes) is divided into 128 byte long chunks and for each chunk a simple [[http://en.wikipedia.org/wiki/Hamming_code 20-bit Hamming code]] is calculated and stored in three bytes

The first byte contains the column (or bit-wise) parity bits, with the even groups in the lower nibble and the odd groups in the upper nibble. The second and third bytes contain the even and odd groups respectively for the line (or byte-wise) parity bits

The 3 ECC bytes for each of the 4 chunks are stored in order in the page's spare area for a total of 12 bytes


Source: [[http://www.csclub.uwaterloo.ca:11068/mymc/ps2mcfs.html PlayStation 2 Memory Card File System - By Ross Ridge]]