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---
title: FAT (Memory Card File System)
type: format
summary: File system of the Memory Card and the PDA.
category: File formats
info: Capacity = 1 Mbit (128 KB)
info: Block size = 8 KB
info: Sector size = 128 bytes
---

## Overview

A Memory Card holds 1 Mbit (128 KB) of flash memory. The memory is organized in blocks of 8 KB.[^ff53]

The Memory Card is managed with its own file system. Sony calls it the FAT. PDA application data is also managed in the blocks.[^ff53]

Writes to flash memory are made in 128-byte units known as sectors. Each block has 64 sectors.[^ff53]

## Block Layout

The blocks of a Memory Card are as follows:[^ff53]

Table: Layout of Memory Card blocks

| Block No. | Contents |
| --- | --- |
| 0 | FAT block |
| 1 | Data block 1 |
| 2..14 | Data blocks 2 to 14 |
| 15 | Data block 15 |

## FAT Block

The sectors of the FAT block are as follows:[^ff53]

Table: FAT block memory map

| Sector No. | Contents |
| --- | --- |
| 0 | Format ID sector |
| 1..15 | Block information sectors 1 to 15 |
| 16..35 | Alternate information sectors 1 to 20 |
| 36..55 | Alternate sectors 1 to 20 |
| 56..62 | Reserved sectors 1 to 7 |
| 63 | Dummy write sector |

### Format ID Sector

The first 2 bytes of the format ID are 'M' and 'C'. The remaining bytes are 0 up to the checksum in the 128th byte.[^ff54]

A card whose first 2 bytes are 'MC' is a formatted Memory Card. Any other card is unformatted.[^ff54]

### Block Information Sector

Each data block has one block information sector:[^ff54]

Table: Structure of block information sector

| Contents | Data type | Size (bytes) |
| --- | --- | --- |
| Block list information | unsigned long | 4 |
| File size | long | 4 |
| Next block | unsigned short | 2 |
| Filename | char x 21 | 21 |
| Reserved | unsigned char | 1 |
| Unused | | 94 |
| PDA application | unsigned char | 1 |
| Checksum | unsigned char | 1 |

The block list information gives the state of the block:[^ff54]

Table: Meaning of block list information

| Value | Contents |
| --- | --- |
| 51 | Header block |
| 52 | Intermediate block |
| 53 | End block |
| A0 | Free block |
| A1 | Header block with delete mark |
| A2 | Intermediate block with delete mark |
| A3 | End block with delete mark |

Formatting sets every block list information field to A0. A new file gets the values 51 to 53.[^ff54]

A deleted file keeps its blocks with the values A1 to A3. Restoring the original values restores the file.[^ff54]

A new file can break the chain from header block to end block.[^ff54]

The next FAT read then sets every block of the broken chain to A0.[^ff54]

A 1-block file has only the value 51 (or A1). A 2-block file has 51 and 53 (or A1 and A3) and no 52.[^ff54]

### Block Information Fields

File size is in bytes. It equals 8192 bytes times the number of blocks given when the file is created.[^ff55]

Next block points to the next block of a file.[^ff55]

The pointer is 1 less than the block number. Blocks 1 to 15 are stored as 0 to 14.[^ff55]

Next block is 0xFFFF when there is no next block.[^ff55]

Filename holds the file name. The string ends with a NULL (0x00).[^ff55]

McxExecFlag() sets the PDA application flag to 1 for a PDA application. Otherwise the flag is clear.[^ff55]

libcard and libmcrd do not copy the PDA application flag. A PDA application copied from the PlayStation has the flag set to 0.[^ff55]

The checksum is the XOR of the first 127 bytes of the sector.[^ff55]

### Alternate Sectors

An alternate information sector holds a substituted sector number and a checksum.[^ff55]

The alternate sector replaces the sector named in its alternate information sector.[^ff55]

If alternate information sector 3 holds 123, reads and writes of sector 123 go to alternate sector 3.[^ff55]

The dummy write sector takes dummy writes that clear unidentified flags.[^ff55]

## FAT Operation

The format operation writes the following values (hex):[^ff55]

Table: State of formatted FAT

| Target sector | 0 | 1 | 2 | 3 | 4..7 | 8 | 9 | 10..126 | 127 |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 0 | 4D | 43 | 00 | 00 | 00 | 00 | 00 | 00 | sum |
| 1..15 | A0 | 00 | 00 | 00 | 00 | FF | FF | 00 | sum |
| 16..35 | FF | FF | FF | FF | 00 | FF | FF | 00 | sum |

The sum in byte 127 is the XOR of bytes 0 to 126.[^ff56]

Sectors from alternate sector 1 to the dummy write sector need no initial value.[^ff57]

Delete changes the high 4 bits of the first byte of each block information sector of the file from 5 to A.[^ff56]

Undelete changes the same bits from A back to 5. Delete and undelete leave all other data unchanged except the checksum.[^ff56]

## PDA Processing

A write to the FAT sector of a block that holds a running PDA application is refused with an error.[^ff56]

The library takes this state to mean that the Memory Card was swapped.[^ff56]

The libmcx command "display while transferring file" disables writes to sectors 16 to 55. A write to them gives an error.[^ff56]

## References

[^ff53]: Sony Computer Entertainment Inc. File Formats. November 1998. Page 5-3, Tables 5-1 and 5-2.
[^ff54]: Sony Computer Entertainment Inc. File Formats. November 1998. Page 5-4, Tables 5-3 and 5-4.
[^ff55]: Sony Computer Entertainment Inc. File Formats. November 1998. Page 5-5, Table 5-5.
[^ff56]: Sony Computer Entertainment Inc. File Formats. November 1998. Page 5-6.
[^ff57]: Sony Computer Entertainment Inc. File Formats. November 1998. Page 5-7.