************Please help~SD Card @ LPC2368*****************

A normal SPI interface has one data line, one MOSI (Master Out Slave In) and one MISO (Master In Slave Out). So each clock transition will transfer a single bit from the memory card to the processor and the reverse.

The SD memories has a mode where they can use four data lines, transmitting a nibble at a time. This is obviously four times faster for a given clock frequency, but will require that you either implement the bit transfers in software, or select a processor with specific support for SD cards.

Your specific processor can run four bits concurrently.

A normal SPI interface has one data line, one MOSI (Master Out Slave In) and one MISO (Master In Slave Out). So each clock transition will transfer a single bit from the memory card to the processor and the reverse.

The SD memories has a mode where they can use four data lines, transmitting a nibble at a time. This is obviously four times faster for a given clock frequency, but will require that you either implement the bit transfers in software, or select a processor with specific support for SD cards.

Your specific processor can run four bits concurrently.

That is, A normal SPI interface has one data line in each direction

The sentence was actually intended to read:
"A normal SPI interface has one clock line, one MOSI (Master Out Slave In) and one MISO (Master In Slave Out)."

"one clock line, one MOSI (Master Out Slave In) and one MISO (Master In Slave Out)."

and, in some cases (including the SD card), a Slave-Select (SS) line.

aka "Chip Select".

Yes, a slave select is needed for the slave side to be able to synchronize the bit sequence.

However, a number of SPI controllers do not have a dedicated slave-select signal in master mode and requires you to use a normal GPIO signal. For slave mode, the controller should have a dedicated slave-select line.

Requiring the master to use GPIO signals instead of a dedicated slave-select pin allows the master to have multiple slaves connected. The master may then select which slave to communicate with. And if only the MOSI signal is used, i.e. no data is sent from slave to master, then the master may activate multiple slave-select signals and send the same information to multiple slaves.