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Appendix
POST (Power On Self Test)
When you turn on the computer, it will first run through the POST, a series of software-controlled
diagnostic tests. The POST checks system memory, the motherboard circuitry, the display, the key-
board, the diskette drive, and other I/O devices.
PS/2 Port
PS/2 ports are based on IBM Micro Channel Architecture. This type of architecture transfers data through
a 16-bit or 32-bit bus. A PS/2 mouse and/or keyboard may be used on ATX motherboards.
RAM (Random Access Memory)
There are several different types of RAM such as DRAM (Dynamic RAM), EDO DRAM (Extended
Data Output DRAM), SDRAM (Synchronous DRAM).
ROM (Read Only Memory)
ROM is nonvolatile memory used to store permanent programs (called firmware) used in certain com-
puter components. Flash ROM (or EEPROM) can be reprogrammed with new programs (or BIOS).
SP-DIF
SP-DIF is the Sony and Philips Digital Interconnect Format. It can carry a stereo pair of channels with
a sampling rate of up to 48 Ksps (kilo-samples per second) and with a sample precision of up to 24 bits.
The SP-DIF output from CD player fits inside this envelope, being only 16 bits per sample at 44.1
Ksps. SP-DIF receivers can often automatically adapt to the rate and precision being delivered to them.
When different sampling precisions are used, the most significant bit is always at the same position in
the frame. This means that if the transmitted precision is greater or lower than the receiver can render,
then the least significant bits become automatically dropped or padded with zeros respectively.
The physical link for SP-DIF carries a Biphase Manchester Coded stream with a line level of 0.5 volts
and transformer isolation at both ends. Manchester Coding is class of line coding methods which
combining a data stream with a clock on a single channel where there are up to two transitions on the
line for each bit conveyed. With Biphase Manchester, there is a line transition at each end of a bit
period and a central transition if the data is a one. For CD audio at 44.1 Ksps the line rate is 5.6448
megabaud and the effective data rate is 2.8224 Mbps or 352.8 kilobytes per second. RCA/phono sock-
ets are normally used.
SP-DIF was first used in the commercial hi-fi world to interconnect CD mechanisms to external DACs,
however at least one hi-fi company today makes hi-fi separates which are interconnected using SP-DIF,
including an SP-DIF preamplifier with digital input and output and active loudspeakers with SP-DIF
input and digital crossovers. SP-DIF is now widely found on DAT players and home theatre separates.
Apart from the pair of audio channels, SP-DIF also carries a subcode similar to the subcode on CDs
which indicates the current track number and current time within the track. For SP-DIF the only widely
used subcode component is SCMS, the serial copying management system. This enables a stream to be
marked as an original or a copy. A DAT recorder sold for the consumer market or digital recording
studio component should mark as a copy anything it records from the digital input and is not supposed
to allow the user to make copies of material which is already marked as a copy. Many contemporary
DAT recorders my be switched between the consumer and professional mode.
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